In order to solve the problem of large range negative velocity measurement in dynamic response measurement of structure, a photonic Doppler velocimetry (PDV) measurement system based on two laser sources is designed. Compared with the single laser source PDV system based on acoustic optical modulator, the range of negative velocity measurement is greatly improved. However, it is found in the explosion experiment that the displacement baseline drift and oscillation are caused by the wavelength fluctuation of the laser source. For this reason, one reference reflector is introduced to generate the background signal which is used to compensate the displacement. Then, the data compensation algorithm is studied. The experimental results show that the displacement baseline drift after compensation is in the order of micron. PDV based on two laser sources and the compensation method are feasible and effective.

To investigate the impact tensile response of silicone rubber subjected to different strain rates, quasi-static uniaxial tension tests at the strain rate of 0.001 s^–1, moderate strain-rate tensile tests at the strain rate of 15 s^–1 and high strain-rate tensile tests at the strain rates of 350 and 1400 s^–1 were performed. Experimental results show that the tensile behavior of the filled silicone rubber exhibits apparent nonlinear elastic characteristic and strain-rate sensitivity. A phenomenological visco-hyperelastic constitutive model was proposed based on the obtained responses. The model is composed of a hyper-elastic spring and a Maxwell element with rate-dependent relaxation time, corresponding to hyper-elasticity and viscoelasticity respectively. The model results have good agreement with the experimental data, indicating that the model has the ability to describe the nonlinear and rate-dependent tension behavior of the filled silicone rubber.

Free vibration of pre/post-buckled graphene-reinforced nanocomposite beams was analyzed by the differential quadrature method. Considering the random distribution and directional arrangement of graphene nanoplatelets in the matrix, Young’s moduli of graphene nanocomposites in two modes were estimated by Halpin-Tsai micromechanical model. The first-order shear deformation theory was used to establish the governing equations of beams by Hamilton principle. The critical buckling loads of the graphene-reinforced nanocomposite beam and the natural frequencies in the pre/post-buckling regimes were calculated by the differential quadrature method. Numerical results show that dispersing more graphene platelets with less single layers and arranging them in a reasonable mode will greatly increase the critical buckling loads of the beams and the natural frequencies in pre-buckling regime. However, the same approach reduces the stiffnesses of the beams in the post-buckling regime.

The plate impact experiment was carried out through use of one-stage gas gun platform to study the spall of sintered Nd-Fe-B magnet subjected to one-dimensional loading. The free-surface velocity profile was measured using fiber velocity interferometer system for any reflector, and the spall strength was determined. The main results show that spall strength increases and then decreases when the impact stress increases from 0.377 GPa to 2.512 GPa. The reason is attributed to compression damage of the material when the impacted stress exceeds a stress threshold. Furthermore, the fractured morphology of sinter Nd-Fe-B was analyzed by scanning electron microscopy and the transgranular fracture was observed.

As one of the typical brittle materials, ceramics are highly sensitive to deformation. Under strong dynamic loads, it exhibits mechanical response characteristics completely different from ductile metal materials which involve damage and destructive behavior. In this study, the split Hopkinson bar test system is used to carry out impact loading tests on Al₂O₃ ceramics obtaining the dynamic tensile/compressive properties of the ceramics, as well as the relationship of fracture characteristics with strain rate. In addition, the mechanical properties and fragment size of brittle ceramic materials under different strain rates are further studied by using the theoretical methods of energy conservation and dynamics. The results show that the tensile and compressive strength of Al₂O₃ ceramics is positively correlated with strain rate under impact loading. Furthermore, the particle sizes of Al₂O₃ ceramic samples vary greatly under the action of the one-dimensional stress wave. With the increase of loading strain rate, the total number of broken ceramic particles will increase and the average particle size will decrease, while the influence of stress concentration will gradually weaken. Finally, the fragment size of brittle materials simulated by the DID model is consistent with the experimental results. However, Grady model is derived from the fact that the generalization of ductile materials is quite different from the experimental results.

Piezoelectric ceramics are the core components of piezoelectric impact sensors. The mechanical and electrical behaviors of PZT-5 piezoelectric ceramics were studied by split Hopkinson pressure bar (SHPB) experimental technique. The tests were carried out at speeds of 4–14 m/s. In order to ensure the insulation between specimen and pressure bar, a process of sputtering Al₂N₃ on the surface that with less influence on the test piece was used, and the sputtering thickness was 1–3 ${{\text{μ}}{\rm{m}}}$. The experimental results of SHPB were analyzed and discussed. The results show that the strain change of PZT-5 piezoelectric ceramics exhibits viscous properties during impact loading, and the charge generated is related to the stress and strain of the specimen during loading. When the loading speed exceeds a certain level, the piezoelectric ceramic may be damaged during the loading process, and the degree of damage also affects the generation of charge. The mechanical and electrical properties of PZT-5 piezoelectric ceramics have obvious rate correlation.

The penetration/perforation effects of high-speed ogive-nosed projectiles on reinforced concrete (RC) targets were experimentally investigated. The projectiles with a mass of approximately 10 kg were launched by a 100 mm power gun to striking velocities between 820 and 1195 m/s and impacted on the RC targets with the unconfined cylinder compressive strength from 31.0 MPa to 43.6 MPa. The end-point trajectory data of projectiles penetrating/perforating into RC targets are obtained. The penetration/perforation depths and deformations of high-speed projectiles, free surface effects of RC targets were analyzed. The results show that the penetration/perforation depths of high-speed projectiles ranges from 2.2 m to 2.8 m. The predicted penetration/perforation depths by some empirical formulas were in good agreement with the experimental data. Furthermore, those targets with smaller relative surface size and the projectile with higher velocity, the free surface effects were more significant. In addition, the projectile behaves from rigid to semi-fluid mechanism when the striking velocity reaches to 1195 m/s.

A coupled FEM-SPH model for an ogival-nosed projectile penetrating into a steel plate was established. The influence of friction coefficient between projectile and plate on residual velocity estimation for projectile was analyzed. Based on the experimental data, a suitable friction coefficient was determined such that the model can accurately predict residual velocities of projectile and ballistic limit of target. Based on the model, effects of projectile rotation on its residual velocity and ballistic deflection were studied for normal and oblique penetration with two different incident velocities and different incident angles. For normal penetration, rotation has a significant influence on residual velocity of projectile while few effects on ballistic deflection. The residual velocity and penetration capability of projectile increase with the growth of rotation speed. For oblique penetration, rotation has obvious effects on both residual velocity and ballistic deflection of projectile. The penetration capability of projectile does not monotonically increase with the growth of rotation speed and is dependent on incident angle and velocity. Deflections out of incident plane are induced by projectile rotation, and the deflection direction is related to the rotation direction of projectile.

Spallation is an important damage and failure mechanism produced by the interactions of decompression waves from the material interfaces, and is mesoscopically attributed to the nucleation, growth and coalescence of microdamages (microvoids and microcracks). Based on the works of Grady, Curran and Johnson, who respectively won George E. Duvall Shock Compression Science Award of the American Physical Society in 2007, 2009 and 2011, this paper gives a review of the progress and brief history for dynamic material spall. Further physical insights may be obtained based on those known physical models and experimental techniques for dynamic material spallation. In the meantime, some valuable results obtained are presented as follows. (1) Experimental technique of double layer targets, used to freeze the state of spall damage, is based on the same basic physical principle of Hopkinson pressure bar. (2) The nucleation, growth to fragmentation (NAG/FRAG) model, which is mathematically inconsistent and physically incomplete, is modified by inheriting the same size exponential distribution and nucleation rate from the original model by assuming the growth rate of microvoid’s radius proportional to the microvoid’s radius for ductile spall. A modified nucleation and growth (MNAG) model is obtained. The MNAG model is mathematically consistent and physically closed, and owns an analytical damage evolution equation. (3) It is pointed out that the damage can usually be obtained from the equation of microdamage’s number for Lagrangian formulation rather than from the equation for Eulerian formulation presented by Bai Yilong et al. (4) The damage function model or the Feng-Jiapo model is derived by a simpler way.

Results of Raman scattering measurements under pressure up to 25 GPa on adamantane (C₁₀H₁₆) carried out at room temperature are reported. The analysis of Raman data indicated four phase transitions. The ambient pressure disordered Fm3m structure ($\alpha$-C₁₀H₁₆) transformed to a high pressure ordered phase at 0.6 GPa. Continue to pressurize to 1.7 GPa, the second structure phase transition began, and completely accomplished until 3.2 GPa. The third transition began at 6.3 GPa, ended at 7.7 GPa. C₁₀H₁₆ transformed to a new phase at 22.9 GPa. Because of the new lattice peak occurred during the third transition, it was defined to a first-order transition.

We performed in situ electrical conductivity measurements on pure and iron FeS-bearing olivine in a multi–anvil apparatus using the impedance spectroscopy technique under the condition of 1–3 GPa and 723–1273 K. The experimental results indicated that the electrical conductivities of 15% (mass fraction) FeS–bearing olivine, in the range of 0.1–10 S/m, are 2 to 3 orders of magnitude higher than that of pure olivine in the experimental temperature range. The electrical conductivities of pure and 15% FeS-bearing olivine increase with increasing temperature. The dependence of the electrical conductivity of pure olivine on temperature is much stronger. The effect of pressure on the electrical conductivity of pure and iron FeS-bearing olivine is different. With the rise of pressure, the electrical conductivity of pure olivine slightly decreases, whereas the electrical conductivity of the 15% FeS-bearing olivine increases significantly. Based on the experimental results including the Arrhenius parameters, it is proposed that the 15% FeS can form an interconnected network in olivine, which dominates the conduction process of olivine.

To know the stress distribution mechanism of shock propagating across grain interface is of great significance to understand the interacting phenomena and plastic principles of shock and polycrystalline metal material. With molecular dynamics (MD), shock impacting on four kinds of metals with FCC (face-centered cubic) crystal lattice are numerically simulated. The stress tensor components distribution, scale and correlations of shock propagating in monocrystal and across grain interface on {100} lattice plane are computed and analyzed. It is concluded as follows: (1) The stress generated after shock propagating along different lattice arrangement orientations presents different characteristics between parallel and perpendicular shock direction, which is in accordance with force interaction difference due to the lattice arrangement and interaction mechanism between atoms. The results of such difference are corresponding to the plasticity variation with lattice orientations. (2) An independent tensor is found to be in charge of stress distribution in elastic shock propagating across a single grain interface. This tensor has uniform style and similar coefficients for different materials with the same lattice arrangement, presenting a kind of generality. (3) The coherent predictability and accuracy of stress distribution tensor for FCC lattice are validated by simulation results for shock impacting on a single grain interfaces at different velocities and lattice arrangement orientations, indicating the intrinsic property of the interaction between shock and lattice atoms.

Helium diffusion in carbonate minerals is important for studying the physical and chemical properties and dynamic processes of Earth’s degassing. This paper discussed helium incorporation and diffusion mechanism in crystals of calcite and aragonite based on density functional theory calculations. The diffusion pathways, activation energies (E_a), and frequency factors (v) of helium under the surface and mantle condition were calculated. Calculations show an apperant anisotropy of helium diffusion in calcite, with more energetically favorable directions along a(b) axis. The moderate anisotropy of helium diffusion is showed in aragonite, in which the diffusion rate along c axis is slower than that along a axis. Under high pressure conditions, the activation energies of helium diffusion in aragonite increase with pressure. The closure temperature for calcite crystal varies from −54 ℃ to −25 ℃ in the direction [010], and for aragonite varies from −12 ℃ to 23 ℃ in [100]. Aragonite may be more retentive for helium than calcite under surface condition, which agrees well with previous experimental studies.

Based on first-principle calculations and the structure prediction method CALYPSO of particle swarm optimization algorithms, phase transition behaviors and physical properties of IrSb in the pressure range of 0–100 GPa have been systematically studied. At ambient pressure, the space group of $\alpha $-IrSb phase with cubic structure is P6₃/mmc, in consistency with experimental results. A new cubic structure, $\beta $-IrSb phase, is found at 16.4 GPa with the space group of C2/c. When the pressure is above 76.5 GPa, the space group becomes P-1. The phonon dispersion shows that $\alpha $-, $\beta $- and $\gamma $-IrSb phases have no virtual frequency in the whole Brillouin zone, thus the three phases are dynamically stable. Calculated results show that the formation enthalpy of three phases are less than zero, indicating that all the three phases have the thermodynamic stability. Band structure calculations show that all the three phases have the overlapping of conduction bands and valence bands near Fermi surface, thus are metallic phases. The charge transfer of each phase is calculated and discussed, in which Ir atoms are the acceptor and Sb atoms are the donor.

In order to solve the problem that the existing acceleration reconstruction methods rely on a large number of test data, this paper compares the performances of two different acceleration reconstruction methods, the damped sine and the wavelet. The evaluation of the quality in reconstructing shock response spectrum (SRS) is transformed into the minimum optimization problem of the matching degree of the reconstructed SRS with the target spectrum. The adaptive genetic algorithm (AGA) is applied to the optimization problem of SRS reconstruction for the first time. This paper compares the performances of three different AGAs in time domain reconstruction and optimization of SRS, which are crossover first, mutation first and uncertain-order AGAs, and compares them with the genetic algorithm (GA). Numerical tests show that AGA’s optimization results are much better than GA’s, and the results obtained by uncertain-order AGA are the best among the three AGA methods, through which all frequency points are within the tolerance range of (–3/+6)dB. This research provides support for further improving the response simulation accuracy of spacecraft structure under pyrotechnic shock loads.

This paper describes an artificial interface compression technique for the multi-fluid piecewise parabolic method (PPM). The proposed approach enables the simulation of interfaces between compressible multi-fluid flows with high density ratios and strong shock waves. A compression source term incorporated both interface compression and density correction is added to the mass conservation equation. The compression source term is solved in pseudo-time steps using the interface compression technique and the advection part is solved by multi-fluid PPM. The Strang splitting algorithm achieves second-order accuracy by combining the solutions of the advection operator and the interface compression operator. Numerical tests on the interaction of shock waves with interfaces in compressible multi-fluid flows reveal that multi-fluid PPM combined with the artificial interface compression technique can effectively prevent the smearing phenomenon, which is often observed at the contact interface. For long-time simulations, artificial interface compression with interface sharpening can constrain the thickness of the diffused interface to a few cells and maintain the interface profile. This artificial interface compression technique works well with multi-fluid PPM and the effect is obvious. It is a significant step in the accurate simulation of the collapse of air cavities in water, which involves strong rarefaction waves.

The smoothed particle hydrodynamics (SPH) method is used to simulate the deformation of penetration of granite at large strain and high strain rates. In order to describe the nonlinear deformation and failure characteristics of the projectile and target, the Holmquist-Johnson-Cook (HJC) constitutive model, damage model, Johnson-Cook (J-C) constitutive model and Grüneisen equation of state for granite are introduced, in which the projectile and the fortifications are discretized into Lagrangian particles. In simulation of three-dimensional penetration process of granite targets by self-made program at the speed from 0 m/s to 4000 m/s, we compare and analyzes the penetration results of steel balls under different projectile conditions. The curve of the penetration depth with the penetration velocity is fitted in solid penetration, semi-fluid penetration and fluid invasion. The numerical results show that the penetration depth increases with the increase of the penetration velocity in the solid penetration interval ($ {v_0} < 1421\;\,{\rm{m}}/{\rm{s}} $). A decreasing trend is shown in the semi-fluid penetration interval ($ 1421\;{\rm{m}}/{\rm{s}} \leqslant {v_0} \leqslant 1700\;{\rm{m}}/{\rm{s}} $), while an increasing trend is shown in the fluid penetration interval ($ 1421\;{\rm{m}}/{\rm{s}} < {v_0} <1700\;{\rm{m}}/{\rm{s}} $) and gradually tended to reach the peak.

Aluminum-polytetrafluoroethylene (Al/PTFE) specimens with different aluminum particle sizes of 10, 30 and 200 ${\text{μ}}{\rm{m}}$ and different molding pressures were prepared by compression molding and sintering. The impact-initiation test was carried out with split Hopkinson pressure bar (SHPB), and the reaction of the reactive materials was recorded by a high-speed photography device. It shows that with the increase of molding pressure, the speed threshold of impact-initiation of the specimen increases and then decreases. When the particle sizes of aluminum powder is around 10 ${\text{μ}}{\rm{m}}$ or 30 ${\text{μ}}{\rm{m}}$, specimens with higher molding pressure can react with ignition delay time of 1000–1100 ${\text{μ}}{\rm{s}}$, causing a sudden drawdown of the speed threshold of impact-initiation; for the specimens with 200 ${\text{μ}}{\rm{m}}$ aluminum powder, the ignition delay time stays around 600 ${\text{μ}}{\rm{s}}$. The speed threshold of impact-initiation raises as the particle size of aluminum increases, under the same molding pressure. The impact ignition of the reactive material is related to the microscopic defects, the propagation of the stress wave in the SHPB device, the amplitude of the stress pulse and the destruction process of the material.

Quasi-static tensile/compression and SHPB (split Hopkinson pressure bar) compression tests were conducted in order to study the mechanical properties of steel fragments with different hardness. Furthermore, the fragments were launched by a ballistic gun at different velocities into a Q235A steel plate with finite thickness. The correlation between the mechanical properties and the failure mode of fragments was analyzed based on the ballistic test results. Combined with the dimensional analysis method, the empirical relationship of the ballistic limit velocity of the steel fragments with different hardness penetrating into the Q235A steel plate was obtained. The results show that the mass loss of the fragments decreases with the increase of the hardness of the fragments, while the residual length of the fragments decreases with the increase of the hardness. The penetration ability of fragments increases with the increase of the hardness. The residual velocity of the fragments with HRC36 was relatively higher than that with HRC20 after penetration. The predicted values of the determined empirical relationships agree well with the experimental results.

Shock wave propagation and bubble jet in the shallow water explosion near a rigid column are affected by many factors. Considering the influence of free water surface, water bottom boundary and rigid column, the coupling numerical model was established based on LS-DYNA, and the feasibility of numerical method is assured by comparison of simulation results and empirical results. The results show that the accuracy of numerical simulation can be better guaranteed if one-third and one-half of the explosive diameter as mesh size is adapted. During the shock wave propagation, the peak pressure in front of the column rises while the cut-off phenomenon causes during the shock wave pressure decreases, and the peak pressure behind the column decreases by approximately 50% while load duration increases. The jet is formed directivity to the column at the complete moment of the first bubble pulsation. The bubble impulse pressure increases most dramatically when the explosive is at a distance of explosive radius from the column, and the depth of the maximum impulse pressure is higher than the depth of explosive.

As the main energy absorbing component of bearing and collision in the automobile and aviation industry, the hat-section beam structure absorbs energy through plastic deformation of its own structure, which is the main criteria for previous safety design. Therefore, it is of great significance to study the deformation characteristics and energy absorption characteristics of the hat-section and thin-walled beam structure under impact load. In this paper, the axial dropping impact tests of DP780 and DP980 duplex steel with hat-section thin-walled beam structures are carried out with a dropping hammer designed by ourselves, and the maximum displacement, peak load, deformation modes and energy absorption are obtained. The results show that the plastic buckling of the upper part of the specimen is formed and the deformation of the lower part is unobvious for DP980 and DP780 hat-section beams under impact loads. The DP980 hat-section beam has less impact deformation and higher residual height, which can be used as the protection structure of anti-impact deformation. The DP780 hat-section beam has more wrinkles produced by final buckling deformation, and its impact time increases and the peak load is much lower, which can be used as the protection structure of anti-impact load. The energy absorption capacity of the DP980 hat-section beam is similar to that of the DP780 hat-section beam. The results provide the basis for the selection of anti-impact performance with thin-walled structure.

The deformation law and energy absorption performance of the multi-hierarchical sandwich structure under quasi-static compression have been studied by numerical and theoretical methods. The calculation formula of the critical failure load of the structure is established and compared with the numerical simulation results. The theoretical prediction is in good agreement with the numerical simulation results. Finite element models of the hierarchical corrugated core sandwich structure were established. The effects of core thickness on the deformation mode and energy absorption performance of secondary structure under quasi-static compression load were studied and compared with that of the primary structure.The results show that the energy absorption properties of the secondary core structure are significantly better than that of the primary core layer. As the thickness of the core increases, the specific energy absorption of the second order structure for single-layer is higher than that of the second order structure for two-layers and three-layers, and the specific energy absorption of the second order structure for two-layers is slightly higher than that of the second order structure for three-layers.