Wave propagation and permanent densification in a porous steel submitted to laser-driven shocks

Instrumented laser shock experiments have been performed to investigate the response of a sintered porous steel to uniaxial compressive loading at very high strain rates. The water-confinement technique has been used to increase both amplitude and duration of the laser shocks. Two steels of different initial porosities have been studied. Wave profiles have been measured with thick piezoelectric transducers stuck at the back of the steel targets. Residual compaction has been estimated by post-shock microscopic examination of the recovered samples. A simple constitutive material model, based on a macroscopic description involving the equation of state of the compact steel and a traditional P-α compaction model, has been adapted and introduced in a one-dimensional hydrocode to simulate the tests. A correct overall agreement has been obtained between measured and computed wave profiles, and the residual porosity distribution predicted by the model has been compared to that observed along the direction of wave propagation

Behaviour of metals at ultra-high strain rate by using femtosecond laser shockwaves

The mechanical behavior of materials under extreme conditions can be investigated by using laser driven shocks. Actually, femtosecond (fs) technologies allow to reach strong pressures over a very fast duration. This work is dedicated to characterize metals behavior in this ultra-short mode, (aluminum, tantalum), leading to an extreme dynamic solicitation in the target (>107s−1). The study includes the validation of experimental results obtained on the LULI 100TW facility by comparison with numerical model. Three modeling steps are considered. First, we characterize the pressure loading resulting from the fs laser-matter interaction, different from what happens in the classical nanosecond regime. Then, the shock wave propagation is observed through the target and particularly its pressure decay, strong in this regime. The elastic-plastic influence on the shock attenuation is discussed, particularly for tantalum which has a high elastic limit. Dynamic damage appears with spallation. Experimentally, spallation is characterized by VISAR measurements and post-test observations. Shots with different thicknesses have been carried out to determine the damage properties in function of strain rate. We show in this work that a simple instantaneous rupture criterion is not sufficient to reproduce the damage induced in the sample. Only the Kanel model, which includes damage kinetics, is able to reproduce experimental data (VISAR measurements, spall thickness). A generalization of this model to any strain rate can be performed by confronting these results to other shock generators data (ns laser driven shocks, plate impacts). One remarkable result is that every Kanel parameters follows a power law with strain rate in dynamic regime (105 to 108s−1) for both aluminum and tantalum

Measurement of the Effects of High-Pressure Laser Shocks on Metallic Targets

Piezoelectric measurements have been performed behind metallic samples submitted to short laser shocks of intensities up to 7 TW/cm2, using recently developed polymeric transducers. Some records exhibit a recompression indicating spall damage, confirmed by post-test microscopic observations. Computations involving a laser-matter interaction model and a wave-propagation code lead to a correct agreement on the gauge records. They indicate peak pressures of 7 to 150 GPa in the targets. A phenomenological spall model of the literature provides an approximated description of the relaxation associated with spallation, and a fair estimate of the damage level and location in the target.Des mesures piézoélectriques ont été réalisées à l'arrière de cibles métalliques soumises à des chocs laser brefs d'intensité pouvant atteindre 7 TW/cm2, au moyen de capteurs polymériques. Certains signaux comportent une recompression traduisant un écaillage des cibles, confirmé par un examen post-test. La simulation des expériences avec un modèle d'interaction laser-matière et un code de propagation est en accord correct avec les enregistrements. Elle indique des pressions maximales de 7 à 150 GPa dans les cibles. Un modèle phénoménologique d'écaillage fournit une description approximative de la relaxation associée à la rupture, et de la distribution de l'endommagement dans la cible

Spallation and microjetting in laser-shock-loaded aluminium and gold

Dynamic fragmentation of shock-loaded metals is an issue of considerable importance for both basic science and a variety of technological applications, such as inertial confinement fusion, which involves high energy laser irradiation of thin metallic shells. In this context, we present an experimental and numerical study of fragmentation and debris ejection in laser shock-loaded aluminium and gold, under both nanosecond and sub-picosecond laser pulses. Such fragmentation is mainly governed by two distinct processes: microjetting, that is ejection of thin jets upon shock breakout at the (rough) free surface, and spall fracture, which occurs upon tensile loading due to wave interactions inside the sample. Experimental results consist of time-resolved velocity measurements, transverse optical shadowgraphy of ejected debris, and post-shock observations of recovered targets. They are compared to numerical computations performed with two hydrocodes, and a correct overall consistency is obtained

Poly(lactic acid) and poly(lactic-co-glycolic acid) particles as versatile carrier platforms for vaccine delivery.

The development of safe and effective vaccines for cancer and infectious diseases remains a major goal in public health. Over the last two decades, controlled release of vaccine antigens and immunostimulant molecules has been achieved using nanometer or micron-sized delivery vehicles synthesized using biodegradable polymers. In addition to achieving a depot effect, enhanced vaccine efficacy using such delivery vehicles has been attributed to efficient targeting of antigen presenting cells such as dendritic cells. Biodegradable and biocompatible poly(lactic acid) and poly(lactic-co-glycolic acid) polymers belong to one such family of polymers that have been a popular choice of material used in the design of these delivery vehicles. This review summarizes research findings from ourselves and others highlighting the promise of poly(lactic acid)- and poly(lactic-co-glycolic acid)-based vaccine carriers in enhancing immune responses

Poly(lactic acid) and poly(lactic-co-glycolic acid) particles as versatile carrier platforms for vaccine delivery.

The development of safe and effective vaccines for cancer and infectious diseases remains a major goal in public health. Over the last two decades, controlled release of vaccine antigens and immunostimulant molecules has been achieved using nanometer or micron-sized delivery vehicles synthesized using biodegradable polymers. In addition to achieving a depot effect, enhanced vaccine efficacy using such delivery vehicles has been attributed to efficient targeting of antigen presenting cells such as dendritic cells. Biodegradable and biocompatible poly(lactic acid) and poly(lactic-co-glycolic acid) polymers belong to one such family of polymers that have been a popular choice of material used in the design of these delivery vehicles. This review summarizes research findings from ourselves and others highlighting the promise of poly(lactic acid)- and poly(lactic-co-glycolic acid)-based vaccine carriers in enhancing immune responses

Study of spallation by sub-picosecond laser driven shocks in metals

Spallation induced by a laser driven shock has been studied for two decades on time scales of nanosecond order. The evolution of laser technologies now provides access to sources whose pulse duration is under the picosecond, corresponding to characteristic times of numerous microscopic phenomena. In this ultra-short irradiation regime, spallation experiments have been performed with time-resolved measurements of the free surface. In this solicitation type, damage occurs at small scale, leading to micrometric spalls. The VISAR measurements have been complemented with post-test observations and microtomography and compared with numerical simulations to check the models consistency of the laser-matter interaction, shock wave propagation and the dynamic damage criteria ability to reproduce spallation at this ultra-short time scale, inducing strong tensile stress states at very high strain rates