Дисертації: "Multiaxial damage and failure"

1

Amaya, Peter. "Progressive Damage and Failure Model for Composite Laminates under Multiaxial Loading Conditions." The Ohio State University, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=osu1338381439.

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2

Tamoud, Abderrahman. "Mécanique multi-échelle et multiaxiale des composites souples multicouches : application à l'annulus fibrosus humain." Electronic Thesis or Diss., Université de Lille (2018-2021), 2021. http://www.theses.fr/2021LILUN034.

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L’endommagement dans les tissus souples de l'annulus fibrosus est un phénomène multi-échelle complexe dû à un arrangement structural complexe du réseau de collagène à différentes échelles d'organisation hiérarchique. Une représentation constitutive entièrement tridimensionnelle, considérant la variation régionale de la complexité structurale, n'a pas encore été développée, pour estimer la mécanique multiaxiale de l'annulus jusqu'à la rupture. Dans la présente thèse de doctorat, un modèle, formulé dans le cadre de la mécanique non linéaire des milieux continues, est développé pour prédire l’endommagement et la rupture de l'annulus induits par la déformation sous des histoires de chargements multiaxiaux en considérant comme processus physique dépendant du temps à la fois les effets volumétriques induits chimiquement et l'accumulation de l’endommagement.Dans une première partie, un modèle basé sur la microstructure est proposé pour relier les caractéristiques structurales aux propriétés mécaniques intrinsèques et électrochimiques des tissus souples de l'annulus. Le modèle lamellaire/interlamellaire multicouche est construit en considérant les interactions effectives entre les couches adjacentes et la contrainte volumétrique induite chimiquement. La comparaison modèle/expériences démontre que l'évaluation de la réponse globale dépendante du temps implique de considérer simultanément la contrainte, le changement volumétrique et la caractéristique auxétique en relation avec les caractéristiques structurales.Dans une deuxième partie, le modèle est enrichi en considérant la structure hiérarchique des tissus souples depuis les fibrilles de collagène de taille nanométrique jusqu'aux fibres de collagène orientées de taille microscopique. Le processus stochastique d'événements progressifs d’endommagement, opérant à différentes échelles de la phase solide, est introduit pour la matrice extracellulaire, les fibres microscopiques et le réseau de fibrilles nanométriques. Les effets directionnels sur la réponse mécanique et la rupture de l’annulus sont mis en évidence en relation avec le mode de chargement externe, les caractéristiques de la structure, les événements d'endommagement et l'hydratation.Dans une troisième partie, le modèle est développé en considérant la variation régionale de l'organisation structurale complexe du réseau de collagène à différentes échelles pour prédire l’endommagement multiaxial anisotrope régional du disque intervertébral. Après identification du modèle à l'aide de lamelles simples extraites de différentes régions du disque, le caractère prédictif du modèle est vérifié pour divers modes de chargement élémentaires multiaxiaux représentatifs du mouvement de la colonne vertébrale. Les étirements dans les directions circonférentielle et radiale jusqu'à la rupture ont servi à vérifier les capacités prédictives du modèle pour les différentes régions. Les résultats du modèle sous cisaillement simple, étirement biaxial et compression en déformation plane sont également présentés et discutés.Dans une quatrième partie, un modèle de disque humain complet est construit afin d’examiner la mécanique hétérogène dans le cœur du disque. Les champs d'endommagement au sein du disque sont analysés, sous compression axiale, torsion axiale et chargements combinés, afin d’évaluer les zones où le risque de rupture est le plus élevé
The damage in annulus fibrosus soft tissues is a complex multiscale phenomenon due to a complex structural arrangement of collagen network at different scales of hierarchical organization. A fully three-dimensional constitutive representation that considers the regional variation of the structural complexity to estimate annulus multiaxial mechanics till failure has not yet been developed. In the present PhD dissertation, a model, formulated within the framework of nonlinear continuum mechanics, is developed to predict deformation-induced damage and failure of annulus under multiaxial loading histories considering as time-dependent physical process both chemical-induced volumetric effects and damage accumulation.In a first part, a microstructure-based model is proposed to connect structural features, intrinsic mechanics and electro-chemical properties of annulus soft tissues. The multi-layered lamellar/inter-lamellar annulus model is constructed by considering the effective interactions between adjacent layers and the chemical-induced volumetric strain. The model/experiments comparison demonstrates that the evaluation of the overall time-dependent response involves considering stress, volumetric change and auxetic feature simultaneously in relation to structural features.In a second part, the model is enriched by considering the hierarchical structure of the soft tissue from the nano-sized collagen fibrils to the micro-sized oriented collagen fibers. The stochastic process of progressive damage events operating at different scales of the solid phase is introduced for the extracellular matrix and the network of nano-sized fibrils/micro-sized fibers. The directional effects on annulus mechanics and failure are highlighted in relation to external loading mode, structure features, damage events and hydration.In a third part, the model is further developed by considering the regional variation of the complex structural organization of collagen network at different scales to predict the regional anisotropic multiaxial damage of the intervertebral disc. After model identification using single lamellae extracted from different disc regions, the model predictability is verified for various multiaxial elementary loading modes representative of the spine movement. The stretching along the circumferential and radial directions till failure serves to check the predictive capacities of the annulus model for the different regions. Model results under simple shear, biaxial stretching and plane-strain compression are further presented and discussed.In a fourth part, a full human disc model is constructed using the regional annulus model to examine the heterogeneous mechanics in the disc core. Damage fields in the disc are analyzed under axial compression, axial twist and combined loadings to assess the areas where the risk of failure is the highest

3

Triantafillou, Thanasis C. (Thanasis Christos). "Multiaxial failure criteria for celluar materials." Thesis, Massachusetts Institute of Technology, 1989. http://hdl.handle.net/1721.1/14315.

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4

Swalla, Dana Ray. "Fretting fatigue damage prediction using multiaxial fatigue criteria." Thesis, Georgia Institute of Technology, 1999. http://hdl.handle.net/1853/17033.

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5

Chen, Weinong Ravichandran G. "Dynamic failure behavior of ceramics under multiaxial compression /." Diss., Pasadena, Calif. : California Institute of Technology, 1995. http://resolver.caltech.edu/CaltechETD:etd-11032003-101839.

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6

Juneja, Lokesh Kumar. "Multiaxial fatigue damage model for random amplitude loading histories." Thesis, Virginia Tech, 1992. http://hdl.handle.net/10919/41522.

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In spite of many multiaxial fatigue life prediction methods proposed over decades of research, no universally accepted approach yet exists. A multiaxial fatigue damage model developed for approximately proportional random amplitude loading is proposed in this study. A normal strain based analysis incorporating the multiaxial state of stress is conducted along a critical orientation assuming a constant strain ratio. The dominant deformation direction is chosen to be the critical orientation which is selected with the help of a principal strain histogram generated from the given multiaxial loading history. The uniaxial cyclic stress-strain curve is modified for the biaxial state of stress present along the critical orientation for the plane stress conditions. Modified versions of Morrow's and of Smith, Watson, and Topper's (SWT) mean-stress models are used to incorporate mean stresses. A maximum shear strain based analysis is, in addition, conducted to check for the shear dominant fatigue crack growth possibility along the critical direction. The most damaging maximum shear strain is chosen after analyzing the in-plane and the two out-of-plane shear strains.

The minimum of the two life values obtained from SWT model and the shear strain model is compared with the life estimated by the proposed model with the modified Morrow's mean stress model. The former is essentially the life predicted by Socie. The results of the proposed model, as reduced to the uniaxial case, are also compared with the experimental data obtained by conducting one-channel random amplitude loading history experiments.
Master of Science

7

Suman, Sandip Kumar. "Nonlinear Fatigue Damage Accumulation in Aircraft Engine Alloys Multiaxial Loading." Diss., North Dakota State University, 2013. https://hdl.handle.net/10365/26885.

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Fatigue is considered to be one of the most frequent phenomena in the failure of many machine parts. Most of the prior studies on fatigue have been limited to uniaxial loading cases with a primary focus on constant amplitude cycles. A detailed exploration of multiaxial fatigue under constant and variable amplitude loading scenarios for a wide variety of aircraft engine alloys has been performed in this study, and a new methodology for the accurate prediction of fatigue damage is developed. A critical-plane based constant amplitude fatigue damage model has been developed in this study which is simple in comparison to prior models developed by other researchers and reduces the computational effort. The constant amplitude fatigue damage model is further used in the development of a multiaxial variable amplitude damage estimation method, with an emphasis on estimating the damage created by both low cycle fatigue (LCF) and high cycle fatigue (HCF) cycles. A significant increase in overall fatigue damage was observed in the tests with the introduction of HCF cycles in the mission histories. The damage due to the HCF cycles has been found to be much greater than predicted by linear damage accumulation theories, although the degree of interaction between the LCF and HCF cycles was found to be very dependent on the multiaxial load paths. In addition, the HCF cycles did not contribute significantly to the accumulation of damage until a certain amount of ?pre-damage? had been caused by the LCF cycles. Separate HCF damage computing approaches have been adopted in this study to accurately compute the damage produced by tensile and shear dominant HCF cycles, and a significant improvement in the accuracy of fatigue life prediction has been achieved using the new methodology.
General Electric (Aviation)
Airforce Office of Scientific Research

8

Schmitt, James Tyler. "Damage initiation and post-damage response of composite laminates by multiaxial testing and nonlinear optimization." Thesis, Montana State University, 2008. http://etd.lib.montana.edu/etd/2008/schmitt/SchmittJ1208.pdf.

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Fiber reinforced plastics are increasingly being used in the construction of primary structures in the aerospace and energy industries. While their elastic behavior and fatigue response have been the subject of considerable research, less is known about the performance of continuous fiber composites following initial damage. Several competing models for the post-damage response of orthotropic composite materials are explored in this thesis. Each of these models includes only the in-plane loads experienced by the material and characterizes damage based on the local state of strain. Starting with previous work performed at the Naval Research Laboratory and at MSU, the energy dissipated in multiaxially loaded coupons was used to optimize an empirical function that relates the three in-plane strains to the local dissipated energy density. This function was used to approximate a three dimensional damage initiation envelope as well as to quantify the severity of damage following first ply failure in a fiberglass laminate. Carbon fiber reinforced epoxy was characterized using an assumed bilinear constitutive response. The elastic properties of the material were first optimized to minimize deviation from experimental data and then the necessary coefficients for a per-axis strain softening response were found using a similar optimization. This model provides detailed insight into the residual strength of significantly damaged material, as well as dissipated energy as a direct consequence. To facilitate the need of these models for diverse local in-plane loading configurations, the MSU In-Plane Loader (IPL) was utilized. The tests performed in the IPL for this thesis were instrumental in validating a new image-correlation-based displacement monitoring system.

9

Ho, Kwang-Il. "An anisotropic continuum damage model for creep-dominated, multiaxial loading histories." Diss., Georgia Institute of Technology, 1987. http://hdl.handle.net/1853/20043.

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10

Searle, Andrew Arthur. "The creep and failure of engineering ceramics under multiaxial states of stress." Thesis, University of Leicester, 1993. http://hdl.handle.net/2381/34827.

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The effort dedicated to developing the material properties of engineering ceramics has not been accompanied by a similar effort in developing design methods that would allow engineers to make full use of these materials. In particular the high temperature creep behaviour of engineering ceramics has received little attention. In this thesis two parallel approaches, one theoretical and one practical, have been taken towards the final aim of constructing design codes for the creep of ceramic materials. In the theoretical work the principles developed for modelling creep and failure in metals were employed and adapted where necessary to provide new models that describe the behaviour of ceramics under multiaxial stresses. Important changes were made to account for differences in microstructure between these two classes of materials. In the practical work equipment was developed to provide suitable multiaxial creep test data with which to verify and further construct models. This involved the construction of a tension/torsion creep testing machine featuring a radio-frequency heating furnace, cooled grip heads, extensometry equipment, biaxial loading system and a temperature measurement and control system. The machine was capable of operating for at least 300 hours at a temperature of at least 1400 °C. Nine creep tests were conducted on reaction bonded silicon nitride specimens including two unique tests under pure torsion and combined tension/torsion. Four tests were conducted on aluminium oxide specimens including a unique test under combined tension/torsion. Tensile test results showed good agreement with previously published data for both materials confirming the equipment accuracy. Results from the multiaxial tests indicated that reaction bonded silicon nitride fails in response to the value of the effective stress. In addition reasonable agreement was obtained between the test data and predictions from the new models.

11

Zand, Behrad. "Modeling of composite laminates subjected to multiaxial loadings." Columbus, Ohio : Ohio State University, 2007. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1189468229.

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Ninic, Dejan Mechanical &amp Manufacturing Engineering Faculty of Engineering UNSW. "Fatigue in automatic transmissions." Awarded by:University of New South Wales. School of Mechanical and Manufacturing Engineering, 2006. http://handle.unsw.edu.au/1959.4/28056.

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A novel method of predicting the multiaxial high-cycle fatigue strength of metallic components is proposed and verified for various steel, aluminium and cast iron alloys. The proposed Fatigue Damage Function shows superior multiaxial fatigue strength prediction compared to the established methods of Gough and Pollard, McDiarmid and Carpinteri and Spagnoli. A new material property, the Normal Stress Sensitivity Factor, is also introduced and its applicability is verified according to published test results of sixteen different structural alloys. To highlight the effectiveness of the proposed criterion, for industrial applications, a case study has been conducted on heat-treated and not heat-treated automatic transmission output shafts.

13

Šebek, František. "Ductile Fracture Criteria in Multiaxial Loading – Theory, Experiments and Application." Doctoral thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2016. http://www.nusl.cz/ntk/nusl-256582.

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Práce se zabývá tvárným lomem, který je výsledkem víceosého kvazi-statického monotónního namáhání doprovázeného rozsáhlými plastickými deformacemi, přičemž pro degradaci materiálu je uvažován lokální přístup. Ve výpočtech o rozvoji poškození rozhodují použité mezní podmínky tvárného lomu. Tyto byly teoreticky studovány v úvodu práce a po výběru vhodné mezní podmínky byl stanoven postup kalibrace. Dále byl rozpracován plán měření a realizovány zkoušky při pokojové teplotě na slitině hliníku 2024-T351, zahrnující tah, krut a tlak, pro studium rozvoje poškození a věrohodnou kalibraci vybraného fenomenologického modelu tvárného porušování, vyjádřeného pomocí lomového přetvoření a závislého na hydrostatickém tlaku a deviátoru tenzoru napětí. Mezní podmínka tvárného lomu byla posléze svázána s podmínkou plasticity. Plasticita byla pro zkoumaný materiál uvažována ve tvaru zohledňujícím i stav třetího invariantu deviátoru tenzoru napětí. Celý navržený přístup, plně aplikovatelný na víceosé úlohy, byl implementován pomocí uživatelské rutiny do komerčního programu založeného na explicitní variantě metody konečných prvků. V závěru práce je předložena aplikace navrženého přístupu k modelování tvárného porušování v podobě verifikace na vybraných zkušebních testech, z níž plynou závěry a doporučení pro další práci.

14

Shipsha, Andrey. "Failure of Sandwich Structures with Sub-Interface Damage." Doctoral thesis, Stockholm, 2001. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3184.

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15

DiPeri, Timothy P. "Neuromodulation Therapy Mitigates Heart Failure Induced Hippocampal Damage." Digital Commons @ East Tennessee State University, 2014. https://dc.etsu.edu/honors/208.

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Cardiovascular disease (CVD) is the leading cause of death in the United States. Nearly half of the people diagnosed with heart failure (HF) die within 5 years of diagnosis. Brain abnormalities secondary to CVD have been observed in many discrete regions, including the hippocampus. Nearly 25% of patients with CVD also have major depressive disorder (MDD), and hippocampal dysfunction is a characteristic of both diseases. In this study, the hippocampus and an area of the hippocampal formation, the dentate gyrus (DG), were studied in a canine model of HF. Using this canine HF model previously, we have determined that myocardial infarction with mitral valve regurgitation (MI/MR) + spinal cord stimulation (SCS) can preserve cardiac function. The goal of this study was to determine if the SCS can also protect the brain in a similar fashion. Both the entire hippocampus and the DG tissues were dissected from canine brains and analyzed. These findings provide strong evidence that, in addition to the cardioprotective effects observed previously, SCS following MI/MR induces neuroprotective effects in the brain.

16

Wilkinson, Ann Elizabeth. "Skeletal muscle damage in patients with multiple organ failure." Thesis, University of Liverpool, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.283453.

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17

Chambers, Jeffrey Thomas. "Lengthscale effects in the damage and failure of composites." Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/90598.

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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Aeronautics and Astronautics, 2014.
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 625-636).
The primary objective of this work is to investigate and identify lengthscale effects associated with damage in composite materials and their structures, and to determine how these lengthscales vary across levels of composites and can be used in assessing the overall response of composite structures. This is an advancement in a much larger pursuit towards developing a new methodology that utilizes composite failure and material data collected across all levels in order to predict the occurrence of damage and its effects at any operative level of composite structures. Documentation procedures are developed to capture qualitative and quantitative information on damage within experimental specimens, and computed microtomography provides additional information on the damage process. Specimens containing structural details are investigated postmortem to identify lengthscales associated with damage modes. Finite element models are developed in order to investigate the interaction of lengthscales associated with structural details with those associated with the basic damage modes. Based on these experimental and numerical results, lengthscales associated with five basic damage modes, as identified from previous studies, and the four structural details included in this investigation are identified and discussed, as are their interactions and importance. It is found that it is important to recognize two damage regimes, initiation and propagation, in characterizing lengthscales associated with damage modes. Identifying key lengthscales within each regime allows investigation of how the critical lengthscale(s) controlling the damage mode(s) change(s) across regimes. The concept of the "observable lengthscale" is identified as an important consideration when investigating lengthscales in experimental specimens and structures in that the observable lengthscale sets the ability to resolve damage and interactions of such. In a manner analogous to the "observable lengthscale," key lengthscales of basic damage modes and of structural details need to be used when choosing the scale of finite element models so that models have a resolution at least as fine as the key lengthscale of the mode under investigation. The results of the work show that the concept of lengthscales is a viable tool to characterize the overall response of composite structures, particularly involving damage initiation, damage propagation, and overall failure. The determination of how these lengthscales vary across levels in composites provides an important tool that can be used to assess this overall response of composite structures. Particular conclusions considering each damage mode are offered. In addition, a new damage type, called "transverse zigzag," is identified and studied, resulting in a finding that loads can "bypass" and "carry-through" regions of damage, depending on the geometry and laminate. Recommendations for further investigations are proposed based on the understanding of the role of lengthscales in the damage and failure of composites acquired from this work, and the needs identified to further this understanding.
by Jeffrey Thomas Chambers.
Ph. D.

18

Alves, Marcilio. "Damage mechanics applied to structural impact." Thesis, University of Liverpool, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.484220.

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Giordani, Felipe André. "Estudo de metodologias para medir a vida em fadiga multiaxial não proporcional." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2015. http://hdl.handle.net/10183/118864.

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É conhecida ao longo da história da humanidade a grande quantidade de acidentes vinculados à ação de cargas cíclicas. Há mais de 100 anos, metodologias levam em conta o fenômeno de fadiga em projetos de novos componentes. As metodologias existentes para avaliar a vida em fadiga são empíricas e têm sido aplicadas com sucesso na determinação da vida do componente em fadiga quando o mesmo é submetido a carregamento uniaxial ou a carregamento multiaxial proporcional. Mas a evidencia experimental tem mostrado que quando a solicitação é multiaxial e não proporcional, as leis antes mencionadas deixam de ser adequadas. Dessa forma os critérios clássicos utilizados não preveem corretamente a vida do componente. Neste contexto o presente trabalho avalia algumas das metodologias de fadiga multiaxial não proporcionais disponíveis na bibliografia especializada. Os resultados obtidos com estes métodos são comparados entre sim e com os resultados obtidos utilizando a metodologia de fadiga multiaxial proporcional. Para comparar as metodologias citadas é apresentado um exemplo de solicitação simples, e também a análise do componente de uma máquina agrícola solicitada por um histórico de tensões típicas, obtida a partir do teste da máquina em campo. Finalmente são apresentadas as conclusões sobre as metodologias utilizadas e sobre a importância de levar em conta a não proporcionalidade de um estado de tensões multiaxial oscilantes.
It is known throughout human history the large amount of accidents linked to action of cyclic loading. For over 100 years, methodologies take into account the fatigue phenomenon of new components projects. Existing methodologies for assessing the fatigue life are empirical and have been successfully applied in the determination of fatigue life of the component when it is subjected to uniaxial loading or proportional multiaxial loading. But the experimental evidence has shown that when the request is multiaxial and not proportional, the laws mentioned above are no longer adequate. Thus the classical criteria used not correctly predict component life. In this context, this paper analyzes some of the methodologies of multiaxial fatigue non proportionate available in the relevant literature. The results obtained with these methods are compared with the results so obtained and using the proportional multiaxial fatigue methodology. To compare the methods mentioned is an example of simple request, and also the analysis component of an agricultural machine requested by a history of typical strains, obtained from the machine field testing on a test track. Finally conclusions on the methodologies used and the importance of taking into account the non-proportionality of a state of oscillating multiaxial stresses are presented.

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魏勇 and Yong Wei. "On fatigue failure prediction with damage mechanics: theory and application." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1993. http://hub.hku.hk/bib/B31233260.

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Chen, Boyang. "Numerical modelling of scale-dependent damage and failure of composites." Thesis, Imperial College London, 2013. http://hdl.handle.net/10044/1/24169.

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A computational study of the size effects of open-hole tension composite laminates is carried out. The thickness-dependence of translaminar fracture toughness is accounted for in the numerical model, which enables the sublaminate-scaling effect of strength to be accurately predicted by a deterministic model. Neglecting delamination in modelling is found to cause mesh-dependence and over-estimation in strength predictions. A smeared crack model with cohesive elements between plies can reliably predict the failure mode, but not the strength, for laminates failed by delamination. A floating node method is developed for explicitly modelling multiple discontinuities within an element. The degree-of-freedom vectors do not have associated initial coordinates; they are assigned to new material points when needed during analysis. The proposed method is well suited for modelling strong, weak and cohesive discontinuities, for the representation of complex crack networks, and for the accurate modelling of matrix crack/delamination interactions in composites.

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Halbert, Keith. "Estimation of probability of failure for damage-tolerant aerospace structures." Thesis, Temple University, 2014. http://pqdtopen.proquest.com/#viewpdf?dispub=3623167.

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The majority of aircraft structures are designed to be damage-tolerant such that safe operation can continue in the presence of minor damage. It is necessary to schedule inspections so that minor damage can be found and repaired. It is generally not possible to perform structural inspections prior to every flight. The scheduling is traditionally accomplished through a deterministic set of methods referred to as Damage Tolerance Analysis (DTA). DTA has proven to produce safe aircraft but does not provide estimates of the probability of failure of future flights or the probability of repair of future inspections. Without these estimates maintenance costs cannot be accurately predicted. Also, estimation of failure probabilities is now a regulatory requirement for some aircraft.

The set of methods concerned with the probabilistic formulation of this problem are collectively referred to as Probabilistic Damage Tolerance Analysis (PDTA). The goal of PDTA is to control the failure probability while holding maintenance costs to a reasonable level. This work focuses specifically on PDTA for fatigue cracking of metallic aircraft structures. The growth of a crack (or cracks) must be modeled using all available data and engineering knowledge. The length of a crack can be assessed only indirectly through evidence such as non-destructive inspection results, failures or lack of failures, and the observed severity of usage of the structure.

The current set of industry PDTA tools are lacking in several ways: they may in some cases yield poor estimates of failure probabilities, they cannot realistically represent the variety of possible failure and maintenance scenarios, and they do not allow for model updates which incorporate observed evidence. A PDTA modeling methodology must be flexible enough to estimate accurately the failure and repair probabilities under a variety of maintenance scenarios, and be capable of incorporating observed evidence as it becomes available.

This dissertation describes and develops new PDTA methodologies that directly address the deficiencies of the currently used tools. The new methods are implemented as a free, publicly licensed and open source R software package that can be downloaded from the Comprehensive R Archive Network. The tools consist of two main components. First, an explicit (and expensive) Monte Carlo approach is presented which simulates the life of an aircraft structural component flight-by-flight. This straightforward MC routine can be used to provide defensible estimates of the failure probabilities for future flights and repair probabilities for future inspections under a variety of failure and maintenance scenarios. This routine is intended to provide baseline estimates against which to compare the results of other, more efficient approaches.

Second, an original approach is described which models the fatigue process and future scheduled inspections as a hidden Markov model. This model is solved using a particle-based approximation and the sequential importance sampling algorithm, which provides an efficient solution to the PDTA problem. Sequential importance sampling is an extension of importance sampling to a Markov process, allowing for efficient Bayesian updating of model parameters. This model updating capability, the benefit of which is demonstrated, is lacking in other PDTA approaches. The results of this approach are shown to agree with the results of the explicit Monte Carlo routine for a number of PDTA problems.

Extensions to the typical PDTA problem, which cannot be solved using currently available tools, are presented and solved in this work. These extensions include incorporating observed evidence (such as non-destructive inspection results), more realistic treatment of possible future repairs, and the modeling of failure involving more than one crack (the so-called continuing damage problem).

The described hidden Markov model / sequential importance sampling approach to PDTA has the potential to improve aerospace structural safety and reduce maintenance costs by providing a more accurate assessment of the risk of failure and the likelihood of repairs throughout the life of an aircraft.

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Wei, Yong. "On fatigue failure prediction with damage mechanics : theory and application /." [Hong Kong : University of Hong Kong], 1993. http://sunzi.lib.hku.hk/hkuto/record.jsp?B13420410.

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24

Dannemann, Kathryn Ann. "Damage development and failure of fiber-reinforced ceramic matrix composites." Thesis, Massachusetts Institute of Technology, 1989. http://hdl.handle.net/1721.1/14197.

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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1989.
Vita.
Includes bibliographical references (leaves 111-120).
by Kathryn Ann Dannemann.
Ph.D.

25

Chen, Fuh-Sheng. "Damage and failure analysis of continuous fiber-reinforced polymer composites." Case Western Reserve University School of Graduate Studies / OhioLINK, 1992. http://rave.ohiolink.edu/etdc/view?acc_num=case1056554068.

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26

Sedman, Andrew James. "Mechanical failure of bone and antler : the accumulation of damage." Thesis, University of York, 1993. http://etheses.whiterose.ac.uk/14047/.

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27

Berthier, Estelle. "Quasi-brittle failure of heterogeneous materials : damage statistics and localization." Thesis, Paris 6, 2015. http://www.theses.fr/2015PA066588/document.

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Nous proposons une nouvelle approche inspirée des modèles d'endommagement non-locaux pour décrire la ruine des matériaux quasi-fragiles désordonnés. Les hétérogénéités matériaux sont introduites à une échelle continue mésoscopique via des variations spatiales de la résistance à l'endommagement alors que le mécanisme de redistribution des contraintes est décrit à travers une fonction d'interaction que l'on peut faire varier. L'évolution spatio-temporelle de l'endommagement est déterminée à partir du principe de conservation d'énergie et caractérisée via une étude statistique des précurseurs à la rupture. Cette approche nous permet de prédire la valeur des seuils de localisation et de rupture en fonction de la nature des redistributions. A l'approche de la rupture, nous mettons également en évidence une augmentation en loi de puissance du taux d'énergie dissipée ainsi qu'une longueur de corrélation, supportant l'interprétation de la rupture quasi-fragile comme un phénomène critique. En effet, nous démontrons que notre model d'endommagement s'apparente à la loi d'évolution d'une interface élastique évoluant dans un milieu désordonné. Cette analogie nous permet d'identifier les paramètres d'ordre et de contrôle de cette transition critique et d'expliquer les invariances d'échelle des fluctuations dans la limite champ moyen. Enfin, nous appliquons ces concepts théoriques à travers l'étude expérimentale de la compression d'un empilement bidimensionnel de cylindres élastiques. Notre approche permet de décrire de façon quantitative la réponse mécanique non-linéaire du matériau, et en particulier la statistique des précurseurs ainsi que la localisation des déformations
We propose a novel approach inspired from non-local damage continuum mechanics to describe damage evolution and quasi-brittle failure of disordered solids. Heterogeneities are introduced at a mesoscopic continuous scale through spatial variations of the material resistance to damage. The central role played by the load redistribution during damage growth is analyzed by varying the interaction function used in the non-local model formulation. The spatio-temporal evolution of the damage field is obtained from energy conservation arguments, so that the formulation is thermodynamically consistent. We analytically determine the onsets of localization and failure that appear controlled by the redistribution function. Damage spreading is characterized through a complete statistical analysis of the spatio-temporal organization of the precursors to failure. The power law increase of the rate of energy dissipated by damage and an extracted correlation length close to failure supports the interpretation of quasi-brittle failure as a critical phenomena. Indeed, we establish a connection between our damage model and the evolution law of an elastic interface driven in a disordered medium. It allows to identify the order and control parameters of the critical transition, and capture the scale-free statistical properties of the precursors within the mean field limit. Finally, we experimentally investigate the coaction of localized dissipative events and elastic redistributions in disordered media via compression experiments of two-dimensional arrays of hollow soft cylinders. Our experimental observations show a quantitative agreement with the predictions derived following our approach

28

Cao, Caihua. "Damage and Failure Analysis of Co-Cured Fiber-Reinforced Composite Joints." Diss., Georgia Institute of Technology, 2003. http://hdl.handle.net/1853/5298.

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Joints represent a design challenge, especially for composite structures. Among the available joining methods, co-curing is an efficient way to integrate parts for some applications. Coates and Armanios have proposed a Single Nested Overlap (SNO) co-cured joint configuration, obtained from a single lap joint through the overlap/interleafing of the adjoining top/bottom adherend plies, respectively. Through a comparative investigation, they have demonstrated joint strength and fatigue life improvements over the single lap joint counterparts for unidirectional and quasi-isotropic adherend lay-ups. This research extends the comparative investigation of Coates and Armanios by focusing upon characterizing and differentiating the damage initiation and progression mechanisms under quasi-static loading. Six specimen configurations are manufactured and tested. It is confirmed that single nested overlap joints show 29.2% and 27.4% average improvement in strength over single lap counterparts for zero-degree unidirectional and quasi-isotropic lay-ups, respectively. Several nondestructive evaluation techniques are used to observe and analyze damage initiation, damage progression and failure modes of the studied specimens and to monitor their mechanical response. Using X-ray Radiography and Optical Microscopy techniques during quasi-static loading, a physical characterization of damage and failure mechanisms is obtained. The acoustic emission data acquired during monotonic loading could reveal the overall picture of AE activities produced by the damage initiation, development and accumulation mechanisms within the specimen via parametric analysis. Further AE analysis by a selected supervised clustering method is carried out and shown successful in differentiating and clustering the AE data. Correlation with physical observations from other techniques suggests that the resulting clusters may be associated to specific damage modes and failure mechanisms.

29

Whitehouse, Anne Frances. "Damage and failure of discontinuously reinforced aluminium composites during tensile deformation." Thesis, University of Cambridge, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.319543.

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30

Manger, Christopher I. C. "Failure of notched woven GFRP composites : damage analysis and strength modelling." Thesis, University of Surrey, 1999. http://epubs.surrey.ac.uk/738/.

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31

Greve, Lars. "Damage and failure modelling of carbon/epoxy non-crimp fabtic composites." Thesis, Cranfield University, 2005. http://dspace.lib.cranfield.ac.uk/handle/1826/10710.

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32

Ribeiro, Marcelo Leite. "Damage and progressive failure analysis for aeronautic composite structures with curvature." Universidade de São Paulo, 2013. http://www.teses.usp.br/teses/disponiveis/18/18148/tde-18112013-140301/.

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Recent improvements in manufacturing processes and materials properties associated with excellent mechanical characteristics and low weight have became composite materials very attractive for application on civil aircraft structures. However, even new designs are still very conservative, because the composite structure failure phenomena are very complex. Several failure criteria and theories have been developed to describe the damage process and how it evolves, but the solution of the problem is still open. Moreover, modern manufacturing processes, e.g. filament winding, have been used to produce a wide variety of structural shapes. Therefore, this work presents the development of a damage model and its application to simulate the progressive failure of flat composite laminates as well as for composite cylinders made by filament winding process. The proposed damage model has been implemented as a UMAT (User Material Subroutine) and VUMAT (User Material Subroutine for explicit simulations), which were linked to ABAQUSTM Finite Element (FE) commercial package. Progressive failure analyses have been carried out using FE Method in order to simulate the failure of filament wound composite structures under different quasi-static and impact loading conditions. In addition, experiments have been performed not only to identify parameters related to the material model but also to evaluate both the potentialities and the limitations of the proposed model.
As recentes melhorias nos processos de fabricação e nas propriedades dos materiais associadas a excelentes características mecânicas e baixo peso tornam os materiais compósitos muito atrativos para aplicação em estruturas aeronáuticas. No entanto, mesmo novos projetos, ainda são muito conservadores, pois os fenômenos de falha dos compósitos são muito complexos. Vários critérios e teorias de falha têm sido desenvolvidos para descrever o processo de dano e sua evolução, mas a solução do problema ainda está em aberto. Além disso, técnicas modernas de fabricação, como o enrolamento filamentar (filament winding) vêm sendo utilizadas para produzir uma ampla variedade de formas estruturais. Assim, este trabalho apresenta o desenvolvimento de um modelo de dano e a sua aplicação para simular a falha progressiva de estruturas planas e cilíndricas fabricadas em material compósito através do processo de filament winding. O modelo de dano proposto foi implementado como sub-rotinas em linguagem FORTRAN (UMAT-User Material Subroutine e, VUMAT-User Material Subroutine para simulações explícitas), que foram compiladas junto ao programa comercial de Elementos Finitos ABAQUSTM. Várias análises numéricas foram realizadas via elementos finitos, a fim de prever a falha dessas estruturas de material compósito sob diferentes condições de carregamentos quase-estáticos e de impacto. Além disso, vários ensaios experimentais foram realizados, a fim de identificar os parâmetros relacionados com o modelo de material, bem como avaliar as potencialidades e as limitações do modelo proposto.

33

Wang, Xiaofeng. "Computational technology for damage and failure analysis of quasi-brittle materials." Thesis, University of Manchester, 2015. https://www.research.manchester.ac.uk/portal/en/theses/computational-technology-for-damage-and-failure-analysis-of-quasibrittle-materials(a7c91eb6-5058-4e73-95de-b2f3efd645d2).html.

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The thesis presents the development and validation of novel computational technology for modelling and analysis of damage and failure in quasi-brittle materials. The technology is demonstrated mostly on concrete, which is the most widely used quasi-brittle material exhibiting non-linear behaviour. Original algorithms and procedures for generating two-dimensional (2D) and three-dimensional (3D) heterogeneous material samples are developed, in which the mesoscale features of concrete, such as shape, size, volume fraction and spatial distribution of inclusions and pores/voids are randomised. Firstly, zero-thickness cohesive interface elements with softening traction-separation relations are pre-inserted within solid element meshes to simulate complex crack initiation and propagation. Monte Carlo simulations (MCS) of 2D and 3D uniaxial tension tests are carried out to investigate the effects of key mesoscale features on the fracture patterns and load-carrying capacities. Size effect in 2D concrete is then investigated by finite element analyses of meso-structural models of specimens with increasing sizes. Secondly, a 3D meso-structural damage-plasticity model for damage and failure analysis of concrete is developed and applied in tension and compression. A new scheme for identifying interfacial transition zones (ITZs) in concrete is presented, whereby ITZs are modelled by very thin layers of solid finite elements with damage-plasticity constitutive relations. Finally, a new coupled method named non-matching scaled boundary finite element-finite element coupled method is proposed to simulate crack propagation problems based on the linear elastic fracture mechanics. It combines the advantage of the scaled boundary finite element method in modelling crack propagation and also preserves the flexibility of the finite element method in re-meshing. The efficiency and effectiveness of the developed computational technology is demonstrated by simulations of crack initiation and propagation problems.

34

Mascarenhas, Wesley Novaes. "A Damage model for the ductile failure analysis of plastic components." Florianópolis, SC, 2011. http://repositorio.ufsc.br/xmlui/handle/123456789/95895.

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Tese (doutorado) - Universidade Federal de Santa Catarina, Centro Tecnológico, Programa de Pós-Graduação em Engenharia Mecânica, Florianópolis, 2011
Made available in DSpace on 2012-10-26T06:55:21Z (GMT). No. of bitstreams: 1 292560.pdf: 8869260 bytes, checksum: 119e3987b4e602d2a0ca1e47c42b6231 (MD5)
O objetivo deste trabalho é propor um modelo matemático e um sistema computacional, baseado no método dos elementos finitos, capaz de auxiliar a atividade de análise estrutural de componentes de plástico submetidos à falha dúctil. Basicamente, este sistema computacional será composto por um modelo elasto-viscoplástico acoplado ao dano, a fim de ser possível descrever a evolução das deformações inelásticas e os processos degradativos que conduzirão à falha e, assim, auxiliar no dimensionamento de componentes. O referido modelo foi desenvolvido sob as teorias propostas por Lemaitre [1], Fremond e Nedjar [2] e sob as abordagens da termodinâmica dos meios contínuos e do método do estado local, onde foram introduzidos os conceitos de potenciais termodinâmicos e de variáveis de estado. Ao se utilizar estas abordagens, assegura-se que os modelos produzirão resultados termodinamicamente consistentes. A fim de certificar o modelo proposto e validar o sistema numérico, realizou-se um ensaio uniaxial, em que o corpo de provas foi deformado até a sua fratura. Os dados obtidos do referido ensaio e de outros ensaios complementares foram utilizados na identificação das propriedades e constantes materiais, que definem o modelo proposto. Os procedimentos experimentais foram realizados no Departamento de Fibras e Tecnologia de Polímeros do Instituto Real de Tecnologia (KTH), em Estocolmo, Suécia.
The objective of this work is to propose a mathematical model and a numerical scheme, based on the finite element method, to be used to analyze mechanical components manufactured with plastic material, subjected to monotonic loading conditions that undergo a ductile failure. Basically, this numerical scheme will be composed by an elasto-viscoplastic model coupled with a non-local damage theory, in order to describe the evolution of the inelastic strains and the damaging processes of the material, which will consequently lead to the failure of the component. The cited model has been developed by means of the theories proposed by Lemaitre [1], Fremond and Nedjar [2], among others, and makes use of the method of local state variables and is derived within the scope of the consistent thermodynamics of the continuum medium. The main advantage of using these approaches is the confidence they give that the models can not produce thermodynamically unreasonable results. In order to attest the proposed model and to validate the numerical scheme, one considers an experimental uniaxial test, in which the specimen is deformed up to its ductile fracture. The data obtained from the given experimental uniaxial test and from other complementary experimental tests is then employed for the identification of the material properties and parameters, which define the proposed damage model. The experimental procedures have been performed at the Fibre and Polymer Technology Department of the Royal Institute of Technology (KTH), in Stockholm, Sweden.

35

Greve, Lars. "Damage and failure modelling of carbon/epoxy Non Crimp Fabric composites." Thesis, Cranfield University, 2005. http://dspace.lib.cranfield.ac.uk/handle/1826/10710.

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Advanced material models for the intra- and inter-laminar damage and failure prediction of biaxial carbon/epoxy Non Crimp Fabric (NCF) composites are presented, which enable application to large scale practical composite structures for the automotive industry. The model established for intra-laminar failure combines the elasto-plastic continuum damage constitutive model first proposed by Ladevèze, with the matrix failure model of Puck, and improves the shear damage representation by using an exponential damage evolution law. An extensive test program has been conducted using biaxial NCF composites with differing degrees of fabric pre-shear. The presheared biaxial NCF are considered to take into account potential changes of the damage and failure properties occurring due to the draping process in real structures. The database established is used to identify parameters for the proposed Ladevèze-Puck matrix damage and failure model, allowing prediction of the main matrix failure modes of unsheared and presheared biaxial NCF composites. Furthermore, the failure prediction within zones of stress concentrations is addressed utilising flat NCF laminates with different holes and lay-ups. For numerical elastic failure prediction of these tests a simple fibre criterion is presented which is related to a characteristic element size. The Puck failure model is adopted to represent the inter-laminar (delamination) crack initiation strength of the investigated NCF. This stress based model for delamination crack initiation operates in conjunction with existing methods for the simulation of delamination crack propagation, which are related to the critical strain energy release rate. All material models that have been combined and further developed during the course of this work have been implemented in a research version of a commercial crashworthiness Finite Element code. The intra-laminar failure model is validated against a test series of transversely loaded circular- composite discs having differing degrees of fabric pre-shear. The final validation example for intra-laminar failure has considered a complex composite door structure subjected to lateral punch intrusion. The enhanced delamination failure model is validated using a composite beam structure, exhibiting delamination failure under local transverse tension loading. For all validation tests a good agreement between simulations and experiments has been demonstrated. It is believed by the author that the new contributions presented in this thesis significantly raise the level of numerical prediction of deformation, damage, and failure for Continuous Carbon Fibre Reinforced Composites. Special emphasis is placed on the fact that all material model parameters have been obtained from simple specimen tests, and have been used without adjustment for the simulation of subsequent Validation tests utilising Composite structures of high complexity. This continuous approach is in contrast to the majority of similar investigations found in the literature, in which the adjustment of material model parameters appeared to be necessary in order to achieve a good agreement between simulations and experiments of complex structures.

36

Fouinneteau, M. R. C. "Damage and failure modelling of carbon and glass 2D braided composites." Thesis, Cranfield University, 2006. http://dspace.lib.cranfield.ac.uk/handle/1826/1555.

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Composite materials have been increasingly used in the past two decades since they offer significant potential weight reduction, part design flexibility and improved specific mechanical performance compared to traditional metals. For specific applications, braid reinforced composites offer better near net shape part and manufacturing flexibility than conventional unidirectional laminates, albeit at the expense of slightly lower in-plane stiffness and strength. Furthermore, for impact and crash applications, which is the emphasis of this thesis, their tow waviness and interlocking can offer excellent damage tolerance and energy absorption. In this work, heavy tow (24k) biaxial carbon and glass braided preforms were used to manufacture coupons and beam structures to undertake an extensive testing campaign to characterise different damage and failure mechanisms occurring in braided composites. Due to large shear deformation and surface degradation, non conventional measurement techniques based on marker tracking and Digital Image Correlation were successfully used to measure strains in the damaging material. The modelling of braided composites was conducted using the meso-scale damage approach first proposed by P. Ladevèze for unidirectional composites. The calibration of an equivalent braid unidirectional ply was achieved using the experimental results obtained for different braided coupons. Furthermore, failure mechanisms observed experimentally, such as tow stretching and fibre re-orientation occurring during loading history, were integrated into the model. A new unidirectional ply formulation was subsequently implemented into the explicit finite element code PAM-CRASHTM. Validation of the new model using single element, coupons and beams were conducted that provided a satisfying correlation between experimental tests and numerical predictions.

37

Chung, Timothy Kwang-Joon. "Study of multi-axial failure properties of planar biological soft tissues." Diss., University of Iowa, 2017. https://ir.uiowa.edu/etd/5732.

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Rupture of abdominal aortic aneurysm (AAA) is a catastrophic event that leads to high mortality and morbidity in patients. The primary causes associated with aneurysm rupture remain poorly understood despite rigorous investigations. Reports have shown that AAA that went on to rupture or present ruptured had higher peak wall tension (stress resultant) than those that did not go on to rupture or present ruptured. Studies investigating the material strength of ruptured AAA and unruptured AAA revealed that the uniaxial failure strength in ruptured AAA is no different on average than unruptured AAA. However, it is poorly understood whether uniaxial failure properties are reliable as they are not indicative of the manner in which failure occurs in biological soft tissues. Multi-axial failure properties using a bubble inflation test (BIT) have been implemented by various groups but have not been directly compared against uniaxial failure properties. The current study seeks to develop a BIT apparatus, to compare multi-axial and uniaxial failure properties of fibrous anisotropic biological soft tissues (bovine aorta) and non-fibrous isotropic molded silicon, and to perform a survey of computational indices at the rupture sites of four ruptured AAA. Two versions of the BIT apparatus were developed: a manual that was developed allows for a large amount of failure properties to be extracted that can identify localized weaknesses. It was found that circumferentially oriented multi-axial failure was correlated with longitudinally oriented uniaxial failure properties, however, for oblique oriented multi-axial failure the correlation decreased. Utilizing the insights gained from the multi-axial experiments it was determined that the failure properties used in the computational study with the data from Raghavan et al. were appropriate for use in retrospective assessment of the rupture site in four ruptured AAA computational models. Although the study was inconclusive in finding causation, the rupture line of each aneurysm had indices ranging between the third quartile and peak values for tension to failure tension ratio, nodal displacement magnitude, strain energy per unit volume and strain energy per unit surface area. This study provides a framework for interrogating failure properties at a higher density of measurement and a heterogeneous computational model that has the potential to predict AAA rupture in the future.

38

Johansson, Nils. "Estimation of fatigue life by using a cyclic plasticity model and multiaxial notch correction." Thesis, Linköpings universitet, Mekanik och hållfasthetslära, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-158095.

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Mechanical components often possess notches. These notches give rise to stress concentrations, which in turn increases the likelihood that the material will undergo yielding. The finite element method (FEM) can be used to calculate transient stress and strain to be used in fatigue analyses. However, since yielding occurs, an elastic-plastic finite element analysis (FEA) must be performed. If the loading sequence to be analysed with respect to fatigue is long, the elastic-plastic FEA is often not a viable option because of its high computational requirements. In this thesis, a method that estimates the elastic-plastic stress and strain response as a result of input elastic stress and strain using plasticity modelling with the incremental Neuber rule has been derived and implemented. A numerical methodology to increase the accuracy when using the Neuber rule with cyclic loading has been proposed and validated for proportional loading. The results show fair albeit not ideal accuracy when compared to elastic-plastic finite element analysis. Different types of loading have been tested, including proportional and non-proportional as well as complex loadings with several load reversions. Based on the computed elastic-plastic stresses and strains, fatigue life is predicted by the critical plane method. Such a method has been reviewed, implemented and tested in this thesis. A comparison has been made between using a new damage parameter by Ince and an established damage parameter by Fatemi and Socie (FS). The implemented algorithm and damage parameters were evaluated by comparing the results of the program using either damage parameter to fatigue experiments of several different load cases, including non-proportional loading. The results are fairly accurate for both damage parameters, but the one by Ince tend to be slightly more accurate, if no fitted constant to use in the FS damage parameter can be obtained.

39

Anwar, Khurshid. "Role of apoptosis (programmed cell death) in acute liver failure." Thesis, University of Surrey, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.370058.

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40

Björklund, Oscar. "Modelling of failure." Thesis, Linköping University, Department of Management and Engineering, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-11466.

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This report is a review of some failure models today used for determine failure in thin sheets of high strength steels. Focus has been given on phenomenlogical models and only some simple simulations have been carried out. The phenomenlogical models that have been summarized here are of four different categories, namely stress based, strain based, combined stress and strain based and damaged models. However, the simulations have only been preformed for some of the models.

41

Stewart, Calvin. "TERTIARY CREEP DAMAGE MODELING OF A TRANSVERSELY ISOTROPIC NI-BASED SUPERALLOY." Master's thesis, University of Central Florida, 2009. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/3606.

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Anisotropic tertiary creep damage formulations have become an increasingly important prediction technique for high temperature components due to drives in the gas turbine industry for increased combustion chamber exit pressures, temperature, and the use of anisotropic materials such as metal matrix composites and directionally-solidified (DS) Ni-base superalloys. Typically, isotropic creep damage formulations are implemented for simple cases involving a uniaxial state of stress; however, these formulations can be further developed for multiaxial states of stress where materials are found to exhibit induced anisotropy. In addition, anisotropic materials necessitate a fully-developed creep strain tensor. This thesis describes the development of a new anisotropic tertiary creep damage formulation implemented in a general-purpose finite element analysis (FEA) software. Creep deformation and rupture tests are conducted on L, T, and 45°-oriented specimen of subject alloy DS GTD-111. Using the Kachanov-Rabotnov isotropic creep damage formulation and the optimization software uSHARP, the damage constants associated with the creep tests are determined. The damage constants, secondary creep, and derived Hill Constants are applied directly into the improved formulation. Comparison between the isotropic and improved anisotropic creep damage formulations demonstrates modeling accuracy. An examination of the off-axis creep strain terms using the improved formulation is conducted. Integration of the isotropic creep damage formulation provides time to failure predictions which are compared with rupture tests. Integration of the improved anisotropic creep damage produces time to failure predictions at intermediate orientations and any state of stress. A parametric study examining various states of stress, and materials orientations is performed to verify the flexibility of the improved formulation. A parametric exercise of the time to failure predictions for various levels of uniaxial stress is conducted.
M.S.M.E.
Department of Mechanical, Materials and Aerospace Engineering;
Engineering and Computer Science
Mechanical Engineering MSME

42

Shaw, John Henry. "Effects of Fiber Architecture on Damage and Failure in C/SiC Composites." Thesis, University of California, Santa Barbara, 2015. http://pqdtopen.proquest.com/#viewpdf?dispub=3682976.

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Carbon-fiber/SiC-matrix composites are under development for applications in hypersonic vehicles due to their exceptional capabilities at high temperatures. As a subset of these materials, textile-based composites are of particular interest because they offer the possibility of accommodating complex geometries and features in engineering components. Among the numerous obstacles hindering the widespread adoption of these composites, two are addressed in the present work: (i) the incomplete understanding of the influence of textile architecture on thermoelastic properties, damage initiation and failure, and (ii) the lack of robust computational tools for predicting their thermomechanical performance at the appropriate length scales. Accordingly, an experimental study is performed of the thermal and mechanical properties of several prototypical textile C/SiC composites with various fiber architectures. In turn, the experimental results are used to guide the development of computational tools for predicting composite response that explicitly account for fiber architecture.

Textile architecture is found to influence composite response at four length-scales: the panel, the coupon, the tow, and the sub-tow. At the panel scale, distortions to the architecture introduced during weaving or handling of the fabric influence the packing density and the relative rotation of tows. Even when large distortions are intentionally introduced their influence on mechanical response is minimal. At the coupon scale the tow architecture has the largest effects on composite mechanical response. Young's modulus, ultimate tensile strength, and strain to failure are all influenced. Changes in each of these are a function of tow shape, tow anisotropy, and the degree of constraint provided by the matrix. At the tow scale, architecture effects give rise to heterogeneity in measured surface strains under both tensile and thermal loading. Methods for the calibration of tow-scale elastic and thermoelastic properties were developed to enable simulation of these effects with a geometrically-accurate virtual model. Virtual tensile and thermal tests using this model have indicated that interaction between tows has an important influence on local strains. At the sub-tow scale, architecture effects influence the location of matrix cracking. Simulations of the cooling cycle following matrix processing predict that matrix cracks should develop in the matrix above underlying tows due to thermal expansion mismatch between the tows and the matrix. This is consistent with experimental observations. Two methods are presented to extend the virtual tests to explicitly simulate the onset and evolution of these cracks.

43

Kholkin, A. "Numerical simulation of damage and failure of laminated 3-point bending specimens." Master's thesis, Universidade de Aveiro, 2012. http://hdl.handle.net/10773/10013.

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Анотація:

Mestrado em Engenharia Mecânica
Polímeros reforçados por fibras (PRF) tem sido utilizados durante muito tempo para aplicações estruturais, particularmente com laminados. No projeto de laminados é importante caracterizar o seu comportamento mecânico. O comportamento mecânico é caracterizado por uma rigidez inicial e pela fractura. A estratégia de modelação utilizada nesta dissertação permite não só prever o “first-ply-failure”, como também modelar a sequência de eventos a seguir, como a delaminação e a fractura final da estrutura. Para isso é utilizado um modelo para a interface e para as camadas, permitindo a interação entre eles. A rigidez inicial também é avaliada com diferentes ratios comprimento para espessura, permitindo também diferentes contribuições do cisalhamento transversal e de flexão. Nesta dissertação com o método dos elementos finitos (FEM) é investigado o comportamento estrutural de uma viga compósita sobe ensaios de flexão em três pontos. Para este fim o programa comercial Abaqus é utilizado, permitindo simulações numéricas com elementos continuum casca e elementos convencionais casca. Também são realizadas simulações numéricas de modo a preparar a resultados para uma futura experiência, para o qual o tamanho do provete é escolhido com recomendações do EN ISO 14125
Fiber-reinforced polymers (FRP) have been used for a long time for structural applications, particularly with laminates. It is important to characterize the mechanical behavior of laminates for their design. This behavior is characterized by an initial stiffness and by failure. The modeling strategy used in this thesis allows to predict not only first-ply-failure (FPF), but also to model the sequence of events afterwards, such as delamination and the final failure of the structure. This is achieved by using a damage model for the ply and for the interface, allowing the interaction between them. The initial stiffness is also evaluated with different length to thickness ratios, allowing different contributions from transverse shear and bending. In this thesis, with the finite element method (FEM) the structural behavior of a laminate composite beam under a three point bending configuration is investigated. For this purpose the commercial FEM package Abaqus is used, allowing numerical simulations with continuum shell and conventional shell elements. Also simulations are conducted, in order to prepare a future experiment for which the specimen size was chosen with recommendations from EN ISO 14125.

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Morgan, Stephanie. "How do chemotherapeutic agents damage the ovary?" Thesis, University of Edinburgh, 2014. http://hdl.handle.net/1842/9543.

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Chemotherapy treatment in premenopausal women has been linked to premature ovarian failure (POF), and hence infertility, through ovarian follicle loss. The exact mechanisms that lie behind this loss are unclear and so the action of two commonly used chemotherapeutic agents were compared here. Cisplatin is a DNA cross-linking agent commonly used in the treatment of ovarian, lung and bladder cancers, while the anthracycline doxorubicin is commonly used to treat leukaemia and breast cancer. Neonatal mouse ovaries were cultured in vitro and exposed to cisplatin or doxorubicin in order to determine their effects on primordial and early growing follicles. Both drugs caused a dose dependant follicle loss but targeted different cell types. Cisplatin caused a significant increase in follicles with unhealthy oocytes; furthermore primary stage follicles were the follicle class most affected (up to 98% classified as unhealthy compared with 13% in control, p<0.001). In contrast, doxorubicin caused a significant increase in follicles with unhealthy granulosa cells and affected all follicle stages present. When the mechanism of cell death was further investigated, apoptosis was the main pathway through which these drugs cause ovarian cell death. Doxorubicin in particular caused a significant increase in apoptosis of ovarian somatic cells including the granulosa cells and stroma. Imatinib mesylate, a tyrosine kinase inhibitor which is also used as a chemotherapeutic agent, has been implicated as a potential therapy to block the ovotoxic effects of cisplatin. Results here confirm this finding (29% of follicles classified as unhealthy in the cisplatin only group compared to 8% in the cisplatin and imatinib co-treatment group, p<0.001) and found further, that imatinib was unable to protect against doxorubicin-induced damage (28% of follicles classified as unhealthy in the doxorubicin treated group compared to 19% in the doxorubicin and imatinib cotreatment group). Imatinib treatment alone in newborn ovaries caused a significant increase in the number of follicles present at the end of culture compared to control (402±43 in the imatinib group compared to 188±34 in control, p<0.001), which is likely due to an effect on follicle formation. In conclusion, the work presented in this thesis demonstrates drug specific actions of cisplatin and doxorubicin on the mouse ovary. This suggests that any therapy designed to confer ovarian protection in the future may have to be tailored to be drug specific.

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Munden, Daniel Christopher. "Development of a Progressive Failure Model for Notched Woven Composite Laminates." Thesis, Virginia Tech, 2018. http://hdl.handle.net/10919/85058.

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As part of the Composite Technology for Exploration (CTE) project at NASA, woven fabric composites are being investigated for their use in Space Launch System (SLS) hardware. Composites are more difficult to analyze than isotropic materials and require more complex methods for predicting failure. NASA is seeking a method for predicting the damage initiation and propagation of woven fabric composites in order to utilize these materials effectively in SLS hardware. This work focuses on notched woven fabric composites under tensile loading. An analytical model consisting of a macro-level failure criterion and damage propagation was developed and implemented in explicit finite element analysis to simulate woven composite materials. Several failure criteria and propagation models were investigated and compared. A response surface was used to better understand the effects of damage parameters on the failure load of a specimen. The model chosen to have best represented the physical specimen used the Tsai-Wu failure criterion. Additional physical tests are needed to further validate the model.
Master of Science
A composite material consists of two or more different materials that are joined together to form a new material with improved properties. Woven fabric composites weave strips of fibers and a bonding material into a pattern to increase the material’s ability to withstand loads in various directions. NASA is seeking a method to predict the conditions under which woven fabric composites will break. A greater understanding of the capabilities of woven fabric composites will help NASA improve the structures involved in space exploration. This work attempts to build an analytical model that can predict the loads under which a woven fabric composite will break in tension. Several different analytical theories were used to model a woven fabric composite and the results were compared with lab tests. One of the theories, the Tsai-Wu failure criterion, was selected as the best representation of the physical specimen. Further additional physical tests are necessary to further validate the analytical model.

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Von, Forell Gregory Allen. "Computational and Experimental Study of Degeneration, Damage and Failure in Biological Soft Tissues." BYU ScholarsArchive, 2013. https://scholarsarchive.byu.edu/etd/3951.

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The purpose of this work was to analyze the biomechanics of degeneration, damage, and failure in biological soft tissues both experimentally and computationally to provide insight into tendon or ligament tearing, tendo-achilles lengthening and lumbar spine dysfunction. For soft tissue tearing, experimental studies for calculating fracture toughness were performed and determined that tendons and ligaments are able to completely resist tear propagation. For tendo-achilles lengthening, a damage model was developed to mimic the behavior of the lengthening that occurs as a result of the percutaneous triple hemisection technique. The model provided insight for predicting the amount of lengthening that occurs during the procedure. For lumbar spine dysfunction, a finite element model was validated against experimental testing and simulated using boundary conditions representing physiological loading. The model was able to predict how biomechanical changes can lead to pain and how the prevalence of Schmorl's nodes can be predicted. For each of the situations, the best verification and validation methods were selected and are presented throughout the research to demonstrate the predictive capabilities and limitations of the work. Results of these studies are presented along with how those results influence the clinical endeavors associated with the degeneration, damage and failure of soft tissues.

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Horton, Brandon Alexander. "Comprehensive Multi-Scale Progressive Failure Analysis for Damage Arresting Advanced Aerospace Hybrid Structures." Diss., Virginia Tech, 2017. http://hdl.handle.net/10919/93961.

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In recent years, the prevalence and application of composite materials has exploded. Due to the demands of commercial transportation, the aviation industry has taken a leading role in the integration of composite structures. Among the leading concepts to develop lighter, more fuel-efficient commercial transport is the Pultruded Rod Stitched Efficient Unitized Structure (PRSEUS) concept. The highly integrated structure of PRSEUS allows pressurized, non-circular fuselage designs to be implemented, enabling the feasibility of Hybrid Wing Body (HWB) aircraft. In addition to its unique fabrication process, the through-thickness stitching utilized by PRSEUS overcomes the low post-damage strength present in typical composites. Although many proof-of-concept tests have been performed that demonstrate the potential for PRSEUS, efficient computational tools must be developed before the concept can be commercially certified and implemented. In an attempt to address this need, a comprehensive modeling approach is developed that investigates PRSEUS at multiple scales. The majority of available experiments for comparison have been conducted at the coupon level. Therefore, a computational methodology is progressively developed based on physically realistic concepts without the use of tuning parameters. A thorough verification study is performed to identify the most effective approach to model PRSEUS, including the effect of element type, boundary conditions, bonding properties, and model fidelity. Using the results of this baseline study, a high fidelity stringer model is created at the component scale and validated against the existing experiments. Finally, the validated model is extended to larger scales to compare PRSEUS to the current state-of-the-art. Throughout the current work, the developed methodology is demonstrated to make accurate predictions that are well beyond the capability of existing predictive models. While using commercially available predictive tools, the methodology developed herein can accurately predict local behavior up to and beyond failure for stitched structures such as PRSEUS for the first time. Additionally, by extending the methodology to a large scale fuselage section drop scenario, the dynamic behavior of PRSEUS was investigated for the first time. With the predictive capabilities and unique insight provided, the work herein may serve to benefit future iteration of PRSEUS as well as certification by analysis efforts for future airframe development.
PHD

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Sutherland, Hazel. "The effects of pattern and frequency of stimulation on transformation and damage in mammalian skeletal muscle." Thesis, University of Liverpool, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.367198.

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Hazra, Kalyan. "The influence of stitch architecture in multiaxial warp-knit fabrics on the damage tolerance and environmental durability of carbon fibre-reinforced composites." Thesis, Loughborough University, 2006. https://dspace.lboro.ac.uk/2134/34825.

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Among all the 3D textile reinforcements, Multiaxial Warp Knit (MWK) fabrics have brought together the advantages of textile technology: high deposition rates, unlimited shelf-life, lower cost and finally an improvement in the damage tolerance by the use of stitching. However, the stitching in MWKs is slightly different from that traditionally used, i.e. overstitching. The effect of this type of stitching has been investigated and is reported in this work. Three different variants of stitch architectures of carbon MWK, used in an epoxy matrix, were considered. Interlaminar shear strength, low energy impact, through penetration impact and compression strength testing were carried out on dry samples, while interlaminar shear strength, compression strength, DMTA, FTIR, Raman spectroscopic analysis were carried out on aged samples.

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Martin, Anthony Russell. "Impact damage detection in filament wound tubes using embedded optical fibre sensors." Thesis, Brunel University, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.266542.

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Дисертації з теми "Multiaxial damage and failure"

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