The ballistic impact of Twaron CT709® plain weave fabrics is studied using an explicit finite element method. Many existing approximations pertaining to woven fabrics cannot adequately represent strain rate-dependent behavior exhibited by the Twaron fabrics. One-dimensional models based on linear viscoelasticity can account for rate dependency but are limited by the simplifying assumptions on the fabric architecture and stress state. In the current study, a three-dimensional fabric model is developed by treating each individual yarn as a continuum. The yarn behavior is phenomenologically described using a three-dimensional linear viscoelastic constitutive relation. A user subroutine VUMAT for ABAQUS/Explicit® is developed to incorporate the constitutive behavior. By using the newly developed viscoelasticity model, a parametric study is carried out to analyze the effects of various parameters on the impact behavior of the Twaron fabrics, which include projectile shape and mass, gripping conditions, inter-yarn friction, and the number of fabric layers. The study leads to the determination of the optimal number of fabric layers and the optimized level of inter-yarn friction that are needed to achieve the maximum energy absorption at specified impact speeds. The present study successfully utilizes the combination of 3D weave architecture and the strain rate dependent material behavior. Majority of the existing work is based either on geometry simplification or assumption of elastic material behavior. Another significant advantage with the present approach is that the mechanical constitutive relation, coded in FORTRAN®, is universal in application. The desired material behavior can be obtained by just varying the material constants in the code. This allows for the extension of this work to any fabric material which exhibits a strain-rate dependent behavior in addition to Twaron®. The results pertaining to optimal number of fabric layers and inter-yarn friction levels can aid in the manufacturing of fabric with regard to the desired level of lubrication/additives to improve the fabric performance under impact.

In the last several decades the number of the fatalities related to criminally inflicted cranial gunshot wounds has increased (Aarabi et al.; Jena et al., 2014; Mota et al., 2003). Back-spattered bloodstain patterns are often important in investigations of cranial gunshot fatalities, particularly when there is a doubt whether the death is suicide or homicide. Back-spatter is the projection of blood and tissue back toward the firearm. However, the mechanism of creation of the backspatter is not understood well. There are several hypotheses, which describe the formation of the backspatter. However, as it is difficult to study the internal mechanics of formation of the backspatter in animal experiments as the head is opaque and sample properties vary from animal to animal. Performing ballistic experiments on human cadavers is rarely not possible for ethical reasons. An alternative is to build a realistic physical 3D model of the human head, which can be used for reconstruction of crime scenes and BPA training purposes. This requires a simulant material for each layer of the human head. In order to build a realistic model of human head, it is necessary to understand the effect of the each layer of the human head to the generation of the back-spatter. Simulant materials offer the possibility of safe, well‐controlled experiments. Suitable simulants must be biologically inert, be stable over some reasonable shelf‐life, and respond to ballistic penetration in the same way as the responding human tissues. Traditionally 10-20% (w/w) gelatine have been used as a simulant for human soft tissues in ballistic experiments. However, 10-20% of gelatine has never been validated as a brain simulant. Moreover, due to the viscoelastic nature of the brain it is not possible to find the exact mechanical properties of the brain at ballistic strain rates. Therefore, in this study several experiments were designed to obtain qualitative and quantitative data using high speed cameras to compare different concentrations of gelatine and new composite material with the bovine and ovine brains. Factors such as the form of the fragmentation, velocity of the ejected material, expansion rate, stopping distance, absorption of kinetic energy and effect of the suction as well as ejection of the air from the wound cavity and its involvement in the generation of the backspatter have been investigated. Furthermore, in this study a new composite material has been developed, which is able to create more realistic form of the fragmentation and expansion rate compared to the all different percentage of the gelatine. The results of this study suggested that none of the concentrations the gelatine used in this study were capable of recreating the form of the damage to the one observed from bovine and ovine brain. The elastic response of the brain tissue is much lower that observed in gelatine samples. None of the simulants reproduced the stopping distance or form of the damage seen in bovine brain. Suction and ejection of the air as a result of creation of the temporary cavity has a direct relation to the elasticity of the material. For example, by reducing the percentage of the gelatine the velocity of the air drawn into the cavity increases however, the reverse scenario can be seen for the ejection of the air. This study showed that elastic response of the brain tissue was not enough to eject the brain and biological materials out of the cranium. However, the intracranial pressure raises as the projectile passes through the head. This pressure has the potential of ejecting the brain and biological material backward and create back-spatter. Finally, the results of this study suggested that for each specific type of experiment, a unique simulant must be designed to meet the requirements for that particular experiment.

Polymer matrix composites (PMCs) offer several advantages compared to traditional metallic counterparts when employed in high-performance products that need to be lightweight, yet strong enough to sustain harsh loading conditions - such as aerospace components and protective structures in military applications- armours, helmets, and fabrications retrofitted to transport vehicles and bunkers. These are often subjected to highly dynamic loading conditions under blast and ballistic impacts. Severe impact energy involved in these dynamic loading events can initiate discrete damage modes in PMCs such as matrix cracking, matrix splitting, delamination, fibre-matrix debonding, fibre micro-buckling and fibre pull-out. Interaction of these damage modes can severely reduce the load carrying capacity of such structures. This needs to be understood to design structures with improved resistance to such loading.

Impact damage resistance is an essential requirement of lightweight structural components for high-performance applications. The aim of this thesis is to study the impact damage and perforation behaviour of lightweight materials including thin aluminium alloy plates and carbon fibre reinforced epoxy composites. The focus of this investigation is on the stress state and strain rate dependence of failure, and the effect of microstructural modifications on indentation and impact response. The thesis is divided into three parts. In the first part (Chapter 2) the impact response of thin monolithic ductile aluminium alloy plates is investigated. Impact perforation experiments are performed using different projectile nose shapes to span a wide range of stress states at the onset of ductile fracture. Impact perforation behaviour, ballistic limit velocity, energy absorption capability and sensitivity to projectile tip geometry are evaluated. Modes of deformation and failure during impact are assessed experimentally. It is shown that modelling the stress state and strain rate dependence of plasticity and failure is crucial to accurately predict ductile fracture initiation in thin metal plates. In the second part (Chapters 3 and 4), the stress state and strain rate dependent yield and failure behaviour of epoxy resin is investigated. An iterative numerical-experimental approach is shown to be essential to develop a material model capable of predicting the failure behaviour of epoxy for a wide range of stress triaxialities across different regimes of failure. The influence of microstructural modifications in epoxy, through two different toughening strategies, on its failure behaviour is investigated. The effect of increasing the applied strain rate on the stress state dependent response of epoxy is investigated to provide an insight into the impact damage resistance of carbon fibre reinforced epoxy composites. In the third part (Chapter 5), experimental studies are conducted on the quasi-static indentation and impact perforation response of plain weave carbon fibre reinforced epoxy composites to investigate the effect of toughening the epoxy matrix to improve resistance to indentation and impact. The nose shape sensitivity of failure initiation in carbon/epoxy composite targets is assessed by considering indenters with different tip geometries. Conclusions and suggestions for future work are presented in Chapter 6.

A physically motivated Internal State Variable (ISV) constitutive model is extended to account for shear influenced void evolution for predicting damage behavior in ductile solids. The revised ISV model is calibrated for an aluminum 7085-T711 alloy using a series of microstructure and mechanical property quantification experiments. The calibrated ISV model for the aluminum alloy is implemented in an implicit finite-element code (Abaqus) to simulate the deformation of notch Bridgman tension specimens at a variety of stress states and temperatures. The model revisions and calibrated aluminum ISV model are validated through successful prediction of mechanical and microstructure evolution for structures subjected to a variety of complex stress state conditions. The extended ISV model framework is used to study shear influenced plasticity and damage mechanisms resulting from ballistic impact of metals. A Rolled Homogeneous Armor (RHA) steel alloy is selected for the impact model due to wide availability of documented penetration characteristics and ballistic performance data of RHA steel. Finite Element Analysis (FEA) simulations of ballistic impact of rolled homogeneous armor (RHA) steel projectiles against RHA steel plates are performed using a calibrated ISV constitutive model for RHA steel. An FEA simulation based parametric study is performed to assess the effect of a variety of microstructure and mechanical properties on the ballistic performance of RHA steel targets. FEA simulations are used to predict a transition in ballistic perforation mechanisms for high hardness steel alloys by accounting for variations in microstructure properties qualitatively documented in the literature.

This study is devoted to the development of an integrated numerical modeling enabling one to investigate the static and the dynamic behaviors and failures of 2-D textile composite as well as 3-D orthogonal woven composite structures weakened by cracks and subjected to static-, impact- and ballistic-type loads. As more complicated modeling about textile composite structures is introduced, some of homogenization schemes, geometrical modeling and crack propagations become more difficult problems to solve. To overcome these problems, this study presents effective mesh-generation schemes, homogenization modeling based on a repeating unit cell and sinusoidal functions, and also a cohesive element to study micro-crack shapes. This proposed research has two: 1) studying behavior of textile composites under static loads, 2) studying dynamic responses of these textile composite structures subjected to the transient/ballistic loading. In the first part, efficient homogenization schemes are suggested to show the influence of textile architectures on mechanical characteristics considering the micro modeling of repeating unit cell. Furthermore, the structures of multi-layered or multi-phase composites combined with different laminar such as a sub-laminate, are considered to find the mechanical characteristics. A simple progressive failure mechanism for the textile composites is also presented. In the second part, this study focuses on three main phenomena to solve the dynamic problems: micro-crack shapes, textile architectures and textile effective moduli. To obtain a good solutions of the dynamic problems, this research attempts to use four approaches: I) determination of governing equations via a three-level hierarchy: micro-mechanical unit cell analysis, layer-wise analysis accounting for transverse strains and stresses, and structural analysis based on anisotropic plate layers, II) development of an efficient computational approach enabling one to perform transient response analyses of 2-D plain woven, 2-D braided and 3-D orthogonal woven composite structures featuring matrix cracking and exposed to time-dependent ballistic loads, III) determination of the structural characteristics of the textile-layered composites and their degraded features under smeared and discrete cracks, and assessment of the implications of stiffness degradation on dynamic response to impact loads, and finally, IV) the study of the micro-crack propagation in the textile/ceramic layered plates. A number of numerical models have been carried out to investigate the mechanical behavior of 2-D plain woven, 2-D braided and 3-D orthogonal woven textile composites with several geometrical representations, and also study the dynamic responses of multi-layered or textile layered composite structures subjected to ballistic impact penetrations with a developed in-house code. / Ph. D.

Graphite epoxy composites lack effective mechanisms for absorbing local impact energy often resulting in penetration and a structural strength reduction. The effect of adding small amounts of two types of high strain hybrid components on the impact resistance of graphite epoxy composites subjected to projectiles traveling at ballistic velocities (greater than 900 ft/sec) has been studied. The hybrid components tested include superelastic shape memory alloy (SMA), a material having an unusually high stra in to failure (15 - 20%), and a high performance extended chain polyethylene (ECPE) known as Spectra™, a polymer fiber traditionally used in soft and hard body armor applications. 1.2% volume fraction superelastic SMA fiber layer was embedded on the specimens front, middle, and backface to determine the best location for a hybrid component in the graphite composite. From visual observation and energy absorption values, it was concluded that the backface is the most suitable location for a high strain hybrid component. Unlike the front and middle locations, the hybrid component is not restricted from straining by surrounding graphite material. However, no significant increases in energy absorption were found when two perpendicular SMA layers and an SMA-aramid weave configuration were tested on the backface. In all cases, the embedded SMA fibers were pulled through the graphite without straining to their full potential. It is believed that this is due to high strain rate effects coupled with a strain mismatch between the tough SMA and the brittle epoxy resin. However, a significant increase in energy absorption was found by adding ECPE layers to the backface of the composite . With only a 12% increase in total composite mass, a 99% increase in energy absorption was observed. / Master of Science

O presente trabalho é um estudo qualitativo do comportamento mecânico do laminado metal-fibra GLARE-5 2/1, submetido a impacto balístico subsônico em condições que simulam à amplitude térmica em aplicações espaciais. Para isto, os corpos de prova foram submetidos e ao impacto balístico de um projétil cilíndrico e alguns destes foram submetidos ao choque térmico, alternando entre -196 e 100°C. Os danos causados por estes ensaios foram analisados com as técnicas de microscopia óptica e tomografia computadorizada de raios X (X-Ray CT), que permitiram o entendimento dos danos em duas e três dimensões. Comparouse o resultado entre estas técnicas e a influência do ordenamento das amostras no escaneamento deste material. Concluiu-se que a X-Ray CT é uma técnica não destrutiva que proporciona boa informação para o entendimento dos danos internos causados pelo impacto no GLARE, embora não replicou com exatidão os danos observados na microscopia óptica. Além disso, o agrupamento de amostras do GLARE para o escaneamento permitiu melhorar a qualidade das imagens resultantes destes escaneamentos. Os danos mais comuns causados pelo impacto foram delaminações metal-fibra, trincamentos na matriz polimérica e delaminações fibra-fibra, sendo a condição criogênica a que resultou em maior volume de danos. Amostras submetidas ao choque térmico mostraram uma queda de sua temperatura de transição vítrea e ganho na resistência ao impacto. / This is a qualitative study of the mechanical behavior of the metal-fiber laminate GLARE-5 2/1 subjected to subsonic ballistic impact under conditions that simulate thermal amplitude in space applications. For this, the specimens were submitted to the ballistic impact of a cylindrical projectile; some specimens were previously thermal shocked, alternating between - 196 and 100 ° C. The damages caused by these tests were analyzed by optical microscopy and X-ray CT (X-Ray CT), which allows the understanding of damage in two and three dimensions. Were compared the results between these techniques and the influence of the ordering of the samples in the scanning of this material. It was concluded that X-Ray CT is a non-destructive technique that provides good information for understanding the internal damage caused by impact on GLARE, although it did not replicate accurately the damage observed under light microscopy. In addition, GLARE sample collation for scanning has improved the quality of the images resulting from these scans. The most common damages caused by the impact were metal-fiber delamination, cracking in the polymer matrix and fiber-fiber delamination, the cryogenic condition being the result of greater damage. Samples subjected to thermal shock showed a drop in their glass transition temperature and gain in impact resistance.

Quasi-isotropic (QI) structure for multi-layer fabric panel is believed to be a promising construction to manufacture soft body armour with higher efficiency of ballistic protection based on two hypotheses. The first one is that QI structure panel could involve more secondary yarns in transverse deformation, and the second one is that the more involvement of the secondary yarns could result in the corresponding increase of the energy absorption. However, recent study found that the advantage of QI panel made from Dyneema® woven fabrics was very limited over the aligned panel and potential reasons have not been identified for the lack of systematic studies. Accordingly, this research aims to provide explicit guidance on how to improve the QI structure panels for ballistic protection by studying the mechanisms of aligned and QI panels of multi-layer Dyneema® woven fabrics. The two hypotheses were tested to identify the mechanisms. The ballistic performance of the aligned and QI panels of 2-layer, 3-layer and 4-layer Dyneema® woven fabrics were experimentally investigated using a ballistic test apparatus and a panel clamping system to evaluate the energy absorption of specimens. In order to further study the response of the ballistic panel, a yarn-level Dyneema® woven fabric model was developed. The shear moduli of the yarn (G13 and G23) was found to be the most important elastic constants in simulating ballistic fabrics using orthogonal experiments in this study, and were identified to 0.27GPa and 0.80GPa. The model was agreeably validated by comparing the FE modelling results of multi-layer panels under ballistic impact with the experimental counterparts. Based on this validated model, the areas, shapes of the transverse deformation bases were specifically evaluated. The first hypothesis was verified that the areas of the deformation bases of the back layer fabrics in QI panels of 2-layer, 3-layer, and 4-layer fabric models were more than 10% larger than the areas of the corresponding parts in aligned panel models, especially at medium and late stages. Moreover, the increases of the areas were attributed to the more involvements of the secondary yarns in the deformation, and more circular shapes of the deformation bases of the fabrics in QI panels were identified by using a mathematic measurement method created in this study. The kinetic energy (KE) and total strain energy (IE) evolution of primary yarns and secondary yarns in two panels were further specified. It was found that altering the aligned panel to QI panel not only changed the energy absorption of secondary yarns, also significantly changed that of primary yarns. This indicated that the second hypothesis was not suitable for the cases of panels of the Dyneema® woven fabrics for the influence of the primary yarns after the panel structure changed were neglected. The reason of the alterations of the primary yarns was that the slip-off time or failure time of most primary yarns was changed. The morphology evolution of primary yarns in 2-layer aligned and QI panels were investigated and the results showed that the space between adjacent warp or weft primary yarns and the interactions between some primary yarns and the adjacent primary yarns in another layer significantly affected the slip-off time and failure time of most primary yarns. The influence of these two factors derived from the feature of woven fabrics, which was the crimp. In order to verify the new understanding of the QI ballistic panels from the numerical analysis, a non-crimp fabric, namely Dyneema® SB51, was used to investigate the ballistic performance of the aligned and QI panels. It was found that the energy taken by QI panels was approximately 25% higher than the energy taken by the corresponding aligned panels. This result verifies the analysis conclusion and paves the solid way for further investigation of QI structure panels made up of biaxial fabrics.

Dans le contexte de la biomécanique, les outils numériques constituent des moyens puissants et indispensables dans la compréhension des mécanismes de blessures. Ils permettent de pallier les freins que sont les expérimentations sur l'humain, liés à des raisons d'éthique qui limitent la possibilité d'essais sur des SHPM (Sujets Humain Post Mortem). Le développement de ces outils numériques a conduit à celui de plusieurs mannequins numériques permettant de stimuler diverses sollicitations (civiles ou militaires), nous donnant ainsi accès à des limites de tolérances.En vue d'explorer la réponse dynamique du corps humain soumis à des sollicitations diverses, un modèle de mannequin numérique a été développé au sein du laboratoire. Ce travail de thèse tente donc d'apporter une contribution dans la recherche sur la définition d'un critère de blessure et l'établissement de limites de tolérance du corps humain soumis aux chargements violents de la partie thoracique dans des contextes militaires. / The development of computer science has allowed an increase in the use of numerical approaches such as finite elements method in order to understand physical mechanisms. These numerical tools are often used to extend and complete experimental investigations wich are limited because of high financial cost and ethical issues. Thus, the use of simulation to avoid thes limitations becomes essential in biomechanics investigations. Many numericalmodels of the thorax/abdomen system have been developped over the last two decades. In that framework, a finite element model of the human body, dedicated to high speed loadings, has been developed in the laboratory. In this context, the objective of this Ph.D Thesis is to investigate the consequences of such loadings on the human body and to contribute to the research of injuries criteria and tolerance limit definition.