A variety of interesting physical phenomena such as semiconductor-metal transition, superconductivity, and high spin-low spin transition in FePSe₃ can be realized under high pressure. However, the current results of its crystal structures under high pressure are mainly based on theoretical research, and the uncertainty of its structure hinders the in-depth study of its physical properties. In this paper, the behavior of FePSe₃ under high pressure was studied by using diamond anvil cell, Raman spectroscopy, synchrotron X-ray diffraction and electrical transport measurement. The results clearly show that FePSe₃ undergoes three structural transitions in the pressure range of 0–60.0 GPa, completing a transition of LP–HP1–HP2–HP3. The two new high pressure phases, HP2 and HP3, were observed experimentally for the first time, and the possible space groups were discussed. The superconducting transition temperature measured in HP2 and HP3 typically decrease with increasing pressure, leading to a dome-shaped superconducting diagram. This paper provides important experimental support for further clarifying the pressure-induced phase transition behavior of FePSe₃.

Equations of state (EOS), combined with the partial differential equations of describing conservations of energy, momentum and mass, form a complete set of fluid dynamics equations on solving dynamic compression behaviors of material. Under dynamic compression, phase transition of material may lead to discontinuous changes of its internal energy, density, strength and other properties, and a multiphase EOS is needed to accurately describe these changes. An automated modeling code of multiphase equations of state (AEOS) is developed, which can construct multiphase EOS model in an automatic way and calibrate parameters of EOS models with a computer intelligent optimization algorithm. By applying AEOS to tin, we obtain three sets of multiphase EOSs. The theoretical results of all the three sets of EOSs are consistent well with the experimental results, which validates the good performance of the AEOS code. And we find that the isentropic release path of tin passes through the three-phase point of the β, the body centered tetragonal (bct), and the liquid phases, when tin is impacted to 17 GPa and then isentropically released to atmospheric pressure. In addition, this result can well explain the experimental phenomenon that tin ejection particles are in a solid-liquid mixture state under the very low impact pressure of 15.4 GPa. The good performance of AEOS insures that it can be widely applied to integrated digital scientific research platforms and scenarios of high-flux material property calculations in the near future.

In this study, for the muzzle brake with a side hole angle of 120° and the hole diameter of 16 mm used in a first-stage gas gun with a diameter of 50 mm, the flow field morphology is simulated, based on 3D unsteady Navier-Stokes equations and multi-region dynamic grid technology. The characteristics of the formation, development and attenuation of shock wave, as well as the brake efficiency, induced by different launch pressures are analyzed. The launching platform of the first-stage gas gun was built experimentally, and the muzzle brake efficiency was tested. The results show that the maximum deviation of the simulated brake efficiency is less than 1.25% compared with the experiment, and the dynamic development of the brake flow field highly agrees with the experiment. The brake efficiency increases linearly with the launch pressure. For the muzzle brake with a side hole angle of 120° and the diameter of 16 mm, when the launch pressure increases from 5 MPa to 10 MPa, the brake efficiency increases from 4.87% to 12.71%.

To study the dynamic mechanical properties of G550 cold-formed steel under high temperature and high strain rate, high-temperature synchronous controlled dynamic loading device (split Hopkinson tensile bar) was implemented. The medium strain rate tensile tests were also conducted with the high-speed hydraulic tensile testing machine. The constitutive model and the influence of temperature and strain rate on the flow stress were built and explored through the stress-strain curve and the microscopic analysis. The results show that G550 cold-formed steel has significant strain rate strengthening and temperature softening effects. In the specific high strain rate range (1000−1500 s⁻¹), the influence of temperature on the flow stress is more significant than that of strain rate. Then, a modified Johnson-Cook constitutive model of G550 cold-formed steel was proposed according to the temperature softening coefficient. This model can better describe the dynamic mechanical behavior of G550 cold-formed steel under high temperature and high strain rate, and can contribute to the finite element simulation of G550 cold-formed steel under high temperature and explosion impact.

The spallation behavior of the ductile metals is a process involving nucleation, growth and coalescence of voids, and the coalescence of voids is difficult to directly observe experimentally. In this paper, the finite element analysis method was used to study the coalescence behavior and competition mechanism among the voids in the process of the ductile metal spallation. Influences of the initial ligament distance, the void diameter, and the void location distribution on the void coalescence were discussed. Through the real-time statistics of the change in diameter during the growth of the voids, the starting time of the coalescence of the voids was quantitatively analyzed. Results show that when the initial ligament distance increases from 20 μm to 50 μm, the initial time of coalescence among the same voids increases continuously, and the accelerations of the diameter increase decreases from about 1.717 Gm/s² to 0.602 Gm/s². When the coalescence occurs between voids with different aperture ratios, small voids preferentially aggregate to big voids. Voids with an angle of 45° have the largest diameter growth acceleration about 3.179 Gm/s² in the growth stage, and the earliest coalescence occurs. For the coalescence among three voids, the calculation results show that the same voids with the same initial ligament distance aggregate and penetrate almost simultaneously, and the starting time of the coalescence between the voids increases with the increasing of the initial ligament distance. The aggregation of big voids to nearby small voids start later. Calculations in this paper reveal the mesoscopic physical process of void growth and coalescence, which is difficult to observe in spallation experiments, and have important reference value for the entire physical process and nature of the material spallation.

Carbon fiber reinforced polymer (CFRP) is gradually applied to the design of anti-explosion and anti-shock engineering of warships due to its excellent anti-penetration performance. In order to study the protective performance of steel-CFRP laminates under the action of shaped charge projectile, numerical models of the damage analyses of steel-CFRP laminates under air explosion of shaped charge were established based on the arbitrary Lagrangian-Eulerian (ALE) method. The load characteristics and corresponding damage mechanism to steel-CFRP laminates were investigated. According to equal surface density method, various forms of steel-CFRP laminates with CFRP as face plate, back plate and sandwich core layer were designed. The anti-penetration performance of laminates with CFRP at different positions was compared and analyzed through the deceleration of the shaped charge projectile head and the size of the laminate crevasse, and a better laying form was obtained. On this basis, the thickness of the laminate was optimized. The results show that the three-layer sandwich structure of CFRP-steel-CFRP performs the best protective effect, and its better thickness ratio is 4.0∶1.4∶4.0.

In the process of underground space development and construction, the blasting seismic wave induced by drilling and blasting is very important to the safety of underground pipeline. When the explosion is close to the pipe, the curvature of the wave front will have a significant impact on the blasting dynamic response of the pipe. In this paper, the wave function expansion method was used to study the dynamic stress concentration of pipelines under the blasting effect of cylindrical SH wave. The distribution law of the dynamic stress concentration factor (DSCF) of concrete pipe and PVC pipe was discussed. Then the effects of the distance from the wave source to the pipe axis r₀, the incident frequency of cylindrical SH waves, and the shear modulus ratio η of the pipe and soil layer on the DSCF of the pipe inner wall were also discussed. The results show that the distribution shape of DSCF of the inner wall of the concrete pipe is more sensitive to the frequency of cylindrical SH wave than that of PVC pipe. η is an important index affecting the concentration of dynamic stress in the pipeline. When the incident wave frequency is constant, the maximum DSCF of the pipeline increases with the increase of η. When η is constant, the maximum DSCF decreases with the increase of incident frequency. The distance from the wave source to the pipe axis influences the failure position of the pipeline due to the curvature of the wave front, but it has little effect on the maximum DSCF value.

The effect of crystal orientation on the void growth in face centered cubic (FCC) metal under impact loading was studied by adopting rate-dependent crystal plastic constitutive model. VUMAT subroutine was used to embed the rate-dependent crystal plastic constitutive model into the ABAQUS finite element software, and the growth behavior of a single crystal inner void, a bicrystal boundary void and a triangular boundary void was analyzed. The results showed that the void deformation pattern is related to three factors: crystal orientation, grain boundary position (relative orientation of impact loading direction and grain boundary) and loading direction. The relation between the crystal slip line model and grain boundary position can reflect the void growth direction. For intracrystalline voids, the closer the loading direction is to [011], the later the beginning of void deformation is, the greater the overall void deformation is. The closer the loading direction is to [111], the earlier the void starts to deform, the smaller the overall void deformation. For voids at grain boundaries, the location of grain boundaries affect part of the deformation of voids, but not the overall deformation. When the deformation direction of the crystal after the impact is intracrystalline, the grain boundary promotes the growth of voids along the intracrystalline. When the deformation direction is along the grain boundary, the grain boundary promotes the growth of voids along the grain boundary, and inhibits their growth into the crystal.

As the main force components of engineering structures, reinforced concrete slab are prone to damage when it is subjected to terrorist attacks or accidental explosions, and even cause the overall collapse of the structure. Therefore, it is of great significance to understand and predict the dynamic response of concrete slab under the action of explosions to enhance the anti-explosion protection ability of engineering structure and reduce the economic loss of life and property. In this paper, the numerical simulation data of ordinary reinforced concrete slab explosion test and parametric analysis based on the test in the literature in China and abroad are collected. The support vector machine and Gaussian process regression algorithms in machine learning regression algorithm are used to predict the maximum displacement of reinforced concrete slab under near-field explosion. The generalization performance of the model is analyzed by using the improved deviation-variance decomposition principle. At the same time, the machine learning model is compared with the existing prediction methods. Finally, the replacement feature importance and Sobol global sensitivity analysis method are used to explain the model from the local and global to increase the reliability of the model. The above results show that the generalization performance of the two machine learning methods is better, but the prediction effect of the Gaussian process regression algorithm is better than that of the support vector machine algorithm. At the same time, compared with the existing prediction methods, it is found that the machine learning method is better, with higher prediction accuracy and computational efficiency. The influence of different input parameters on the output results of the model is obtained, which realizes the interpretability of the output results and further increases its reliability.

Based on the Kong-Fang concrete material model proposed recently and the three-dimensional mesoscopic model, the penetration of a typical warhead into rock-rubble overlays was numerically simulated. The influence of interface modelling of rock-rubble overlays on the projectile overload (or acceleration), penetration depth and failure in concrete and rock was discussed by considering two well-known methods, i.e., the conode method and surface-to-surface contact method. Numerical results demonstrated that the interface between concrete and rock is overestimated when using the conode method, leading to a larger projectile acceleration and a smaller penetration depth. While the surface-to-surface contact method underestimates the interface effect, resulting in a smaller projectile acceleration and a larger penetration depth. Furthermore, the damage evolutions are different: it is continuous and develops along the interface of concrete and rock using the conode method, while it is only continuous in the area near the projectile and becomes discontinuous beyond this area. Finally, based on the numerical simulations, the practical suggestions for engineering design of rock-rubble overlays are given.

Aiming at the parameter missing problem of the shock initiation criteria of JO-9C(Ⅲ) explosive, parameters of three different forms of initiation criteria of JO-9C(Ⅲ) explosive were obtained by fitting the theoretical model and simulation results. The simulation models of shock initiation of JO-9C(Ⅲ) explosive with different sizes of titanium flyer were established by AUTODYN software, and the critical velocities for shock initiation of JO-9C(Ⅲ) explosive with different sizes of titanium flyers were obtained. The incident shock wave front parameters of JO-9C(Ⅲ) were calculated based on the shock initiation theory and critical initiation velocities of flyers. Combined with the three initiation criteria forms of p-τ, James, and Π-τ, the corresponding initiation criteria parameters of JO-9C(Ⅲ) explosive were fitted. The parameters fitting accuracy of the three initiation criterion from high to low is Π-τ, p-τ, James.

In order to accurately evaluate damage effect of underwater explosion shock wave on flat plate structure, the power parameter category with the effective impulse as the damage criterion is proposed, and a correction method considering the oblique incidence effect of the spherical wave is given. The new criterion compares the damage effect by the actual impulse of the plate structure, which is calculated by the momentum conservation equation. The new criterion is expressed in the joint form of peak pressure of shock wave, time constant and characteristic parameters of plate structure. With the help of simulation and literature data, the accuracy and applicability of the criteria are compared and analyzed. The results show that the new damage criterion has less error in evaluating the damage degree of flat plate structure, compared with single power parameters such as peak pressure of shock wave, specific impulse and energy flux density. In comparing the damage power of different explosives and predicting the damage effect under unknown conditions, the relative error of the new criterion is within 10%. The proposed damage criterion has good versatility when used to compare and evaluate the damage effect of underwater explosion shock wave on plate structure.

In order to explore the effect of constraints on the displacement law of broken ceramics and the penetration resistance of ceramic composite armor, the SPH-FEM (smoothed particle hydrodynamics-finite element method) coupling method was used to simulate the penetration of cylindrical bullets into ceramic/steel composite target plates. According to the failure response characteristics of the ceramic composite armor, the movement of the bullet and the change of the force on the bullet, the penetration process was divided into stages. Based on this, the influence of self-restraint, circumferential restraint and panel restraint on the displacement law of broken ceramics was analyzed. The influence of different constraint forms on the improvement of target protection performance was also studied. In addition, the results show that limiting the displacement of ceramic cone by imposing constraints is the key to give full play to the protective ability of ceramic composite armor. The application of the three restraint forms can reduce the lateral or longitudinal displacement of the broken ceramics, thus the penetration resistance of the ceramic composite target can be improved in a certain range.

Based on the velocity distribution of fragments of a metal hemispherical shell subjected to explosive loading, a new fragment recovery system with the combination of polyurethane, water and polyurethane medium was designed. The applied waterproof polyurethane foam barrel is made up of three symmetric components each with sidewall and bottom formed in a mold. The foam barrel is filled with water at the bottom, and an additional floating foam board with a certain thickness is applied in order to protect the outer recovery tank from the impact of fragments. The full recovery experiment with the foam barrel was carried out for a 45 steel hemispherical shell under central point explosion. The results showed that more than 88% fragments, which penetrated through the sidewall of the foam barrel and the floating foam board, could be directly recovered from the bottom of the recovery tank. The fragments have well discernible inner and outer surfaces. The floating board and water would effectively reduce the speed of formed fragments, and the bottom of the foam barrel remained undamaged. The newly designed recovery system can recover flying fragments close to 2π solid angles, thus is suitable for a large range of recovery experiments in which experiment device is on one side of the initiation point. This indicates the appearance type of experiment devices is extended. Besides, the new system reduces the total size of the combined attenuation layer to 70 cm in the vertical direction, thus providing a basis for further optimizing and reducing the size of the recovery tank. The characteristic distribution of the fragment, including mass, thickness and size, et al., was analyzed based on the recovery technique. The difference of characteristic between hemispherical shell fragments and cylindrical shell fragments was also analyzed briefly. Results show that the fracture strain of hemispherical shell is obviously less than that of cylindrical shell. This research provides useful experimental data supporting the study of fracture mechanism of expanding shells under different stress states.

To ensure safety and stability of the reconstruction and expansion of the newly built station under a nearly 50 years long-term service station, the structural status of main structure and auxiliary structure of an operating station and a reserved station is inspected. The construction deformation control standard is formulated referring to the structural state. The construction impacts of different expansion construction schemes are compared by using numerical simulation. Then the effect of an optimized scheme is verified in combination with an on-site implementation. The results show that there is a series of problems in the early-built station structure, such as decoration layer falling, concrete cracking, spalling, carbonization, steel corrosion, floor leakage, interval water accumulation and uneven settlement of deformation joints. For the CRD (central cross diagram) scheme, the maximum settlement of the reserved Line 3 station is 2.2 mm, and the surface settlement is 1.7 mm. For the PBA (pile beam arch) scheme, the maximum settlement of the station is 1.3 mm, and the surface settlement is 1.1 mm. The PBA method is recommended for the reconstruction and expansion project after a comprehensive consideration of various factors. After adopting the PBA construction scheme, the maximum vertical deformations of Line 2 and Line 3 structures are −1.28 and −1.01 mm, and the monitoring indicators are within the safety thresholds. The research results can provide a reference for similar subway station reconstruction and expansion projects.