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Abstract: Ballistic limit equation (BLE) is an important tool for spacecraft shield design. An approach for constituting dual/multi wall BLE by single wall BLE is proposed. A new single wall BLE is built first based on the current BLE form analysis. A total of 100 experimental test data collected from the literature are introduced for verifications and comparisons. The new single wall BLE has obtained a better correct prediction rate of 83% than other tested BLEs. Secondly, the new Whipple shield (double wall) BLE is constituted of the new single wall BLE. In the low velocity regime the projectile isn't completely fragmented behind the bumper, the Whipple shield BLE is therefore obtained just by the summation of the single wall BLEs of the bumper and the rear wall. While in the hypervelocity regime, the expansion effect of the completely fragmented debris cloud is taken into consideration. The single wall BLE of the rear wall is multiplied by a correction term of the spacing between the two walls before the summation. The shatter regime BLE is obtained by the linear interpolation of the endpoints. A total of 268 experimental test data collected from the literature are introduced for verifications and comparisons. The new Whipple shield BLE has obtained a better correct prediction rate of 72% than other tested BLEs. Finally, the new multi-shock shield BLE is preliminarily constituted of the new single wall BLE and the Whipple shield BLE. The new multi-shock BLE is used to predict 5 experimental test cases and all of which are correct. [Copyright &y& Elsevier]

Abstract: The differences between the effects of irradiation and thermal quenching were studied in SiO2–B2O3–Na2O glass by molecular dynamics. Classical molecular dynamics simulations reproduced quenching rates between 2×1012 K/s and instantaneous quenching. Each configuration was then subjected to a series of displacement cascades. An acceleration of the quenching rate and the accumulation of ballistic collisions result in qualitatively similar effects: swelling, increasing disorder, depolymerization of the glassy network, a decrease in the mean coordination number of B atoms. Nevertheless, ballistic processes induce specific effects that are not reproduced by accelerated quenching: an even larger degree of disorder, higher potential energy, greater depolymerization around B sites and different free volume distribution. The memory of the initial quenching rate is largely lost following an accumulation of displacement cascades, and the structure of the irradiated glasses adopts a final configuration weakly dependant on the initial state. This study shows that comparing the structure of the initial glass prepared at different quenching rates with the structure of irradiated glasses makes it possible to discriminate between thermal quenching and ballistic effects. [Copyright &y& Elsevier]

Abstract: When a material is subjected to irradiation, many primary defects are created at the atomic level by sequences of ballistic collision events to form highly disordered regions defined as displacement cascades. The long term evolution of materials under irradiation is dictated by the number and the spatial distribution of the surviving defects in the displacement cascade. The peculiar power law shape of collision cross sections is responsible for the fractal feature of atomic trajectories set and then the fragmentation of a displacement cascade into smaller subcascades. We present a criterion to describe the fragmentation of a displacement cascade into subcascades and to calculate the volume fraction of subcascades in the overall cascade due to this fragmentation. Such a volume fraction then provides a natural framework to estimate the efficiency of different projectiles to induce phase transformation or amorphisation in solids under irradiation. From this definition of the fragmentation of a displacement cascade, this work gives some new insights to compare different irradiations performed with different particles. [Copyright &y& Elsevier]

The thrust provided by a plasma source, open at one end, is calculated for an arbitrary ratio of collision to ionization rates. If the plasma is of a low collisionality, ion pumping is dominant, and the momentum of the jet exiting the source is carried mostly by the plasma. In the collisional regime, neutrals are accelerated through charge-exchange collisions with ions, leading to neutral pumping, so that most of the momentum of the jet is carried by the neutral gas. It is shown that these ion–neutral collisions increase the thrust for a given power. However, the conventionally defined efficiency for a thruster, reflecting also the propellant utilization, is lower in the collisional regime. [ABSTRACT FROM AUTHOR]

Abstract: In the present study an ultra high strength armour steel was austenatised at 910°C followed by tempering at 200, 300, 400, 500 and 600°C. After heat treatment the properties of tensile strength, ductility, charpy impact strength, hardness and microstructure were evaluated from the mechanical tests and metallographic analysis respectively. The ballistic behavior of the heat-treated plates was evaluated impacting against non-deformable hard steel core projectiles at 840 ± 15 m/s at normal angle of attack. The changes in the microstructure and mechanical properties with heat treatment have been correlated with ballistic performance of the steel. Experimental results showed that 200°C tempering gives the best ballistic performance. [Copyright &y& Elsevier]

Abstract: We report on experimental studies of the collision process between an incident bead and a three-dimensional packing of mono-size beads. The understanding of such a process and the resulting ejection of grains is, in particular, crucial to describe aeolian sand transport. We present here recent experimental results on the collision and ejection process when varying the angle and the speed of the incident bead. We performed numerical simulations of one bead collisions on the surface of a static granular medium. The simulations have been done for two and three dimensional packings of beads. The effects of the incident bead velocity, the shot angle, the mechanical parameters and the packing structure are analyzed for ordered and disordered 2D packings but only disordered 3D packings. The 2D results are in good agreement with available experimental data. The 3D simulations give good preliminary results about the shock wave propagation through the stacking and provides new insights in the ejection process (“splash function”). [Copyright &y& Elsevier]

We consider explicit solutions to the problem of ballistic aggregation of dustlike matter whose particles stick together absolutely inelastically upon collisions—a description of the formation of a large-scale structure in cosmology in terms of the adhesion model, which is a generalization of the Zel’dovich approximation. The two previously suggested different representations of the solutions for a plane-symmetric 1D flow are shown to be equivalent. Explicit representations of the solutions in cylindrical and spherical symmetries are constructed. We provide explicit examples showing that the two representations under consideration cannot be generalized to a multidimensional nonsymmetric flow. [ABSTRACT FROM AUTHOR]

We study the ballistic pendulum in a situation that is not usually considered where the bullet shot into a hanging block requires a finite time (the collision time) to come to rest relative to the block. During this time the block undergoes a non-negligible displacement. A slow collision is one for which the block's displacement during the collision time is an appreciable fraction of its maximum displacement. For slow collisions, the quantitative results of our model differ significantly from the standard ballistic pendulum treatment. Suitably generalized momentum and energy relations are evaluated and provide a check on the numerical solutions. This work extends the treatment of a familiar problem and demonstrates the utility of computational tools accessible to undergraduates. [ABSTRACT FROM AUTHOR]