To see the other types of publications on this topic, follow the link: Damage analysis.
Dissertations / Theses on the topic 'Damage analysis'
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 'Damage analysis.'
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
McNeill, Brad, and Robert C. Balling. "Boyce Thompson Arboretum Freeze Damage Analysis." University of Arizona (Tucson, AZ), 2011. http://hdl.handle.net/10150/556786.
Full text
2
Yanilmaz, Huseyin. "Damage Detection In Beams By Wavelet Analysis." Master's thesis, METU, 2007. http://etd.lib.metu.edu.tr/upload/12609162/index.pdf.
Full textAbstract:
In this thesis, a method proposed by Han et al. [40] for detecting and locating damage in a structural member was adapted. The method was based on the energies that were calculated from the CWT coefficients of vibrational response of a cantilever beam. A transverse cut at varying depths was introduced. The presence and location of crack was investigated by processing experimentally acquired acceleration signals.
Results of modal analysis and wavelet analysis of the beam with different cut depths were compared. In addition, effect of using different mother wavelets in CWT analysis for damage detection capability was investigated. Acceleration data were analyzed through CWT at different scales and CWT coefficients were calculated. Those CWT coefficients obtained from different scales were evaluated from the standpoint of damage detection. Effectiveness of energy indices associated with CWT coefficients in damage detection was demonstrated as independent of the type of mother wavelet.
3
Samal, Mahendra Kumar. "Nonlocal damage models for structural integrity analysis." kostenfrei, 2007. http://nbn-resolving.de/urn:nbn:de:bsz:93-opus-33369.
Full text
4
Kim, Hansang. "Damage evaluation of structures by Wavelet analysis /." Search for this dissertation online, 2004. http://wwwlib.umi.com/cr/ksu/main.
Full text
5
Sathon, Nuttaphon. "Damage and stress analysis on pipework using thermoelastic stress analysis." Thesis, University of Southampton, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.427400.
Full text
6
Mcdonald, Sara. "Systematic proteomic analysis of oxygen mediated DNA damage." Thesis, University of Manchester, 2015. https://www.research.manchester.ac.uk/portal/en/theses/systematic-proteomic-analysis-of-oxygen-mediated-dna-damage(7c9ddcea-4945-4462-9f3a-0a2f4935e057).html.
Full textAbstract:
Blood cell numbers are maintained constant due to an interplay between haemopoiesis and the loss of mature cells. Haemopoiesis is a complex process that generates large numbers of all the blood cells in the body from a relatively small number of haemopoietic stem cells (HSCs). HSCs continually replenish cells that are turned over, or lost by injury or trauma, and must also self-renew to maintain themselves over the lifetime of the organism. HSCs are protected from reactive oxygen species induced DNA damage by the fact that they possess low levels of mitochondrial oxidative metabolism and are enclosed in a protective niche microenvironment. However, DNA damage can occur, which ultimately leads to the expression of mutations in genes such as those encoding protein tyrosine kinases, resulting in dysfunctional haemopoiesis which can lead to diseases such as leukaemias. Discovery phosphoproteomics was used to compare the changes in protein phosphorylation in cells in different phases of haemopoiesis when exposed to hydrogen peroxide (H2O2), which causes DNA-damage via ROS. We identified and relatively quantified thousands of phosphopeptides, with a few hundred being potentially modulated in the presence of H2O2. Novel phosphorylation sites differentially expressed between the different populations were identified, such as UHRF1, in mature cells, and HMGA1, in primitive cells. Bioinformatic analyses have identified pathways and interacting proteins of these targets, multiple reaction monitoring confirmed the identified phosphosites. The same method was utilised to analyse the role of CD45. CD45 has a role in the response to oxidative status, is activated by H2O2 treatment, and is reduced in its levels by oncogenic PTKs in the pathway initiated by CXCL12 that results in cell motility. Thousands of phosphopeptides were identified and quantified, and bioinformatics analysis was used to identify their interactors and the pathways in which they are involved. The data was also compared to data from several other studies. Our investigation revealed multiple targets which help unravel the relationship between ROS, the CD45 pathway and leukaemogenic PTKs to further understand normal and leukaemic haemopoiesis.
7
Liu, Bangyan. "Fatigue and damage tolerance analysis of composite laminates - stiffness loss, damage modellig, and life prediction." Thesis, McGill University, 1992. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=60701.
Full textAbstract:
The prediction of fatigue life and evaluation of onset and growth of matrix cracks and delamination for general composite laminates are studied analytically using theories of damage tolerance, residual modulus degradation and residual strength degradation. Damage onset including matrix cracks and edge delamination are predicted by using a total strain energy release rate criterion which accounts for interactive effects of matrix cracks and delamination. The analytical models for modulus degradation, matrix crack density and delamination size growth as function of fatigue stress and fatigue cycles are proposed. The proposed approach provides four choices for predicting tension-tension fatigue life and for assessing fail-safety for structures made of composite laminates. The direct relation of physical damage to fatigue life and analytical equations for calculating residual elastic moduli E$ rm{ sb1, E sb2, v sb{12}}$ and G$ sb{12}$ in terms of fatigue load and fatigue cycles are proposed. The proposed approach enables prediction of fatigue behaviour of general laminates using experimental data of a basic lay-up such as unidirectional laminate. The finite element technique was utilized to model the fatigue failure process of notched laminates. A simple example of a laminate with a central hole under tension-tension fatigue loading was performed.
8
Goi, Yoshinao. "Bayesian Damage Detection for Vibration Based Bridge Health Monitoring." Kyoto University, 2018. http://hdl.handle.net/2433/232013.
Full text
9
Kuriakose, Sunil. "Analysis of damage in composite laminates under bending." Diss., Georgia Institute of Technology, 2002. http://hdl.handle.net/1853/12054.
Full text
10
Zhou, Rongxin. "Mesoscopic analysis of damage mechanisms in concrete material." Thesis, University of Edinburgh, 2016. http://hdl.handle.net/1842/23650.
Full textAbstract:
Concrete is a highly non-homogeneous composite with large heterogeneities of quasi-brittle character. Failure of concrete structures is usually accompanied by cracking of concrete, which is strongly affected by the mesoscale structure and the behaviour of the interface between the aggregates and the mortar matrix, especially under complex stress conditions. Analysis of the failure mechanisms of concrete at the mesoscale is therefore crucial for a better understanding of the macroscopic behaviour of the material, which can in turn contribute to improved design of concrete structures and finding new ways to enhance the material properties. This research aims to investigate the intrinsic failure mechanisms of concrete-like materials from a mesoscale point of view. To do this, continued developments from existing work on mesoscale modelling are carried out to cater the needs of realistically simulating the damage process in concrete under complex loading conditions. The new developments focus on two key aspects. Firstly, techniques to realistically simulate the fracture process of concrete are developed and these involve the incorporation of a combined cohesive and contact mechanisms for the interface between aggregates and mortar matrix. Such interface modelling allows the crack initiation and propagation at the mesoscale to be explicitly represented. Secondly, a full 3D mesoscale finite element model for concrete-like materials with random aggregates and the possibility of high packing density is developed. Use is then made of these enhanced mesoscale models to explore the intrinsic mechanism governing the fundamental behaviour of concrete such as fracture propagation in tension and compression, the well-known size effect and the dynamic strain rate effect. The research investigation begins with an analysis of the size effect in plain concrete beams under three-point bending using a generic 2D mesoscale model. The analysis aims to provide preliminary insight into the use of a mesoscopic computational tool for examining the concrete damage mechanisms with the well-known size effect phenomenon as a benchmark scenario. The shapes and the sizes of the fracture process zone (FPZ) during the whole fracture process are captured. The role of detailed FPZ features is discussed accordingly. On the other hand, the results also point out the deficiencies of the continuum-based mesoscale framework at capturing the evolution of the local fracture process, and to resolve this problem requires explicit simulation of the initiation and propagation of the micro-cracks and thus a realistic reproduction of the fracture process zone, and this becomes the subject of research in much of the later chapters of the thesis. To cater to the needs of better representing the fracture process in concrete, a coupled cohesive-contact interface approach is proposed to model the crack initiation, crack propagation and the friction mechanism within the transition zone between the coarse aggregates and the mortar matrix. The cohesive-contact combined model is verified to perform well under simple as well as complex loading conditions. The interface approach in a mesoscale model framework provides a new platform for investigating the failure mechanisms in terms of the cohesive fracture process and the contact friction process. A more comprehensive and robust mesoscale interface modelling approach, in which the cohesive plus contact interface is inserted along all mesh grids, is developed to study the complex dynamic behaviour of concrete with the consideration that fractures can spread in a fine distributed manner within larger damage areas including the strong aggregate, particularly under high loading rate. By allowing local fractures to develop explicitly, the issues with fracture damage description with a continuum material model can be largely resolved. The effectiveness of such an approach is demonstrated and employed in an investigation into the intrinsic mechanisms governing the sensitivity of the dynamic tension resistance with the loading rate. Subsequently, a re-visit of the size effect in terms of the evolution of the fracture process zones using the mesoscale model with cohesive plus contact interface model is conducted and the results are presented. The preliminary observations from using the continuum-based mesoscale model are examined and verified. Additional insight into the fracture processes in the concrete beams with various sizes is obtained and the intrinsic mechanisms of the size effect are further discussed. On the real 3D mesoscale modelling methodology, the new development focuses on achieving a realistic representation of the actual shapes and sizes of aggregate particles and at the same time allowing for high volumetric ratios of aggregates (packing density) to be attained. In addition to specific techniques to enhance the conventional take-and-place procedure, an algorithm to generate supplementary aggregates to allow increased packing density is proposed and implemented. Example 3D mesoscale specimens so created are then verified against standard experimental tests such as uniaxial compression, uniaxial tension and compression with lateral confinements, and applied to examine the dynamic behaviour of concrete under high strain rate compression.
11
Swiatlo, Jeffrey A. "Analysis of shear damage to southern pine lumber." Thesis, Virginia Polytechnic Institute and State University, 1988. http://hdl.handle.net/10919/53188.
Full textAbstract:
This study was conducted as a second part in the shear damage research project at Virginia Tech. The objectives were to verify the results obtained by Gallagher (1984) in the first study under normal mill operations as well as develop a method to compare and evaluate the extent of shear damage in relation to other defects present in southern pine lumber. This was accomplished through two sawmill studies and two kiln cart surveys performed in different geographic locations.
Visible indicators such as stump-pull that are used to determine shear damage extent are often misleading. Stump-pull, used as a scaling deduction for shear damage, does not fully determine the extent of shear damage present. Shatter is often present in greater amounts over the cross section of the butt of the log. The recommendation of six inches of butt trim that was determined to minimize value losses in the first study is supported by the results obtained in this research. A trim of six inches removed 94 to 99 percent of shear damage in this study.
Defects other than shear damage were present on dried and surfaced lumber. Drying checks and splits along with shake were often observed on the lumber ends. These defects often extend further up on the lumber ends, past the seven inch simulated trim. Shake was determined to be the limiting defect. Shatter, in the absence of shake, was determined to be limiting.
Kiln cart surveys conducted at mills that utilize a large percentage of sheared logs can be an inexpensive and effective tool to enable mill personnel to determine the extent of shear damage in relation to other defects present on lumber ends based on green trim already taken.Master of Science
12
Davis, Ivan Christopher. "Damage Detection in Aluminum Cylinders Using Modal Analysis." Thesis, Virginia Tech, 2002. http://hdl.handle.net/10919/34317.
Full textAbstract:
Many studies have attempted to detect structural damage by examining differences in the frequency response functions of a structure before and after damage. In an experimental setting, this variation can not be attributed solely to the addition of damage. Other sources of variation include testing and structure variation. Examples of testing variation include the error introduced by modal parameter extraction, measurement noise, and the mass loading of the accelerometer. Structure variability is due to slight differences in the supposedly identical structures. Dimensional tolerancing is one example.
This study began with six "identical" undamaged aluminum cylinders, of which three were later damaged to varying extents. The frequency response functions of the undamaged and damaged cylinders were measured. Also, the frequency response function of the same undamaged cylinder was measured multiple times to investigate testing variation. The contributions of testing, cylinder, and damage variation to the differences between cylinder responses was elucidated by specifically examining their frequency response functions in two ways: comparing the natural frequencies and directly investigating the entire frequency response function. The curvature of the frequency response functions was then used to determined the presence, location, and severity of the imparted damage.Master of Science
13
Rahardjo, Budi. "Analysis of damage to food particles during pumping /." The Ohio State University, 1992. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487776801322849.
Full text
14
Patel, Ronak. "CORROSION DAMAGE STUDIES THROUGH MICROSCOPY AND STRESS ANALYSIS." VCU Scholars Compass, 2008. http://scholarscompass.vcu.edu/etd/1620.
Full textAbstract:
Corrosion is the destructive result of chemical reaction between a metal or metal alloy and its environment. Airplanes, power generating plants, chemical process and manufacturing plants, concrete structure, and many others which widely uses aluminum alloy and stainless steel alloys are subjected to corrosion. The estimated cost of corrosion damage is in order of 3 to 5 percent of gross national product (GNP). Out of all forms of corrosion, pitting corrosion is most commonly observed in aluminum alloy 2024 and stainless steel type 316. There is a need to study the stress environment around the pits in order to predict the nucleation of the crack. The objective of this thesis is to investigate the correlation between pits and stresses in AA2024 and SS316 alloys under different types of loading. Corrosion experiments were carried out on both alloys samples for a fixed time interval and were imaged on optical and AFM. The optical microscope provided the information on forms of corrosion expected on the surface while the AFM provided the pit profile on the surface. An analysis procedure was developed using CAD and finite element analysis to predict stresses resulting from corrosion pits under different types of loadings. The average corrosion rate of AA2024 is six times higher than that of SS316 in 2 Molar NaCl corrosive environment. Based on the results from the optical microscope, AA2024 usually initiated with localized corrosion along with pitting and localized regions grows in size and soon uniform corrosion is observed. However, the stainless steel SS316 usually initiated with pitting corrosion and soon followed by film forming corrosion. Based on the analysis, it was observed that the stress distribution and levels on the corroded surface varied due to irregularities in the corrosion process. From the stress analysis result of AA2024 under bending, it was observed that there was 80% stress increase during first 30 min of corrosion and then the increase was about 6% from 30min to 60 min and then soon reaches a plateau. Similar results were obtained for both AA2024 and SS316 materials under different type of loadings. Initially, the stress increases sharply as time increases but the amount of stress increase demises as time progress and soon reaches a plateau. There was a sharp increase of Bending and shear loading are induces higher level of stresses compared to tension loading. From these stresses it is possible to estimate the initiation of crack, from which the life can be estimated for failure in the material.
15
Wood, Michael G. "Damage analysis of bridge structures using vibrational techniques." Thesis, Aston University, 1992. http://publications.aston.ac.uk/11832/.
Full textAbstract:
Much research is currently centred on the detection of damage in structures using vibrational data. The work presented here examined several areas of interest in support of a practical technique for identifying and locating damage within bridge structures using apparent changes in their vibrational response to known excitation. The proposed goals of such a technique included the need for the measurement system to be operated on site by a minimum number of staff and that the procedure should be as non-invasive to the bridge traffic-flow as possible. Initially the research investigated changes in the vibrational bending characteristics of two series of large-scale model bridge-beams in the laboratory and these included ordinary-reinforced and post-tensioned, prestressed designs. Each beam was progressively damaged at predetermined positions and its vibrational response to impact excitation was analysed. For the load-regime utilised the results suggested that the infuced damage manifested itself as a function of the span of a beam rather than a localised area. A power-law relating apparent damage with the applied loading and prestress levels was then proposed, together with a qualitative vibrational measure of structural damage. In parallel with the laboratory experiments a series of tests were undertaken at the sites of a number of highway bridges. The bridges selected had differing types of construction and geometric design including composite-concrete, concrete slab-and-beam, concrete-slab with supporting steel-troughing constructions together with regular-rectangular, skewed and heavily-skewed geometries. Initial investigations were made of the feasibility and reliability of various methods of structure excitation including traffic and impulse methods. It was found that localised impact using a sledge-hammer was ideal for the purposes of this work and that a cartridge `bolt-gun' could be used in some specific cases.
16
Gigliotti, Luigi. "Multiscale analysis of damage-tolerant composite sandwich structures." Thesis, Imperial College London, 2016. http://hdl.handle.net/10044/1/32365.
Full textAbstract:
Composite sandwich structures are widely regarded as a cost/weight-effective alternative to conventional composite stiffened panels and are extensively utilized for lightweight applications in various sectors, including the aeronautical, marine and transport industries. Nevertheless, their damage tolerance remains a critical issue. This work aims to develop reliable analytical and numerical tools for the design of damage-tolerant advanced foam-cored composite sandwich structures for aerospace applications. It comprises of original experimental observations together with novel numerical and analytical developments, as detailed below. A novel analytical model for predicting the post-crushing response of crushable sandwich foam cores is presented. The calibration of the model is performed using experimental data obtained exclusively from standard monotonic compressive tests. Hence, the need for performing time-consuming compressive tests including multiple unloading-reloading cycles is avoided. Subsequently, the translaminar initiation fracture toughness of a carbon-epoxy Non-Crimp Fabric (NCF) composite laminate is measured. The translaminar fracture toughness of the UD fibre tows is related to that of the NCF laminate and the concept of an homogenised blanket-level translaminar fracture toughness was introduced. A multiple length/time-scale framework for the virtual testing of large composite structures is presented. Such framework hinges upon a novel Mesh Superposition Technique (MST) and a novel set of Periodic Boundary Conditions named Multiscale Periodic Boundary Conditions (MPBCs). The MST is used for coupling different areas of the composite structure modelled at different length-scales and whose discretizations consist of different element types. Unlike using a sudden discretization-transition approach, the use of the MST eliminates the undesirable stress disturbances at the interface between differently-discretized subdomains and, as a result, it for instance correctly captures impact-induced damage pattern at a lower computational cost. The MPBCs apply to reduced Unit Cells (rUCs) and enable the two-scale (solid-to- shell) numerical homogenization of periodic structures, including their bending and twisting response. The MPBCs allow to correctly simulate the mechanical response of periodic structures using rUCs (same results as if conventional UCs were used), thus enabling a significant reduction of both modelling/meshing and analysis CPU times. The developments detailed above are finally brought together in a realistic engineering application.
17
Yano, Marcus Omori. "Extrapolation of autoregressive model for damage progression analysis /." Ilha Solteira, 2019. http://hdl.handle.net/11449/182287.
Full textAbstract:
Orientador: Samuel da SilvaResumo: O principal objetivo deste trabalho é usar métodos de extrapolação em coeficientes de modelos autorregressivos (AR), para fornecer informações futuras de condições de estruturas na existência de mecanismo de danos pré-definidos. Os modelos AR são estimados considerando a predição de um passo à frente, verificados e validados a partir de dados de vibração de uma estrutura na condição não danificada. Os erros de predição são usados para extrair um indicador para classificar a condição do sistema. Então, um novo modelo é identificado se qualquer variação de índices de dano ocorrer, e seus coeficientes são comparados com os do modelo de referência. A extrapolação dos coeficientes de AR é realizada através das splines cúbicas por partes que evitam possíveis instabilidades e alterações indesejáveis dos polinômios, obtendo aproximações adequadas através de polinômios de baixa ordem. Uma curva de tendência para o indicador capaz de predizer o comportamento futuro pode ser obtida a partir da extrapolação direta dos coeficientes. Uma estrutura de três andares com um para-choque e uma coluna de alumínio colocada no centro do último andar são analisados com diferentes cenários de dano para ilustrar a abordagem. Os resultados indicam a possibilidade de estimar a condição futura do sistema a partir dos dados de vibração nas condições de danos iniciais.
Abstract: The main purpose of this work is to apply extrapolation methods upon coefficients of autoregressive models (AR), to provide future condition information of structures in the existence of predefined damage mechanism. The AR models are estimated considering one-step-ahead prediction, verified and validated from vibration data of a structure in the undamaged condition. The prediction errors are used to extract an indicator to classify the system state condition. Then, a new model is identified if any variation of damage indices occurs, and its coefficients are compared to the ones from the reference model. The extrapolation of the AR coefficients is performed through the piecewise cubic splines that avoid possible instabilities and undesirable changes of the polynomials, obtaining suitable approximations through low-order polynomials. A trending curve for the indicator capable of predicting future behavior can be obtained from direct coefficient extrapolation. A benchmark of a three-story building structure with a bumper and an aluminum column placed on the center of the top floor is analyzed with different damage scenarios to illustrate the approach. The results indicate the feasibility of estimating the future system state from the vibration data in the initial damage conditions.
Mestre
18
Sawatzky, Rene. "Vibration Based Planetary Gear Analysis and Damage Detection." DigitalCommons@CalPoly, 2014. https://digitalcommons.calpoly.edu/theses/1378.
Full textAbstract:
With this thesis the research at the engineering department is continued, based on previous thesis projects. These projects were considering the possibility of simulation gears with rigid bodies. After researches with different emphasizes on the rigid body simulation, the gained knowledge showed limitations of the rigid body model. Gear failures are very diverse and the actual simulation technique could not represent all necessary failure modes that can occur. That led to this thesis as a research project to find a way to detect and analyze the failure modes that cannot be considered with the current rigid body approach. With the flexible body theory and simulation tools (MSC:Adams) this gap of gear failure detection simulation can be closed. The objective is, making it possible to simulate all failure modes of a gear that can occur. Additionally the previous project on this topic were using gears of small laboratory conditions. An industry sector has been picked to work on a practical application. This application is a wind turbine gearbox. These gearboxes have common run-time errors which influences the profitability of the power generation. To model this system a gear design guide for wind turbine gearboxes is elaborated.
19
Lacy, Thomas E. Jr. "Distribution effects in damage mechanics." Diss., Georgia Institute of Technology, 1998. http://hdl.handle.net/1853/15937.
Full text
20
O'Regan, Paul. "Functional analysis of the XRCC2 DNA repair gene." Thesis, University of Oxford, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.249623.
Full text
21
Hong, Soonyoung. "An effective data mining approach for structure damage identification." Columbus, Ohio : Ohio State University, 2007. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1194903908.
Full text
22
Xia, Jianjun. "Finite Element Analysis of Ship Collisions." Thesis, Virginia Tech, 2001. http://hdl.handle.net/10919/34133.
Full textAbstract:
The serious consequence of ship collisions necessitates the development of regulations and requirements for the subdivision and structural design of ships so that damage and environmental pollution is reduced, and safety is improved. A simplified collision model (SIMCOL) is currently being developed at Virginia Tech to conduct probabilistic analysis of damage in ship collisions and ultimately optimize ship structural designs to improve crashworthiness. Collision data for validation of SIMCOL is very difficult to obtain, and model testing is very costly. Finite Element Analysis (FEA) provides an alternative to physical validation that can be used to increase confidence and insight in simplified model results.
This thesis develops a complete methodology for ship-to-ship collision simulations using the explicit non-linear FE code LS-DYNA3D. Various modeling alternatives are considered. The ability to model a complete ship-to-ship collision is developed incrementally starting with bow collisions with a rigid wall. A super-element (intersection model) approach is considered to increase the calculation speed of bow models. A conventional fine mesh finite element bow model is also developed. Results from both models are compared with each other, and with a closed-form calculation from Pedersen. A fine mesh model is developed for a struck tanker cargo section and integrated in a total ship framework modeling external dynamics and ship-to-ship contact. A series of collision scenarios is simulated using the conventional bow model and a rigid bow model striking a double hull tanker. Results are compared with SIMCOL, DAMAGE, DTU and ALPS/SCOL models. LS-DYNA provides detailed and reasonable results for ship collision analysis and comparison to increase confidence in simplified models.Master of Science
23
Li, Zejun. "Low-energy electron-induced DNA damage product analysis and mechanistic studies of damage in short oligonucleotides." Thèse, Université de Sherbrooke, 2010. http://savoirs.usherbrooke.ca/handle/11143/4317.
Full textAbstract:
The major objective of our group is to understand the mechanism of DNA damage induced by secondary low-energy electrons (LEE) arising from ionizing radiation and its relationship to radiosensitization and radiotherapy. Prof. Sanche has developed a novel low-energy electron irradiation system in which a relatively large area of thin films of DNA constituents can be irradiated with mono-energetic electrons under ultra high vacuum. This permits the irradiation of target DNA and the formation of sufficient degraded material to allow for chemical analysis (HPLC, GC/MS, and LC/MS/MS) of products remaining on the target surface, so as to elucidate the mechanism of LEE-induced DNA damage. My project focuses on simple systems, in which small DNA components nucleosides (dThd), nucleotides (pT, Tp, pTp), oligonucleotides (TT and TTT) and modified oligonucleotides (T5BrUT) are exposed to low-energy electrons, and the subsequent reactions are studied by chemical analysis of the products. My studies revealed three mechanisms of LEE-induced fragmentation reactions in DNA: 1) the terminal phosphate group has a larger cross-section in LEE-induced DNA damage; 2) initial LEE capture and subsequent bond breaking within the intermediate anion depend on the sequence and electron affinity of the bases; and 3) at 10 eV, one electron might induce double events. This study provides a chemical basis for the formation of DNA strand breaks by the interaction of LEE with DNA.
24
Zhai, Jinyuan. "Modeling Ductile Damage of Metallic Materials." University of Akron / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=akron1466471348.
Full text
25
Rule, Ruth Anne. "Vibration-based damage detection in ceramics and glass." Thesis, Loughborough University, 2000. https://dspace.lboro.ac.uk/2134/27153.
Full textAbstract:
This thesis describes the development of the hardware, experimental procedures and algorithms required for vibration based damage identification in small ceramic and glass structures. The results form the basis of a fully automated industrial quality assurance system.
26
Pelà, Luca. "Continuum damage model for nonlinear analysis of masonry structures." Doctoral thesis, Universitat Politècnica de Catalunya, 2009. http://hdl.handle.net/10803/30327.
Full textAbstract:
The present work focuses on the formulation of a Continuum Damage Mechanics model for nonlinear analysis of masonry structural elements. The material is studied at the macro-level, i.e. it is modelled as a homogeneous orthotropic continuum.
The orthotropic behaviour is simulated by means of an original methodology, which is based on nonlinear damage constitutive laws and on the concept of mapped tensors from the anisotropic real space to the isotropic fictitious one. It is based on establishing a one-to-one mapping relationship between the behaviour of an anisotropic real material and that of an isotropic fictitious one. Therefore, the problem is solved in the isotropic fictitious space and the results are transported to the real field. The application of this idea to strain-based Continuum Damage Models is rather innovative.
The proposed theory is a generalization of classical theories and allows us to use the models and algorithms developed for isotropic materials. A first version of the model makes use of an isotropic scalar damage model. The adoption of such a simple constitutive model in the fictitious space, together with an appropriate definition of the mathematical transformation between the two spaces, provides a damage model for orthotropic materials able to reproduce the overall nonlinear behaviour, including stiffness degradation and strain-hardening/softening response.
The relationship between the two spaces is expressed in terms of a transformation tensor which contains all the information concerning the real orthotropy of the material. A major advantage of this working strategy lies in the possibility of adjusting an arbitrary isotropic criterion to the particular behaviour of the orthotropic material. Moreover, orthotropic elastic and inelastic behaviours can be modelled in such a way that totally different mechanical responses can be predicted along the material axes.
The aforementioned approach is then refined in order to account for different behaviours of masonry in tension and compression. The aim of studying a real material via an equivalent fictitious solid is achieved by means of the appropriate definitions of two transformation tensors related to tensile or compressive states, respectively. These important assumptions permit to consider two individual damage criteria, according to different failure mechanisms, i.e. cracking and crushing. The constitutive model adopted in the fictitious space makes use of two scalar variables, which monitor the local damage under tension and compression, respectively. Such a model, which is based on a stress tensor split into tensile and compressive contributions that allows the model to contemplate orthotropic induced damage, permits also to account for masonry unilateral effects. The orthotropic nature of the Tension-Compression Damage Model adopted in the fictitious space is demonstrated. This feature, both with the assumption of two distinct damage criteria for tension and compression, does not permit to term the fictitious space as “isotropic”. Therefore, the proposed formulation turns the original concept of “mapping the real space into an isotropic fictitious one” into the innovative and more general one of “mapping the real space into a favourable (or convenient) fictitious one”. Validation of the model is carried out by means of comparisons with experimental results on different types of orthotropic masonry.
The model is fully formulated for the 2-dimensional case. However, it can be easily extended to the 3-dimensional case. It provides high algorithmic efficiency, a feature of primary importance when analyses of even large scale masonry structures are carried out. To account for this requisite it adopts a strain-driven formalism consistent with standard displacement-based finite element codes. The implementation in finite element programs is straightforward.
Finally, a localized damage model for orthotropic materials is formulated. This is achieved by means of the implementation of a crack tracking algorithm, which forces the crack to develop along a single row of finite elements. Compared with the smeared cracking approach, such an approach shows a better capacity to predict realistic collapsing mechanisms. The resulting damage in the ultimate condition appears localized in individual cracks. Moreover, the results do not suffer from spurious mesh-size or mesh-bias dependence. The numerical tool is finally validated via a finite element analysis of an in-plane loaded masonry shear wall.
27
Lundmark, Peter. "Damage mechanics analysis of inelastic behavior of fiber composites /." Luleå, 2005. http://epubl.luth.se/1402-1544/2005/50.
Full text
28
Mortusewicz, Oliver. "Analysis of the DNA damage response in living cells." Diss., kostenfrei, 2007. http://edoc.ub.uni-muenchen.de/8555/.
Full text
29
Goldstein, Eric D. "Analysis of the repair of topoisomerase II DNA damage." Honors in the Major Thesis, University of Central Florida, 2011. http://digital.library.ucf.edu/cdm/ref/collection/ETH/id/385.
Full textAbstract:
A large number of anti-cancer chemotherapeutics target DNA topoisomerases. Etoposide is a specific topoisomerase II poison which causes reversible double strand DNA breaks. The focus of this project is to analyze the repair of DNA damage induced by etoposide.. Double strand DNA break repair is mediated by through either non-homologous end joining (NHEJ) or homologous recombination. NHEJ repairs through direct ligation of a double stranded break while homologous recombination utilizes a homologous template to recover the wild type sequence. A reporter cassette, RYDR-GFP, has been stably integrated into HeLa cells. This reporter contains an ultra-high affinity topoisomerase II cleavage site (RY) placed in the middle of a mutant GFP sequence. Flanking this sequence is a corresponding stretch of wild type GFP that is used as template to repair the break and restore gene function yielding GFP positive cells. Titrations with etoposide have shown that a logarithmic increase in drug concentration yields a corresponding increase in repair through homologous recombination (HR). This result demonstrates that topoisomerase II mediated damage is efficiently repaired by the process of HR. To examine NHEJ repair, a doxycycline inducible, stably integrated NHEJ HeLa cell reporter cassette was also evaluated. The data indicates that repair of topoisomerase II mediated DNA damage occurs more efficiently through the HR pathway. Collectively, the data suggests that tumor cells proficient in HR repair may effectively elude treatment by topoisomerase II targeting drugs.B.S.
Bachelors
Medicine
Molecular Biology and Microbiology
30
Leong, Chee-Onn. "Antitumour benzothiazoles : analysis of DNA damage induced by Phortress." Thesis, University of Nottingham, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.396792.
Full text
31
Uwayed, Ahmed Noori. "Damage detection in laminated composite structures using dynamic analysis." Thesis, University of Leicester, 2018. http://hdl.handle.net/2381/42921.
Full textAbstract:
Laminated composite materials are used in different applications, for example mechanical, civil and aerospace structures, due to their light weight and excellent mechanical properties. However, fibre breakage and delamination are among the more serious damage that often initiate and propagate due to a number of mechanical and, specifically, dynamic loads during the operational life. Also, these damages destroy design functionality of these structures. To address this issue, damage detection is required in time to provide a good understanding of structure state in advance of any potential failure. There are a number of damage detection approaches reported in the literature and reviewed herein. Some of these are base-line free, whilst others use the intact data as a reference for the detection of damaged sections. However, currently there are a very limited number of experimental studies in the literature that use vibration-based damage detection to detect the delaminated areas, and are almost non-existent for fibre breakage; the majority of simulated studies consider delamination only. Defects in laminated structures are quite complicated and in most cases are hidden. Frequency-based damage detection is considered to be a global approach and is not useful when dealing with complex structures. There has been extensive research to develop the curvature mode shape as a reference for damage detection because it is highly sensitive at show the effects of damage. This sensitivity is tested in this research, as it is extremely difficult to detect damaged sections within composite materials, even with an active approach. Hence, the main objective of this research is to develop the curvature damage index by calculating the irregularity curvature index, and the proposal of a novel index, called the Haar index, to support the damage detection process. Both these indexes are used to detect delamination and fibre breakage on high modulus CFRP plate structures under condition of free vibration. Using these indexes gives an efficient method by which to quantify and localize damaged areas in both theoretical and experimental considerations of different lay-ups. In the modelling section, two finite element software programs, COMSOL Multiphysics 5.1 (Licence No. 7074366) and ABAQUS 6.14-1 (Licence No. 200000000008515), are used. This thesis includes development procedure of the curvature index, calculates the Haar index, gives details of the theoretical and experimental analysis, and reports the consequent results and discussion.
32
Rhead, Andrew T. "Analysis and optimisation of postbuckled damage tolerant composite laminates." Thesis, University of Bath, 2009. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.520992.
Full textAbstract:
Barely Visible Impact Damage (BVID) can occur when laminated composite material is subject to impact, i.e. from runway debris or dropped tools, and may result in a significant reduction in the compressive strength of composite structures. A component containing BVID subjected to compression may fail via a number of mechanisms. However, it is assumed that the impact damage problems to be modelled will fail by delamination buckling leading to propagation of damage away from the original site. This precludes problems where the initial mechanism of failure is via kink banding or buckling of the full laminate. An analytical model is presented, for application to various composite structures, which predicts the level of compressive strain below which growth of BVID following local buckling of a delaminated sublaminate will not occur. The model is capable of predicting the critical through-thickness level for delamination, the stability of delamination growth, the sensitivity to experimental error in geometric measurements of the damage area and additionally establishes properties desirable for laminates optimised for damage tolerance. Problems treated with the model are split into two impact categories; ‘face’ (i.e. an out-of-plane skin impact) and ‘free edge’ (i.e. an in-plane stiffener edge impact) and two compressive loading regimes; ‘static’ and ‘fatigue’. Analytical results for static and fatigue compression of face impacted plates show an agreement of threshold strain to within 4% and 17% of experimental values respectively. In particular, for impacts to the skin under a stiffener subject to static loading the model is accurate to within 5%. An optimised laminate stacking sequence has shown an experimental increase of up to 29% in static strength can be achieved in comparison to a baseline configuration. Finally, compression testing has been undertaken on three coupons in order to validate an analysis of static free edge problems. Analytical results are, on average, within 10% of experimental results. An optimised laminate is theoretically predicted to increase static compression after free edge impact strength by at least 35%.
33
Park, Cecelia Hyun Seon. "Analysis of thermally induced damage in composite space structures." Thesis, Massachusetts Institute of Technology, 1994. http://hdl.handle.net/1721.1/49918.
Full text
34
Reaper, Philip Michael. "Molecular analysis of DNA damage signalling in mammalian cells." Thesis, University of Cambridge, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.614744.
Full text
35
Aidi, Bilel. "Experimental and Numerical Analysis of Damage in Notched Composites." Diss., Virginia Tech, 2016. http://hdl.handle.net/10919/82559.
Full textAbstract:
This dissertation contains the results from an experimental study, numerical, and analytical study conducted on quasi-isotropic carbon fiber laminates containing a center hole (notch) subjected to constant amplitude tension-tension fatigue loading in order to investigate the effect of fatigue damage development on the residual properties. Quasi-static tests were initially performed on notched composites using digital image correlation (DIC) to determine the strain profiles at selected transverse sections of the outer ply of the laminates and the static strength of the laminates. Subsequently, tension-tension fatigue tests were carried out at 70%, 75% and 80% of the nominal static failure load. A finite element model was developed using Abaqus and Digimat in which Digimat was used to implement the damage evolution model via a user-defined material subroutine. Damage initiation has been assessed using Hashin's failure criteria and the Matzenmiller model was adopted for damage evolution. A second finite element model was developed using Abaqus and Autodesk Simulation Composite Analysis (ASCA) in which ASCA was used to implement the user-material subroutine. The subroutine includes a failure initiation criterion based upon multi-continuum theory (MCT) and an energy-based damage evolution law. Numerical and experimental strain results were presented and compared for different section lines on the outer surface of the laminate at different loading stages. Additionally, the experimentally measured notched composite strength was compared with the predictions from the finite element solutions. These results are used as baseline for subsequent comparison with strain profiles obtained using DIC for specimens fatigued at different stress levels and fatigue lifetime fractions. The results showed a significant effect of fatigue damage development on strain redistribution even at early stages of fatigue. The results also showed the capability of DIC technique to identify damage initiation and its location. Furthermore, X-ray computed tomography (CT) was used to examine the sequence of damage development throughout the fatigue lifetime and to connect the observed damage mechanisms with the occurred change of strain profiles.
Experimental vibrational modal analysis tests were also conducted to assess the effect of fatigue damage on the residual frequency responses (RFRs). Vibrational measurements were initially performed on pristine notched composites. The results are used as baseline for subsequent comparison with strain profiles obtained with DIC. Finite element models based on the classical plate theory (Kirchhoff) and the shear deformable theory (Mindlin) within the framework of equivalent single-layer and layer-wise concepts as well as the three-dimensional theory of elasticity are developed to predict the natural frequencies of non-fatigued specimen. These models are implemented using the finite element software, Abaqus, to determine the natural frequencies and the corresponding mode shapes. In addition, an analytical model based on Kirchhoff plate theory is developed. Using this approach, an equivalent bending-torsion beam model for cantilever laminated plates is extracted taking into account the reduction in local stiffness and mass induced by the center hole. Numerical and analytical natural frequency values are then compared with those obtained through experimental vibrational tests, and the accuracy of each finite element (FE) and analytical model type is assessed. It is shown that the natural frequencies obtained using the analytical and FE models are within 8% of the experimentally determined values.Ph. D.
36
Joulaee, Nasim. "Thermo-mechanical damage analysis in solid oxide fuel cell." Université Louis Pasteur (Strasbourg) (1971-2008), 2007. http://www.theses.fr/2007STR13202.
Full text
37
Caceres, Arsenio. "Local damage analysis of fiber reinforced polymer matrix composites." Morgantown, W. Va. : [West Virginia University Libraries], 1998. http://etd.wvu.edu/templates/showETD.cfm?recnum=328.
Full textAbstract:
Thesis (Ph. D.)--West Virginia University, 1998.Title from document title page. Document formatted into pages; contains x, 107 p. : ill. (some col.) Includes abstract. Includes bibliographical references (p. 104-107).
38
Ngwangwa, Harry Magadhlela. "Assessment of structural damage using operational time responses." Pretoria : [s.n.], 2004. http://upetd.up.ac.za/thesis/available/etd-01312006-141711.
Full text
39
Evans, Helen. "How Damage Alters Meaning : An Analysis of the Conservation and Display of War-Damaged Objects in War Museums." Thesis, Royal College of Art, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.503022.
Full textAbstract:
War museums address many of the most controversial aspects of human history, some of which have the potential to be viewed as contradictory, such as: the representation of both the horrors of war and the heroics of soldiering; addressing the darkest aspects of humanity in a context of enlightenment and learning; and - most importantly for this work - depicting loss through the physical presence of material objects. By examining, in-depth, a small selection of war-damaged objects this research explores how some owner institutions have approached the conservation and display of these items and the impact their choices have had on meaning and viewer interpretation. The effectiveness of these treatment and display approaches is evaluated and the potential implications of these methods for the significance and understanding of war-damaged objects in general are examined. This research shows that societal perceptions of war directly influence the way museums conserve and display war-damaged objects. It demonstrates people's belief that individual, war-damaged objects eloquently express the horrors of war. Our inability to grasp the sheer scale of war means that we are best able to understand its devastating effects on an individual level; viewers project their empathy onto war-damaged objects, as condition is seen to mirror that of the victims of war. Personal items are the most effective trigger for this empathic reaction, which is why war-damaged objects of this type are seldom restored. This in turn has negated the perceived importance of war-damage to nonpersonal items. It is concluded that the symbolic associations attributed to war-damaged personal items have sometimes clouded the judgment of museum professionals and resulted in a failure to properly address the long-term preservation needs of the object. Conversely, the devaluing of the importance of war-damage to non-personal items has sometimes resulted in unsympathetic, interventive conservation
40
Marston, Nicola Jane. "Mutational analysis of the tumour suppressor protein, p53." Thesis, Imperial College London, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.387679.
Full text
41
Song, Injun. "Damage analysis in asphalt concrete mixtures based on parameter relationships." Texas A&M University, 2004. http://hdl.handle.net/1969.1/1300.
Full textAbstract:
Asphalt pavements experience damage due to traffic loading under various environmental conditions. Damage can be caused by viscopl
microcracks, fracture due to fatigue cracking, or fracture due to thermal cracking. Asphalt pavements have the capability to remedi
s damage depending on binder surface and rheological properties, filler surface properties, and length of rest periods.
Asphalt mastic (asphalt and fine aggregates) properties play an important role in controlling damage and healing. This dissertation
development of a comprehensive methodology to characterize damage and healing in asphalt mastics and mixtures. The methodology reli
ctive imaging techniques (X-ray CT), principles of continuum damage mechanics, and principles of micromechanics. The X-ray CT yield
meter that quantifies the percentage of cracks and air voids in a specimen. The continuum damage model parameters are derived from
p between applied stress and pseudo strain. The micromechanics model relates the damaged mastic modulus to a reference undamaged mo
ationship is a function of internal structure properties (void size, film thickness, and percentage of voids), binder modulus, aggr
and bond energy between binder and aggregates. The internal structure parameters are all obtained using X-ray CT and correlated.
The developed methodology was used to characterize damage in asphalt mastic and mixture specimens tested using the Dynamic Mechanic
A) and dynamic creep test. The damage parameter measured using X-ray CT correlated very well with the predictions of the continuum
ics models. All damage parameters were able to reflect the accumulation of damage under cyclic loading and were also able to captur
of moisture conditioning on damage. Although this dissertation focused on fatigue cracking at room temperatures, the methodology d
used to assess damage due to different mechanisms such as permanent deformation and low temperature cracking.
42
Liu, Dezheng. "The development of finite element software for creep damage analysis." Thesis, University of Huddersfield, 2015. http://eprints.hud.ac.uk/id/eprint/24966/.
Full textAbstract:
Creep deformation and failure in high temperature structures is a serious problem for industry and is becoming even more so under the current increasing pressures of power, economics and sustainability. Laboratory creep tests can be used in the description of creep damage behaviour; however, it’s usually expensive and time-consuming. Thus, the computer-based finite element (FE) technique is considered here for both time and economic efficiency. This project aims to develop an in-house FE software for creep damage analysis. A novel in-house FE software High Temperature Structural Integrity (HITSI) was developed through the use of Continuum Damage Mechanics (CDM) and finite element method (FEM) in conjunction with an advanced engineering computer programming language (Fortran 2003) based on an objected oriented programming (OOP) approach. This research provides four main contributions. First, a critical review of the current state of obtaining the computational capability for creep damage analysis. This critical review presents the advantages through the use of in-house software in analysing creep damage behaviour and the state-of-the-art research advancements and technologies need to be involved in developing in-house software. Second, the proposed OOP approach in design and development of in-house FE software for creep damage analysis. Third, the prototyping and implementation of a practical in-house FE software HITSI for analysing creep damage behaviour. The general flow diagram and development strategy of HITSI were proposed. Fourth, the benchmark test of HITSI via the numerical investigation of creep damage behaviour of a Cr-Mo-V steam pipe weldment case. The efficiency of the integration algorithms (Euler and Runge-Kutta) and normalized Kachanov-Rabotnov creep damage constitutive equation was investigated and commented. Generally, this project provides a novel in-house software prototype that allow the scientist to simulate the behaviour of creep damage in particular to analysis the evolution of creep damage in welds.
43
Hegaze, Moutaz Mohamed Ebrahim. "Finite element analysis of fatigue damage of composite laminated structures." Thesis, Cranfield University, 2002. http://hdl.handle.net/1826/4064.
Full textAbstract:
Composite materials are increasingly believed to be the materials of the future with potential for
application in high perfon-nance structures. One of the reasons for that is the indication that
composite materials have a rather good rating with regard to life time in fatigue. Fatigue of
composite materials is a quite complex phenomenon, and the fatigue behaviour of these
heterogeneous materials is fundamentally different from the behaviour of metals. Finite element
method is a powerful numerical technique for the solution of such complex problems. The
present work comprises theoretical and experimental research into the implementation of
composite materials in structure applications. A new finite element derivation was carried out
based on a high-order shear deformation theory, which is accurate for a wide range of thickness.
The geometric nonlinearity effect was considered in the derivation of the element. The force
increment method was also introduced to improve the accuracy of nonlinear analysis.
Experimental measurements were carried out with two different types of composite materials,
carbon/epoxy and glass/epoxy, in order to obtain fatigue life diagrams (S/N diagrams) to be used
for the fatigue damage assessment.F atigue damage assessmentsw ere developed to predict the
fatigue behaviour of laminated plates and shells based on two aspects; damage by initiation and
damage by crack growth. A computer package was built based on the proposed finite element
theory to carry out the previous analyses. Several finite element solvers and eigenproblem solvers
are available to users of the package to choose the suitable one for their applications. The
validation of the developed package for some analyses such as stress analysis, natural frequency
analysis, stability analysis and fatigue analysis was successfully achieved using a number of
composite case studies. A parametric study was also carried out to illustrate the potential of the
package to be used as a good optimization tool. Fatigue life assessment by damage growth has
been achieved by a single run of the package, thus saving enormous user effort and computer
resources, compared with the use of commercial finite element packages.
44
ElFallagh, Fathi Ali. "3D Analysis of Indentation Damage by FIB tomography and TEM." Thesis, University of Sheffield, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.500111.
Full text
45
Yang, Chunhui, and 楊春暉. "Numerical and experimental damage analysis of elastic bodies containing defects." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2002. http://hub.hku.hk/bib/B3124385X.
Full text
46
Collins, Richard Anthony. "On the analysis of multiple site damage in stiffened panels." Thesis, University of Southampton, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.310548.
Full text
47
Lucey, Marie Jean. "Analysis of chromium-induced DNA damage in human lung cells." Thesis, Liverpool John Moores University, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.343130.
Full text
48
Martins, Alan. "Analysis of damage mechanisms in composite structures reinforced by tufting." Thesis, Compiègne, 2018. http://www.theses.fr/2018COMP2443/document.
Full textAbstract:
Cette étude portait sur l’évaluation des performances mécaniques et des mécanismes de défaillance des composites cousus dans différentes conditions de chargement. Des plaques stratifiées et des raidisseurs renforcés par tufting ont été fabriqués avec différents paramètres de couture afin d'évaluer leur effet sur les propriétés des composites. L'investigation a été assistée par une caractérisation multi-instrumentée pendant les tests. Les plaques cousues soumises à des tests de cisaillement à poutre courte sont utilisées dans l'analyse du comportement de la densité et de l'angle de couture dans des conditions de chargement en mode II, tandis que des tests d'impact et de compression après impact (CAI) sur la tolérance aux dommages. Des tests de fatigue en éprouvettes trouées ont également été réalisés afin d’évaluer la réponse des coutures, en particulier leur position par rapport au trou central, à la concentration de déformation générée par le trou. La suite de ce travail a consisté en des tests mécaniques sur panneau raidi oméga renforcé par tufting. La procédure a optimisé les paramètres de touffetage utilisés pour renforcer les structures du lot précédent d'échantillons jusqu'à atteindre un point optimal où les propriétés principales, principalement trouvées dans les tests d'arrachement, sont égales ou supérieures à celles des échantillons témoins. Cette amélioration tenait également compte des modifications de la forme des raidisseurs. En outre, une nouvelle approche basée sur l’effet piézorésistif des coutures en fibres de carbone lors du chargement des éprouvettes composites est réalisée. Cela peut faciliter la surveillance de l’état de santé des fils cousus et donc du composite en raison de la nature structurelle des coutures. Les résultats ont montré que les renforts par tufting sont capables d'augmenter considérablement la ténacité entre les composites et la tolérance aux endommagements des composites, principalement en raison de leurs phénomènes de pontage des fissures. Les paramètres de tufting sont des facteurs décisifs pour obtenir les meilleures propriétés mécaniques. Cependant, ces travaux ont montré que les fils de coutures sont également responsables de la création de fissures dues à la concentration de contrainte et aux défauts causés par leur insertion et, par conséquent, à la diminution de la résistance des composites. L'enquête conclut que l'insertion aléatoire des touffes n'est pas idéale pour la performance du matériau et doit donc être évitée. Le développement de l'insertion des coutures dans les raidisseurs oméga a été soutenu par la caractérisation multi-instrumentée qui a permis d'optimiser le renforcement de la structure. Bien que l’étude ait permis d’obtenir des propriétés mécaniques nettement supérieures à celles des panneaux oméga renforcés par touffetage, il est évident que la procédure employée n’est pas optimale. Le présent travail propose également un modèle préliminaire d'éléments finis pour surmonter le coût et la perte de temps des tests expérimentaux. Il vise principalement à optimiser les paramètres de tufting dans la structure. Le modèle développé était capable de prédire les mêmes endommagements que ceux observés expérimentalement, mais encore éloignés des prévisions quantitatives des résultats. Le contrôle de l’état structurel des stratifiés composites cousus par les fils de carbone semble prometteur et pourrait aider à l’avenir à fournir des informations sur l’état de santé des coutures sous chargement qui ne sont pas atteintes par les méthodes de caractérisation classiques utilisées dans ce travailThis study focused mainly on the assessment of the mechanical performance and the failure mechanisms of tufted composites under divers loading conditions. Laminated plates and stiffened panels reinforced by tufting was manufactured with different tufting parameters to evaluate their effect in the properties of the composites. Multi-instrumented characterization carried out during the tests assisted the investigation. The tufted plates subjected to short-beam shear tests aided especially in the behavior analysis of tufting density and angle in mode Il loading condition, while impact and compression after impact (CAI) tests on the damage tolerance. Open-hole fatigue tests were also performed to evaluate the tufts response, especially regarding their position to the center hole, to the strain concentration factor generated by the hole. The following part of this work consisted of the mechanical tests on omega stiffened panel reinforced by tufting. The procedure optimized the tufting parameters employed for reinforcing the structures from the previous batch of specimens until reaching an optimal point that the main properties, primarily found in pull-off tests, are equal or superior to those of the control specimens. This improvement also considered the modifications in the shape of the stiffeners. Furthermore, a novel approach based on the piezoresistive effect of carbon tufts under loading of the composite specimens is performed. This may support the monitoring of the health status on the tufted threads and therefore of the composite because of the structural nature of the tufts. The results showed that tufting reinforcements are capable of increasing the interlaminar fracture toughness and damage tolerance of the composites considerably owing mainly to their crack bridging phenomena. The tufting parameters are decisive factors for achieving the best mechanical properties. However, this work reported that tuft threads are also responsible for generating cracks due to the strain concentration and defects caused by their insertion and consequently, can decrease the strength of the composites. The investigation concludes that the random insertion of the tufts is not ideal for the performance of the material and thus must be avoided. The development of the tufting insertion in the omega stiffeners was supported by the multi-instrumented characterization that led to optimizing reinforcement in the structure. Although the study achieved the goal of obtaining mechanical properties significantly superior to the omega panels reinforced by tufting, it is noticeable that the procedure employed is not optimal. The present work also proposes a preliminary finite element model to overcome the costly and time consuming of the experimental tests. It intends primarily optimizing the tufting parameters in the structure. The model developed was capable of predicting the same damage events as observed experimentally, but it still distant from the quantitative predictions of the results. The structural health monitoring of the tufted composite laminates by the carbon threads seems promising and could help in the future for supplying data about the tufts health status under loading that are not achieved by the conventional characterization methods employed in this work
49
DOMINGUES, STELLA MARIS PIRES. "ANALYSIS OF BRITTLE ELASTIC MATERIALS THROUGH A CONTINUOUS DAMAGE MODEL." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 1996. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=33202@1.
Full textAbstract:
COORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIORCONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO
Este trabalho lida com uma teoria de dano contínuo, desenvolvida em um contexto termodinâmico, capaz de realizar uma descrição macroscópica da degradação de um material induzida pela deformação em estruturas elásticas frágeis (isto é, falha ocorre sem deformações permanentes). Na modelagem, supõe-se que a energia livre de Helmholtz não depende apenas da deformação e da temperatura absoluta, mas também da variável dano e de seu gradiente. Além disso, para levar em conta os efeitos microscópicos, a potência dos esforços internos não depende apenas da velocidade e de seu gradiente, mas também da taxa de evolução do dano e de seu gradiente. Apesar da sofisticação mecânica da teoria, uma técnica numérica simples, baseada no método dos elementos finitos, é proposta para aproximar a solução dos problemas matemáticos não lineares resultantes. Nestes problemas o acoplamento entre as variáveis dano e deformação é contornado por meio da técnica de partição dos operadores. Para validar o modelo e investigar as características principais do método numérico, diversos exemplos são apresentados para mostrar que os algoritmos utilizados não são sensíveis à malha (mesh dependent).
The present work deals with a continuum damage theory, developed within a thennodynamical framework, able to perform a macroscopic description of material degradation induced by deformation in brittle elastic structures (i.e. failure occurs without permanent deformations). In the modeling, the Helmholtz free energy is supposed to depend not only on the strain and on the absolute temperature but on a damage variable and its gradient as well. Besides, to account for microscopic effects, the power of internal forces depends not only on the velocity and its gradient, but also on the damage velocity and its gradient. Despite the mechanical sophistication of the theory, a simple numerical technique, based on the únite element method, is proposed to approximate the solution of the resulting non linear mathematical problems. The coupling between damage and strain variables in these problems is circumvented by means of a splitting technique. In order to analyse the physical coherence of the model and to access the main features of the numerical method, a number of examples is presented showing that the numerical computations are not mesh dependent.
50
Burrage, Joseph. "Analysis of the function of LSH in DNA damage repair." Thesis, University of Edinburgh, 2013. http://hdl.handle.net/1842/9416.
Full textAbstract:
DNA damage from both normal metabolic activities and environmental factors such as UV and radiation can cause as many as 1 million individual lesions to the DNA per cell per day (Lodish et al 2004). Cells respond to this continuous damage by employing many, highly efficient DNA repair mechanisms and undergo apoptosis when normal DNA repair fails. Of the many types of DNA damage that can occur, double strand breaks (DSBs) are the most toxic (Featherstone & Jackson 1999). A single unrepaired DSB is enough to induce cellular apoptosis and several mechanisms have developed to repair DSBs. The recognition, signalling and repair of DSBs involve large multi-‐subunit complexes that bind to both the DNA and modified histone tails, which require modification of the chromatin in order to access their bind sites and function effectively (Allard et al 2004). Consequently several chromatin-‐remodelling proteins have been implicated in DSB repair (van Attikum et al 2004, Chai et al 2005). LSH (Lymphoid specific helicase) is a putative chromatin-‐remodelling enzyme that interacts with DNA methyltransferases and has been connected to DNA methylation (Myant & Stancheva, 2008). Knockouts of LSH or its homologues in A. thaliana and M. musculus show a reduction in DNA methylation of 60-‐70% (Jeddeloh et al 1999, Dennis et al 2001). However in addition to this phenotype, knockout A. thaliana also have an increased sensitivity to DNA damage (Shaked et al 2006). A homologue of LSH has also been identified in S. cerevisiae, which interacts with known repair proteins (Collins et al 2007) and may be involved in DSB repair. Although the majority of Lsh-‐/-‐ mice die shortly after birth, 40% of the line produced by Sun et al survive and show unexplained premature aging (Sun et al 2004). As premature aging is a hallmark of increased acquisition of DNA damage there is the possibility of a conserved role for LSH in mammalian DNA damage repair. Here I show that LSH depleted mammalian cells have an increased sensitivity specifically to DSB inducing agents and show increased levels of apoptosis. Further analysis shows that cells lacking LSH repair DSBs slower, indicating a novel role for LSH in mammalian repair of DSB. I performed an in depth analysis of the DSB defects in LSH depleted cells in an attempt to elucidate the function of LSH in DSB repair. I found that LSH depleted cells can correctly recognise DSBs but recruit downstream signalling and repair factors, such as γH2AX, less efficiently. I show that reduced recruitment of downstream DSB repair factors is not accompanied by extended cell cycle checkpoint signalling. This suggests that LSH depleted cells continue through the mitosis with unrepaired DSBs, which most likely leads to apoptosis and the increased sensitivity to DSB inducing agents. These experiments also showed that recruitment of DSB signalling and repair factors is not impaired equally at all breaks, and I present a model system created to quantitatively compare individually breaks between WT and LSH depleted cells to identify DSB that require LSH for efficient repair. I also preformed an analysis of Lsh-/- MEFs containing WT or catalytic null mutant LSH rescue constructs and I show that WT but not catalytic null LSH can restore efficient DSB repair. These studies identify a novel role for LSH in mammalian DSB repair and demonstrate the importance of its catalytic activity.