Laser ablation driven is a very promising technology to remove centimeter-scale space debris, however, the irregular geometry of the space debris has very complicated influence on the impulse of the laser ablation, which is a difficulty and hot issue in current related research.In this study, based on the impulse coupling law of laser ablation, we presented a method for accurately calculating the impulse magnitude and direction for the irregular target irradiated by laser based on the surface triangulation and three-dimensional reconstruction of irregular objects.The accuracy of this method is verified by 3 targets with typical geometric shapes:cube, sphere and cylinder.Using this method, we studied the impulse generation rule of laser irradiating the regular targets with typical geometrical shapes and the irregular spherical target asteroid "Bennu", and obtained the conditions of the maximum impulse for various geometrically shaped targets under specific laser incidence angle.This method and the results are very useful for the research of active debris removal by laser.

Using a diamond anvil cell apparatus, we investigated the sodium perchlorate (NaClO₄) by Raman spectroscopy at pressure up to 20 GPa, and calculated the Raman spectra of anhydrite-(Cmcm), monazite-(P2₁/n), AgMnO₄-(P2₁/n), and barite-type (Pnma) structures of NaClO₄ by density function theory.The experimental data show that anhydrite-type NaClO₄ undergoes a structural transition at about 4 GPa.A new peak at lower Raman frequencies (975 cm^-1) than that of the ClO₄^- internal mode ν₁ (A_g) of the NaClO₄ ambient phase was obviously observed at 4.4 GPa.At the same time, several peaks at the corresponding wave numbers of the ClO₄^- internal modes (ν₂、ν₃、ν₄) arise.The phase transition is completed at about 6.1 GPa, and remains stable up to 19.5 GPa.The high pressure structure can be recovered at about 3.1 GPa in decompression.By comparison with the calculated Raman spectral profiles (at 8.0 GPa) of three potential high pressure structures, we infer that the high pressure phase has a monoclinic monazite-type structure.The pressure-induced phase transition of NaClO₄ is consistent with the anhydrite-monazite phase transition found in CaSO₄ at about 2 GPa.However, our finding appears inconsistency with the previous observations that the anhydrite-type NaClO₄ transforms to AgMnO₄-type at about 2 GPa and furthermore to the barite-type structure at around 3 GPa.The previous results could probably be influenced by the moisture of the sample combining with the high temperature and high pressure conditions.It may bring more complicated changes by simultaneous high pressure and high temperature environments.The research progress contributes to the understanding of not only the relationship between volcanic activity and the widespread distribution of perchlorate on Mars, but also the changes and functions of chlorine element during the recycles of subduction and mantle plume in the Earth's deep interior.

In this work, we measured the Grüneisen parameter γ of aluminum in 297-494 K under 2.17 GPa and the γ of sodium chloride in 312-608 K under 1.46 GPa, based on the Grüneisen differential equation γ=(K_S/T)(∂T/∂p)_S (where K_S is the adiabatic elastic bulk modulus), combining the rapid compression method with the mean value theorem.A setup for internal heating was designed to produce high temperature in the sample chamber and the rapid compression on sample at different temperatures was carried out in a Bridgman anvil by a self-made rapid compression apparatus.The curves of temperature and pressure rise of the sample were recorded during rapid compression.For compensating the heat loss due to heat conduction, the temperature-rise curve was modified according to the cooling rate of the sample during the pressure-holding process.The temperature-rise curve after compensation is closer to that of adiabatic compression.It was found that for aluminum under 2.17 GPa and sodium chloride under 1.46 GPa, the ΔT/Δp increases with the increasing temperature while the Grüneisen parameters fluctuate, showing no obvious relationship with temperature in the experimental temperature range.

The propagation and interaction of the phase transformation waves is a thermal-mechanical coupling process under shock loading.In this research, we investigated the effect of a fixed temperature interface on the phase transition propagating by theoretical analysis combining with experiment.First, on the basis of the shape memory constitutive model and the one-dimensional characteristic line theory, we analyzed the basic law of interactions between kinds of cross sections and the temperature interface.The results reveal that the property of the interaction is associated with the strength of phase transition wave and the relative size of temperature on two sides of the temperature interface.Then, we carried out the experiment of the phase transition wave propagating in a shape memory TiNi bar with a temperature interface, the results of which is consistent with the theory analysis; and we in situ measured the change of temperature in the process of the phase transformation propagation, showing that the phase transition wave is not only the material cross section, but also the moving temperature interface under shock loading.

In the present work, we developed a high-resolution 3D code based on the FORTRAN platform to investigate the influence of accuracy of WENO schemes on the blast load generated by gas cloud explosion inside a cabin.The 3th, 5th, 7th and 9th WENO finite difference schemes were implemented in the code to capture the shock waves.Several one dimensional Riemann problems such as Sod shock tube and shock-entropy wave interaction were simulated to investigate the computing performance of the schemes preliminarily and validate the developed code.Then, the validated code was used to conduct the simulation of the gas cloud explosion inside a closed cabin and a venting cabin and the influence of the accuracy of WENO schemes on the blast load was discussed as well.The researches indicate that the blast load generated by gas cloud explosion inside the cabin mainly contains multiple peaks shock waves and long duration quasi-static overpressure.The accuracy of WENO schemes has considerable influence on the blast waves and higher order scheme gives sharper pressure peaks, whereas it has much less influence on the quasi-static overpressure.

When simulating the two-dimensional multi-material compressible flows using the Lagrangian method, the distortion of the mesh is often the reason why the process terminates.The dynamic local remeshing is an option to relax the distortion.In this study, we combined the "diagonal-swapping" "edge-splitting" "edge-merging" and "hat-trick" to deal with the distortive mesh.The 4 operations could act not only in single material, but also be extended to the multi-material interface to deal with the distortive mesh on the interface.After the remeshing, the quantities on the old mesh are projected onto the new one.During this process, the mass, momentum and energy are kept conservative.We verified the effectiveness and accuracy of this method by using it to simulate the shock/bubble interaction and the R-T instability.In the R-T instability simulation, the single material and the multi-material models are applied to prove that this method is able to deal with the distortive mesh both inside the material and on the interface.

Nanoparticles tend to aggregate due to the van der Waals force, and the separation and purification of these nanoparticles are difficult in nanometer scale.In this study, we focus on the separation of two SiO₂ nanoparticles attracted by van der Waals force.Assuming them as being stiffness particles in air and applying ultrasonic vibration to one of them, we analyzed and calculated the interaction and distance between the two SiO₂ nanoparticles.It is found that the ratio of diameters, the amplitude, the period and the average energy density of the ultrasonic have different effects on their separation.

Measuring the dynamic constitutive relation of low-impedance materials which are usually used in the field such as energy absorption and cushion by using a split Hopkinson pressure bar (SHPB) device generally does not require a high impact velocity of bullet but a stable one with little error in the experiments.In this study, based on the principle of free fall, we developed a vertical split Hopkinson pressure bar.We can precisely control the bullet impacting speed through the height of the free fall.In order to eliminate the gravity effects on the experiment, we held the incident bar by the friction force, and let the friction force equals the incident bar gravity.We carried out dynamic compression experiments of polyvinyl alcohol (PVA) fiber concrete to verify the reliability of the experimental device.

In this work we studied the processes of applying pre-stress on SiC ceramics by using the finite element software AUTODYN.We established a model of long-rod projectile of different velocities penetrating ceramics with different pre-stress values to investigate the ballistic performance of the pre-stress ceramic, and obtained the stress distributions in the ceramic under different loading conditions through the comparison and analysis of the results, as well as the relation of different pre-stress and ballistic performance of the ceramic.The simulated results show that the appropriate pre-stress can improve the ballistic performance of ceramic, but the ballistic performance of ceramic is reduced when the pre-stress value is greater than 112 MPa, and that there exists a best matching relationship between the pre-stress value and the ballistic performance of the ceramics.

We conducted tests on the dynamic stress-strain relationship of both 30CrMnMoRE and 30CrMnSi at different strain rates using the split Hopkinson pressure bar (SHPB) system to study the mechanical response of alloy metal under high impact, and obtained their dynamic stress-strain curves and yield strength.And combined with the Johnson-Cook model, we obtained the dynamic constitutive model of the two materials.The test results show that the stress-strain relationship and the strength parameters of the two steels have obvious strain rate dependence.With the increase of the strain rate, the dynamic strength of 30CrMnMoRE increased by about 79%, and that of 30CrMnSi increased about by 50%.

In this study, we employed the MTS machine to apply a compressive load to the closed cell aluminum foams with different densities (0.322-0.726g/cm³) at different temperatures (25-500℃) under quasi-static state, and obtained the stress-strain curves of the aluminum foam under uniaxial compression and analyzed the influence of density and temperature on its mechanical behavior.We fitted the stress-strain curves at different densities using the Liu and Subhash constitutive model, and the fitted results accorded well with the experimental curves.Then we analyzed and determined the function between the revised 5 parameters and the varying density, and established a constitutive model of the aluminum foams with density effect taken into consideration.With the temperature softening effect added to the modification of this constitutive model, we eventually established a constitutive model of aluminum foams considering both the temperature effect and the density effect under quasi-static compression.

In this study, we investigated the dynamic buckling of the functionally graded Timoshenko beam whose property parameters continuously change according to the power function along the thickness direction.Based on the first order shear deformation theory, we derived the governing equation of the dynamic buckling of functionally graded material Timoshenko beams under axial step loading by using the Hamilton's principle.Using the Ritz method combining with the de Moivre's formula, we obtained the buckling solution and the expression of the critical load of the dynamic buckling of functionally graded material Timoshenko beam under the clamped-fixed boundary condition.Then, the influence of geometric size, gradient index, modal number, material composition, Poisson's ratio and elastic modulus on the critical load by MATLAB calculation was discussed.The results show that the critical load of the functionally graded material Timoshenko beam decreases with the increase of beam length and the gradient index, and increases with the increase of the modal number, showing that the higher modal number is more easily excited by the increase of impact load.Furthermore, the critical load increases with the increase of the Poisson's ratio and the elastic modulus, and the effect of elastic modulus is greater than Poisson's ratio.The critical load-critical length curve tends to be gentle at the loading end because of the influence of shear term.Buckling mode of beam becomes more complicated when the modal number increases.

In this study, we measured the pressure histories of the shock wave after passing through different thicknesses of PMMA card gaps under ∅100 mm plane wave loading by the PVDF piezofilm stress gauges.The experimental results accord well with the simulated results by LS-DYNA, which shows that the shock wave follows the exponential attenuation principle with an attenuation exponent of 0.028 89.The comparison of this result with those of other researchers' indicates that the attenuation exponent of the solid materials characterizes their attenuation capability, but is affected by given conditions such as the shock wave and the size of experiment facility, thus it is important to choose the attenuation exponent reasonably.

Based on a Doppler pin system, we studied the influence of a 0.5 mm-thick foam layer and an air clearance on the kinetic characteristic of a 45 steel flyer under the detonation of the RHT-901 explosive, and analyzed the difference in this influence as is shown between a single-flyer assembly and a double-flyer assembly according to the free surface velocity-time curves of the flyer of each.The experimental results show that the foam cushion and air clearance significantly affect the kinetic characteristics of the 45 steel flyer, including the take-off time of the flyer, the velocity jump amplitude and the final velocity.Comparing the effect of a foam cushion and that of an air clearance between the explosive and the metal flyer in the single-flyer assembly, we found that the take-off time of the metal flyer in the foam cushion region is later by about 30ns and the speed jump amplitude is higher by about 13% as compared to that in the air clearance area; comparing it in the double-flyer assembly, we found that the take-off time is advanced by about 200ns and the speed jump amplitude is reduced by about 6%.Nevertheless, the final velocities in the foam cushion region are lower than that in the air clearance area in the two experiments.Finally, we analyzed the influence pattern based on the stress wave propagation in continuum matter, and verified the rationality of the theoretical explanation by estimating the velocity of denotation products flying through air.

In this study, we conducted numerical simulations of the oblique perforation of single 1 mm-thick Q235 steel plates subjected to flat-and ogive-nosed projectiles at 0°~60° by invoking the ABAQUS subroutine to introduce a modified J-C constitutive model and a modified three-section failure criterion of stress triaxiality, and examined the effects of the projectile nose shape and the obliquity on the ballistic resistance and failure modes of the targets.We also investigated the angle-deflection of the projectiles perforating targets and proposed a modified semi-theoretical model to describe the angle-deflection laws.The results show that the target perforation by flat-nosed projectiles is easier than that by ogive-nosed projectiles at each oblique angles; the ballistic resistance of targets is closely related to the target damages induced by projectile impact; the target has different failure modes as impacted by flat-nosed projectiles at low and high velocities in the same oblique angle respectively, while the failure modes of single target due to impact of ogive-nosed projectiles at different angles do not show much difference.The results of numerical simulation agree well with those of experiments.

Based on the Johnson-Cook material constitutive and failure criteria, we established the models of 2A12 thin aluminum alloy plates with a thickness of 2 mm impacted by ogival-nosed projectiles using the finite element software ABAQUS, and studied the influence of the attack angles (0°-60°) on the projectiles' impacting processes, energy change and the deformation of targets on the basis of the verification of the models and parameters.The results show that the kinetic energy of the targets slightly increase during the impact process, and the plastic deformation is the main form of energy dissipation; the increase of the attack angle causes the broken area of the target to increase at first and then remain unchanged, and the shape of the hole transits from circular to "L"-shaped; the residual kinetic energy of the projectiles decreases with the increase of the attack angle and remains stable after the attack angle reaches 45°;the ballistic limits of the targets increase first and then decrease slightly with the attack angle, reaching the maximum when the angle was 45°.

In this work we examined and characterized the original velocity and flight velocity attenuation of the nonmetal fragments of a certain low-collateral-damage warhead in combination with its explosive power experiment.We obtained the fragments' original velocity including the shell configuration and material strength factors based on the conservation of energy, and derived the flight velocity attenuation regularity from the analysis of its fragment flight movement in the air and the modification of its resistance formula and the equivalent area of the spherical fragment.Our analytical result was confirmed by the experimental result, thus providing an analytical method for evaluating the fragment damage efficiency of this kind of warhead.

According to the characteristics of the detonation loading process in prefabricated fragment warhead, we designed the sliding detonation unit test model, and obtained the initial velocity and the damage of the prefabricated fragments and light shell under two typical arrangements by the X-ray photographic method, and analyzed the influence of different impedance matching structures on the accelerating character at the same time.The results show that the initial velocity of the prefabricated fragments situated outside the shell (sequential impedance matching structure) with slight damage is relatively high, whereas that of the prefabricated fragments situated inside the shell (reverse impedance matching structure) with stratification cracks is relatively low.

Based on the traditional explosive reactive armor (ERA), we designed a structure of double-layer ERA with wedged flying-plates, to achieve the best performance in jet disturbing.By using the simulation software ANSYS/LSDYNA-3D, we simulated 3 different schemes of ERA structures, and analyzed the flying states of flying-layers, the character of escaped jet, the kinetic energy of jet and the penetrating depth of target by jet separately.The results show that the flying-layer tended to rotate after the sandwich explosive were detonated, and a proper structure arrangement helped to enlarge the active area between the jet and the flying-layer.The kinetic energy of jet declined greatly after across the ERA, resulting in a lower penetrating depth.Of the 3 schemes, Scheme 2 has the smallest penetrating depth by jet into the target, the next is Scheme 3, while Scheme 1 has the maximum penetrating depth, indicating that the structure of Scheme 2 has the best protection effect.This study on the wedged double-layer ERA enriched the structure design of ERA, providing theoretical reference for its further research.

In this study, we used the ANSYS/LS-DYNA software to simulate the fall test of the cabin warhead in order to predict its safety performance, and obtained the structural stress deformation and charge overload response of the combat simulation of the warhead in different states.The results show that the stress and overload of the shell and the main charge are the smallest when the cabin warhead is tilted at 45°, but the deformation of the shell is the most severe; and the stress of the shell is small when the large part of the warhead is dropped vertically, but the stress and overload of the charge are the largest, indicating the worst assessment posture.The actual fall test of the large warhead in cabin is successfully passed, and the numerical simulation can provide theoretical support.

In this work, we researched the influence of a kind of thermal protection coat on the reaction of explosives in projectile by fast cook-off test.Based on the comparison of the reaction state of the test sample with and without the thermal protection coat, the results show that the thermal protection coat had little influence on the test sample's reaction intensity, and delayed the explosives' ignition reaction time by 32 min.The thermal protection coat can obviously win more time for the ammunition succor in fire accidents.Furthermore, the protective effect of the thermal protection coat is related with its own heat-conducting property and the airy space between the coat and the sample protected.

The high noise and low efficiency of explosive welding can be improved by the double-sided explosive welding which can clad two composite plates simultaneously and significantly reduce the critical thickness of stable detonation of explosives.In this study, we simulated the double-sided explosive welding using the explicit finite element program LS-DYNA combined with the SPH (Smoothed Particle Hydrodynamics) and FEM (Finite Element Method) coupling, and compared the simulation results with the experiment and the calculation results.The results showed that the simulation results were in good agreement with the experiment results as well as the theoretical calculation results of Deribas's.It shows that the Deribas's formula and SPH-FEM coupling method can provide theoretical guidance for the engineering application of double-sided explosive welding.