Under shock compression it is believed that crystalline materials undergo complex, rapid, micro-structural changes to relieve the large applied shear stresses. The mechanisms involved, such as dislocation flow and deformation twinning, under the generated high strain rates are not fully understood and in situ measurements of defects have proven elusive. This work presents the development of a nanosecond x-ray diffraction technique based on the white-light Laue method, and its first use in studying shock compressed copper. Observations of diffuse scattering are interpreted as stress-dependent lattice rotations due to dislocation glide. The results are compared with MD simulations of shocks in copper which are shown not to agree. Simulations of tantalum, shocked along the [001] axis, are demonstrated to undergo deformation twinning. A novel order parameter for identifying twin variants is developed and the deformation twinning mechanism under shock compression is identified.

The dynamic response of various geological materials has been investigated through a series of plate impact experiments. The materials involved were supplied from various mines by De Beers and Rio Tinto and were generically termed: sandstone, scilified siltstone, kimberlite, quartz/feldspathic gneiss, biotite schist, amphibolite, amphibolitic gneiss, basalt and iron ore. Investigations into compressional, shear and tensional behaviour were carried out. This project was part of a larger international study to develop models for the explosive loading of rock in a mining environment. This model is known as the Hybrid Stress Blasting Model, or HSBM. For this model to be accurate and relevant to the mining process it is essential to have dynamic data on the various rock types concerned. This was the purpose of the current project. As the material data are destined for use in a computer modelling programme it was essential to attempt to develop prediction methodologies to avoid the need for expensive dynamic characterisation of any new materials encountered in the mining environment. Much of the static data provided with the materials from De Beers proved of little use in predicting behaviour, although crucially it was not possible to determine sufficient dynamic tensile strengths in this investigation to make comparisons with the De Beers data. More success was found in predicting the slope of the Hugoniot with the elastic impedance of the material (for the non-porous linear Hugoniot materials). A fairly strong trend was found, which was backed up with data from the literature. Additionally some effort at further analysis using mineral data was undertaken. Attempts at predicting the HEL were also partially successful. While no specific quantitative prediction method was found, it was noted that the HEL did seem to scale with grain size, in that the large grained materials had a lower value of the HEL (below 2 GPa) compared with the finer grained materials (around 4 GPa and above).

Balancing increased safety against detonation performance is paramount for new explosive energetic materials in the development process. Often these two requirements are in opposition to each other. Sensitivity tests to external stimuli are used to determine how safe an energetic material is to phenomena such as impact, heat, or friction. Meanwhile, detonation performance is assessed by the maximum pressure and shock velocity induced from chemical reactions. Tailoring the performance while maintaining safety of the explosive would be possible with knowledge of the chemical reactions that functional groups provide during detonation. Current knowledge of the chemical reactions that occur during detonation is limited. Several mechanisms have been suggested for first step reactions throughout the detonation process for energetic molecules; however, no single chemical pathway has been irrefutably substantiated by experiments. Alternatively, models can provide insight into the types of reactions that may transpire, but lack direct experimental comparisons. If experiments and models could be compared at the equivalent time and length scales, then measurements could guide the physics and chemistry assumptions present in models. Experiments presented in this document bridge that gap by using an ultrafast laser system to generate shocks in samples and spectroscopically probe vibrational and electronic absorption changes that occur during shock compression. A review of how to turn a benchtop chirped pulse amplifier into a shock physics and chemistry laboratory is first presented. Applications of the spectroscopic techniques developed were then applied to trinitrotoluene (TNT) and pentaerythritol tetranitrate (PETN) during shock compression. Mid-infrared absorption results for shock compressed TNT and PETN were compared to current suggestions on chemical pathways and inconsistencies were present for both materials. It is suggested that a carbon-carbon bond breaking mechanism is present for PETN, and a hydrogenic stretch like hydroxyl or amide bond formation mechanism is suggested for TNT based on the MIR absorption measurements. Recommendations for future experimental thrusts are also provided. The results provided in this document could be directly compared to simulations to refine the assumptions present in models.

Spacecraft and satellites in orbit are under an increasing threat of impact from orbital debris and naturally occurring meteoroids. While objects larger than 10 cm are routinely tracked and avoided, collisions inevitably occur with smaller objects at relative velocities exceeding 10 km/s. Such hypervelocity impacts (HVI) create immense shock pressures and can melt or vaporize aerospace materials, even inducing brief plasmas at higher speeds. Sacrificial shields have been developed to protect critical components from damage under these conditions, but the response of many materials in such an extreme event is still poorly understood. This work presents the summary of computational analysis methods to quantify the relevant physical mechanisms at play in a hypervelocity impact. Strain rate-dependent behavior was investigated using several models, and fluid material descriptions were used to draw parallels under high shear rate loading. The production and expansion of impact plasmas were modeled and compared to experimental evidence. Additionally, a parametric study was performed on a multitude of possible material candidates for sacrificial shield design, and new shielding configurations were proposed. A comparison of material models indicated that the Johnson-Cook and Steinberg-Cochran-Guinan-Lund metallic formulations yielded the most consistent results with the lowest deviation from experimental measures in the strain rate regime of interest. Both meshless Lagrangian and quasi-Eulerian meshed schemes approximated the qualitative and quantitative characteristics of HVI debris clouds with average measurable errors under 5%. While the meshless methods showed better resolution of interfaces and small details, the meshed methods were shown to converge faster under several metrics with fewer regions of spurious instability. Additionally, a new technique was introduced using hypothetical viscous fluids to approximate debris cloud behavior, which showed good correlation to experimental results when such models were constructed using the shear rates seen in hypervelocity impacts. Formulations using non-Newtonian fluids showed additional capability in approximating solid behavior, both quantitatively and qualitatively. Such fluid models are significant, in that they reproduced the qualitative and quantitative characteristics of evolving debris clouds with better fidelity than purely hydrodynamic models using inviscid fluids. This indicates that while inertial effects can dominate overdriven shock phenomena, neglecting shear forces invariably introduces errors; such forces can instead be simplistically approximated via viscous models. The viscous approximation also allowed for a successful scaling analysis using dimensionless Pi terms, which was unfeasible using solid constitutive relations. Attempts to model plasma dynamics saw success in the simulation of a laser ablation-driven flyer plate by using a hot gas with solid initial conditions; similar strategies were used to analyze plasma production in hypervelocity impacts with reasonable correlation to experimental measurements. Lastly, the analysis of bumper material candidates showed that metals with a low density such as beryllium and magnesium yield a higher specific energy and momentum reduction of incident projectiles with lower weight requirements than a similarly constructed bumper using aluminum. Investigations of bumpers using a combination of materials and variations in microstructure showed promise in increasing weight-normalized efficacy. Through these computational models, the parameters which influence damage and debris in hypervelocity impacts are more critically understood. / PHD

<p>High explosives represent a class of materials known as energetic materials, in which providing an external stimulus of impact, heat, and electric shock can result in rapid exothermic reactions. Hence, there has always been a considerable research focus into the development, production, optimization, and control of these materials, aiming to increase explosive capabilities while also decreasing overall sensitivity to ignition.</p><p>The study of impact induced chemical initiation of explosives is an inherent multiscale problem that requires time and length scales not accessible by a single experiment or calculation. The works presented here provide a theoretical effort to contribute to bottom-up modeling of the physics and chemistry phenomena in reacting high explosives using molecular dynamics simulations. Focus will be placed how energy localizes in the molecular crystal TATB, an insensitive high explosive.</p><p>The first energy localization topic covered is an intra-molecular localization and distribution of the kinetic energy. Molecular dynamics is inherently classical, which partition energy equally between all modes. However, most molecular explosives should follow a quantum description, where energy is partitioned between modes following the Bose-Einstein distributions. A semi-classical approximation called the ‘quantum thermal bath’ is applied here to study classical vs. quantum effects for both shock and thermal initiation of chemistry. These results show, not only the importance of the changes to specific heat, which is expected, but the influence of the zero-point energy on reactivity.</p><p>The idea of energy localization is then expanded to the microstructural level, focusing on hotspots, which are areas of extreme temperature following interactions between a shockwave and the microstructure. To date, hotspots have been characterized and described by the localization of their temperature fields only. This work develops a description of the potential energy field in the hotspot, which is markedly different from the temperature field and cannot be predicted from it, as has been previously assumed. This latent potential energy, that is non-thermal, manifests from intra-molecular strain in which individual molecules in the hotspot become highly distorted. This strain energy is shown to be driven by plastic flow during the formation of the hotspot.</p><p>Lastly, the influence of the latent PE in hotspots on chemical reactivity is assessed. Reactive molecular dynamics calculations of shock induced pore collapse creates a hotspot in which deformed molecules can be separately assessed from undeformed ones. Deformed molecules are shown to react faster, follow different ensemble statistics, and undergo different first step reaction pathways. To better study these deformation under equilibrium, the Many-Bodied Steered MD method is developed in which multiple deformation modes are explored. It is shown that different deformation paths in the same molecule leads to different mechanochemical accelerations of kinetics and a different alteration of first step reaction pathways.</p>

Au passage d’un choc sur la surface rugueuse d’un métal, un nuage de débris micrométriques est éjecté. Sa signature spectrale temps-vitesse est mesurée au moyen d’un système optique interférométrique : la Vélocimétrie Hétérodyne (VH).Dans un régime de diffusion simple de la lumière, une étude paramétrique a mis en évidence l’influence des paramètres clés du nuage sur sa réponse Doppler. Nous avons estimé, par Maximum de Vraisemblance, la courbe masse-vitesse d’un nuage d’étain et l’incertitude associée. L’allure de la mesure a également été étudiée en incorporant aux calculs le rendement optique de la sonde.Nous présentons une méthode de calcul Monte Carlo, rendant compte des effets de diffusion multiple. Appliquée à trois expériences d’éjection d’or et d’étain, la présence de vitesses non physiques sur la mesure VH, liée aux diffusions multiples nuage-surface-nuage, a été soulignée, et les décroissances progressives de la visibilité en vitesse et de la puissance rétrodiffusée justifiées. Quelle que soit la masse éjectée, la diffusion multiple doit être intégrée aux calculs, un régime de diffusion simple n’étant valable qu’asymptotiquement, dans les limites d’un temps infini et/ou d’un faisceau sonde de dimension réduite par rapport aux libres parcours moyen de diffusion. / As a shockwave reaches a roughened metal’s surface, high-speed micron-sized particles are ejected. The spectral signature of the cloud can be measured using a fiber-based interferometric setup, so-called Photon Doppler velocimetry (PDV).In the single scattering regime, we study how the parametric dependencies of the cloud influence its Doppler response. Using a Maximum Likelihood technique, we estimate the mass-velocity function of ejected material, and its uncertainty. The time-dependent statistical properties of the spectrum, coming from the complex optical collection efficiency of the probe, are also explained.We present a Monte Carlo method to incorporate multiple scattering. Three different ejecta experiments are studied and the presence of non-physical velocities attributed to multiple scattering between surface and ejecta. Cloud’s visibility and backscattered power decrease with time due to the existence of different scattering regimes. Whatever the ejected mass, multiple scattering effects have to be integrated in PDV calculations. A single scattering will only be asymptotically valid, when time reaches infinity and/or the beam diameter is negligible with respect to the scattering mean free paths.

This work presents a systematic study of the mechanochemical processes leading to chemical reactions occurring due to effects of high-strain-rate deformation associated with uniaxial strain and uniaxial stress impact loading in highly heterogeneous metal powder-based reactive materials, specifically compacted mixtures of Ti/Al/B powders. This system was selected because of the large exothermic heat of reaction in the Ti+2B reaction, which can support the subsequent Al-combustion reaction. The unique deformation state achievable by such high-pressure loading methods can drive chemical reactions, mediated by microstructure-dependent meso-scale phenomena. Design of the next generation of multifunctional energetic structural materials (MESMs) consisting of metal-metal mixtures requires an understanding of the mechanochemical processes leading to chemical reactions under dynamic loading to properly engineer the materials. The highly heterogeneous and hierarchical microstructures inherent in compacted powder mixtures further complicate understanding of the mechanochemical origins of shock-induced reaction events due to the disparate length and time scales involved. A two-pronged approach is taken where impact experiments in both the uniaxial stress (rod-on-anvil Taylor impact experiments) and uniaxial strain (instrumented parallel-plate gas-gun experiments) load configurations are performed in conjunction with highly-resolved microstructure-based simulations replicating the experimental setup. The simulations capture the bulk response of the powder to the loading, and provide a look at the meso-scale deformation features observed under conditions of uniaxial stress or strain. Experiments under uniaxial stress loading reveal an optimal stoichiometry for Ti+2B mixtures containing up to 50% Al by volume, based on a reduced impact velocity threshold required for impact-induced reaction initiation as evidenced by observation of light emission. Uniaxial strain experiments on the Ti+2B binary mixture show possible expanded states in the powder at pressures greater than 6 GPa, consistent with the Ballotechnic hypothesis for shock-induced chemical reactions. Rise-time dispersive signatures are consistently observed under uniaxial strain loading, indicating complex compaction phenomena, which are reproducible by the meso-scale simulations. The simulations show the prevalence of shear banding and particle agglomeration in the uniaxial stress case, providing a possible rationale for the lower observed reaction threshold. Bulk shock response is captured by the uniaxial strain meso-scale simulations and is compared with PVDF stress gauge and VISAR traces to validate the simulation scheme. The simulations also reveal the meso-mechanical origins of the wave dispersion experimentally recorded by PVDF stress gauges.

A research study has been conducted to simulate liquefaction in saturated sandy soil induced by nearby controlled blasts. The purpose of the study is to help quantify soil characteristics under multiple and consecutive high-magnitude shock environments similar to those produced by large earthquakes. The simulation procedure involved the modeling of a three-dimensional half-space soil region with pre-defined, embedded, and strategically located explosive charges to be detonated at specific time intervals. LS-DYNA, a commercially available finite element hydrocode, was the solver used to simulate the event. A new geo-material model developed under the direction of the U.S. Federal Highway Administration was applied to evaluate the liquefaction potential of saturated sandy soil subjected to sequential blast environments. Additional procedural enhancements were integrated into the analysis process to represent volumetric effects of the saturated soil's transition from solid to liquid during the liquefaction process. Explosive charge detonation and pressure development characteristics were modeled using proven and accepted modeling techniques. As explosive charges were detonated in a pre-defined order, development of pore water pressure, volumetric (compressive) strains, shear strains, and particle accelerations were carefully computed and monitored using custom developed MathCad and C/C++ routines. Results of the study were compared against blast-test data gathered at the Fraser River Delta region of Vancouver, British Columbia in May of 2005 to validate and verify the modeling procedure's ability to simulate and predict blast-induced liquefaction events. Reasonable correlations between predicted and measured data were observed from the study.

La technique de reconstruction de forme par lumière structurée (ou projection de motifs) permet d’acquérir la topographie d’une surface objet avec une précision et un échantillonnage de points dense, de manière strictement non invasive. Pour ces raisons, elle fait depuis plusieurs années l’objet d’un fort intérêt. Les travaux présentés ici ont pour objectif d’adapter cette technique aux conditions sévères des expériences de physique des chocs : aspect monocoup, grande brièveté des phénomènes, diversité des échelles d’observation (de quelques millimètres au décimètre). Pour répondre à ces exigences, nous proposons de réaliser un dispositif autour d’un système d’imagerie rapide par éclairage laser nanoseconde, présentant des performances éprouvées et bien adaptées. La première partie des travaux s’intéresse à analyser les phénomènes prépondérants pour la qualité des images. Nous montrons quels sont les contributeurs principaux à la dégradation des signaux, et une technique efficace de lissage du speckle par fibrage est présentée. La deuxième partie donne une formulation projective de la reconstruction de forme ; celle-ci est rigoureuse, ne nécessitant pas de travailler dans l’approximation de faible perspective, ou de contraindre la géométrie de l’instrument. Un protocole d’étalonnage étendant la technique DLT (Direct Linear Transformation) aux systèmes à lumière structurée est proposé. Le modèle permet aussi, pour une expérience donnée, de prédire les performances de l’instrument par l’évaluation a priori des incertitudes de reconstruction. Nous montrons comment elles dépendent des paramètres du positionnement des sous-ensembles et de la forme-même de l’objet. Une démarche d’optimisation de la configuration de l’instrument pour une reconstruction donnée est introduite. La profondeur de champ limitant le champ objet minimal observable, la troisième partie propose de l’étendre par codage pupillaire : une démarche de conception originale est exposée. L’optimisation des composants est réalisée par algorithme génétique, sur la base de critères et de métriques définis dans l’espace de Fourier. Afin d’illustrer les performances de cette approche, un masque binaire annulaire a été conçu, réalisé et testé expérimentalement. Il corrige des défauts de mise au point très significatifs (Ψ≥±40 radians) sans impératif de filtrage de l’image. Nous montrons aussi que ce procédé donne accès à des composants tolérant des défauts de mise au point extrêmes (Ψ≈±100 radians , après filtrage). La dernière partie présente une validation expérimentale de l’instrument dans différents régimes, et à différentes échelles. Il a notamment été mis en œuvre sur l’installation LULI2000, où il a permis de mesurer dynamiquement la déformation et la fragmentation d’un matériau à base de carbone (champs millimétriques). Nous présentons également les mesures obtenues sous sollicitation pyrotechnique sur un revêtement de cuivre cylindrique de dimensions décimétriques. L’apparition et la croissance rapide de déformations radiales submillimétriques est mesurée à la surface du revêtement. / A Structured Light System (SLS) is an efficient means to measure a surface topography, as it features both high accuracy and dense spatial sampling in a strict non-invasive way. For these reasons, it became in the past years a technique of reference. The aim of the PhD is to bring this technique to the field of shock physics. Experiments involving shocks are indeed very specific: they only allow single-shot acquisition of extremely short phenomena occurring under a large range of spatial extensions (from a few mm to decimeters). In order to address these difficulties, we have envisioned the use of a well-known high-speed technique: pulsed laser illumination. The first part of the work deals with the evaluation of the key-parameters that have to be taken into account if one wants to get sharp acquisitions. The extensive study demonstrates that speckle effect and depth of field limitation are of particular importance. In this part, we provide an effective way to smooth speckle in nanosecond regime, leaving 14% of residual contrast. Second part introduces an original projective formulation for object-points reconstruction. This geometric approach is rigorous; it doesn’t involve any weak-perspective assumptions or geometric constraints (like camera-projector crossing of optical axis in object space). From this formulation, a calibration procedure is derived; we demonstrate that calibrating any structured-light system can be done by extending the Direct Linear Transformation (DLT) photogrammetric approach to SLS. Finally, we demonstrate that reconstruction uncertainties can be derived from the proposed model in an a priori manner; the accuracy of the reconstruction depends both on the configuration of the instrument and on the object shape itself. We finally introduce a procedure for optimizing the configuration of the instrument in order to lower the uncertainties for a given object. Since depth of field puts a limitation on the lowest measurable field extension, the third part focuses on extending it through pupil coding. We present an original way of designing phase components, based on criteria and metrics defined in Fourier space. The design of a binary annular phase mask is exhibited theoretically and experimentally. This one tolerates a defocus as high as Ψ≥±40 radians, without the need for image processing. We also demonstrate that masks designed with our method can restore extremely high defoci (Ψ≈±100 radians) after processing, hence extending depth of focus by amounts unseen yet. Finally, the fourth part exhibits experimental measurements obtained with the setup in different high-speed regimes and for different scales. It was embedded on LULI2000 high energy laser facility, and allowed measurements of the deformation and dynamic fragmentation of a sample of carbon. Finally, sub-millimetric deformations measured in ultra-high speed regime, on a cylinder of copper under pyrotechnic solicitation are presented.