The development of improved numerical methods for computer simulation of high velocity impact dynamics is of importance in a variety of science and engineering fields. The growth of computing capabilities has created a demand for improved parallel algorithms for high velocity impact modeling. In addition, there are selected impact applications where experimentation is very costly, or even impossible (e.g. when certain bioimpact or space debris problems are of interest). This dissertation extends significantly the class of problems where particle-element based impact simulation techniques may be effectively applied in engineering design. This dissertation develops a hybrid particle-finite element method for a general hexahedral mesh. This work included the formulation of a numerical algorithm for the generation of an ellipsoidal particle set for an unstructured hex mesh, and a new interpolation kernel for the density. The discrete model is constructed using thermomechanical Lagrange equations. The formulation is validated via simulation of published impact experiments. / text

Aircraft disasters during take-off and landing by the impact of foreign object debris (FOD) have always been an important issue. When the wing is lifted, its upper and bottom surfaces are subjected to compressive and tensile stresses, respectively. The bottom surface of the aircraft wing is vulnerable due to the threat of runway debris, which may travel at high speed, leading to the catastrophic failure of structures under tension. This thesis studies the ballistic performance of a structural panel subjected to projectile impact when the influence of in-plane pretension is considered. An experimental program was proposed to obtain the laboratory testing results where a special rig was designed to apply pretension to the panel as it is being hit by a projectile launched from a gas gun at velocities between 60 to 160 m/s. Instrumentation was used to record impact and residual velocities at different stages of the impact process. The panel was supported on opposing sides in one direction with two free sides in the other direction. Two target materials related to aircraft structure were considered, i.e., aluminium alloy, 2014-T6 and carbon fiber reinforced plastic (CFRP). Two projectile nose shapes - including flat and hemisphere - were used to account for the influence of debris on the ballistic performance of the target. Target materials were fully characterized in the experimental program. Finite element (FE) models were established and validated, and were used to simulate the response and damage of the panels in the experiments when the influence of pretension is considered. The damage of aluminium alloy, 2014-T6 was modeled using shear failure criterion with damage evolution. For CFRP, the in-plane damage initiation was modeled using Hashin’s damage criterion with damage evolution in terms of fracture energy. Parametric studies were done for both aluminium alloy 2014-T6 and CFRP panels with various pretensions of up to 50% of the material ultimate strength. It has been shown that the pretension has more profound effect on the ballistic behavior of the CFRP panel in comparison with its influence on the ballistic behavior of aluminium alloy panel. The simplified analyses and the numerical modeling reflect the physical nature of the impact response and damage of aluminium alloy and CFRP target panels. Hashin’s damage model for CFRP needs to be extended from in-plane to out-of-plane in order to include shear failure, which may happen for the flat nose projectile impact.

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Image-charge detection is an analytical technique in which a highly-charged particle is detected by the magnitude of the image current that it generates in a detecting electrode. This current is represented as a voltage between the charged particle and the sensing electrode. It is a single particle detection method, ideal for the analysis of large, variable mass particles such as biological cells. Some of the physical properties of Bacillus subtilis spores were explored using different applications of image-charge detection. B. subtilis is a gram-negative spore-forming bacteria that has been shown to exhibit extremophile behavior. The particular extremophile behavior that was investigated in this study is the resistance to extreme mechanical stress. The effects of high-velocity impacts upon these spores were studied using image-charge detection. The elastic properties of these spores as well as spore survivability to high-velocity impacts were investigated. Spores were shown to survive impacts at velocities up to 299 ± 28 m/s. The average kinetic energy loss experienced by impacting spores, regardless of velocity at impact, was between 71 and 72%. Both conventional and novel image-charge detection techniques were used for these studies. The novel version of a charge detector that was demonstrated was fabricated using patterned metal electrodes on printed circuit boards. The simplicity and versatility of this method was demonstrated with a multi-stage charge detector, a unique bouncing detector, and charge-detection mass spectrometry detector which is capable of measuring the absolute mass of a single highly-charged particle.

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To enhance material performance at different length scales, this study strives to develop a reliable analytical and computational tool with the help of internal state variables spanning micro and macro-level behaviors. First, the practical relevance of a nonlocal damage integral added to an internal state variable (BCJ) model is studied to alleviate numerical instabilities associated within the post-bifurcation regime. The characteristic length scale in the nonlocal damage, which is mathematical in nature, can be calibrated using a series of notch tensile tests. Then the same length scale from the notch tests is used in solving the problem of a high-velocity (between 89 and 107 m/s) rigid projectile colliding against a 6061-T6 aluminum-disk. The investigation indicates that incorporating a characteristic length scale to the constitutive model eliminates the pathological mesh-dependency associated with material instabilities. In addition, the numerical calculations agree well with experimental data. Next, an effort is made rather to introduce a physically motivated length scale than to apply a mathematical-one in the deformation analysis. Along this line, a dislocation based plasticity model is developed where an intrinsic length scale is introduced in the forms of spatial gradients of mobile and immobile dislocation densities. The spatial gradients are naturally invoked from balance laws within a consistent kinematic and thermodynamic framework. An analytical solution of the model variables is derived at homogenous steady state using the linear stability and bifurcation analysis. The model qualitatively captures the formation of dislocation cell-structures through material instabilities at the microscopic level. Finally, the model satisfactorily predicts macroscopic mechanical behaviors - e.g., multi-strain rate uniaxial compression, simple shear, and stress relaxation - and validates experimental results.

Pour prémunir les structures spatiales d'impacts hyper-véloces, le secteur aérospatial est continuellement à la recherche de matériaux toujours plus performants. Dans cette optique, les verres métalliques massifs se présentent comme de potentiels éléments de blindages spatiaux. De récentes études ont mis en exergue une meilleure résistance à la pénétration de ces matériaux comparativement aux blindages actuels. Les impacts par lanceurs permettent d'étudier et caractériser le comportement sous chocs des matériaux. Cependant, les vitesses des projectiles se retrouvent actuellement limitées à 10 km/s, correspondant aux niveaux d'impacts hyper-véloces les plus modérés. Pour s'affranchir de cette limitation, il est possible de se tourner vers les lasers de puissance. Ces dispositifs permettent de générer des ondes de choc dont les niveaux de pression et de vitesse de déformation sont supérieurs aux lanceurs. Les travaux menés ont permis d'étudier et de caractériser le comportement et l'endommagement de plusieurs verres métalliques ternaires ZrCuAl sous choc laser. Plusieurs campagnes expérimentales ont été réalisées sur les installations du Laboratoire pour l'Utilisation des Lasers Intenses (LULI2000 et ELFIE). Une partie de l'équation d'état des nuances étudiées a été obtenue à la fois par choc laser et compression isentropique. Les processus d'endommagement, l'influence des vitesses de déformation et de composition sur la rupture ont été étudiés. Pour des régimes de vitesse de déformation supérieurs de trois ordres de grandeur à ceux disponibles dans la littérature, il a été mis en évidence que les verres métalliques étudiés présentaient une limite à la rupture cinq à dix fois supérieure. / Space industry is always searching for efficient materials to protect space structures from high-velocity impacts. In this context, bulk metallic glasses appear as suitable elements of space debris shielding assemblies. Recent studies revealed a higher tolerance to impact of metallic glasses compared to materials currently used in shield assemblies. Gas-gun and powder launchers are usually used to study and characterize the dynamic and shock behaviour of materials. However, projectiles velocities are currently limited to 10 km/s, corresponding to the lowest high-velocity impacts levels. To overcome this limitation, one may consider shock waves induced by high-power laser facilities, whose pressure and strain rate levels can exceed those induced by canons. Hence, this work enabled to study and to characterize the dynamic and damage behaviours of several compositions of ternary ZrCuAl bulk metallic glasses subjected to shock waves induced by laser irradiation. Several experimental campaigns have been conducted on various laser facilities of the Laboratoire pour l'Utilisation des Lasers Intenses (LULI2000 and ELFIE). A part of the equation of state of the studied compositions was established using both shock waves and quasi-isentropic compressions. Damage processes and the composition and strain rate effects on fracture were also studied. For strain rate levels higher of three or more orders of magnitude than those available in the literature, it was shown that studied bulk metallic glasses displayed a five to ten times higher dynamic tensile limit.

Fibre reinforced composites have higher specific strength and stiffness in comparison to metals. However, composites are susceptible to impact damage resulting in degradation of mechanical properties especially compression strength. Numerous studies have been conducted to improve the impact damage tolerance of composite laminates using modified resin systems, thermoplastic matrices, 3-D fibre architectures and through thickness reinforcement. This work is primarily focussed on incorporating non dissolvable polypropylene fibres (PP) in a thermoset matrix for improving the damage tolerance. Commingling and wrapping techniques have been investigated. PP fibres have been incorporated at the preform stage and hence do not adversely affect the viscosity of the resin during infusion. The healing effect of PP fibres on impact damaged composite laminates when heating is introduced has also been studied. High velocity impact test results showed that using commingled glass/PP fibres increased the total energy absorption of composite laminates by 20% due to the extensive plastic deformation of the PP fibres and through the use of toughening mechanisms in the form of resin cracking and delamination. It has been found that PP fibres provide protection to the glass fibres during low velocity impact loading, so fewer fibre breakages occur which lead to improved residual properties compared with pristine glass laminates. Compression after impact (CAI) tests showed that the residual strength as a percentage of non-impacted strength increased with percentage of PP fibres used. For impact of 20-50J, glass/epoxy laminates retained 32 45% of their compressive strength while laminates with 7%, 13% and 18% PP fibres retained 37 50%, 42-52% and 43-60% of their compressive strength, respectively. It was also observed that glass/PP woven laminates had better compressive strength retention (62 83%) than the glass/PP non-crimp laminates (37-50%). Composite laminates with high-modulus PP fibres (Innegra) exhibited higher residual compression strengths in comparison to laminates with lower modulus PP fibres. For 15-50J impact, glass/Innegra laminates showed residual compression strength of 50 63% in comparison to 39-60%; laminates without thermoplastic fibres exhibited 33 43% residual compression strength. Modulus of thermoplastic fibres appears to be important at higher energy levels. Healing of damaged commingled laminates produced a significant reduction in the damage area and a corresponding increase in CAI strength after heating at 200ºC; CAI strength of healed laminates is about 85% of undamaged samples in comparison to 60% for non-healed samples. A novel micro-wrapping technique, developed in this work, demonstrated significant reduction in damage area (46%) in comparison to the commingling method. Core wrapped laminates had higher residual strength (43-60%) than glass laminates (33-43%). Better PP distribution in core-wrapped composites helped to decrease the PP rich areas and the impact damage did not propagate easily in comparison to commingled composites. However due to the reduction in damage area, impact energy absorption in core wrapped laminates was lower than for commingled.