To see the other types of publications on this topic, follow the link: Compression and Indentation testing.
Dissertations / Theses on the topic 'Compression and Indentation testing'
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 dissertations / theses for your research on the topic 'Compression and Indentation testing.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
1
Shirmohammadi, Maryam. "Process modelling and simulation of tissue damage during mechanical peeling of pumpkin as a tough skinned vegetable." Thesis, Queensland University of Technology, 2014. https://eprints.qut.edu.au/67921/1/Maryam_Shirmohammadi_Thesis.pdf.
Full textAbstract:
Food waste is a current challenge that both developing and developed countries face. This project applied a novel combination of available methods in Mechanical, agricultural and food engineering to address these challenges. A systematic approach was devised to investigate possibilities of reducing food waste and increasing the efficiency of industry by applying engineering concepts and theories including experimental, mathematical and computational modelling methods. This study highlights the impact of comprehensive understanding of agricultural and food material response to the mechanical operations and its direct relation to the volume of food wasted globally.
2
Pour, Shahid Saeed Abadi Parisa. "Mechanical behavior of carbon nanotube forests under compressive loading." Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/47699.
Full textAbstract:
Carbon nanotube (CNT) forests are an important class of nanomaterials with many potential applications due to their unique properties such as mechanical compliance, thermal and electrical conductance, etc. Their deformation and failure in compression loading is critical in any application involving contact because the deformation changes the nature of the contact and thus impacts the transfer of load, heat, and charge carriers across the interface. The micro- and nano-structure of the CNT forest can vary along their height and from sample to sample due to different growth parameters. The morphology of CNTs and their interaction contribute to their mechanical behavior with change of load distribution in the CNT forest. However, the relationship is complicated due to involvement of many factors such as density, orientation, and entanglement of CNTs. None of these effects, however, are well understood. This dissertation aims to advance the knowledge of the structure-property relation in CNT forests and find methodologies for tuning their mechanical behavior. The mechanical behavior of CNT forests grown with different methodologies is studied. Furthermore, the effects of coating and wetting of CNT forests are investigated as methods to tailor the degree of interaction between CNTs. In situ micro-indentation of uncoated CNT forests with distinct growth-induced structures are performed to elucidate the effects of change of morphology along the height of CNT forests on their deformation mechanism. CNT aerial density and tortuosity are found to dictate the location of incipient deformation along height of CNT forests. Macro-compression testing of uncoated CNT forests reveals mechanical failure of CNT forests by delamination at the CNT-growth substrate. Tensile loading of CNT roots due to post-buckling bending of CNTs is proposed to be the cause of this failure and simple bending theory is shown to estimate the failure load to be on the same order of magnitude as experimental measurements. Furthermore, delamination is observed to occur in the in situ micro-indentation of CNT forests coated with aluminum on the top surface, which demonstrates the role of the mechanical constraints within the CNT forest in the occurrence of delamination at the CNT-substrate interface. In addition, this dissertation explores the mechanical behavior of CNT forests coated conformally (from top to bottom) with alumina by atomic layer deposition. In situ micro-indentation testing demonstrates that the deformation mechanism of CNT forests does not change with a thin coating (2 nm) but does change with a sufficiently thick coating (10 nm) that causes fracturing of the hybrid nanotubes. Ex situ flat punch and Berkovich indentations reveal an increase in stiffness of the CNT forests that are in range with those predicted by compression and bending theories. An increase in the recoverability of the CNTs is also detected. Finally, solvent infiltration is proposed as a method of decreasing stiffness of CNT forests and changing the deformation mechanism from local to global deformations (i.e., buckling in the entire height). Presence of solvents between CNTs decreases the van der Waals forces between them and produces CNT forests with lower stiffness. The results demonstrate the effect of interaction between CNTs on the mechanical behavior. This dissertation reveals important information on the mechanical behavior of CNT forests as it relates to CNT morphology and tube-to-tube interactions. In addition, it provides a framework for future systematic experimental and theoretical investigations of the structure-property relationship in CNT forests, as well as a framework for tuning the properties of CNT forests for diverse applications.
3
Xia, Yang. "A robust statistical method for determining material properties and indentation size effect using instrumented indentation testing." Thesis, Compiègne, 2014. http://www.theses.fr/2014COMP1982/document.
Full textAbstract:
L'indentation instrumentée est un outil pratique et puissant pour sonder les propriétés mécaniques des matériaux à petite échelle. Cependant, plusieurs erreurs (rugosité de surface, effet de taille d’indentation, la détermination de premier point de contact, etc.) affectent l'essai d’indentation instrumentée (e.g. non reproductibilité de la courbe d’indentation) et conduisent à des imprécisions dans la détermination des propriétés mécaniques des matériaux analysés. Une approche originale est développée dans cette thèse pour la caractérisation précise des propriétés mécaniques des matériaux. Cette approche fondée sur une analyse statistique des courbes d’indentation avec la prise en compte d’erreur dans la détermination du premier point de contact et des effets de la rugosité de surface. L’approche est basée sur une minimisation de la distance (défini comme l'erreur de la profondeur de contact initiale) entre l’ensemble des courbes expérimentales et celles simulées par le modèle de Bernhard de manière à générer une courbe maitresse « unique » représentative du faisceau de courbes expérimentales. La méthode proposée permet de calculer à partir de cette courbe maitresse la macro-dureté et le module d’Young du matériau en tenant compte des erreurs dues à la rugosité de surface et à l'effet de taille en indentation pour les faibles profondeurs de pénétration. La robustesse de la méthode est prouvée par son application à différents groupes d’échantillons, i.e. panels de matériaux à propriétés mécaniques diverses, différents traitements de surface (polissage, sablage) et différentes pointes d’indentation permettant de générer différents états de contraintes locaux. Une liaison quantitative entre la rugosité de surface et l'écart type de l'erreur de la profondeur de contact initiale est établie grâce à une analyse multi- échelle de la rugosité de la surface. La méthode proposée permet de caractériser les propriétés mécaniques des matériaux sans avoir recours à la préparation de surface pouvant potentiellement altérer ses propriétés (e.g. génération de contraintes résiduelles, contamination de surface…)<br>Instrumented indentation is a practical and powerful tool for probing the mechanical properties of materials at small scales. However, several errors (surface roughness, indentation size effect, determination of first contact point, etc…) affect the instrumented indentation testing (e.g. the low reproducibility of the indentation curves) and lead to inaccuracies in the determination of mechanical properties of materials analyzed. An original approach is developed in this thesis for the accurate characterization of the mechanical properties of materials. This approach is established by a statistical analysis of the indentation curves with taking account of error in determining the first contact point and effects of the surface roughness. This approach is basing on a minimization of the distance (defined as the initial contact depth error) between the experimental indentation curves and the ones simulated with Bernhard’s model in order to generate a “unique” representative curve which enables to represent all the experimental curves. The proposed method permits to calculate the macro-hardness and the Young’s modulus of materials from this representative curve with the consideration of the errors due to the surface roughness and the indentation size effect for shallow penetration. The robustness of the method is proved by its application to different groups of specimens, i.e. different materials with various mechanical properties, different surface preparation methods (polishing, sandblasting) and different indenter tips to generate different states of local stresses. A quantitative link between the surface roughness and the standard deviation of initial contact depth error is established by a multi-scale surface roughness analyzing. The proposed method enables to characterize the mechanical properties of materials without resorting to the surface preparation which may potentially alter its properties (e.g. generation of residual stresses, surface contamination ...)
4
Koray, Erge. "Numerical And Experimental Analysis Of Indentation." Master's thesis, METU, 2005. http://etd.lib.metu.edu.tr/upload/2/12605953/index.pdf.
Full textAbstract:
Indentation tests are widely used with simultaneous measurements of indentation depth and force especially for determining material properties. In this study<br>numerical and experimental investigation of the force-indentation measurements is presented. For indentation tests on anisotropic metals, a novel indenter which is not self similar is used with three transducers to measure the displacements. It is seen that in order to have high repeatability and accuracy at the tests, workpiece and indenter parameters have crucial importance. These parameters in the indentations are analyzed by finite element methods. Ideal dimensions of the workpiece are determined. It is shown that plane strain conditions can only be achieved by embedded indentations. Effect of surface quality and clamping on repeatability are
investigated. It is shown that surface treatments have significant effects on the results. Also it is seen that clamping increases the repeatability drastically. Moreover, indentation tests are conducted to verify the results of numerical
simulations. Effect of anisotropy on the force-displacement curves is clearly observed.
5
Dhaigude, Mayuresh Mukund. "Anvil effect in spherical indentation testing on sheet metal." [College Station, Tex. : Texas A&M University, 2006. http://hdl.handle.net/1969.1/ETD-TAMU-1818.
Full text
6
Vadlakonda, Suman. "Indentation induced deformation in metallic materials." Thesis, University of North Texas, 2005. https://digital.library.unt.edu/ark:/67531/metadc4904/.
Full textAbstract:
Nanoindentation has brought in many features of research over the past decade. This novel technique is capable of producing insights into the small ranges of deformation. This special point has brought a lot of focus in understanding the deformation behavior under the indenter. Nickel, iron, tungsten and copper-niobium alloy system were considered for a surface deformation study. All the samples exhibited a spectrum of residual deformation. The change in behavior with indentation and the materials responses to deformation at low and high loads is addressed in this study. A study on indenter geometry, which has a huge influence on the contact area and subsequently the hardness and modulus value, has been attempted. Deformation mechanisms that govern the plastic flow in materials at low loads of indentation and their sensitivity to the rate of strain imparted has been studied. A transition to elastic, plastic kind of a tendency to an elasto-plastic tendency was seen with an increase in the strain rate. All samples exhibited the same kind of behavior and a special focus is drawn in comparing the FCC nickel with BCC tungsten and iron where the persistence of the elastic, plastic response was addressed. However there is no absolute reason for the inconsistencies in the mechanical properties observed in preliminary testing, more insights can be provided with advanced microscopy techniques where the study can be focused more to understand the deformation behavior under the indenter. These experiments demonstrate that there is a wealth of information in the initial stages of indentation and has led to much more insights into the incipient stages of plasticity.
7
Hong, Edwin S. "Group testing for image compression /." Thesis, Connect to this title online; UW restricted, 2001. http://hdl.handle.net/1773/6900.
Full text
8
Wang, Yan, and 王焱. "Hertzian indentation failure of dental restorative materials." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2005. http://hub.hku.hk/bib/B36528067.
Full text
9
Tuck, Jonathan R. "Indentation characterisation for design of coated systems." Thesis, University of Newcastle Upon Tyne, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.364800.
Full text
10
Monelli, Bernardo Disma. "Mechanical Characterization of Metallic Materials by Instrumented Spherical Indentation Testing." Doctoral thesis, Università degli studi di Trento, 2010. https://hdl.handle.net/11572/368675.
Full textAbstract:
Instrumented indentation testing is now considered one of the most attractive tools for characterizing engineering materials. A large number of materials properties can be investigated. The present dissertation was aimed at developing a new methodology for inferring the material behaviour of metallic materials from their indentation response.
11
Monelli, Bernardo Disma. "Mechanical Characterization of Metallic Materials by Instrumented Spherical Indentation Testing." Doctoral thesis, University of Trento, 2010. http://eprints-phd.biblio.unitn.it/436/1/Bernardo-Monelli_PhD.pdf.
Full textAbstract:
Instrumented indentation testing is now considered one of the most attractive tools for characterizing engineering materials. A large number of materials properties can be investigated. The present dissertation was aimed at developing a new methodology for inferring the material behaviour of metallic materials from their indentation response.
12
Lin, Shiann. "Crack analysis by distributed strain nuclei with application to indentation testing." Thesis, University of Oxford, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.339286.
Full text
13
Poolthong, Suchit. "Determination Of The Mechanical Properties Of Enamel Dentine And Cementum By An Ultra Micro-Indentation System." Thesis, The University of Sydney, 1998. http://hdl.handle.net/2123/4963.
Full text
14
Mahawish, Ali Hassan. "Axisymmetric compression testing of concrete by nitrogen." Thesis, Cardiff University, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.316326.
Full text
15
Sjöstrand, Björn. "Evaluation of Compression Testing and Compression Failure Modes of Paperboard : Video analysis of paperboard during short-span compression and the suitability of short- and long-span compression testing of paperboard." Thesis, Karlstads universitet, Institutionen för ingenjörs- och kemivetenskaper (from 2013), 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kau:diva-27519.
Full textAbstract:
The objectives of the thesis were to find the mechanisms that govern compression failures in paperboard and to find the link between manufacturing process and paperboard properties. The thesis also investigates two different test methods and evaluates how suitable they are for paperboard grades. The materials are several commercial board grades and a set of hand-formed dynamic sheets that are made to mimic the construction of commercial paperboard. The method consists of mounting a stereomicroscope on a short-span compression tester and recording the compression failure on video, long-span compression testing and standard properties testing. The observed failure modes of paperboard under compression were classified into four categories depending on the appearance of the failures. Initiation of failure takes place where the structure is weakest and fiber buckling happens after the initiation, which consists of breaking of fiber-fiber bonds or fiber wall delamination. The compression strength is correlated to density and operations and raw materials that increase the density also increases the compression strength. Short-span compression and Long-span compression are not suitable for testing all kinds of papers; the clamps in short-span give bulky specimens an initial geometrical shape that can affect the given value of compression strength. Long-span compression is only suitable for a limited range of papers, one problem with too thin papers are low wavelength buckling.
16
Totty, Jennifer L. "Linear cellular copper in bending, compression and shear." Thesis, Georgia Institute of Technology, 2003. http://hdl.handle.net/1853/16913.
Full text
17
Lohonka, Radek. "Plasticity of the compound semiconductors at low temperatures : modelling of the uniaxial compression and indentation tests." Toulouse, INSA, 2002. http://www.theses.fr/2002ISAT0013.
Full textAbstract:
Ce travail est une contribution à l'étude de la plasticité des semi-conducteurs composés dans le domaine basse température--forte contrainte. La compression uniaxiale est simulée à partir des formalismes de Haasen-Alexander ou de Schoeck, adaptés pour des dislocations de mobilité différente, en glissement simple ou multiple. Il est impossible de décrire la plasticité en deçà d'une température critique à l'aide des lois de vitesses de dislocations disponibles, ce qui suggère un changement de mécanisme microscopique. L'effet photoplastique négatif est également abordé. La zone plastique autour d'une indentation Vickers est modélisée en considérant les expressions analytiques du tenseur des contraintes élastiques: un champ de contrainte sphérique constitue une bonne approximation. Les premiers stades de la formation de cette zone sont calculés par la méthode des éléments finis en introduisant les lois constitutives de la plasticité<br>This thesis deals with the plastic behaviour of compound semiconductors in the low temperature--high stress regime. Compressive stress-strain curves are calculated with models based on the formalisms of Alexander-Haasen or Schoeck extended to include simple glide/multiglide and one/three types of perfect dislocations with different mobilities. The impossibility to describe the crystal plasticity below some temperature with the available dislocation velocities data suggests a change in the controlling microscopic mechanisms. The negative photoplastic effect in GaAs is simulated. Modelling the response of the crystal to Vickers indentation is performed using elastic analytical expressions for the stress tensor: the stress distribution can be considered as nearly spherical although the plastic zone is far from it. Early stages of the formation of the plastic zone are described with the continuum crystal plasticity theory implementing the constitutive laws into the finite element method
18
Koka, Exaud Noe. "Laterally loaded wood compression members : finite element and reliability analysis." Thesis, University of British Columbia, 1987. http://hdl.handle.net/2429/26709.
Full textAbstract:
This thesis consists of two parts. The first part describes the analysis and implementation of a finite element computer model for the general prediction of failure of wood members in bending or in combined bending and axial compression. Both instability and material strength failures are included. The program is verified using available analytical and test results. A good agreement with the results predicted by this program is observed.
The second part describes a procedure for the structural reliability evaluation of a compression member assuming random loads and material variables. The program developed here for the reliability study links the finite element program and the Rackwitz-Fiessler algorithm for the calculation of the reliability index β. The gradient of the failure function, which is a necessary input to the Rackwitz-Fiessler algorithm, is computed numerically using the finite element routine. The results of the reliability study for a typical column problem are compared against the available results obtained by following the code procedures [as outlined in CAN3-086.1-M84 (1984)] for different slenderness ratios.
A performance factor ɸ⍴ = 0.75, for compression members of any length is recommended in order to obtain a more accurate and consistent level of reliability in the design process. It is estimated that if this factor ɸ⍴ = 0.75 adopted in the current design practices, a level reliability index of the order of 4.0 can be achieved.<br>Applied Science, Faculty of<br>Civil Engineering, Department of<br>Graduate
19
McNaughton, Adam L. "High Temperature Compression Testing of Monolithic Silicon Carbide (SiC)." Fogler Library, University of Maine, 2007. http://www.library.umaine.edu/theses/pdf/McNaughtonAL2007.pdf.
Full text
20
Mata, Martha Patricia Guerrero. "Finite element modelling of hot plane strain compression testing." Thesis, University of Sheffield, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.245644.
Full text
21
Stander, Melchior. "Development of an intermediate strain rate compression testing machine." Master's thesis, University of Cape Town, 2014. http://hdl.handle.net/11427/9131.
Full textAbstract:
Includes bibliographical references.<br>The further development of the wedge bar Intermediate Strain rate Tester (IST) presented by Cloete and Oxtoby [1] is presented in this dissertation. The concept uses a wedge mechanism to deform 5 mm diameter, 5 mm long specimens at strain rates in the region of 10 s, up to strains of 30. As impact principles are used to start and stop the experiment, it takes less than 1 of the testing duration to reach testing speed and to stop the experiment. The kinetic energy stored in the wedge bar helps ensure a near constant loading rate over the duration of the experiment. The yield stress is captured at above 80 of the average strain rate for the experiment for most of the materials investigated. The design work focuses primarily around the design of the new load-frame, load-cell, loading platforms and wedge bar displacement sensor. Finite Element Analysis (FEA) was used to investigate the dynamic response of the IST and modify the design of components where necessary. The modifications made the load-frame and load-cell result in a significant improvement in the quality of the measured signals. The wedge bar displacement sensor performed well. The back pressure driven loading concept shows potential but needs more development before it is suitable for routine testing. A range of common engineering materials was tested at quasi static, intermediate and high strain rates and compared to the results found in the literature. The results match well, however, friction effects dominate the large strain response of the metal specimens. In its current configuration the IST is used effective for testing polymers up to large strains as well as yield stress and small strain measurement of metals. For materials for which specimen friction effects are a problem, interrupted tests can be used to extend the maximum strain achievable.
22
Lam, Hung-yiu. "Pulse compression filter design for ultrasonic non-destructive testing /." Hong Kong : University of Hong Kong, 1994. http://sunzi.lib.hku.hk/hkuto/record.jsp?B18933580.
Full text
23
Lin, Xin-Yu. "Lossless image compression for aerospace non-destructive testing applications." Thesis, University of Central Lancashire, 2004. http://clok.uclan.ac.uk/18830/.
Full textAbstract:
This thesis studies areas of image compression and relevant image processmg techniques with the application to Non-destructive Testing (NDT) images of aircraft components. The research project includes investigation of current data compression techniques and design of efficient compression methods for NDT images. Literature review was done initially to investigate the fundamental principles of data compression and existing methods of lossless and lossy image compression techniques. Such investigation provides not only the theoretical background, but also the comparative benchmarks for the research project. Chapter 2 provides general knowledge of image compression. The basic predictive coding strategy is introduced at the beginning of chapter 3. Fundamental theories of the Integer Wavelet Transform (IWT) can be found in chapter 4. The research projects proposed mainly three innovative methods for lossless compression of NDT images. Namely, the region-based method that employs regionoriented adaptation; the texture-based method that employs a mixed model for the prediction of image regions with strong texture patterns; and a hybrid method that utilizes advantages from both predictive coding and IWT coding. The main philosophy of lossless image compression is to de-correlate the original image data as much as possible by mapping from spatial domain to spatial domain in the predictive coding strategy or from spatial domain to transform domain in the IWT coding strategy. The proposed region-based method aims to achieve the best mapping by adapting the de-correlation to the statistical properties of decomposed regions using the component's CAD model. With the aid of component CAD models to divide the NDT images of aircraft components into different regions based on the material structures, the design of the predictors and the choice of the IWT are optimised according to the specific image features contained in each region having the same material structure. The texture-based method achieves the best de-correlation by using a mixed data model in the region possessing strong texture patterns. A hybrid scheme for lossless compression of the NDT images of aircraft components is presented. The method combines the predictive coding and the IWT. After region-based predictive coding, the IWT is applied to the error images produced for each decomposed region to achieve further image de-correlation by preserving the information contained in the error images with fewer transform coefficients. The main advantages of using the IWT are its multi-resolution nature and lossless property with integer grey level values in images mapped to integer wavelet coefficients. The proposed methods are shown to offer a significantly higher compression ratio than other compression methods. The high compression efficiency is seen to be achieved by not only a combination of the predictive coding and the IWT, but also optimisation in the design of the predictor and the choice of the transform according to the specific image features contained in each region having similar material structures.
24
Ibrahim, Nidal. "Caractérisation des propriétés mécaniques des géomatériaux par technique de micro indentation." Thesis, Lille 1, 2008. http://www.theses.fr/2008LIL10048/document.
Full textAbstract:
La technologie de micro indentation est un des moyens de caractérisation (à partir de petits échantillons) qui s'est imposé ces derniers temps dans différents domaines (pharmaceutique, génie civil, industrie pétrolière etc.). Il répond à un certain nombre d'exigences en matière de solution au problème d'échantillonnage. Cette thèse est consacrée à la caractérisation des propriétés mécanique des géomatériaux, et spécialement pour les roches pétrolières comme l'argilite, le grès, la craie ... qui ont été utilisées pour les différentes études expérimentales menées au cours de la thèse. Après avoir présenté la méthode de dépouillement du test d'indentation pour un milieu isotrope, nous avons développé une méthode semi-analytique basée sur la fonction de Green pour caractériser le milieu isotrope transverse en déterminant les cinq paramètres élastique de ce milieu. L'influence des différentes sollicitations (mécaniques, thermiques, hydriques) sur les propriétés mécaniques des roches a été étudiée en utilisant la technologie de micro indentation avec la méthode de dépouillement isotrope transverse. Nous avons essayé de caractériser les paramètres de rupture (C et f) à l'aide du test d'indentation et d'un test de micro compression simple (MCS) effectué par la même machine d'indentation. Par l'essai d'indentation et une méthode d'analyse inverse, nous avons identifié les paramètres d'une loi de comportement élastoplastique (Drucker Prager). En l'absence d'une solution directe du problème d'indentation en régime plastique, nous avons eu recours à une modélisation numérique par un code de calcule élément finis (ABAQUS) pour déterminer la courbe d'indentation calculée. Cette détermination s'est révélée tout à fait probante et a été de plus validée par une simulation d'essais de compression triaxiale sur le même matériau<br>The technology of micro indentation is one of the techniques ofmateriaJ characterization (by using small specimens) in various fields (mechanical engineering, civil engineering, oil industry, and pharmaceutical industry). Its main advantage lies in a certain number of practical requirements as regards the solution to the problem of small specimens. The present study is devoted the characterization of the mechanical properties of geomaterials, especially rocks involved in petroleum engineering. After having presented the methodology of the indentation test for isotropic rocks, we developed a semi-analytical method based on the use of Green function to characterize transverse isotropic rocks (five elastic parameters of these rocks). The influence of the various loadings (mechanical, thermal, hydrous) on the rock mechanics properties was studied by using the technology of micro indentation and the methodology proposed for isotropic transverse were used. Moreover, we characterize the failure parameters (C and f) by a combined approach of the indentation test and a test of micro compression (MCS) carried out the indentation device. Finally, we use inverse analysis in order to identify the parameters of a Drucker Prager mode!. ln the absence of a direct solution of the problem of indentation (in plastic regime), we had recourse to a numerical modelling by a finite element code (ABAQUS) to determine the calculated curve of indentation. This determination appeared completely convincing and moreover was validated by a simulation of triaxial compression tests on the same material
25
Lesko, John James. "Indentation testing of composite materials : a novel approach to measuring interfacial characteristics and engineering properties /." This resource online, 1991. http://scholar.lib.vt.edu/theses/available/etd-03172010-020329/.
Full text
26
Lesko, John J. "Indentation testing of composite materials: a novel approach to measuring interfacial characteristics and engineering properties." Thesis, Virginia Tech, 1991. http://hdl.handle.net/10919/41677.
Full textAbstract:
Findings made through the indentation testing of composites are presented in this thesis. The concept was developed as an attempt to evaluate the interfacial shear strength at a mesolevel, possibly overcoming the deficiencies of present techniques. Vickers Microhardness Testing and Continuous Ball Indentation Testing (CBIT) of composite materials provided data for assessing the sensitivity of indentation techniques to interfacial characteristics and engineering properties.
Both methods proved capable of discerning the level of fiber-matrix adhesion. The CBIT presented the greatest potential for making quantitative measures of interfacial shear strength. A unique micromechanics model of the contact situation predicted failure events and trends consistent with the observed data from the CBIT. The present elastic model predicted an interfacial shear strength slightly higher than those reported in the literature. However, the interface strength obtained through the CBIT provides more of an engineering assessment of the interfacial quality when compared to other techniques. Both experimental and analytical results suggest that indentation testing of composites is most sensitive to shearing characteristics of the system. Vickers and ball penetration results displayed some correlation to global laminate properties. Vickers hardness shows a close relationship to IITRI compression strength only when fiber compressive failure is observed in the laminate test. The CBIT provides the best opportunity for exploring fiber composite stress-strain information.<br>Master of Science
27
董旭東 and Xudong Dong. "Stress distribution and failure mode of dental ceramic structures under Hertzian indentation." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2001. http://hub.hku.hk/bib/B31241621.
Full text
28
Czerepinski, Przemyslaw Jan. "Displaced frame difference coding for video compression." Thesis, University of Bristol, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.267009.
Full text
29
Patel, Chaitanya I. "Design and characterization of direct compression excipients." Thesis, University of Bath, 1986. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.370466.
Full text
30
Syed, Asif S. A. "Time dependent micro deformation of materials." Thesis, University of Oxford, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.362108.
Full text
31
Li, S. "Experimental testing and numerical investigation of materials with embedded systems during indentation and complex loading conditions." Thesis, Liverpool John Moores University, 2018. http://researchonline.ljmu.ac.uk/8981/.
Full textAbstract:
In this work, parametric FE (Finite Element) modelling has been developed and used to study the deformation of soft materials with different embedded systems under indentation and more complex conditions. The deformation of a soft material with an embedded stiffer layer under cylindrical flat indenter was investigated through FE modelling. A practical approach in modelling embedded system is evaluated and presented. The FE results are correlated with an analytical solution for homogenous materials and results from a mathematical approach for embedded systems in a half space. The influence of auxeticity on the indentation stiffness ratio and the de-formation of the embedded system under different conditions (indenter size, thickness and embedment depth of the embedded layer) was established and key mechanisms of the Poisson’s ratio effect are highlighted. The results show that the auxeticity of the matrix has a direct influence on the indentation stiffness of the system with an embedded layer. The enhancement of indentation resistance due to embedment increases, as the matrix Poisson’s ratio is decreased to zero and to negative values. The indentation stiffness could be increased by over 30% with a thin inextensible shell on top of a negative Poisson’s ratio matrix. The deformation of the embedded layer is found to be significantly influenced by the auxeticity of the matrix. Selected case studies show that the modelling approach developed is effective in simulating piezoelectrical sensors, and force sensitive resistor, as well as investigating the deformation and embedded auxetic meshes. A full scale parametric FE foot model is developed to simulate the deformation of the human foot under different conditions including soles with embedded shells and negative Poisson’s ratio. The models used a full bone structure and effective embedded structure method to increase the modelling efficiency. A hexahedral dominated meshing scheme was applied on the surface of the foot bones and skin. An explicit solver (Abaqus/Explicit) was used to simulate the transient landing process. Navicular drop tests have been performed and the displacement of the Navicular bone is measured using a 3D image analysing system. The experimental results show a good agreement with the numerical models and published data. The detailed deformation of the Navicular bone and factors affecting the Navicular bone displacement and measurement is discussed. The stress level and rate of stress increase in the Metatarsals and the injury risk in the foot between forefoot strike (FS) and rearfoot (RS) is evaluated and discussed. A detailed full parametric FE foot model is developed and validated. The deformation and internal energy of the foot and stresses in the metatarsals are comparatively investigated. The results for forefoot strike tests showed an overall higher average stress level in the metatarsals during the entire landing cycle than that for rearfoot strike. The increased rate of the metatarsal stress from the 0.5 body weight (BW) to 2 BW load point is 30.76% for forefoot strike and 21.39% for rearfoot strike. The maximum rate of stress increase among the five metatarsals is observed on the 1st metatarsal in both landing modes. The results indicate that high stress level during forefoot landing phase may increase potential of metatarsal injuries. The FE was used to evaluate the effect of embedded shell and auxetic materials on the foot-shoe sole interaction influencing both the contact area and the pressure. The work suggests that application of the auxetic matrix with embedded shell can reinforce the indentation resistance without changing the elastic modulus of the material which can optimise the wearing experience as well as providing enough support for wearers. . Potential approaches of using auxetic structures and randomly distributed 2D inclusion embedded in a soft matrix for footwear application is discussed. The design and modelling of foot prosthetic, which resembles the human foot structure with a rigid structure embedded in soft matrix is also presented and discussed.
32
林鴻耀 and Hung-yiu Lam. "Pulse compression filter design for ultrasonic non-destructivetesting." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1994. http://hub.hku.hk/bib/B3121423X.
Full text
33
Gardner, Kevin Alexander. "Experimental Techniques for Shear Testing of Thin Sheet Metals and Compression Testing at Intermediate Strain Rates." The Ohio State University, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=osu1366199322.
Full text
34
Kassou, Belynda. "Mécanique des lits de silices granulaires pour l’optimisation des cœurs de panneaux isolants sous vide (PIV)." Thesis, Lyon, 2018. http://www.theses.fr/2018LYSEI007/document.
Full textAbstract:
En Europe, le secteur du bâtiment représente près de la moitié de la consommation énergétique totale (dont 60 % pour le chauffage et la climatisation) et des rejets de CO2. Ainsi, une maîtrise de la consommation énergétique dans différents secteurs (bâtiment, transports et industrie) est nécessaire. L’utilisation de matériaux « super-isolants » thermiques tels que les panneaux isolants sous vide (PIV) dans la rénovation et dans de nouvelles constructions à très faible consommation énergétique sont prometteurs. Un PIV est composé d’un matériau de cœur thermoscellé dans une enveloppe hermétique mise sous vide. Le cœur est constitué d’un empilement de nano poudres de silices à très forte porosité (> 90%) et à très fine structure poreuse (< 200 nm). Deux types de silices sont utilisés : les silices pyrogénées (FS) avec lesquelles on obtient des PIV manipulables pour une densité de cœur de 160 kg/m3 après compaction contre 250 kg/m3 pour les silices précipitées (PS). Les PIV à base de silices FS sont plus efficaces thermiquement et mécaniquement que ceux à base de silice PS, mais restent plus coûteux. Cette étude propose de comprendre les différences de propriétés mécaniques entre les compacts de silice FS et PS. Ainsi, les comportements en compression œdométrique et en indentation sphérique d’une silice pyrogénée Konasil 200 et de deux silices précipitées Tixosil 43 et 365 ont été analysés. Ceux-ci sont complétés par des observations structurales en microscopie électronique à transmission (MET) et en diffusion de rayons X aux petits angles (SAXS). Le couplage de ces résultats à l’étude du vieillissement et de la structure multiéchelles des poudres permet d'identifier les causes des écarts des propriétés observées entre silices FS et PS. Ainsi, l’impact de la chimie de surface et de l’organisation multiéchelles entre les objets observés est mis en évidence pour expliquer les différences de propriétés mécaniques entre silices FS et PS<br>Buildings account for almost the half of the total energy consumption (60% for heating and cooling) and CO2 emissions in Europe. Thus, the control of energy consumption in building appears as critical. In that perspective, "super-thermal insulating" materials such as vacuum insulation panels (VIP) are promising, both for buildings renovation, and for new energy-efficient constructions. A VIP is composed by a sealed core material in which vacuum is established. The core is made of an open nanoporous stack of silica powders with very high porosity (> 90%) and very fine porous structure (< 200 nm). Two types of silica are typically used: first fumed silica (FS) which enable to process panels with a sufficient compression strength for handling for a density as low as 160 kg/m3, second precipitated silica (PS) which enable to process denser panels with a minimal density of about 250 kg/m3. VIPs made of FS powders are more efficient in terms of thermal and mechanical properties as compared of VIP made of PS powders. However, their price is higher. This study aims at understanding the differences in mechanical properties noted between compacted FS and PS powders. Oedometric compression tests and spherical indentation test were carried out on compacts of Konasil 200 FS silica and on compacts of Tixosil 43 and 365 PS silica. In addition, structural observations of the powders were made using transmission electron microscopy (TEM) and small angle X-ray scattering (SAXS). These results permit to identify the parameters leading differences between FS and PS powders. Thus, surface chemistry, multiscale organization and interactions forces are highlighted to explain the differences in mechanical properties between compacts of FS and PS silica
35
Kittang, Lars Oskar Osnes. "Development and testing of a Linnik Interference Microscope for Sub-surface Inspection of Silicon during moving Indentation." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for fysikk, 2012. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-19258.
Full textAbstract:
Fixed-abrasive diamond wire sawing is a promising technique for reduction of costs related to sawing of silicon wafers for solar cells. The microscopic mechanisms of material removal in the process are however not fully understood, and must be surveyed in order for costs to be further reduced.An interference microscope for sub-surface inspection of mono-crystalline silicon has been built based on the Linnik configuration, with specific application to in-situ monitoring of moving indentations. The working principles of the instrument are explained from a literature study on relevant theory, combining concepts of optical interference and coherence with imaging theory. The optical system has been experimentally tested in terms of its performance in conventional imaging as well as its interferometric capabilities. Tests on the imaging performance show that a large magnification is accompanied by a lateral resolution with a lower limit of $0.9mumathrm{m}$ and an adequately long depth of field. This provides improved conditions for imaging of internal reflections in silicon, compared to a previously used prototype.Using a light source of low temporal coherence, the capability of the system to measure depth profiles of silicon surfaces has been tested. The technique calculates depths from interferograms recorded by scanning of a reference field. Preliminary results from a flat test surface show that depths are not determined accurately enough for calculated profiles to be considered as reliable reconstructions. It is discussed that the inaccuracy is caused by a number of experimental factors including non-uniform illumination, undesired reflections and non-uniform sampling intervals in scanning.Two experiments with moving indentations on silicon surfaces have been performed, monitored by conventional imaging and calculation of interferometric phase maps, respectively. Results are seen in context with the theoretical understanding of material removal mechanisms in fixed-abrasive diamond wire sawing. The evolution of surface damage is observed as interconnection of chippings in both experiments. In addition, sub-surface lateral cracks are identified from interferometric phase maps. The phase maps of surface damage can, however, only to a limited extent be interpreted as topographic contour lines of surface depth. A deeper knowledge of removal mechanisms requires quantitative measurements of depths. This can be better achieved by calculating accurate depth profiles from interferograms. Future enhancement of the system is dependent on a reevaluation of the optical design as well as better control of sampling intervals in scanning.
36
Toledo, García Gustavo A. "High temperature compression testing of hardened steels for plasticity behavior modeling." Thesis, Georgia Institute of Technology, 2002. http://hdl.handle.net/1853/16909.
Full text
37
Thompson, Luke Francis. "Through-thickness compression testing and theory of carbon fibre composite materials." Thesis, University of Manchester, 2011. https://www.research.manchester.ac.uk/portal/en/theses/throughthickness-compression-testing-and-theory-of-carbon-fibre-composite-materials(02ad7cfa-b779-4e69-9361-3c5bb44c6114).html.
Full textAbstract:
This study investigates the through-thickness behaviour of carbon/epoxy laminates. A through-thickness compression test regime was conducted utilising three specimen designs, which are waisted, hollow cylindrical and cubic specimens. An assessment and comparison of each specimen is given regarding their advantages and disadvantages in characterising the through-thickness response of [+45/-45/90/0]s quasi-isotropic AS4/8552 carbon/epoxy laminates. A finite element (FE) study of the three specimens is presented which results in specimen geometries that provided a macroscopically uniform stress response throughout the gauge length whilst also minimising other features such as stress concentrations. Further to the final geometries being presented, the method of manufacture for the laminate and machining processes for each of the specimens is given. A mesoscopic FE study is presented relating to the free-edge effects induced by through-thickness loading in quasi-isotropic laminates. The results presented show that free-edge effects will be present in the test specimens and will have a larger overall impact on the hollow cylindrical specimen. The free-edge effects also increase the stress concentrations present in the corners of the waisted and cubic specimens. Characteristic stress strain curves are presented for each specimen with strain data taken from post yield strain gauges attached to the specimens. The extracted initial Young's modulus Ez and Poisson's ratios vzx and vzy show a small variation between specimens. The strength values for the three specimens vary greatly with the waisted specimen being the strongest and cylindrical specimen the weakest, indicating that the chosen specimen geometry dominates failure. The experimental data will be used for test case 12 in the Second World Wide Failure Exercise (WWFE-II). A study is presented to predict the effective elastic properties of Z-pinned laminates. The materials under consideration are UD and [0/90]s cross-ply AS4/3501-6 carbon/epoxy laminates. Estimates on the effective properties are provided by two FE approaches and two analytical bounding approaches; namely Voigt and Reuss bounds and Walpole's bounding theory. The two FE approaches are based on extreme assumptions about the in-plane fibre volume fraction in the presence of Z-pins and provide a tight range of values in which the real result should lie. Furthermore, whilst the bounding methods are simple and in the case of Young's moduli produce very wide bounds the selection of the suitable bound result can lead to a good estimate in comparison with the FE data. Typically the best bounding method result for each elastic property is within 10% of the FE predictions.
38
Hongkarnjanakul, Natthawat. "Modélisation numérique pour la tolérance aux dommages d’impact sur stratifié composite : de l’impact à la résistance résiduelle en compression." Thesis, Toulouse, ISAE, 2013. http://www.theses.fr/2013ESAE0037/document.
Full textAbstract:
Les impacts sur structures composites peuvent fortement diminuer leur résistance résiduelle sans laisser de marque visible sur la surface extérieure. Dans le domaine aéronautique, un seuil minimum de détection de l’endommagement d’impact est défini, basé sur l’indentation permanente laissée par l’impact. En deçà de ce seuil, la structure doit résister à un chargement défini : c’est la notion de tolérance aux dommages d’impact. Dimensionner numériquement une structure composite en tenant compte des aspects détectabilité et tolérance aux dommages nécessite donc de savoir modéliser à la fois l’impact, l’indentation permanente et la résistance résiduelle sous compression.Ces travaux se focalisent sur la modélisation numérique des composites stratifiés formés de plis unidirectionnels. L’objectif est d’établir un modèle prédictif de la tenue résiduelle après impact. Une étude expérimentale a été réalisée afin d’étudier le scénario d’endommagement à l’impact et sous compression après impact (CAI), et de fournir des résultats expérimentaux pour valider les modèles numériques.Une modélisation par éléments finis avec une approche de type Discrete Ply Model (DPM) est effectuée, basée sur des travaux précédents. Le modèle d'impact est amélioré et validé sur différentes séquences d'empilement pour assurer la robustesse du modèle. Des essais de flexion trois points spécifiques sont réalisés pour apporter une meilleure compréhension de la formation de l'indentation permanente. Un nouveau modèle d'indentation permanente est alors proposé et appliqué dans le modèle d'impact. Enfin, un modèle de CAI est construit pour prédire la résistance résiduelle. Les trois étapes : impact, indentation et CAI sont combinées au sein d’un unique modèle<br>Impacts on composite structures can greatly reduce their residual strength without leaving a visible mark on the outer surface. In aeronautics, a minimum detection threshold of the impact damage is defined, based on the permanent indentation left after impact. Below this threshold, the structure must withstand a defined load: it is the notion of impact damage tolerance. The numerical design of a composite structure taking into account aspects such as detectability and damage tolerance thus requires to know how to represent impact, permanent indentation and residual strength under compression.This work focuses on the numerical modeling of composite laminates made of unidirectional plies. The objective is to develop a predictive model of post-impact residual strength. An experimental study was conducted to investigate the damage scenario during impact and compression after impact (CAI), and provide experimental data to validate the simulations.A finite element modeling with a Discrete Ply Model (DPM) approach is performed based on previous work done at the laboratory. The impact model is improved and validated on different stacking sequences to ensure the robustness of the model. Specific three-point bending tests are performed to have a better understanding of the formation of permanent indentation. A new model of permanent indentation is then proposed and applied in the impact model. Finally, a model is built to predict CAI residual strength. The three steps: impact, indentation and CAI are combined into a single model
39
Mirzadeh, Farshad. "Compressive strength and behavior of 8H C3000/PMR15 woven composite material." Diss., Virginia Polytechnic Institute and State University, 1988. http://hdl.handle.net/10919/54337.
Full textAbstract:
Center-notched and unnotched specimens cut from Celion 3000/PMR15 woven composite panels with 60% fiber volume fraction were tested under quasi-static compressive load to failure at room temperature. Micrographic evidence clearly identifies the mode of compressive failure as fiber kinking. Each fiber in the kink fractures because of a combination of compressive and shear stresses. A post failure mechanism follows the local fiber bundle failures, which completely deforms the material by large cracks. ln center notched specimens, fiber kinks start from the notch and propagate to some distance from the notch before the post failure takes place. The effect of bundle interactions on stresses and strains was clearly distinguished by comparing the results of the finite element analysis of a bundle surrounded by other plies to the results of the Moire interferometry on the edge of a laminate. A model was introduced which incorporated the micromechanical geometry as well as the constituent properties to predict the notched and unnotched compressive strengths of the woven material. For notched strength predictions, the Average Stress Criterion was used, and the characteristic distance was found to be a function of laminate thickness. Predicted notched and unnotched strengths correlate very well with the experimental results.<br>Ph. D.
40
Sylvain, Wilgens. "Étude de la plasticité du monocristal de phase MAX par déformation aux petites échelles." Thesis, Poitiers, 2016. http://www.theses.fr/2016POIT2307/document.
Full textAbstract:
L'objectif de cette thèse est l'étude de la déformation, à l'échelle microscopique, de la phase MAX Ti2AlN, synthétisée par métallurgie des poudres. Ce travail se divise en trois parties : une première dans laquelle l'accent a été mis sur l'hystérèse mécanique des phases MAX via des essais cyclés, en nanoindentation sphérique et compression ex-situ de micro-piliers, sur des grains d'orientations différentes déterminées par l'EBSD. Dans la deuxième nous nous sommes intéressés à la déformation de micropiliers via des essais de compression cyclés in-situ couplés à la micro-diffraction Laue. L'objectif a été d'analyser les taches diffraction au cours de la déformation du pilier afin de mettre en évidence les mécanismes de déformation élémentaires mis en jeu et d'observer les structures finales via des images MEB post-mortem des piliers. Enfin, une dernière dans laquelle l'objectif a été l'étude des mécanismes de déformation en température à l'échelle microscopique via des essais de nano-indentation allant jusqu'à 800°C. La caractérisation des lignes de glissement en surface et des configurations microstructurales sous l'empreinte a été réalisée par AFM et MET respectivement. Toutes les données recueillies par ces divers essais aux petites échelles, ont permis d'affiner notre compréhension des mécanismes de déformation du monocristal de phase MAX, notamment vis à vis des modèles usuellement proposés dans la littérature<br>The thesis's goal is to study the deformation, at microscopic scale, of the MAX phase Ti2AlN synthesized by powder metallurgy. This work is divided into three parts: in the first part, the interest has been put on the hysteretic behavior of the MAX phases via cyclic mechanical solicitations, during spherical indentation tests and ex-situ compression of micro-pillars, on differently orientated grains beforehand determined by EBSD. In the second part, we were interested into the micro-pillar's deformation via insitu cyclic compression tests coupled with Laue micro-diffraction. The goal was to analyse the evolution diffraction lines during the pillar's deformation in order to highlight the elementary deformation mechanisms and to observe the finale structures via the post-mortem SEM imaging of the pillars. Finally, a last part was devoted to study the deformation mechanisms in temperature at microscopic scale via nano-indentation tests up to 800°C. The characterization of the slip lines on the surface has been revealed by AFM and that of t he microstructural configurations (dislocations) under the indent has been done by TEM. All data collected by these various tests at the small scales have refined our understanding of the deformation mechanisms of crystal MAX phase, particularly with respect to the models usually proposed in the literature
41
Heatwole, Edwin L. "Allowable bending strength enhancement of 2 by 4 lumber by tension and compression proofloading." Thesis, Virginia Polytechnic Institute and State University, 1987. http://hdl.handle.net/10919/53718.
Full textAbstract:
Research has established that correlations exist between bending and tension, and bending and compression strength of lumber. Because of this correlation, improvement in bending strength may be realized from proofloading in tension or compression.
The data utilized in a reliability analysis was from Galligan et al. (1986) that characterized the properties of 2-inch softwood dimension lumber with regressions and probability distributions. Randomly selected groups of 2 by 4 1650f-1.5E Hem-fir and No.2 KD Southern Pine were evaluated for bending strength. One group from each species was selected as a control and tested in bending. The other groups were proofloaded in tension and compression at two stress levels and the survivors were tested in bending to failure.
Based on the concept of equal reliability and utilizing the load distributions from Thurmond (1986), the tensile and compressive proofloaded strength distributions were compared to the control. The probability of failure for the control group is found, then with an iterative approach, the bending strength values of the proofloaded sample distribution are artificially altered by a factor K until the probabilities of failure for the proofloaded and control groups are similar. The K is a shift factor relating the amount the proofloaded strength distribution must be shifted on the x-axis to give the same reliability as the control.
Simple 5th percentile comparisons, the advanced first order second moment (AFOSM) and numerical integration analysis methods were used to evaluate increases in allowable bending strength from proofloading in tension and compression. Proofloading in tension or in compression both produced significant increases in allowable bending strength for the Hem-fir grade. Proofloading in tension to a target 15 percent breakage level, or 2,838. psi, yielded for the survivors an increase of 72 percent in allowable bending strength. The allowable bending strength increased 60 percent due to a compressive proofloading to a target 15 percent breakage level.
The allowable bending strength increased as the proofloading level increased for both tension and compression proofloading with the Hem-fir grade. The southern pine visual stress grade did not show a consistent trend between proofloading level and improvement in allowable bending strength. The lack of a trend between proofloading level and allowable bending strength was attributed to possible sampling error.
The fifth percentile analysis method, the AFOSM method and numerical integration method were compared. For lumber strength comparisons, a simple fifth percentile analysis was not the preferred method. The AFOSM method and the numerical integration method provided identical results in terms of their application in adjusting allowable bending stresses. It was not possible to show that the approximate AFOSM method can be used exclusively in lieu of the numerical integration method for reliability calculations.<br>Master of Science
42
St, John Ashlee Nicole. "Compression effects on the phase behavior of microgel assemblies." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/22666.
Full textAbstract:
Thesis (Ph. D.)--Chemistry and Biochemistry, Georgia Institute of Technology, 2008.<br>Committee Chair: Lyon, L. Andrew; Committee Member: Breedveld, Victor; Committee Member: Hernandez, Rigoberto; Committee Member: Srininvasarao, Mohan; Committee Member: Weeks, Eric R.
43
Siradj, Eddy Sumarno. "Strain induced precipitation kinetics of Nb(Cn) in Nb-HSLA steel as a function of thermomechanical history." Thesis, University of Sheffield, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.264438.
Full text
44
Beegan, Andrew Peter. "Wavelet-based Image Compression Using Human Visual System Models." Thesis, Virginia Tech, 2001. http://hdl.handle.net/10919/32939.
Full textAbstract:
Recent research in transform-based image compression has focused on the wavelet transform due to its superior performance over other transforms. Performance is often measured solely in terms of peak signal-to-noise ratio (PSNR) and compression algorithms are optimized for this quantitative metric. The performance in terms of subjective quality is typically not evaluated. Moreover, the sensitivities of the human visual system (HVS) are often not incorporated into compression schemes.
This paper develops new wavelet models of the HVS and illustrates their performance for various scalar wavelet and multiwavelet transforms. The performance is measured quantitatively (PSNR) and qualitatively using our new perceptual testing procedure.
Our new HVS model is comprised of two components: CSF masking and asymmetric compression. CSF masking weights the wavelet coefficients according to the contrast sensitivity function (CSF)---a model of humans' sensitivity to spatial frequency. This mask gives the most perceptible information the highest priority in the quantizer. The second component of our HVS model is called asymmetric compression. It is well known that humans are more sensitive to luminance stimuli than they are to chrominance stimuli; asymmetric compression quantizes the chrominance spaces more severely than the luminance component.
The results of extensive trials indicate that our HVS model improves both quantitative and qualitative performance. These trials included 14 observers, 4 grayscale images and 10 color images (both natural and synthetic). For grayscale images, although our HVS scheme lowers PSNR, it improves subjective quality. For color images, our HVS model improves both PSNR and subjective quality. A benchmark for our HVS method is the latest version of the international image compression standard---JPEG2000. In terms of subjective quality, our scheme is superior to JPEG2000 for all images; it also outperforms JPEG2000 by 1 to 3 dB in PSNR.<br>Master of Science
45
Mihajlovic, Bojan. "Compression and security platform for the testing of wireless sensor network nodes." Thesis, McGill University, 2008. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=18820.
Full textAbstract:
This thesis considers the in-field testing of wireless sensor network (WSN) nodes as a means of providing increased network uptime. Such nodes operate with strict limits on energy, cost, computing power, and are prone to attack. While testing through software-based self-test (SBST) programs has advantages on WSN nodes, energy efficiency can be increased by compressing SBST programs before distributing them. Of several compression schemes considered for the task, the BSTW algorithm with Rice coding demonstrates node energy savings while providing a low memory footprint and good compression ratios. Test security is provided through a multi-layer scheme which uses a wireless transceiver chip to offload AES protocol cryptographic functions. The entire security scheme is found to add only approximately 2.5% to the energy needs of SBST program distribution. Finally, a testing protocol is created to combine high-level testing commands with the compression and security schemes.<br>Cette thèse étudie le test sur le terrain de noeuds de résaux de senseurs sans-fil (RSSF) afin d'obtenir un temps de vie accru. De tels noeuds opeèrent avec des limites strictes en énergie, cot, puissance en travail, et sont sensibles d'être attaqués. Alors que l'auto-test basé en logiciel (ATBL) a ses avantages sur des noeuds RSSF, l'efficacité en énergie peut être améliorée en comprimant les programes ATBL avant de les distribuer. Une parmi plusieurs méthodes de compression étudiées pour la tâche, l'algorithme BSTW avec codage Rice démontre des économies d'énergie, tout en nécessitant une faible quantité de mémoire et de bons ratios de compression. La sécurité du test est assurée à travers une approche à plusieurs niveaux qui utilise une puce émetteur-récepteur sans-fil sur lequel décharger les fonctions cryptographiques AES. Toute l'approche concernant la sécurité ne rajoute qu'un 2.5 pourcent de besoin en énergie pour la distribution du programme ATBL. Finalement, le protocol de test est créé pour combiner des commandes de test de haut niveau avec des méthodes de compression et de sécurité.
46
Valero, Diana (Diana E. ). "Compression testing and measurement of material properties of a double network hydrogel." Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/98758.
Full textAbstract:
Thesis: S.B., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2015.<br>Cataloged from PDF version of thesis.<br>Includes bibliographical references (page 26).<br>Double network hydrogel samples were synthesized and manufactured out of polyacrylamide (PAAm) and alginate solutions. They were casted into cube molds with each side measuring 20 mm. Samples were tested under compressive loads in cyclic compression tests and stress relaxation tests. A viscoelastic model was applied and material properties were calculated using the experimental data. The elastic modulus of these PAAm-alginate gels was found to be 35kPa, while the viscosity, [eta], was found to be 1.43 kPa-s. The viscous response was found to have a dependency on the strain rate by an exponential factor of 0.26. Using the applied theoretical model and the experimentally determined material properties, you can then characterize the mechanical response of the PAAm-alginate hydrogel when it undergoes small strains.<br>by Diana Valero.<br>S.B.
47
Forrester, Hsuan-Hsiou. "High strain rate compression testing of polymers : PTFE, PCTFE, PVC and PMMA." Thesis, Loughborough University, 2013. https://dspace.lboro.ac.uk/2134/13624.
Full textAbstract:
The mechanically compressive flow stress sensitivities of various polymers are investigated at high strain rates above 103 s-1. Temperatures near the glass transition temperature are investigated and the polymer stress-strain responses have been studied from ambient temperature to 100°C. Previous work has reported peaks in flow stress as a function of strain rate [Al-Maliky/Parry 1994, Al-Maliky 1997]. The analyses showed rapid increases of flow stress followed by a sudden drop at elevated strain rates, which is unlike the well known linear relationship documented at the low strain rates. The mechanics and stipulation of what bring about this phenomenon, or the types of polymers influenced are still unclear. Two fluoropolymers, polytetrafluoroethylene (PTFE) and polychlorotrifluoroethylene (PCTFE), and two vinyl polymers, polyvinylchloride (PVC) and polymethylmethacrylate (PMMA), are chosen for this study. PTFE, PCTFE and PVC are semi-crystalline polymers with different percentage of crystallinity contents, whereas PMMA is an amorphous polymer. The glass transition temperature, Tg, is the characteristic of the amorphous content in polymers, which has been suggested to influence the flow stress peaks [Swallowe/Lee 2003]. Tg of the semi-crystalline polymers are within the test temperature range. High strain rate compression tests have been carried out using the split Hopkinson pressure bar (SHPB). This is a well-established method for determining the stress, strain, and strain rate of materials. The strain rate range of interest is 103 s-1 to 105 s-1 where the strain rate sensitivity has previously been identified [Al-Maliky/Parry 1994, Al-Maliky 1997, Walley/Field 1994]. Two thermal analyses techniques are used to quantify the dependency of the viscoelastic behaviour in relation to time and temperature. Differential scanning calorimetry (DSC) measures the enthalpy of the polymers to show how the materials are affected by heat, and Dynamic mechanical analysis (DMA) is used to characterise the time-temperature dependence of the elastic storage and loss moduli of the polymers A total of 42 PCTFE, 44 PTFE, 45 PVC and 55 PMMA specimens were tested using the SHPB system, with the strain rate varying between 1600 s-1 and 6100 s-1. Initial results for PMMA have been reported [Forrester/Swallowe 2009]. The rate of strain where specimens begin to show crazing is identified. The value of yield stress increases with the increase of strain rate and the decrease in temperature. Large strain hardening can be seen in all three semi-crystalline polymers at higher strain rates. The temperature rise during plastic flow of compression is calculated by the stress-strain rate curves. In this thesis, the emphasis is on the relation of yield/flow stress to strain rate as the polymers deform under high strain compression. The mechanism behind the cause of high strain rate deformation responses for amorphous to semi-crystalline polymers in ductile state is discussed, with a view to understanding the sensitivity of yield/flow stresses as a function of strain rate. Also, the modelling of the polymers has been carried in order to alleviate doubts about the validity of the real experimental results that may arise due to the nature of the decomposition of the polymers. It has been shown that the strain energy density pulses through the sample in response to the compression wave in various circular intensities.
48
Wilson, Keith. "A review of compression testing procedure with reference to a Trenton limestone /." Thesis, McGill University, 1992. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=47028.
Full text
49
Galatanu, Anca Daniela. "Behaviour and design of hollow flange beams under axial compression." Thesis, Queensland University of Technology, 1997. https://eprints.qut.edu.au/36012/1/36012_Galatanu_1997.pdf.
Full textAbstract:
The Hollow Flange Beam (HFB) is a relatively new cold-formed steel section
developed by Palmer Tube Mills (Australia) Pty. Ltd., released into Australian
markets in November 1993, and targeting applications in the light industrial and
domestic markets.
It was envisaged early in the product development that the section will be primarily
used as a flexural member. Therefore research and development effort was
concentrated in this area, and little is kno,vn about the HFB behaviour under axial
compression. Furthermore, because of its unique fabrication process and distorsional
buckling behaviour, the HFB is not completely compliant with either the ColdFormed
Steel Structures code AS 1538 (SA, 1988) or the Australian Steel Structures
code AS4100 (SA, 1990). As the HFB is a cold-formed steel section, current design
procedures are based on the general provisions of the Cold-Formed Steel Structures
code AS 1538. However, the manufacturers and designers of HFBs prefer the new
section to be designed according to the provisions of AS4100 as they allow for
greater benefits to be gained for HFBs.
The main objectives of this project were to investigate the behaviour of the HFB
members under axial compression and to determine whether the HFB could be
incorporated into the more popular Australian Steel Structures code AS4100.
Finite element analyses and experimental tests were conducted to investigate the
buckling and ultimate strength performance of the HFB members subject to axial
compression. Analytical and experimental results were compared with AS4 l 00
design specifications in order to establish an appropriate column curve for the design
of HFB sections. The results obtained from this investigation sho,ved that the HFB
sections can be designed using the provisions of the AS4 l 00 code. The column
curve with the member section constant a6 = 0.5 was recommended as a safe design
curve for HFB compression members. However, the column curve with ah = 0 may
prove to be a more appropriate design curve based on a reliability analysis.
50
Jaramillo, Fulvio E. "Axially loaded stainless steel compression members." Thesis, Available online, Georgia Institute of Technology, 2006, 2006. http://etd.gatech.edu/theses/available/etd-07102006-144943/.
Full textAbstract:
Thesis (M. S.)--Civil and Environmental Engineering, Georgia Institute of Technology, 2007.<br>Leroy Z. Emkin, Committee Member ; Lawrence F. Kahn, Committee Member ; Abdul-Hamid Zureick, Committee Chair.