Dissertations / Theses on the topic 'Mechanical Properties Optimization'

The research activity here reported spans different areas of the nanocomposite material science, giving a contribution toward the advancement in its state of the art. The study of the effects of the filler distribution on the mechanical properties of nanomodified polymers is a major research topic which is carried out. Different computational and theoretical approaches have been developed, considering statistics, finite element analyses and micromechanics. Several nanomodified epoxy resins have been manufactured along with glass fibre reinforced laminates with nanomodified matrix. The effects of the nanomodification on the mechanical properties of these composites have been studied, in order to validate predictive models and supply technical data to material designers. The results obtained so far highlight the importance, in this class of materials, of the study of interactions at the nanoscale between the nanoreinforcement and the matrix. The thesis is articulated in an introduction, followed by two sections, dedicated to the experimental activity and the modelling one, and by an appendix. The introduction presents a brief overview on nanocomposites giving a primer to a reader devoid of prior experience with this class of materials. The experimental activity section is constituted by four chapters. The first one contains the results of mechanical tests performed on a nanoparticle reinforced epoxy, alongside an analysis on the processing parameters employed in the composite preparation. The enhancement in the nanocomposite fracture toughness is compared with a theoretical model, showing a satisfactory agreement. The second chapter reports the study of the effect of the testing temperature on the fracture toughness of the same material. The analysis highlights the fundamental importance of the processing parameters and of the testing temperature on the nanomodification effects. The third chapter considers a different aspect of the nanomodification: a nanoplatelet reinforced epoxy is used to prepare notched specimens and the strength analysis of the notched component is carried out. The fourth chapter reports the research activity performed on the study of the matrix nanomodification of glass fibre reinforced laminates. The effects on the matrix dominated mechanical properties and the feasibility in the production of a laminate with antibacterial bulk properties are analysed. The modelling section is constituted by three chapters. The first one contains a comparison between two approaches for the estimation of the elastic properties of a nanocomposite material, considering explicitly the presence of an interphase surrounding the nanoreinforcements. The first approach implements a two-step micromechanical model, while the second one is based on a finite element analysis. The second chapter reports the research activity carried out on the generation of representative volume elements of nanoparticle reinforced materials. A statistically based algorithm is implemented to minimize the volume element size while retaining its representativeness. The study of the interphase extent and of the overall elastic modulus, through finite element analyses, is reported. The third chapter extends these considerations to the generation of volume elements for nanoplatelet reinforced materials. The random sequential absorption approach is implemented and its hidden effects on the filler distribution highlighted. A new version of the algorithm is proposed to remove these unwanted behaviours. The appendix section is dedicated to the implementation activity of approaches which have not been completed yet. The results obtained on the use of molecular dynamics in the simulation of polymers and nanomodified polymers are reported. While a detailed procedure for the simulation of epoxy resins is listed, the approach for the study of nanoplatelet-epoxy interactions is still in progress.<br>L'attività di ricerca riportata nella presente tesi riguarda diverse aree della scienza dei materiali nanocompositi e mira a dare un contributo nell'avanzamento del suo stato dell'arte. Uno degli ambiti principali di indagine è stato inerente allo studio degli effetti della distribuzione dei rinforzi sulle proprietà meccaniche esibite dai polimeri nanomodificati. Diversi approcci, computazionali e teorici, sono stati sviluppati, sfruttando considerazioni statistiche, l'analisi agli elementi finiti e la modellazione micromeccanica. E' stata eseguita la nanomodificazione di diverse resine epossidiche e la produzione di laminati in fibra di vetro con matrici nanomodificate. Sono quindi stati studiati gli effetti della nanomodificazione sulle proprietà meccaniche di questi compositi, al fine di validare modelli previsionali e fornire dati ai progettisti di materiali. I risultati finora conseguiti evidenziano l'importanza che, in questa classe di materiali, ricopre lo studio delle interazioni alla nanoscala che si sviluppano tra i nanorinforzi e la matrice. La tesi è articolata in una introduzione, seguita da due sezioni dedicate all'attività sperimentale e alla modellazione, e da una appendice a concludere. La sezione inerente l'attività sperimentale è costituita da quattro capitoli. Il primo contiene i risultati dei test sperimentali eseguiti su resine epossidiche nanomodificate, volti ad indagarne le proprietà meccaniche includendo l'effetto dei parametri di processo. E' inoltre riportato il confronto tra l'incremento della tenacità a frattura misurato sperimentalmente e le previsioni di un modello teorico, evidenziando una soddisfacente congruenza dei risultati. Il secondo capitolo riporta lo studio degli effetti della temperatura sulla tenacità a frattura dello stesso materiale. Tale analisi rimarca la fondamentale importanza dei parametri di processo e della temperatura di prova sugli effetti della nanomodificazione. Il terzo capitolo considera un diverso aspetto della nanomodificazione, ovvero la resistenza di campioni intagliati, prodotti con resine epossidiche rinforzate con nanoplatelets. Il quarto capitolo riporta l'attività di ricerca portata avanti sull'impiego di matrici nanomodificate in laminati rinforzati in fibra di vetro. Oggetto di analisi sono le proprietà meccaniche dipendenti dalla matrice e la possibilità di produrre laminati con proprietà antibatteriche. La sezione inerente l'attività di modellazione è invece costituita da tre capitoli. Il primo contiene un confronto tra due approcci volti alla stima delle proprietà elastiche di un materiale nanocomposito, considerando in modo esplicito la presenza di una interfase che circonda i nanorinforzi. Il primo degli approcci implementati è un modello micromeccanico in due passi, mentre il secondo è basato su una analisi agli elementi finiti. Il secondo capitolo riporta l'attività di ricerca inerente la creazione di volumi rappresentativi di materiali rinforzati da nanoparticelle. Tale studio si basa sull'impiego di un algoritmo in grado di considerare aspetti statistici volti alla riduzione della dimensione del volume di controllo, pur mantenendone la rappresentatività. Sono quindi riportate le analisi sull'estensione dell'interfase e sulle proprietà elastiche globali del composito, valutate tramite analisi agli elementi finiti. Il terzo capitolo estende i concetti esposti nel precedente per la generazione di volumi rappresentativi di materiali rinforzati con nanoplatelets. Un approccio basato sull'algoritmo di random sequential absorption è stato implementato, evidenziando gli effetti che questo comporta sulla distribuzione dei rinforzi. E' stata quindi proposta una nuova versione di questo algoritmo, capace di rimuovere queste conseguenze indesiderate. L'appendice è dedicata all'esposizione dell'attività svolta nell'implementazione di approcci che però non sono ancora stati completati. In essa sono riportati i risultati finora conseguiti sull'uso della dinamica molecolare nella simulazione di polimeri e nanocompositi. In particolare è elencata una procedura dettagliata per la simulazione di resine epossidiche, e la prima parte di un approccio per lo studio di resine epossidiche rinforzate con nanoclay.

This research investigates the synthesis and manufacture of shape-memory polymer (SMP) systems for use in biomedical and commodity applications. The research centers on improving the mechanical properties of thermoset acrylate copolymers with memory properties at reasonable cost through various design and manufacturing techniques: high-strain polymer synthesis and radiation crosslinking. The research assesses combinations of linear monomers and a low density of crosslinker to characterize new functional materials and optimize emerging mechanical properties such as the glass transition temperature (Tg) and rubbery modulus (ER). Exploring materials with large recoverable strains, a model copolymer of photo-polymerized methyl acrylate (MA), isobornyl acrylate and crosslinker bisphenol A ethoxylate dimethacrylate was shown to strain above 800%, twice the previously published value for SMPs, and recover fully. In the quest to maximize fully recoverable strains, a new hybrid molecule nicknamed Xini, which serves as both an initiator and a crosslinker, was also theorized, synthesized, polymerized into SMP networks and characterized. In the past, thermoset SMPs were made into complex shapes using expensive top-down techniques. A block of polymer was made and custom machining was required to craft complex parts. This prohibited devices in cost-competitive commodity application spaces. This research has proposed and validated a new method for accurately tuning the thermomechanical properties of network acrylates with shape-memory properties: Mnemosynation, eponymously named for the Greek goddess of memory. This novel manufacturing process imparts long term 'memory' on an otherwise amorphous thermoplastic material utilizing radiation-induced covalent crosslinking, and can be likened to Vulcanization, which imparts strength on natural rubber utilizing sulfur crosslinks. Adjustment of ER in the range from below 1 MPa to above 13 MPa has been demonstrated. ER was tailored by varying both radiation dose between 5 and 300 kGy and crosslinker concentration between 1.00 and 25.0 wt%. Tg manipulation was demonstrated between 23 ˚C and 70 ˚C. Mnemosynation combines advances in radiation grafting and acrylic SMP synthesis to enable both traditional plastics processing (blow molding, injection molding, etc.) and control of thermoset shape-memory properties. Combining advances in both high strain polymer synthesis and radiation crosslinking, a new paradigm in SMP composites manufacture-namely, that materials can be designed to enhance strain capacity at moderate stress, rather than maximum strength-was established. Various fibers with very different mechanical properties were impregnated with SMPs and thermo-mechanically assessed to develop an understanding of the technical parameters necessary to craft self-adjusting, multi-actuated, SMP-fiber composite orthopedic casts. This exploration syncs with the overarching aim of the research, which is to understand the fundamental scientific drivers necessary to enable new devices mass-manufactured from acrylate copolymers and optimize their emerging mechanical properties.

Electrospinning is a polymer processing technique which allows for the production of nano to micro size fibers and scaffolds which can be composed of numerous synthetic biodegradable materials and natural biopolymers. Natively, elastin and collagen are the main components of vascular tissue. Arranged in a tri-layered structure, they create a specific mechanical environment that can withstand the rigors of circulation. The goal of this study was to develop a mechanically ‘biomimicking’ vascular graft composed of three distinct layers through the process of electrospinning. We hypothesize that the use of bioactive agents such as elastin, collagen, and silk to supplement poly(caprolactone) at specified ratios for each layer would provide a finely tuned vascular replacement. This was accomplished by establishing cross-linking parameters for the biopolymer materials and then assessing the mechanical properties of individual materials and eventually a whole tri-layered graft. Additionally, while mechanical testing can lead to a good graft, a replacement graft requires excellent cellular properties as well to promote cell infiltration, proliferation, and migration. Therefore, the conclusion of this study examines the integrin binding characteristics of the electrospun biopolymers. First, the results from the preliminary cross-linking study examined the dissipation of soluble elastin when uncross-linked v. cross-linked. It was determined through this initial study that synthetic scaffolds blended with soluble proteins such as elastin require a fixation in order to retain their protein mass within the scaffold. Retaining this mass, incrementally changed the material properties of the blended scaffolds. This initial study was then carried further to establish optimal cross-linking parameters using two different types of reagents: carbodiimide and genipin. It was found that lower cross-linking molarities produced excellent results based on assays performed to assess cross-linking percentages and rate of reaction. Some differences in mechanical properties were seen, but they did not constitute a choice of one cross-linker over the other. The next portion of this study aimed to design a tri-layered graft. This was performed with the aid of mathematical analysis to observe circumferential wall stresses based on simple tensile properties. A series of tri-layered grafts were electrospun using poly(caprolactone), elastin, and collagen. The medial layers of these grafts were changed while the intima and adventitia remained constant. Differences were demonstrated as the elastin content of the medial layer decreased, proving that each layer had an affect on the overall graft properties and that it was possible to tune graft mechanics. A larger tri-layered study looked to evaluate changes in the adventitial and medial layers while keeping the intimal layer constant using poly(caprolactone), elastin, collagen, and silk fibroin. In this study, differences were exhibited under compliance and burst strength testing, narrowing the scope of material choices. Results from a 4 week degradation study with the best tri-layered grafts revealed no evidence of degradation, but did generate some positive compliance results for two of the grafts. Finally, integrin binding and protein analysis portrayed results that were indicative of the existence of ligand binding sites for collagen scaffolds and the possibility of a small amount of ligand sites on silk. Elastin, however, displayed low to non-existent adhesion. These studies produced results that allowed us to continuously narrow the scope of materials as the experiment progressed towards an optimized tri-layered vascular graft.

The control of stresses and liquid pressure surges in pipes is an important problem in the design of hydraulic pipe networks. The method of characteristics has been used to solve the transient stresses and pressures in liquid-filled piping systems. The friction force is included in the equations of motion for the fluid and the pipe wall. The maximum pressure and maximum stress at any point along the length of the pipe are evaluated for the entire simulation time. A nonlinear search technique has been developed using the simplex method. The optimal valve closure is sought, that will minimize the maximum pressure and/or stresses. A continuous optimal valve closure policy is specified using spline functions. Numerical examples are presented showing the reduction of the dynamic pressure and the dynamic stress from linear valve closure to optimal valve closure for a simple pipeline and a complex pipeline. Also, a method for choosing the shortest time of closure which will keep the stresses below specified allowable stresses is presented.

Includes abstract.<br>Includes bibliographical references.<br>Current replacements for diseased arteries include autologous and artificial grafts. The availability of autologous grafts is limited and artificial grafts tend to fail when applied to small calibre vessels (<;6 mm) due to graft thrombosis and mechanical mismatch between artery and graft. Tissue engineering offers a promising approach to overcome these shortcomings. With porosity as a fundamental prerequisite for tissue ingrowth, several techniques have been introduced for producing porous scaffolds including electro-spinning. This study involved the development and optimisation of electro-spun biodegradable scaffolds for vascular tissue regeneration by tailoring parameters of the electro-spinning process and investigating the change in mechanical and physical properties of the scaffolds associated with hydrolytic in vitro degradation.

For the last decades usage of aluminium alloys have been increasing tremendously. They have been used in aerospace industry widely and now aluminium alloys are becoming more and more popular in automotive and defense industries. Consequently<br>successful welding of aluminium alloys gains importance. In this study a research is carried out on eldability of plates having different thicknesses of composition 5754 aluminium and 6063 aluminium in T-fillet geometry using Gas-metal Arc Welding technique. It was aimed to have a successful joint without using pre-weld and post-weld heat treatments. During tests welding current and voltage were the varying parameters as welding speed was held constant. Macro-examinations were performed to see the penetration of the weld metal. It was seen that the type of filler wire greatly effects weld penetration. Hardness tests, tensile tests were done to compare the mechanical properties of the welded joints with different filler wires. Despite having better penetration in 4043 filler wire used weld joints, 5356 filler wire used weld joints had higher tensile strength and ductility. In the second part of the study, a dynamic loading machine was designed and manufactured to see the behavior of the fillet welds under dynamic loading. The amount of stress and strain given to the specimen on this machine was adjustable but can&rsquo<br>t be measured. The tests that were made with this machine aimed only to compare the number of cycles of specimens before fracture. For dynamic loading tests two groups of specimens were prepared with filler wire 4043<br>each group having been welded with different heat inputs. It was aimed to see the effect of welding heat input on service lifes but no significant difference between cycle numbers of specimen groups having been welded with different heat inputs was observed. Microstructure examinations of these specimens revealed that coarsening the grains, grain boundaries, particles in PMZ and HAZ regions between Al 6063 base metal and weld zone made these areas more susceptible and favorable for crack propogation than Al 6063 base metal.

Additive manufacturing (AM), also called 3D-printing, are technologies where parts are formed from the bottom up by adding material layer-by-layer on top of each other. Electron Beam Melting (EBM) is an AM technique capable of manufacturing fully solid metallic parts, using a high-intensity electron beam to melt powder particles in layers to form finished components. Compared to conventional machining, EBM offers enhanced efficiency for production of customized and patient specific parts such as e.g. dental prosthetics. However, dental prosthetics are challenging to produce by EBM, as their small sizes mean that mechanical and surface properties may be altered as part sizes decreases. The aim of this thesis is to gain new insights that could lead to optimization for production of small sized components in the EBM. The work is focused to understand the process-property relationships for small size components production. To improve the surface resolution and part detailing, a smaller sized powder was used for production and compared to parts made with standard sized powder. The surface-, chemical and mechanical properties were evaluated for parts produced with both types of powders. The results indicate that the surface roughness may be influenced by powder and build layer thickness size, whereas the mechanical properties showed no influence of the layer-wise production. However, the mechanical properties are dependent on part size. The outermost surface of the parts consists of a surface oxide dominated by TiO2, formed as a result of reaction between the surface and residual gases in the EBM build chamber. The surface oxide thickness is comparable to that of a conventionally machined surface, but is dependent on build height. This work concludes that the surface resolution and component detailing can be improved by various measures. Provided that proper process themes are used, the EBM manufactured material is homogenous with properties comparable to conventional produced titanium. It has also been shown that the material properties will be altered for small components. The results point towards different ways of optimizing manufacturing of dental prosthetics by EBM, which will make dental prosthetics available for an increased number of patients.

In this thesis the problems of identification accuracy of elastic properties of materials are examined. The main object of study is samples of various materials and their elastic properties. This is an important subject of theoretical studies of various materials. The main thesis objective is to create an effective technology for precise identification of all the elastic characteristics of the sample. The de-veloped algorithms are to be applied in the material manufacturing industry. Thesis also aims at exploring accuracy and sensitivity of the identification of elastic properties of materials. The paper deals with a number of objectives: 1) to optimize the geometric parameters of the sample striving for more accurate identification results of elas-tic properties; 2) to identify mode shapes of sample and regulate their place in spectrum of eigenvalues in order to minimize the distortion of the objective function; 3) to create the implementation algorithms of proposed technologies and verify their capabilities experimentally. The first task is formulated taking into account the relatively high level of identification error of elastic properties of composite materials. The second objective relates to distortion of the objec-tive function in the process of updating the mathematical model with the pre-sumed elastic characteristics of material. The thesis is composed of four chapters, the summary of results, the list of literature and the list of author’s publications on the topic... [to full text]<br>Disertacijoje nagrinėjamos medžiagų tamprumo rodiklių identifikavimo tikslumo problemos. Pagrindinis tyrimo objektas yra įvairių medžiagų bandiniai, jų tamprumo rodikliai. Šis objektas yra svarbus įvairių medžiagų teoriniams tyrimams. Pagrindinis disertacijos tikslas yra sukurti efektyvią technologiją, leidžiančią pakankamu tikslumu surasti visus bandinio tamprumo rodiklius. Sukurtų algoritmų taikymo sritis yra medžiagų gamybos pramonė. Disertacijoje tiriamas siūlomos technologijos tikslumas ieškant įvairių medžiagų tamprumo rodiklių. Darbe sprendžiami keli pagrindiniai uždaviniai: optimizuojami bandinio geometriniai parametrai siekiant tikslesnių tamprumo rodiklių identifikavimo rezultatų; atpažįstamos bandinio modų formos ir reguliuojama jų vieta tikrinių reikšmių spektre siekiant sumažinti tikslo funkcijos iškraipymus; sukuriami pasiūlytų technologijų įgyvendinimo algoritmai ir bandymais patikrinamos jų galimybės. Pirmasis uždavinys suformuluotas atsižvelgiant į palyginti didelę kompozitinių medžiagų tamprumo rodiklių identifikavimo paklaidą. Antrasis siejasi su tikslo funkcijos iškraipymu atnaujinant matematinį medžiagos modelį spėjamais tamprumo rodikliais. Disertaciją sudaro keturi skyriai, rezultatų apibendrinimas, naudotos literatūros ir autoriaus publikacijų disertacijos tema sąrašai. Įvadiniame skyriuje aptariamas problemos aktualumas, tyrimo objektas, formuluojamas darbo tikslas bei uždaviniai, aprašoma tyrimų metodika, darbo mokslinis naujumas, darbo rezultatų... [toliau žr. visą tekstą]

Geopolymers are good alternatives for replacing ordinary Portland cement (OPC) due to their comparable properties and feasibility to be obtained from industrial by-products. As OPC, geopolymers have superior compressive strength but a brittle behavior that the addition of fibers can improve. When the first macrocrack appears, fibers develop bridging mechanisms to allow the proper distribution of loads, so the composite can enable multiple cracks and enhance its ductility. At present, a wide range of materials can be used to reinforce cementitious matrices, from synthetics such as steel, glass, carbon, and polypropylene to natural fibers such as cotton, sweet sorghum, oil palm, coir, jute, sisal, flax, bamboo, etc. Natural fibers are among the most accepted resources to reinforce composites because they are biodegradable, renewable and generally, have a less environmental impact than their synthetic counterparts. They have low density and specific mechanical properties comparable to fibers made of glass, making them materials with a good performance-price ratio. However, their high variability of properties and hydrophilic behavior can create issues when reinforcing a matrix. Chemical treatments are used to clean chemical compounds that do not contribute to the fiber strength and favor moisture absorption. After treatment, the fiber surface increases its roughness which enhances the interlocking within the composite. This thesis investigates the mechanical properties of Agave americana fibers obtained by beating and boiling the leaves. The fibers were subjected at 1%, 5%, and 20% NaOH concentrations over 0.5 hr, 1 hr, and 3 hr and tested to determine the tensile strength. The surfaces were also analyzed by scanning electron microscopy (SEM). After treatment, most of the fibers enhanced the tensile strength and strain and 1% NaOH concentration over 1 hr was chosen as the optimum condition. Then, fibers were treated at the optimum condition and added to the geopolymer mixture at different doses: 0.5%, 0.75%, and 1% by weight of fly ash. The geopolymers were tested at compressive, flexural, and splitting tensile loads at 7 days of age. The compressive strength increased by 12% at 0.75 (wt.%) and the modulus of elasticity in compression, 13% at 1% (wt.%). Also, the tensile strength increased by 36% at 1 (wt.%). However, the flexural strength decreased probably due to the fiber length. Still, further studies are needed to understand the influence of the fiber length on the mechanical properties of geopolymers. Finally, the SEM analysis was conducted to identify the fiber failure modes.

Formation plays an important role in the end-use properties of paper products, but before formation can be optimized to achieve superior properties, an understanding about the causes of formation must be developed. Formation is caused by variations in the basis weight of paper that are results of fiber floc formation before and during the forming of the sheet. This project is a first step in a larger research program aimed at studying formation. By observing the effects that mechanical energy dissipation (in the form of turbulence) and retention chemical dosage have on floc formation, we may develop a better understanding of how to control formation. In this study, a rectangular cross-section flow channel was constructed to aid in the acquisition of digital images of a flowing fiber suspension. The furnish consisted of a 55:45 spruce:pine bleached market pulp mix from a Western Canadian mill. Turbulence was varied by changing the flow rate; Reynolds numbers achieved range from 20,000 to 40,000. The retention aid used was a cationic polyacrylamide with a medium charge density. Dosage of the retention aid was varied from 0 to 2 pounds per ton OD fiber. Digital images of the flowing fiber suspension were acquired with a professional digital SLR camera with a forensics-quality lens. Three separate image analysis techniques were used to measure the flocculation state of the fiber suspension: morphological image operations, formation number analysis, and fast Fourier transform analysis. Morphological image analysis was capable of measuring floc size increases seen in the acquired floc images. It was shown how floc diameter could increase simultaneously with decreasing total floc area and total floc number. A regression model relating retention aid dosage and energy dissipation was constructed in an effort to predict flocculation. The regression model was used to predict F2 (formation number squared) results from the study. The interaction effect RE was shown to have a differing effect across the retention aid dosage levels. As a result, this model and technique may prove to be a beneficial tool in optimizing retention aid applications.

The underlying principles of how the nervous system selects specific muscle activation pattern, among many that produce the same movement, remain unknown. Experimental studies suggest that the nervous system may use fixed groups of muscles, referred to as muscle synergies, to produce functional motor outputs relevant to the task. In contrast, predictions from biomechanical models suggest that minimizing muscular effort may be the criteria how a muscle coordination pattern is organized for muscle synergies. However, both experimental and modeling evidence shows that stability, as well as energetic efficiency, also needs to be considered. Based on the hypothesis that the nervous system uses functionally stable muscle activation pattern for a muscle synergy, we investigated the stability of muscle patterns using a neuromechanical model of the cat hindlimb. Five unique muscle patterns that generate each of the five experimentally-identified muscle synergy force vectors at the endpoint were found using a minimum-effort criterion. We subjected the model to various perturbed conditions and evaluated functional stability of each of the five minimum-effort muscle synergies using a set of empirical criteria derived from experimental observations. Results show that minimum-effort muscle synergies can be functionally stable or unstable, suggesting that minimum-effort criterion is not always sufficient to predict physiologically relevant postural muscle synergies. Also, linearized system characteristics can robustly predict the behavior exhibited by fully dynamic and nonlinear biomechanical simulations. We conclude that functional stability, which assesses stability of a biomechanical system in a physiological context, must be considered when choosing a muscle activation pattern for a given motor task.

The diploma thesis deals with possibilities for processing aluminium alloy EN AW 2618 using Selective laser melting (SLM). The theoretical part contains basic knowledge about production by this technology and possibilities of evaluation of relative density of samples. It also contains an overview of the current state of knowledge about the processing of aluminium alloys by SLM technology. Above all, aluminium alloys of the series 2000, where the main alloying element is copper. In the experimental part testing samples were designed based on the research. These samples can be divided into three areas: single-track specimens, volume samples and samples for tensile testing. Single-track and volume samples were used to find appropriate processing parameters to achieve a relative density close to full volume of material. For this purpose, the effect of the different scanning strategies on the relative density of the sample were examined. The limiting factor has been the occurrence of small cracks in the broad range of parameters studied. Mechanical properties of samples produced by SLM were compared with extruded material. It was found that the material processed by SLM achieves only half the yield strength and tensile strength of extruded material. This is mainly due to the occurrence of small cracks and other defects in the structure of the material.

Thesis (MEng)--Stellenbosch University, 2014.<br>ENGLISH ABSTRACT: Over the past 50 years smart materials have made their appearance in many structures. The thermopiezoelectric ceramic is one of these smart materials. When thermal e ects are considered negligible, then the materials are classified as piezo-ceramic and piezoelectric materials. These so called piezo-ceramics are used as actuator and sensor components in many structures. The use of these components with composite materials is significant due to their application in the aerospace and aeronautics fields. The interaction that the piezoelectric material has with a composite body can be improved in order to reduce the energy requirement of the material for deformation. An objective in the optimisation of composite material structures is to minimise compliance or maximise sti ness uT f, with the laminate ply orientations as design variables, where u and f are displacement and force vectors, respectively. Here, the objective is not the maximisation of sti ness but the maximisation of compliance, with typical constraints being failure criteria. These failure criteria can include theories such as the maximum principle stress, the Tsai-Hill or Tsai-Wu failure theories. The compliance is maximised to accentuate any piezoelectric movement and is for theoretical treatment only. Piezoelectric materials once polarized the materials becomes quasi-isotropic. The piezoelectric materials are isotropic in the plane normal to the direction of the voltage being applied and have altered properties normal to this plane. This change in the material properties can be exploited so that the layup can be altered in orientation to improve performance. The idea is to improve the mechanical capabilities of the structure subject to an electrical input or vice versa. In the works by both Carrera et al. and Piefort, First Order Shear Deformation Theory (FSDT) is used in finite element analysis to characterise the structural and electrical behaviour of a plate or shell. FSDT, also known as the Mindlin-Reissner theory, is a plate bending theory that assumes a transverse shear distribution through the thickness of the plate. This theory is considered an improvement on the standard theories such as the Kircho or Timoshenko theories. Many optimisation techniques exist and are classed as either being direct search or gradient based methods. Particle Swarm Optimisation (PSO) is a direct search method. It mimics the behaviour of a flock of birds or school of fish in their attempt to find food. The PSO’s mathematical statement characterises a set of initial unknown particles within a designated search space that are compared to a set of local best particles and a single global best particle. This comparison is used to update the swarm each run cycle. Regression is a procedure whereby a set of testing data is used to fit a pseudo-function that represents the form the data should take in practice. The aim of this work is to optimise the piezoelectric-composite layer interaction to improve the overall compliance of a structure. Extensive modelling is performed and tested with peer reviewed literature to demonstrate its accuracy.<br>AFRIKAANSE OPSOMMING: Oor die afgelope 50 jaar het slim materiale hulle verskyning gemaak in verskeie strukture. Termopiezo-elektriese keramieke is een van hierdie nuwe materiale. Wanneer termiese e ekte onbeduidend is, word hierdie materiale as piezo-elektriese materiale geklassifiseer. Hierdie sogenaamde piezo-keramieke word gebruik as aandrywers en sensoriese onderdele in verskeie strukture. Die kombinasie van hierdie onderdele met saamgestelde materiale het belangrike toepassings in die ruimte- en lugvaartkunde. Die interaksie van die piezo-elektriese materiale met die saamgestelde materiaal strukture kan verbeter word om die energie-vereistes van die materiaal vir vervorming te verminder. ’n Tipiese doel in die optimering van saamgestelde materiaalstrukture is om styfheid uT f te maksimeer met die gelamineerde laag-oriëntasies as ontwerpsveranderlikes, waar u en f onderskeidelik verplasing en kragvektor voorstel. In teenstelling met die optimering van die samestelling wat voorheen gedoen is, is die doel hier nie die maksimering van styfheid nie, maar die minimering van styfheid, met falingskriteria as tipiese beperkings. Die falingskriteria sluit die volgende in: die maksimum spanningsteorie, en die Tsai-Hill of Tsai-Wu falingsteorieë. Die styfheid word geminimeer om piezo-elektriese verplasing te versterk, maar word hierin net teoreties bekyk. Sodra piezo-elektriese materiale gepolariseer word, word hulle quasi-isotropies. Die piezoelektriese materiale is isotropies in die vlak gelyk aan die rigting van die stroomspanning wat daarop toegepas word en het ander eienskappe normaal tot die vlak. Die verandering in die materiaal se eienskappe kan gebruik word sodat beide die saamgestelde materiaal en die piezoelektriese laag se oriëntasie aangepas kan word vir verbeterde werkverrigting. Die idee is om die meganiese vermoëns te verbeter van ’n struktuur wat onderwerp word aan ’n elektriese inset of vice versa. In die literatuur van beide Carrera et al. en Piefort word Eerste Orde Skuifvervormings Teorie (EOST) gebruik in eindige element analises om die strukturele en elektriese gedrag van ’n plaat of dop te karakteriseer. EOST, ook bekend as Mindlin-Reissner teorie, is ’n plaat buigings-teorie wat ’n dwarsvervormingverspreiding aanneem deur die dikte van die plaat. Hierdie teorie word gesien as ’n verbetering op die standaard teorieë soos bv. Kircho of Timoshenko se teorieë. Daar bestaan baie optimeringstegnieke wat geklassifiseer word as ’direkte soek’ of ’hellinggebaseerde’ metodes. Partikel swerm-optimering (PSO) is ’n direkte soekmetode. Dit boots die gedrag van ’n swerm voëls of ’n skool visse in hulle poging om kos te vind, na. PSO se wiskundige stelling karakteriseer ’n aanvanklike stel onbekende partikels binne ’n afgebakende soekgebied wat vergelyk word met ’n stel van die beste plaaslike partikels sowel as ’n enkele beste globale partikel. Die vergelykings word gebruik om die swerm met elke siklus op te dateer. Regressie is ’n metode waarin toetsdata gebruik word om ’n benaderde funksie te konstrueer wat ongeveer voorspel hoe die regte funksie lyk. Die doel van hierdie werk is om die piezoelektriese saamgestelde laag te optimeer en die interaksie van die totale gedrag van die struktuur te verbeter. Uitgebreide modellering word uitgevoer en getoets met eweknie-beoordeelde literatuur om die akkuraatheid en korrektheid te bewys.

Nature develops several materials with remarkable functional properties composed of comparatively simple base substances. Biological materials are often composites, which optime the conformation to their function. On the other hand, synthetic materials are designed a priori, structuring them according to the performance to be achieved. 3D printing manufacturing is the most direct method for specific component production and earmarks the sample with material and geometry designed ad-hoc for a defined purpose, starting from a biomimetic approach to functional structures. The technique has the advantage of being quick, accurate, and with a limited waste of materials. The sample printing occurs through the deposition of material layer by layer. Furthermore, the material is often a composite, which matches the characteristics of components with different geometry and properties, achieving better mechanical and physical performances. This thesis analyses the mechanics of natural and custom-made composites: the spider body and the manufacturing of metallic and non-metallic graphene composites. The spider body is investigated in different sections of the exoskeleton and specifically the fangs. The study involves the mechanical characterization of the single components by the nanoindentation technique, with a special focus on the hardness and Young's modulus. The experimental results were mapped, purposing to present an accurate comparison of the mechanical properties of the spider body. The different stiffness of components is due to the tuning of the same basic material (the cuticle, i.e. mainly composed of chitin) for achieving different mechanical functions, which have improved the animal adaptation to specific evolutive requirements. The synthetic composites, suitable for 3D printing fabrication, are metallic and non-metallic matrices combined with carbon-based fillers. Non-metallic graphene composites are multiscale compounds. Specifically, the material is a blend of acrylonitrile-butadiene-styrene (ABS) matrix and different percentages of micro-carbon fibers (MCF). In the second step, nanoscale filler of carbon nanotubes (CNT) or graphene nanoplatelets (GNP) are added to the base mixture. The production process of composite materials followed a specific protocol for the optimal procedure and the machine parameters, as also foreseen in the literature. This method allowed the control over the percentages of the different materials to be adopted and ensured a homogeneous distribution of fillers in the plastic matrix. Multiscale compounds provide the basic materials for the extrusion of fused filaments, suitable for 3D printing of the samples. The composites were tested in the configuration of compression moulded sheets, as reference tests, and also in the corresponding 3D printed specimens. The addition of the micro-filler inside the ABS matrix caused a notable increment in stiffness and a slight increase in strength, with a significant reduction in deformation at the break. Concurrently, the addition of nanofillers was very effective in improving electrical conductivity compared to pure ABS and micro-composites, even at the lowest filler content. Composites with GNP as a nano-filler had a good impact on the stiffness of the materials, while the electrical conductivity of the composites is favoured by the presence of CNTs. Moreover, the extrusion of the filament and the print of fused filament fabrication led to the creation of voids within the structure, causing a significant loss of mechanical properties and a slight improvement in the electrical conductivity of the multiscale moulded composites. The final aim of this work is the identification of 3D-printed multiscale composites capable of the best matching of mechanical and electrical properties among the different compounds proposed. Since structures with metallic matrix and high mechanical performances are suitable for aerospace and automotive industry applications, metallic graphene composites are studied in the additive manufacturing sector. A comprehensive study of the mechanical and electrical properties of an innovative copper-graphene oxide composite (Cu-GO) was developed in collaboration with Fondazione E. Amaldi, in Rome. An extensive survey campaign on the working conditions was developed, leading to the definition of an optimal protocol of printing parameters for obtaining the samples with the highest density. The composite powders were prepared following two different routes to disperse the nanofiller into Cu matrix and, afterward, were processed by selective laser melting (SLM) technique. Analyses of the morphology, macroscopic and microscopic structure, and degree of oxidation of the printed samples were performed. Samples prepared followed the mechanical mixing procedure showed a better response to the 3D printing process in all tests. The mechanical characterization has instead provided a clear increase in the resistance of the material prepared with the ultrasonicated bath method, despite the greater porosity of specimens. The interesting comparison obtained between samples from different routes highlights the influence of powder preparation and working conditions on the printing results. We hope that the research could be useful to investigate in detail the potential applications suitable for composites in different technological fields and stimulate further comparative analysis.

Disertacijoje nagrinėjamos medžiagų tamprumo rodiklių identifikavimo tikslumo problemos. Pagrindinis tyrimo objektas yra įvairių medžiagų bandiniai, jų tamprumo rodikliai. Šis objektas yra svarbus įvairių medžiagų teoriniams tyrimams. Pagrindinis disertacijos tikslas yra sukurti efektyvią technologiją, leidžiančią pakankamu tikslumu surasti visus bandinio tamprumo rodiklius. Sukurtų algoritmų taikymo sritis yra medžiagų gamybos pramonė. Disertacijoje tiriamas siūlomos technologijos tikslumas ieškant įvairių medžiagų tamprumo rodiklių. Darbe sprendžiami keli pagrindiniai uždaviniai: optimizuojami bandinio geometriniai parametrai siekiant tikslesnių tamprumo rodiklių identifikavimo rezultatų; atpažįstamos bandinio modų formos ir reguliuojama jų vieta tikrinių reikšmių spektre siekiant sumažinti tikslo funkcijos iškraipymus; sukuriami pasiūlytų technologijų įgyvendinimo algoritmai ir bandymais patikrinamos jų galimybės. Pirmasis uždavinys suformuluotas atsižvelgiant į palyginti didelę kompozitinių medžiagų tamprumo rodiklių identifikavimo paklaidą. Antrasis siejasi su tikslo funkcijos iškraipymu atnaujinant matematinį medžiagos modelį spėjamais tamprumo rodikliais. Disertaciją sudaro keturi skyriai, rezultatų apibendrinimas, naudotos literatūros ir autoriaus publikacijų disertacijos tema sąrašai. Įvadiniame skyriuje aptariamas problemos aktualumas, tyrimo objektas, formuluojamas darbo tikslas bei uždaviniai, aprašoma tyrimų metodika, darbo mokslinis naujumas, darbo rezultatų... [toliau žr. visą tekstą]<br>In this thesis the problems of identification accuracy of elastic properties of materials are examined. The main object of study is samples of various materials and their elastic properties. This is an important subject of theoretical studies of various materials. The main thesis objective is to create an effective technology for precise identification of all the elastic characteristics of the sample. The de-veloped algorithms are to be applied in the material manufacturing industry. Thesis also aims at exploring accuracy and sensitivity of the identification of elastic properties of materials. The paper deals with a number of objectives: 1) to optimize the geometric parameters of the sample striving for more accurate identification results of elas-tic properties; 2) to identify mode shapes of sample and regulate their place in spectrum of eigenvalues in order to minimize the distortion of the objective function; 3) to create the implementation algorithms of proposed technologies and verify their capabilities experimentally. The first task is formulated taking into account the relatively high level of identification error of elastic properties of composite materials. The second objective relates to distortion of the objec-tive function in the process of updating the mathematical model with the pre-sumed elastic characteristics of material. The thesis is composed of four chapters, the summary of results, the list of literature and the list of author’s publications on the topic... [to full text]

The main goal of this doctoral thesis is the development and optimization of inkjet- based technologies for hybrid electronic circuits manufacturing, as well contribute on the development of the incoming low cost electronics. Regarding that, a novel solution for connecting regular SMDs and standard silicon SMD packages by inkjet printing is proposed. The novel connecting method allows the assembling at very low temperatures, and thus assures the compatibility with the incoming substrates. Electrical contact resistance and shear strength measurements performed by silver nanoparticle- based ink are comparable to benchmark connecting materials. In sum up, flexible hybrid circuit is successfully manufactured by silver nanoparticle-based ink on paper, where different SMDs size-shaped are assembled demonstrating the reliability and feasibility of the proposed method. Another objective of the work is to apply and adapt the print-on-slope technique to assemble directly the silicon dies on PCB, proposing a novel strategy to overcome the drawbacks of the wire bonding in the Conductive AFM measurements. Then, a novel setup for conductive AFM mode 2D materials characterization was manufactured. The 2D connection on ramp-shape terminations gives a better functionality than current wire bonding connections. The AFM tip moves over the silicon die without physical obstruction, giving a unique solution at this novel method to characterize the material degradation. In the field of multilayer hybrid PCB manufacturing, the goal is to prove the potentiality of different metal-insulator-metal structures inkjet-printed and evaluate their reliability and the electrical performance for low cost multilayer circuit based on paper substrate. In the light of the results, heterogeneous structures combining inorganic and organic dielectric material, where PVP fills the inorganic cracks and voids, possess a similar and outstanding feasibility in both paper and glass substrate without short-circuits. The greatest achievement of this work is the development and optimization of a novel capillarity-assisted SMD assembling method for the manufacturing of hybrid circuits inkjet-printed. In addition, taking advantage of print-on-slope technique, direct assembling of silicon die integrated circuits to PCB is successfully applied. Moreover, heterogeneous structures inkjet-printed open new solutions for multilayer hybrid circuits.<br>L’objectiu principal d’aquesta tesi doctoral és el desenvolupament i l’optimització de tecnologies basades en injecció de tinta per a la fabricació de circuits electrònics híbrids, així com contribuir al desenvolupament de l’electrònica de baix cost. Es proposa una nova solució per connectar els dispositius de muntatge superficial (SMDs) mitjançant impressió de tinta amb càrrega de nanopartícules de plata. El nou mètode de soldadura permet fer la connexió a temperatures molt baixes i, per tant, assegura la compatibilitat amb els substrats tèrmicament menys resistents. Les mesures elèctriques de resistència de contacte i les mesures mecàniques de resistència de cisalla obtingudes són comparables a als obtinguts amb materials de connexió convencionals. En definitiva, s’ha aconseguit fabricar circuits hídrids flexibles amb èxit mitjançant tinta basada en nanopartícules de plata sobre paper, on diferents dimensions de SMDs han estat soldats, la qual cosa demostra la fiabilitat i la viabilitat del mètode proposat. Un altre dels objectius del treball és aplicar i adaptar la tècnica d'impressió mitjançant rampes per muntar directament microelectrònica sobre circuits impresos. Mitjançant aquesta tècnica, s’han superat els inconvenients provocats per les unions de fil d’or al realitzar mesures conductives mitjançant AFM. Així, s’ha utilitzat una nova estratègia per a la caracterització de materials 2D mitjançant la tècnica de CAFM. Les connexions 2D proporcionen una millor funcionalitat que les connexions actuals mitjançant fils. De fet, la punta AFM es mou sobre la mostra de silici sense obstrucció física, donant una solució única en aquest mètode per caracteritzar la degradació del material. En el camp de la fabricació de PCB híbrida multicapa, l'objectiu és provar la potencialitat de diferents estructures metall-aïllant-metall impreses mitjançant inkjet i avaluar la seva fiabilitat i les propietats elèctriques per a un circuit multicapa de baix cost basat en substrat de paper. A la vista dels resultats, les estructures heterogènies que combinen material dielèctric inorgànic i orgànic, on el PVP omple les esquerdes i els buits de les capes de material inorgànic, presenten unes bones prestacions elèctriques i tenen una viabilitat similar tant en paper com en substrat de vidre sense curtcircuits. La fita més rellevant d’aquest treball és el desenvolupament i l’optimització d’un nou mètode de soldadura de SMDs mitjançant inkjet i assistit per capil·laritat. Aprofitant la tècnica d'impressió sobre rampes, s’ha aconseguit muntar directament circuits integrats de silici sobre PCBs. A més, les estructures heterogènies impreses per injecció de tinta obren noves solucions per a circuits híbrids multicapa.

In the present study low pressure plasma pretreatment has been investigated as an alternative to chemical primer pretreatment. The mechanical properties of Polypropylene-Cyanoacrylate bonding which were both, plasma and primer pretreated were compared. From the investigations, where the plasma parameters were systematically varied, it can be concluded that a very short exposure to an oxygen plasma and new curing conditions led to the best results. The shear strength after plasma pretreatment became even higher than after primer pretreatment.

Metallic glasses possess attractive properties, such as high strength, good corrosion resistance, and superior soft magnetic performance. They also serve as precursors for synthesizing nanocrystalline materials. In addition, a new class of composites having crystalline phases embedded in amorphous matrix is evolving based on selective crystallization of metallic glasses. Therefore, crystallization of metallic glasses and its effects on properties has been a subject of interest. Previous investigations from our research group related to laser assisted crystallization of Fe-Si-B metallic glass (an excellent soft magnetic material by itself) showed a further improvement in soft magnetic performance. However, a fundamental understanding of crystallization and mechanical performance of laser treated metallic glass was essential from application point of view. In light of this, the current work employed an integrated experimental and computational approach to understand crystallization and its effects on tensile behavior of laser treated Fe-Si-B metallic glass. The time temperature cycles during laser treatments were predicted using a finite element thermal model. Structural changes in laser treated Fe-Si-B metallic glass including crystallization and phase evolution were investigated with the aid of X-ray diffraction, differential scanning calorimetry, resistivity measurements, and transmission electron microscopy. The mechanical behavior was evaluated by uniaxial tensile tests with an InstronTM universal testing machine. Fracture surfaces of the metallic glass were observed using scanning electron microscopy and site specific transmission electron microscopy. Fe-Si-B metallic glass samples treated with lower laser fluence (<0.49 J/mm2) underwent structural relaxation while higher laser flounces led to partial crystallization. The crystallization temperature experienced an upward shift due to rapid heating rates of the order of 104 K/s during laser treatments. The heating cycle was followed by termination of laser upon treatment attainment of peak temperature and rapid cooling of the similar order. Such dynamic effects resulted in premature arrest of the crystallite growth leading to formation of fine crystallites/grain (~32 nm) of α-(Fe,Si) as the major component and Fe2B as the minor component. The structural relaxation, crystallization fractions of 5.6–8.6 Vol% with α-(Fe,Si) as the main component, and crystallite/grain size of the order of 12 nm obtained in laser fluence range of 0.39-0.49 J/mm2 had minimal/no influence on tensile behavior of the laser treated Fe-Si-B metallic glass foils. An increase in laser fluence led to progressive increase in crystallization fractions with considerable amounts of Fe2B (2-6 Vol%) and increase in grain size to ~30 nm. Such a microstructural evolution severely reduced the strength of Fe-Si-B metallic glass. Moreover, there was a transition in fracture surface morphology of laser treated Fe-Si-B metallic glass from vein pattern to chevron pattern. Tensile loading lacked any marked influence on the crystallization behavior of as-cast and structurally relaxed laser-treated metallic glass foils. However, a significant crystallite/grain growth/coarsening of the order of two and half times was observed in the fractured region compared to the region around it for the laser-treated partially crystallized metallic glass foils. The simultaneous effects of stress generation and temperature rise during tensile loading were considered to play a key role in crystallite/grain growth/coarsening.

The issue of descaling is an important part of the forging and heat treatment of steel and semi products of steel production. Rising of new information and study of this process can increase efficiency and improve the surface quality after descaling. This thesis is focused on the mechanisms of the high pressure hydraulic descaling qualification and study of the chemical compounds of which the scales grown. To achieve all goals of this work and to get a comprehensive view of descaling process, few experimental measurements and numerical analyses were performed. All experimental measurements were focused on obtaining data about fundamental parameters and effects of the hydraulic descaling. The data obtained from measurements were applied to numerical analyses, which aimed to discover a deeper relation and to confirm the experimental results. This thesis can be divided into two main parts. The first part is devoted to parameters of the water jet study. The main studied characteristics of the high pressure hydraulic water jet were heat transfer coefficient and impact pressure at different modes such as standard or pulsating water jet. Experimentally measured data of these parameters were applied in numerical analyses. The numerical analyses were focused on studying the impact of the water jet parameters on the stresses in the oxide scale layers. A further water jet analysis was focused on the influence of the individual parts of the hydraulic system (such as water chamber or stabilizer) on its characteristics. In this part different types of the water chambers in combination with different types of stabilizers on the impact pressure values were investigated. These measurements were supported by fluid flow analysis through the hydraulic system. The second part of this work was focused on getting mechanical properties of the oxide scales from specimens prepared from standard structural steel and specimens from silicon steel. In this thesis, the influence of various parameters and characteristics was studied on these two types of steel. Mechanical properties of oxide scale structures were carried out by the Small Punch Test method. To obtain the fundamental mechanical properties such as Young´s modulus, yield strength and ultimate strength, material parameters based on the measured data were optimized. The whole work was carried out in order to get valuable and comprehensive results about high pressure hydraulic descaling process and influencing factors as well as about oxide scales themselves.

Les bétons végétaux, composés de particules végétales et d'un liant minéral ou organique, constituent une solution à explorer pour limiter l'impact environnemental du bâtiment. Utilisés principalement pour leurs performances thermiques, ces matériaux suscitent l'intérêt de plusieurs organismes de recherche ainsi que de plusieurs entreprises industrielles. La généralisation de leur utilisation dans la construction ne sera pas possible sans résoudre certains problèmes liés à leurs techniques de mise en œuvre, à leur certification et à leur durabilité. Le présent travail a pour objectif de contribuer à la caractérisation de ces matériaux complexes. Il s'agit en particulier d'étudier les comportements mécanique, thermique et hydromécanique du béton de granulats de bois. La stratégie utilisée consiste à combiner l'expérience et la modélisation pour mieux comprendre les mécanismes mis en jeu. Le module de Young et la résistance en compression ont été mesurés expérimentalement à l'aide de la technique de corrélation d'images numériques. L'évolution de ces propriétés dépend des conditions de conservation, de la durée de séchage ainsi que de la teneur en ciment. En raison de l'orientation aléatoire des granulats de bois, le comportement mécanique du béton est isotrope. Un modèle d'homogénéisation basé sur le schéma autocohérent a été développé pour prédire le module de Young du béton et ses résultats sont très satisfaisants. Les mesures de la conductivité thermique montrent que celle-ci reste constante en conditions endogènes. La modélisation de cette propriété par le schéma autocohérent conduit à des résultats cohérents avec les mesures expérimentales. En conditions de dessiccation, la conductivité thermique dépend linéairement de la densité du béton. L'évolution de la conductivité thermique des granulats de bois et de la pâte de ciment au cours du séchage a été modélisée grâce au schéma de Mori-Tanaka. Ces évolutions ont été intégrées dans le modèle autocohérent qui fournit ainsi des résultats satisfaisants, mais qui pourrait être amélioré si l'on disposait des courbes de sorption/désorption des constituants du béton. Les variations dimensionnelles du béton au cours du temps dépendent des conditions de conservation, mais pas de la direction de mesure, ni de la teneur en ciment. Un modèle reposant sur une combinaison des déformations induites par la désorption de l'eau par des constituants et le transfert d'humidité entre ceux-ci a été proposé et a permis de capturer les tendances des déformations du béton sauf au jeune âge. À l'échelle locale, l'étude a montré que les déformations du béton sont du même ordre de grandeur que celles de la pâte de ciment. Elle a aussi mis en évidence un endommagement partiel de l'interface granulat/liant qui mériterait à être pris en compte dans la modélisation<br>Environmentally-friendly concretes, made up of plant-based particles and mineral or organic binder, are solutions worth exploring to reduce the environmental impact of buildings. Mainly used for their thermal performance, these materials have aroused interest of many research organisations and industrial companies. Their widespread use in construction is not possible without resolving some technical problems related to their implementation, certification and durability. This work aims to contribute to characterize these complex materials, in particular to study the mechanical, thermal and hydromechanical behaviors of wood-aggregate concrete. Modeling and experiments have been used to understand the complex mechanisms involved. The Young's modulus and the compressive strength were experimentally measured using digital image correlation. The evolution of these properties depends on the conditions of storage, the drying time and the cement content. Because of the random orientation of the wood aggregates, the material exhibits isotropic behavior. A homogenization model based on a self-consistent scheme was developed to predict the Young's modulus. The results were satisfactory. Measurements show that thermal conductivity remains constant under sealed conditions. The modeling of this property with the self-consistent scheme gives results consistent with experimental measurements. In desiccation conditions, the thermal conductivity depends linearly on the density of concrete. The evolution of the thermal conductivity of the wood aggregates and the cement paste during drying was modeled with the Mori-Tanaka scheme. These evolutions were integrated into the self-consistent model, which yielded satisfactory results, but could be improved if sorption/desorption curves of the phases were available. The macroscopic dimensional variations of the wood-aggregate concretes depended on the storage conditions, but not on the measurement direction, nor on the cement content. A model based on the combination of the strains induced by the desorption of water from the phases and the moisture transfer between them was proposed. It allowed us to capture the trends of the strains of our concrete except at early age. At a local scale, the study showed that the strains of concrete were close to those of the cement paste. The study also shed light on a significant damage of the aggregate/binder interfaces, which would deserve to be taken into account into the modeling

L'objet de ce travail est le developpement et la mise au point de methodes mathematiques et numeriques, ainsi que de techniques experimentales, pour optimiser les essais biaxiaux en double traction sur les metaux lamines anisotropes, et obtenir ainsi des donnees experimentales realistes et fiables pour l'identification correcte des lois de comportement de ces materiaux. Pour la realisation correcte des essais biaxiaux, un programme d'asservissement pour une machine d'essais biaxiale directe, permettant le pilotage des essais a partir des donnees mesurees en temps reel, a ete concu et mis en uvre. De plus, la technique du montage des eprouvettes en rotules ponctuelles a ete adaptee aux essais biaxiaux hors-axes et, pour la premiere fois, une machine d'essais biaxiale est equipee de cette nouvelle technique. Un interet particulier de ce travail porte sur la definition de la meilleure geometrie des eprouvettes pour les essais biaxiaux directs, a l'aide de simulations numeriques en elements finis. A cette fin, un critere mathematique d'optimisation et le modele numerique correspondant ont ete developpes pour l'optimisation de la geometrie des eprouvettes cruciformes, en considerant des materiaux elastiques isotropes, elastiques anisotropes, et elastoplastiques isotropes avec ecrouissage isotrope dans le cadre des grandes deformations. Enfin, un programme experimental a ete realise pour des toles en alliage d'aluminium et en acier doux, dans le but de demontrer la validite et les performances des methodes et techniques proposees

Les propriétés de premier passage en général, et parmi elles le temps moyen de premier passage (MFPT), sont fréquemment utilisées dans les processus limités par la diffusion. Les processus réels de diffusion ne sont pas toujours Browniens : durant les dernières années, les comportements non-Browniens ont été observés dans un nombre toujours croissant de systèmes. Les milieux biologiques sont un exemple frappant où ce genre ce comportement a été observé de façon répétée. Nous présentons dans ce manuscrit une méthode basée sur les propriétés de premier passage permettant d'obtenir des informations sur le processus réel de diffusion, ainsi que sur l'environnement où évolue le marcheur aléatoire. Cette méthode permet de distinguer trois causes possibles de sous-diffusion : les marches aléatoires en temps continu, la diffusion en milieu fractal et le mouvement brownien fractionnaire. Nous étudions également l'efficacité des processus de recherche sur des réseaux discrets. Nous montrons comment obtenir les propriétés de premier passage sur réseau afin d'optimiser ensuite le processus de recherche, et obtenons un encadrement général du temps moyen de premier passage global (GMFPT). Grâce à ces résultats, nous estimons l'impact sur l'efficacité de recherche de plusieurs paramtres, notamment la connectivité de la cible, la mobilité de la cible ou la topologie du réseau.

Cardiac magnetic resonance (MR) imaging can non-invasively assess heart function. Displacement encoding with stimulated echoes (DENSE) is an advanced cardiac MR imaging technique that measures tissue displacement and can be used to quantify cardiac mechanics (e.g. strain and torsion). When combined with clinical risk factors, cardiac mechanics have been shown to be better predictors of mortality than traditional measures of heart function. End-expiratory breath-holds are typically used to minimize respiratory motion artifacts. Unfortunately, requiring subjects to breath-hold introduces limitations with the duration of image acquisition and quality of data acquired, especially in patients with limited ability to hold their breath. Thus, DENSE acquisitions often require respiratory navigator gating, which works by measuring the diaphragm during normal breathing and only acquiring data when the diaphragm is within a pre-defined acceptance window. Unfortunately, navigator gating results in long scan durations due to inconsistent breathing patterns. Also, the navigator echo can be used in different ways to accept or reject image data, which creates several navigator configuration options. Each respiratory navigator configuration has distinct advantages and disadvantages that directly affect scan duration and image quality, which can affect derived cardiac mechanics. Scan duration and image quality need to be optimized to improve the clinical utility of DENSE. Thus, the goal of this project was to optimize those parameters. To accomplish this goal, we set out to complete 3 aims: 1) understand how respiratory gating affects the reproducibility of measures of cardiac mechanics, 2) determine the optimal respiratory navigator configuration, and 3) reduce scan duration by developing and using an interactive videogame to optimize navigator efficiency. Aim 1 of this project demonstrated that the variability in torsion, but not strain, could be significantly reduced through the use of a respiratory navigator compared to traditional breath-holds. Aim 2 demonstrated that, among the configuration options, the dual-navigator configuration resulted in the best image quality compared to the reference standard (traditional breath-holds), but also resulted in the longest scan duration. In Aim 3, we developed an interactive breathing-controlled videogame and demonstrated that its use during cardiac MR can significantly reduce scan duration compared to traditional free-breathing and also led to a small improvement in signal-to-noise ratio of the acquired images. In summary, respiratory navigator gating with DENSE 1) reduces the variability in measured LV torsion, 2) results in the best image quality with the dual-navigator configuration, and 3) results in significantly shorter scan durations through the use of an interactive videogame. Selecting the optimal navigator configuration and using an interactive videogame can improve the clinical utility of DENSE.

Bricks are traditional building materials with ancient origin, but that can respond to the important challenges the industrial research is currently called to face, i.e. in reducing energy consumption, in lowering production costs and in improving physical properties and durability of the finished products. The growing demand for a sustainable production addressed research to obtain new materials designed to meet environmental issues and society welfare. A possible way to achieve these goals and satisfy these different aspects is the optimisation of new mix design, re-using waste materials produced from industrial, urban and excavation activities. The fulfilment of a sustainable production is twofold, determining a reduction in the exploitation of new geo-resources, and mitigating the problem of waste accumulation and management, reassessing residual materials as secondary sources for a new environmental-friendly material production. Although numerous studies have been carried out in the last decades addressing waste reuse as a successful alternative resource in the production of bricks, their implementation in the industrial sector is still very limited. The main reasons are: i) sporadic partnership between academic research and industry in this technological area; ii) lack of specific standards for the evaluation of processes and finished products; and iii) limited public education on the possible sustainable frontiers. Another important issue should be considered in the production of new materials: the maintenance of the aesthetic quality when substituting traditional materials. Bricks are building materials, and innovation should respect parameters such as the "cultural compatibility", understood as the recognition of the territorial identity of a community. This aspect has even of greater relevance when bricks are used as integration or replacement materials in the restoration of damaged historical buildings. This work aims at filling the gap between academic research and industrial development, through a close collaboration between university and industry and the achievement of common objectives. This was possible with the support of a leader company in the production of traditional bricks, SanMarco-Terreal srl (Noale, Italy), which contributed offering technical support, raw materials and consolidate experience in the production of traditional bricks. New mix designs have been developed according to the objectives of Horizon 2020, (https://ec.europa.eu/programmes/horizon2020/), particularly in the field of sustainable use of natural resources, optimization of firing conditions, recycling and gas emission control, in order to satisfy the goals related to the scientific excellence, the societal challenges and the industry leadership. Therefore, the study focused on: 1) the relationship between chemical-mineralogical characteristics and mechanical properties and durability under different stress conditions of bricks already on the market, obtained by different clays and fired at different temperatures (600, 950, 980, 1050°C); 2) the characterisation of the pore system in commercial bricks using a multi-analytical approach, in order to fully understand and describe porosity through a parameterization of the morphological characteristics of pores. This study was also addressed to the optimization of the pore system in fired bricks obtained from different raw materials and fired at different temperatures (600, 950, 1050°C), providing hints for the optimisation of production strategies that can affect the pore system and the brick quality; 3) the study of new mix designs obtained by adding waste material from quarrying activities and industrial sludge for the production of new bricks based on the concepts of reuse and sustainable use of natural resources. The type of waste specifically adopted were: i) trachyte fragments from quarrying activity (Euganean Hills, Italy); ii) sludge resulting from the ceramic industry. The study of the commercial bricks showed that the chemical-mineralogical and physical-mechanical properties, the porosity and the durability of the finished products are highly dependent on the raw material composition and the firing temperatures reached during the production process. The results obtained for the new experimental products demonstrated the real possibility to achieve new bricks reusing waste, maintaining the physical, mechanical and aesthetic features of the traditional materials and improving the quality of the finished product. More in detail, commercial bricks fired at temperature of 1050°C showed considerable mineralogical transformations, with the growth of new phases and a higher vitrification process in the matrix, which determined improvement of the mechanical properties. On the contrary, brick fired at 600°C had good water behaviour, but resulted weaker during accelerated ageing tests. This behaviour is due to the low compactness determined by the absence of vitrification in the matrix and the low rate of new phase crystallisation. Moreover, it was observed how hausmannite (Mn3O4) used as a dye, caused changes not only in the aesthetic aspect of the finished product determining a dark grey colour, but also in its mechanical properties and in the porous system, since it promotes the melting process. The detailed study of the porosity allowed knowing the pore system in each of the samples and assessing the influence of the raw materials and firing temperature on the development of the pore system. Bricks produced with carbonate clay showed higher porosity and pore interconnection due to the decomposition of the carbonate during the firing process. Moreover, in the bricks fired at higher temperatures (1050°C) changes in the morphology of pores occurred, which became larger and rounder due to the release of volatiles. On the contrary, in bricks obtained from the least carbonate clay and fired at 600°C, porosity displayed very different features, with less homogeneous and smaller pores. In the study on the influence of the waste materials used in the production of new bricks, two different cases were considered: i) addition of stone waste from trachyte quarrying activity; ii) addition of ceramic sludge. These materials were added as temper; influence on the physical-mechanical properties and durability were investigated. Results were satisfactory, recognising their potentiality as possible sustainable additives in the brick industry. It was observed that the alkali feldspars in trachyte act as fluxing agents and decrease the melting point. This effect was emphasized with different observations: textural and mineralogical analyses showed a considerable increase of the number of bridges among minerals and a wider recrystallization of the matrix, sonic data an overall increase in compactness, porometry a different evolution of the pores system upon firing. These changes developed not only at increasing temperature, but also at increasing trachyte content. Furthermore, the analysis of the thermal properties, carried out on infrared images showed that the increasing content of trachyte reduces heat transmittance. Only in one case (a brick with 15% of trachyte and fired at 1050°C) an increase in heat transmittance was observed, caused by the high degree of sintering achieved. In general, the good response to stress conditions (under freeze-thaw and salt crystallization cycles) and the relatively homogeneous features among the samples showed that trachyte can be considered as a valid alternative material to the currently used temper which also brings technical advantages. One important result is that the addition of a trachytic temper confers to bricks the same technical features of traditional ones already at a temperature as low as 900°C, opening the possibility to the reduction of production costs, in addition to that of exploitation and use of new geo-resources. The use of sludge from ceramic industry also showed satisfactory results. Colorimetry proved that these bricks have aesthetic characteristics very similar to those of bricks already on the market, as well as mechanical properties determined by uniaxial compressive and ultrasonic tests. Nonetheless, differences arose when durability was evaluated. While during the salt crystallisation tests the experimental bricks preserve almost intact their original appearance and mechanical properties, they resulted to be particularly vulnerable to freeze-thaw cycles. This suggests that they may represent a valid substitute of commercial bricks, but caution should be taken when using in cold climates. PhD thesis is an important starting point to address the improvement of the traditional bricks in a sustainable way, and the assessment of the characteristics for new materials derived from industrial wastes, evaluating quality and durability. Both case studies demonstrated that the reuse of industrial waste could indeed sustain the industrial sector of brick production, providing a reduction in the exploitation of geo-resources, energy consumption and costs. The comprehension of the intrinsic relationships between mineralogical composition, textural features and physical properties resulted to be fundamental for the development of new products.<br>BRICKTECH: Valutazione dell’utilizzo dei materiali di scarto nella produzione di laterizi. Caratterizzazione petrofisica di nuovi mix design e ottimizzazione delle condizioni di cottura. RIASSUNTO Il laterizio é un materiale della tradizione costruttiva dalle antiche origini, ma che può rispondere alle importanti sfide verso cui la ricerca in ambito industriale è attualmente rivolta, ossia il risparmio energetico, l’abbassamento di costi nella produzione e il miglioramento delle qualità del prodotto finito. Inoltre, la crescente domanda di una produzione sostenibile ha indirizzato la ricerca verso nuovi materiali che tengano conto della salvaguardia dell’ambiente e del benessere della società. Una delle strade percorribili per il raggiungimenti di tali traguardi e che congiunge questi diversi aspetti è l’ottimizzazione di nuovi mix design, utilizzando materiali di scarto, risultato di attività industriali, urbane e di escavazione. In questo modo il consolidamento di produzioni di tipo sostenibile ha un duplice valore in quanto non solo determina la diminuzione dell’utilizzo di nuove geo-risorse, ma si risolve anche il problema dell’accumulo e della gestione dei rifiuti, rivalutandoli come fonte secondaria di interesse per la realizzazione di nuovi materiali nel rispetto della tutela dell’ambiente. Nonostante negli ultimi decenni siano stati numerosi gli studi effettuati per la realizzazione di mattoni con materiali di riuso come risorse alternative e questi abbiano dimostrato una vasta applicabilità nel settore del laterizio, l’implementazione in ambito industriale è ancora oggi molto limitata, a causa della mancanza della compartecipazione tra ricerca accademica e le reali necessità industriali, della scarsità di standard specifici di valutazione dei processi di lavorazione e dei prodotti finiti e della limitata educazione pubblica rispetto alle possibili frontiere sostenibili. Un altro aspetto importante che deve essere considerato nella produzione di nuovi materiali è quello del mantenimento delle caratteristiche estetiche del materiale tradizionale. Il mattone, infatti, essendo un materiale da costruzione, deve rispondere a parametri di “compatibilità culturale”, intesa come riconoscimento della identità territoriale di una comunità. Questo aspetto ovviamente ha un valore ancor maggiore nel caso di materiali impiegati con funzione di integrazione o sostituzione per il ripristino e/o restauro di edifici storici danneggiati. Questo lavoro è, pertanto, rivolto a colmare la lacuna di uno scarso dialogo tra ricerca accademica e sviluppo industriale, attraverso la stretta collaborazione tra università e industria e il raggiungimento di obiettivi condivisi. Questo è stato possibile grazie all’affiancamento di una ditta leader nel settore della produzione di laterizi tradizionali, la SanMarco-Terreal srl (Noale, Italia), che ha apportato il suo contributo mettendo a servizio strumentazioni, materie prime e la gran esperienza maturata in quest’ambito lavorativo. I prodotti sono stati sviluppati in linea con gli obiettivi di Horizon 2020 (https://ec.europa.eu/programmes/horizon2020/), soprattutto in termini di sfruttamento sostenibile delle risorse naturali, di miglioramento dei processi di trasformazione delle materie prime, di riciclaggio e della ottimizzazione delle condizioni di cottura, al fine di soddisfare i punti relativi all’eccellenza scientifica, alle sfide per la società e alla leadership industriale. Pertanto, lo studio è stato rivolto a: 1) mettere in relazione le caratteristiche mineralogiche e chimiche con le proprietà meccaniche e la durabilità in diverse condizioni di stress di materiali già in commercio, ottenuti da differenti argille e cotti a diverse temperature (600, 950, 980, 1050°C); 2) analizzare il sistema poroso di materiali industriali al fine di ottenerne una conoscenza affidabile e completa come punto di partenza per definire un protocollo per la quantificazione e la parametrizzazione delle caratteristiche morfologiche dei pori attraverso l'uso combinato di metodi tradizionali e tecniche di elaborazione di immagine a seconda del tipo di materia prima utilizzata e le temperature di cottura raggiunte (600, 950, 1050°C); 3) sperimentare nuovi mix design ottenuti dall'aggiunta di rifiuti provenienti da attività di estrazione di materiale lapideo e industriali per la produzione di nuovi mattoni basata sui concetti di riciclo e di uso sostenibile delle risorse. Il tipo di materiali di ri-uso adottati nello specifico sono stati: i) lo scarto di escavazione di trachite della cava di Rovolon, Colli Euganei, Vicenza (Italia); ii) un fango refluo derivante dall’industria ceramica. Lo studio dei mattoni commerciali ha confermato come le proprietà chimico-mineralogiche, fisico-petrografiche, di porosità e di durabilità dei prodotti finiti siano strettamente dipendenti dalla composizione delle materie prime e dalle temperature di cottura raggiunte durante il processo di produzione. I risultati conseguiti dalle analisi dei mix design sperimentali hanno dimostrato la possibilità di ottenere nuovi laterizi utilizzando materiale di scarto e di implementare strategie industriali con soluzioni sostenibili e compatibili. Più in dettaglio, i mattoni commerciali (1) cotti a temperature superiori a 1050°C hanno mostrato una maggiore evoluzione mineralogica, con la crescita di nuove fasi, e fusione della matrice, con un conseguente miglioramento delle proprietà meccaniche. Al contrario il mattone cotto a 600°C si è distinto per un buon comportamento idrico, rilevandosi però il più debole durante i cicli di invecchiamento accelerato, a causa della bassa compattezza, a questa dovuta all’assenza di vetrificazione nella matrice e alla bassa evoluzione di nuove fasi a tale temperatura. Inoltre, è stato osservato come l’hausmannite (Mn3O4) utilizzata come colorante, comporti cambiamenti non solo sull’aspetto estetico del prodotto finito (determinando un colore grigio scuro), ma agisca anche nelle sue proprietà meccaniche e nel sistema poroso promuovendo il processo di fusione. Lo studio dettagliato della porosità (2) conseguito attraverso l’uso di differenti metodologie di studio ha permesso da un lato di comprendere in maniera più approfondita i limiti di ogni tecnica, dall’altro di conoscere il sistema poroso di ogni campione nella sua complessità. I mattoni prodotti con argilla carbonatica han mostrato una maggiore porosità e interconnessione dei pori, che derivano dalla decomposizione del carbonato durante il processo di cottura. Nei mattoni cotti a temperature più alte (1050°C) è stato riscontrato lo sviluppo della morfologia dei pori, che diventano più grandi e rotondi. Al contrario nel mattone ottenuto con l’uso di una argilla meno carbonatica e cotto a 600°C, la porosità è molto diversa, i pori sono meno omogenei e più piccoli. Nella valutazione dell’influenza dell’utilizzo di materiale di scarto (3) per la produzione di nuovi laterizi, in entrambi i casi di studio i) l’aggiunta di trachite di escavazione (5, 10, 15% in peso) e ii) l’aggiunta del fango ceramico (10% in peso) come inerte, i risultati sono stati soddisfacenti al fine di identificare possibili “alternative sostenibili” ai mattoni attualmente in commercio. i) Si è visto come la presenza di feldspati alcalini nella trachite agiscono come agenti fondenti e diminuiscono il punto di fusione. Questo effetto è stato osservato sotto differenti punti di vista, dall’aumento della connessione tra i minerali, dalla crescente compattezza, dalla maggiore evoluzione della tessitura e del sistema dei pori, tutte caratteristiche che si sviluppano, non sono in corrispondenza dell’aumento della temperatura, ma anche dell’aumento del contenuto di trachite. Inoltre, lo studio delle proprietà termiche, condotto attraverso l’analisi di immagini infrarosse, ha evidenziato come il crescente contenuto di trachite riduca la capacità di trasmissione di calore. Solo nel caso del mattone con 15% di trachite e cotto alla temperatura di 1050°C è stata osservata una trasmissione di calore più rapida, per l’alto livello di sinterizzazione raggiunto. In generale la buona risposta alle condizioni di stress (gelo-disgelo e cristallizzazione di sali) e l’assenza di una forte differenza tra i campioni hanno dimostrato che la trachite può essere considerata un inerte alternativo a quello normalmente utilizzato che inoltre può recare vantaggi nella produzione, con risparmio di energia e di costi, dal momento che agisce come agente fondente. Il suo impiego permette, infatti, di ottenere mattoni cotti a 900°C (temperatura inferiore a quella attualmente utilizzata dalla ditta) e che contengano più del 10% di inerte, limitando lo sfruttamento e l’uso di nuove geo-risorse. ii) Anche la miscela con l’aggiunta del fango di scarto dell’industria ceramica ha ottenuto risultati soddisfacenti. Le prove di colorimetria han dimostrato che il prodotto finito mantiene un aspetto molto simile ad un mattone di colore giallo già in commercio (ottenuto con la stessa argilla, ma con l’inerte standard) suggerendone la possibile sostituzione dal punto di vista estetico. Le prove di compressione uniassiale e l’analisi ad ultrasuoni hanno, inoltre, rilevato anche un comportamento meccanico molto simile a quello del mattone commerciale giallo, indice della sua compatibilità anche nella riposta al carico. Solo dal punto di vista della durabilità il mattone ottenuto con l’aggiunta del fango ha mostrato una risposta più debole. Mentre durante la cristallizzazione dei sali il suo aspetto originario è rimasto quasi intatti, a condizioni forzate di gelo e disgelo si è riscontrato il progressivo deterioramento dei campioni fino alla loro totale disgregazione alla fine della prova. Alla luce di quanto evidenziato questo nuovo mix design può essere a tutti gli effetti considerato un’alternativa sostenibile del mattone commerciale, in particolare per il mantenimento delle proprietà fisico-meccaniche e delle qualità estetiche, ma non può essere messo in opera in edifici situati in situazioni ambientali dove sono possibili cicli di gelo e disgelo. Questa tesi di Dottorato rappresenta un punto di partenza fondamentale per affrontare la riqualificazione di mattoni tradizionali in chiave sostenibile e permettere la valutazione in termini di qualità e durabilità dei mix sperimentali ottenuti con materiali di riciclo, nel caso specifico consistenti in trachite di cava e in un fango ceramico. Entrambi i casi di studio hanno dimostrato di rappresentare una valida alternativa al fine di ottenere nuovi mattoni di interesse per il miglioramento del settore industriale del laterizio, in termini di risparmio di sfruttamento di geo-risorse, energia e costi. Comprendere le relazioni intrinseche tra composizione mineralogica, caratteristiche tessiturali, la microstruttura e le proprietà fisiche del laterizio è la base di una consapevole conoscenza del materiale per lo sviluppo di nuovi mix design.

Road safety is a complicated issue that affects most world economies due to its negative socioeconomic impact. Road safety programs include different programs that cover different areas for minimizing the effects of these impacts. One of these programs focuses road safety against invasion of wildlife into traffic roads. Most economies that heavily include these particular programs, such as Sweden, rely on specific machinery and techniques for clearing road shoulders that allows driver to foresee any possible danger or road invasion in good time. The most common piece of machinery used for covering this type of activity is known as a boom mower. Boom mowers can be pictured as giant lawnmowers that are attached into a long boom crane from wheel loaders or excavators, so they can clear invading vegetation from the road shoulders. Boom mowers suffer from heavy wear due to their dimensions, weight and operating speed which it requires companies to pay extra attention to their construction and choice of materials. Cranab Slagkraft is a Swedish company that has been specialized for providing high quality boom mowers for the last 30 yearsfor clearing vegetation on the Swedish roads. But, despite their higher quality products, these boo mowers are often expensive and complicated to manufacture. For this reason, Cranab has requested a study to minimize the manufacturing burden in order to simplify its production and diminish cost. This research study focuses on the latest components addition into the boom mower construction to assess their performance. For this research, the researcher will put to test the reinforcements of the boom mower’s model SH150 and see what their performance against harmonic vibrations and structural strength against local stresses are. The research follows two complementary analysis. First, a modal analysis on the boom mower’s main structure for evaluating resonance levels at an operating frequency. Second, a structural analysis with idealized conditions at operating speed to determine construction stress resilience. The results in this research reveals that the modal analysis rejects the viability of one group of reinforcements and confirms the implications of the other one. Also, the results reveal that the complicated geometry requires advanced software for providing more conclusive results. In addition, the boom mower’s own geometry and choice of material might play a role in adjusting the harmonic resonance and adjusting the boom mower’s mechanical properties. The latter conclusion should be considered as a theme of study for future research in this same field.<br>Trafiksäkerhet är ett komplicerat ärende som påverkar de flesta världsekonomier på grund av dess negativa socioekonomiska inverkan. I trafiksäkerhetsprogrammen ingår olika program som täcker olika områden för att minimera de socioekonomiska effekterna. Ett av dessa program koncentrerar sig på trafiksäkerhet mot invasion av vilda djur på motorbanor. De flesta världsekonomiers system som omfattar dessa trafiksäkerhetsprogram, till exempel Sverige, är beroende av specifika maskiner och tekniker för röjning av vägarna som gör det möjligt för föraren att i god tid ska kunna förutse eventuell fara eller vilt som kommer in på vägen. Den vanligaste maskinen som används för röjning av vägar kallas kättingröjare. Kättingröjaren kan liknas vid gigantiska gräsklippare som är fastsatta på en grävmaskin, hjullastare och/eller väghyvel så att de kan rensa bort gräs från vägkanten. Kättingröjare lider av kraftigt slitage på grund av deras dimensioner, vikt och driftshastighet. Det kräver att tillverkaren uppmärksammar konstruktionen och materialvalet till kättingröjaren. Cranab Slagkraft är ett svenskt företag som under de senaste 30 åren har specialiserat sig på att leverera högkvalitativa kättingröjare. Kättingröjarna är ofta dyra och komplicerade att tillverka. Av den anledningen har Cranab begärt en studie för att förenkla produktionen och minska tillverkningskostnaderna. Den här studien koncentrerar sig på det senaste komponenttillägget i kättingröjarens konstruktion för att bedöma deras prestanda. I den här studien testas flera förstärkningar i kättingröjarens modell SH150 för att undersöka deras prestanda mot harmonisk vibration och strukturell hållfasthet mot lokala spänningar. I studien ingår två kompletterande analyser. Först görs en modalanalys på kättingröjarens huvudstruktur för utvärdering av resonansnivåer vid driftsfrekvensen. Sedan görs en strukturell analys med idealiserat tillstånd vid driftshastigheten för att bestämma spänningsmotståndet. I resultatet beskrivs en grupp av förstärkningar som inte har någon påverkan för kättingröjarens harmoniska vibration och spänningsmotstånd och en andra grupp som visar påverkan. Även resultaten visar att den komplicerade geometrin kräver avancerad mjukvara för att ge mer avgörande resultat. Dessutom kan kättingröjarens egen geometri och materialval ha påverkan vid justering av dess harmoniska resonans och mekaniska egenskaper. Den senare slutsatsen bör betraktas som ett begrepp för framtida studier inom samma område.

Carbon fiber-reinforced silicon carbide matrix (C/SiC) composite is a ceramic matrixcomposite (CMC) that has considerable promise for use in high-temperature structuralapplications. In this thesis, systematic numerical studies including the prediction of elasticand thermal properties, analysis and optimization of stresses and simulation ofhigh-temperature oxidations are presented for the investigation of C/SiC composites.A strain energy method is firstly proposed for the prediction of the effective elastic constantsand coefficients of thermal expansion (CTEs) of 3D orthotropic composite materials. Thismethod derives the effective elastic tensors and CTEs by analyzing the relationship betweenthe strain energy of the microstructure and that of the homogenized equivalent model underspecific thermo-elastic boundary conditions. Different kinds of composites are tested tovalidate the model.Geometrical configurations of the representative volume cell (RVC) of 2-D woven and 3-Dbraided C/SiC composites are analyzed in details. The finite element models of 2-D wovenand 3-D braided C/SiC composites are then established and combined with the stain energymethod to evaluate the effective elastic constants and CTEs of these composites. Numericalresults obtained by the proposed model are then compared with the results measuredexperimentally.A global/local analysis strategy is developed for the determination of the detailed stresses inthe 2-D woven C/SiC composite structures. On the basis of the finite element analysis, theprocedure is carried out sequentially from the homogenized composite structure of themacro-scale (global model) to the parameterized detailed fiber tow model of the micro-scale(local model). The bridge between two scales is realized by mapping the global analysisresult as the boundary conditions of the local tow model. The stress results by global/localmethod are finally compared to those by conventional finite element analyses.Optimal design for minimizing thermal residual stress (TRS) in 1-D unidirectional C/SiCcomposites is studied. The finite element models of RVC of 1-D unidirectional C/SiCIIcomposites with multi-layer interfaces are generated and finite element analysis is realized todetermine the TRS distributions. An optimization scheme which combines a modifiedParticle Swarm Optimization (PSO) algorithm and the finite element analysis is used toreduce the TRS in the C/SiC composites by controlling the multi-layer interfaces thicknesses.A numerical model is finally developed to study the microstructure oxidation process and thedegradation of elastic properties of 2-D woven C/SiC composites exposed to air oxidizingenvironments at intermediate temperature (T<900°C). The oxidized RVC microstructure ismodeled based on the oxidation kinetics analysis. The strain energy method is then combinedwith the finite element model of oxidized RVC to predict the elastic properties of composites.The environmental parameters, i.e., temperature and pressure are studied to show theirinfluences upon the oxidation behavior of C/SiC composites.

Polypropylene-based composites are widely used in the industrial field, especially in automotive applications, due to their excellent mechanical properties and low cost. This research is directed towards obtaining the optimal values of mechanical properties of long glass fiber-reinforced polypropylene composite (LGFPP) and polymer-layered silicate nanocomposites (PP-OMMT) for different objectives. Though the primary objective was to minimize the cost of the composite, simulations were also performed to obtain specific desired properties of the composite (irrespective of the composite cost). The latter simulation results are useful in designing products where quality of the composite cannot be compromised (while the cost of the composite is secondary). In this study, the properties that were optimized include tensile Young's modulus, flexural Young's modulus, notched I-zod impact, and permeation. Regression models were obtained and used to predict these properties as functions of corresponding compositions of the composites. Further, optimization procedures were simulated using these models along with other constraints and objective functions. All simulations are programmed using MATLAB version 7.10.0 (R2010a).

Dissertação de Mestrado Integrado em Engenharia Química apresentada à Faculdade de Ciências e Tecnologia<br>The mechanical and dimensional properties of the produced paper should comply with increasing quality constraints to guarantee the satisfaction of costumers. Curl is an important dimensional phenomena that is usually linked to problems experienced by end-users such as printer jams. This potentially problematic phenomena should be controlled and/or mitigated. The aim of this work is to explore existing industrial data to improve our understanding about the sources of variability affecting the production of paper, to extract useful insights on how to optimize the production process of paper making. Several tasks were conducted to explore and analyse the industrial data for selected processing areas: integration and cleaning of process variables, pre-processing and exploratory data analysis (EDA) for the pulp properties and for the infrared (IR) curl measurements, and obtaining preliminary models for the IR curl variables. A principal components analysis (PCA) was performed for the pulp properties, confirming the existence of correlations between variables such as the opacity and light scattering coefficient, and the apparent density with the light scattering coefficient. The effect of the refining degree on the pulp properties was also assessed. Properties such as tensile index, tensile stiffness index and apparent density were shown to increase with the refining degree, as expected. On the other hand, the tear index did not change significantly for higher levels of refining. The IR curl quality variable used in the industry, which combines for each jumbo the measurements for five positions in the orthogonal direction (also known as cross-machine direction, CD) relatively to the production path of the paper machine (machine direction, MD), was analysed thoroughly. The process was shown to be unstable and not operating under statistical control. To better understand these results, the IR curl variable was decomposed in the previously mentioned measurements, by position in CD. A variability component analysis was then performed, indicating that around 92% of the variability was due to the intra-jumbo component (i.e., CD position in the jumbo), with only around 8% being due to the inter-jumbo component. The lack of existing structure between the different CD positions of the jumbo rise important questions. Namely, it could limit the practical application of machine learning approaches to optimize the dimensional stability of the produced paper, due to the noisy structure of the IR curl measurements. With this in mind, future work should confirm the origins of the observed variability for the IR curl variables, including the complete assessment of the repeatability of the used measurement apparatus.<br>As propriedades mecânicas e dimensionais dos papéis produzidos devem obedecer com as crescentes restrições na qualidade, de modo a garantir a satisfação dos utilizadores. O curl é um fenómeno dimensional que está normalmente relacionado com problemas para os utilizadores finais, tais como os encravamentos das impressoras. Este fenómeno potencialmente problemático deve ser controlado e/ou mitigado. O objetivo deste trabalho é explorar dados industriais para melhorar o entendimento sobre as fontes de variabilidade que afetam a produção de papel, para extrair conhecimento em como otimizar o processo de produção de papel. Várias etapas foram percorridas para explorar e analisar os dados industriais para as áreas de processo selecionadas: integração e limpeza das variáveis do processo, pré-processamento e análise exploratória dos dados (AED) para as propriedades da pasta e para as medições do curl infravermelho (IV) e obter modelos preliminares para as variáveis do curl IV. Uma análise de componentes principais (PCA) foi realizada para as propriedades da pasta, que confirmou a existência de correlações entre variáveis como a opacidade e o coeficiente de dispersão da luz, e a massa específica e o coeficiente de dispersão da luz. O efeito do grau de refinação nas propriedades da pasta também foi avaliado. Propriedades como o índice de tração, índice de resistência à tração e massa específica demonstraram um aumento com o grau de refinação, como esperado. Por outro lado, o índice de rasgamento não se alterou para níveis mais elevados de refinação. A variável da qualidade do curl IV usada pela indústria, que combina para cada jumbo as medições para cinco posições na direção ortogonal (também conhecida como cross-machine direction, CD) com o sentido de produção da máquina de papel (machine direction, MD), foi analisada detalhadamente. O processo demonstrou-se como instável e operando fora de controlo estatístico, não garantindo que o papel produzido obedecesse às especificações. Para compreender melhor estes resultados, a variável do curl IV foi decomposta nas medidas previamente mencionadas por posição em CD. Uma análise de componentes de variabilidade foi realizada, indicando que cerca de 92% da variabilidade era devido à componente intra-jumbo (i.e., posição CD do jumbo), com apenas 8% devido à componente inter-jumbo. A falta de estrutura existente entre as diferentes posições em CD do jumbo levanta questões importantes. Pode impedir a aplicação prática de abordagens de Machine Learning para otimizar a estabilidade dimensional do papel produzido, pela obtenção de modelos inúteis que relacionam as medições do curl IV com as variáveis operacionais. Com isto em mente, trabalho futuro deve confirmar as origens da variabilidade observada para as variáveis do curl IV, incluindo a análise da repetibilidade do aparelho utilizado para a sua medição.

碩士<br>國立勤益科技大學<br>化工與材料工程系<br>102<br>This study discusses the process optimization of epoxy nanocomposites, epoxy/glass fiber nanocomposites, and epoxy/carbon fiber nanocomposites. A prediction model for properties of composite materials reinforced with nanoparticles was developed using Taguchi’s method and regression analysis technique. Four main factors including nano-silica weight ratio concentration, alumina weight ratio, carbon black weight ratio, and diluent weight ratio each at three levels were considered for designing. Then we analyzed the optimization through a two-stage simulated annealing method. Finally, the sensitivity analysis was used to explore the influence of various parameters on quality characteristics. The results show that the sensitive parameter for the thermal decomposition temperature of the epoxy/glass fiber and epoxy/carbon fiber nanocomposites is alumina powder content, nanocomposite is silica powder content. The sensitive parameter for the glass temperature of the epoxy/glass fiber is carbon black powder content, epoxy/carbon fiber nanocomposites and nanocomposite is silica powder content. The sensitive parameters for the thermal expansion coefficient (α1) of the epoxy/glass fiber and epoxy/carbon fiber nanocomposites is carbon black powder content, nanocomposite is alumina powder content. The sensitive parameter for the thermal expansion coefficient (α2) of the epoxy/glass fiber nanocomposites is carbon black powder content, the epoxy/carbon fiber nanocomposites is carbon black powder content, the nanocomposites is alumina powder content. The sensitive parameters for Shore D hardness of the epoxy/glass fiber nanocomposites is silica powder content, the epoxy/carbon fiber composites is carbon black powder content, the nanocomposite is silica powder content. The various mechanical and thermal properties of the material are dominated by different compositional elements. Overall, the two-stage simulated annealing and sensitivity analysis methods can help identify the content of the most effective factor, efficiently reduce the number of experiments and improve the quality characteristics, and reaches to enhance effectiveness.

The present study involves the analysis and design optimization of thin and thick laminated composite structures using symbolic computation. The fibre angle and wall thickness of balanced and unbalanced thin composite pressure vessels are optimized subject to a strength criterion in order to maximise internal pressure or minimise weight, and the effects of axial and torsional forces on the optimum design are investigated. Special purpose symbolic computation routines are developed in the C programming language for the transformation of coordinate axes, failure analysis and the calculation of design sensitivities. In the study of thin-walled laminated structures, the analytical expression for the thickness of a laminate under in-plane loading and its sensitivity with respect to the fibre orientation are determined in terms of the fibre orientation using symbolic computation. In the design optimization of thin composite pressure vessels, the computational efficiency of the optimization algorithm is improved via symbolic computation. A new higher-order theory which includes the effects of transverse shear and normal deformation is developed for the analysis of laminated composite plates and shells with transversely isotropic layers. The Mathematica symbolic computation package is employed for obtaining analytical and numerical results on the basis of the higher-order theory. It is observed that these numerical results are in excellent agreement with exact three-dimensional elasticity solutions. The computational efficiency of optimization algorithms is important and therefore special purpose symbolic computation routines are developed in the C programming language for the design optimization of thick laminated structures based on the higher-order theory. Three optimal design problems for thick laminated sandwich plates are considered, namely, the minimum weight, minimum deflection and minimum stress design. In the minimum weight problem, the core thickness and the fibre content of the surface layers are optimally determined by using equations of micromechanics to express the elastic constants. In the minimum deflection problem, the thicknesses of the surface layers are chosen as the design variables. In the minimum stress problem, the relative thicknesses of the layers are computed such that the maximum normal stress will be minimized. It is shown that this design analysis cannot be performed using a classical or shear-deformable theory for the thick panels under consideration due to the substantial effect of normal deformation on the design variables.<br>Thesis (Ph.D.)-University of Natal, Durban, 1994.

博士<br>國立中央大學<br>機械工程研究所<br>98<br>This study investigates the influence of injection molding process parameters on fiber orientation and mechanical properties of short glass fiber reinforced polyoxymethlene (POM/GF) composites. Filling time, melt temperature, mold temperature and packing pressure were considered as the controllable factors during the injection molding process. Taguchi experimental design, ANOVA analysis and principle component analysis were adopted in order to optimize the process conditions. Moreover, the fiber orientation and fracture surfaces were observed with a scanning electron microscope (SEM). Two distinct layers existed in the cross section of the POM/GF tensile specimen. The fibers in the frozen layer were parallel to the tensile direction, while those in the core layer were perpendicular to the tensile direction. In addition, three distinct layers existed in the cross section of wear specimens. The fibers in the frozen and the core layer were perpendicular to the melt flow direction, but the fibers were parallel to the melt flow in the intermediate layer. The tensile strength and friction coefficient increased with the amount of glass fiber. The friction coefficient and the wear volume loss also depended on the sliding direction. The specimen with sliding direction paralleling the melt flow had low friction coefficient and wear volume loss. To obtain the best tensile strength and tribological properties POM/GF composites, the injection molding conditions were as follows: filling time 1.5 s, melt temperature 215℃, mold temperature 75℃, and packing pressure 65 MPa. Though the fiber-avulse and the fiber-snap were the major fracture mechanisms of frozen layer, the fiber-breakage and the pull-out were the major fracture mechanism of the core layer for the tensile specimens. In addition, SEM photographs revealed that peel-off and grooves were the major wear mechanisms of the neat POM. Grooves, debris, cracks and debonded fibers were the major wear mechanisms of the POM/GF composites. With respect to the optimum injection molding process of POM/25wt.% composites, it was found that the most influential factor depended on the target mechanical property. For a multi-response case with the tensile strength, elongation, and friction coefficients (P-type), the optimal injection molding process conditions were filling time 1.5 s, melt temperature 215℃, mold temperature 75℃, and packing pressure 65 MPa. Moreover, the most influential factor was packing pressure, and its contribution was 50.99%.

碩士<br>國立交通大學<br>機械工程系所<br>103<br>Hybrid rocket propulsion has been an important research subject for the past few years because of some outstanding characteristics such as system simplicity, high operation safety, and thrust controllability. In hybrid propulsion system, one of the commonest fuel grains is Hydroxyl-terminated Polybutadiene (HTPB). To design a stable hybrid propulsion system, complete characterization of the material properties of HTPB grain is necessary. In this thesis, baseline and advanced processes of preparing fuel grain are developed and tested. For the baseline process, we have used HTPB and IPDI (Isophorone diisocyanate) with different mixing ratios with addition of a small amount of carbon powder for preventing radiation transfer from the flame through the grain. For the advanced process, we have added castor oil for reducing mixture viscosity and catalyst for greatly speeding up necessary curing process. Several important mechanical properties are measured, respectively, for the baseline and advanced processed fuel grains. The results show that the maximal fraction of IPDI is 12.5%, above which bubbles are trapped in the grain even after a long period of curing time with vacuum pumping. In addition, it is found that 5% of castor oil can effectively reduce the mixture viscosity without affecting the material properties much as compared the baseline procedure. Moreover, addition of 0.02% of catalyst can dramatically shorten the required curing time and can still make bubbles pumped out efficiently. Finally, we have performed several static burn tests and have found that Isp (specific impulse) of the fuel grain with 5% addition of castor oil is higher than that of the baseline procedure, which is in consistent with the prediction made by a public available software, Propep.