High-pressure regulation has played an important role in enhancing the superconducting transition temperature (T_c) and revealing the competing electronic orders and superconducting mechanisms of iron-based superconductors. A large number of high-pressure studies have shown that different pressure conditions (hydrostatic vs. non-hydrostatic pressure) can make great differences in the physical properties of condensed matters under high pressure. To unveil the discrepancies of different high-pressure studies on tetragonal FeS, we performed high-pressure magnetic susceptibility and resistivity measurements on tetragonal FeS single crystal up to 11 GPa by using a piston-cylinder and a cubic anvil cell that can produce good hydrostatic pressures. It is found that its T_c decreases monotonically with increasing pressure with a slope of dT_c/dp≈−1.5 K/GPa, which indicates that the superconductivity can be completely suppressed at about 3 GPa. When the tetragonal-hexagonal structural phase transition occurs at about 4−5 GPa, the temperature-dependent resistivity changes from metallic to semiconducting behavior, and the resistivity shows continuous increase upon further increasing pressure. No second superconducting phase was observed up to 11 GPa, and our results thus do not support the conclusion that FeS has two superconducting phases at high pressure. Finally, in light of the structural information under pressure, we discussed briefly the underlying mechanism for the distinct pressure evolutions of the physical properties in FeS and FeSe.

The fundamental properties of condensed matter strongly depend on its microscopic configuration and electronic structure. High pressure can effectively reduce the distance between atoms, result in the rearrangement of electronic configuration and change the bonding mode, so that enabling the matter to exist in unconventional physical and chemical state, forming new structures, new phenomena and new properties that cannot be obtained under ambient pressure. In this paper, taking the main-group halogens as example, the abnormal physical properties of halogen compounds under high pressure are briefly introduced. Related studies have shown that the valence states, coordination, and bonding modes of halogen compounds under high pressure are different from those under ambient pressure. These studies not only enhance the basic understanding of halogen, but also broaden the view of high-pressure physics.

Thermoelectric material is a kind of functional material which could realize the conversion between thermal energy and electric energy. Silicon-germanium (SiGe) alloy is used in deep space exploration as a kind of high temperature thermoelectric material. In this work, P-doped n-type SiGe alloy was prepared by high pressure synthesis method. The electrical and thermal transport properties of Si₈₀Ge₂₀P_x (x=0, 1, 2) were characterized. The results show that the samples synthesized under high pressure have multi-scale defects. P-doping could optimize the electrical conductivity and Seebeck coefficient of SiGe alloy, the power factor of Si₈₀Ge₂₀P₁ sample is 100% higher than that of the undoped sample at 1050 K. Furthermore, the increase of P content leads to the decrease of lattice thermal conductivity, and the thermal conductivity of Si₈₀Ge₂₀P₂ sample decreases by about 80% at 1050 K. The thermoelectric properties of SiGe alloy are significantly improved, and the maximum figure of merit of Si₈₀Ge₂₀P₂ sample reached 1.1 at 1050 K.

In order to investigate the compressibility of cerium-lanthanum (CeLa) alloys in the γ phase and the effects of the strain rate on the phase transformation behaviors, two loading techniques, including both the powder-gun-driven planar impact and the magnetically driven ramp compression, are adopted to investigate the Ce-5%La alloys (the mass fraction of La is 5%). The elastic-plastic transition behavior, the equation of state in the γ phase, and the γ→α phase transition pressures, are obtained from the velocity profile measurement. It is found that isentropic compression waves can be generated upon planar impact into the CeLa alloy, which verifies that the CeLa alloy shows a theoretically predicted abnormal compressibility in the γ phase. Due to the abnormal compressibility, the strain rates of compression obtained from the diagnostic side of the CeLa alloys are close to each other, even though two different loading techniques are applied, as a result, the pressure of γ→α phase transition in the CeLa alloys is not sensitive to the loading strain rate. The addition of lanthanum into cerium alloys increases the pressure for the dynamic phase transition, showing the feature of phase transformation driven by 4f electron in strongly correlated systems.

In this study, the effect of ignition pattern on the wavelet features of rotating detonation waves (RDWs) is numerically investigated with Euler equations and two-step induction-reaction model. The influences of the size, the number and the spacing of the ignition zone were considered. The theoretical Chapman-Jouguet (C-J) detonation wave was used as the ignition zone, and different ignition patterns were obtained by changing the size of the C-J detonation wave. The numerical results indicate that the wavelet features of rotating detonation waves closely depend on the ignition zone size. Only the two-wave and the three-wave modes are observed for the single ignition zone with various sizes, and the relation between the quantity of RDWs and the ignition size is non-linear. For the single ignition zone with the same width, the occurrence probability of the two-wave mode is approximately greater than 80%, while the three-wave mode is a completely random phenomenon. The formation mechanisms of the multiple-wave modes can be summarized as follows: (1) the first RDW is directly produced from the initial C-J detonation wave near the top of the combustor; (2) the subsequent RDW is induced by the interaction between the compressed wave produced by the initial C-J detonation and the jet flow from the micro-nozzles. The quantity of RDWs increases with the quantity or the spacing of ignition zone, but their relations are both non-linear.

In order to study the propagation law of blasting seismic waves in general strata induced by underground engineering constructions, shear horizontal (SH) waves were selected as the research object and the stiffness matrix and dynamic balance equation of general layered strata were established based on elastic wave theory. The propagation law of plane SH waves in the soil-rock stratum was studied, and the influence of soil-rock impedance ratio, thickness of soil layers, frequency and incident angle of incident waves on the ratio of ground velocity to soil-rock interface velocity |u₁/u₂| was analyzed. Results show that the peak |u₁/u₂| decreases with the increase of the frequency of incident waves, and the secondary peak is obviously smaller than the first peak. In practical engineering, the focus is on the first predominant frequency of the soil layer; as the impedance of the soil layer increases, the high-frequency response becomes stronger and stronger, and it is also increasingly affected by the incident angle. When the soil layer is thin, the high-frequency response of |u₁/u₂| is more obvious, but it becomes smaller and smaller as the thickness increases. This indicates that the high frequency filtering effect of the soil layer increases with the increase of the thickness.

This paper aims to experimentally and numerically investigate the effect of perturbation on the detonation initiation. In a round tube with 90 mm inner diameter, a stable detonation is firstly failed by an orifice plate with the blockage ratio of 0.923, and then the small-scale perturbation created by a cylindrical obstacle with a 2 mm diameter is introduced to a position 0.5 m downstream of the orifice plate to study the role of the perturbation on detonation re-initiation. Three different obstacles with blockage ratio of 0.03, 0.04 and 0.07 can be obtained by changing the number of the cylindrical obstacles equal to 1, 2 and 3. PCB gauges are used to record the time-of-arrival of the detonation, from which the detonation speed can be calculated. The smoked foil technique is used to record the cellular structures. The experimental results indicate that the small-scale perturbation can significantly facilitate the detonation initiation, and the critical pressure can be decreased from 37 kPa to 25 kPa in the smooth tube. By analyzing the cellular structures, it can be found that the perturbation can enhance the cellular instability inducing the local explosion centers, which is the main reason causing the detonation initiation. Near the limit, the detonation initiation mechanism can be approximately quantified as D_H/λ>1, where D_H is hydraulic diameter and λ represents the cell size. In the simulation, the reactive Euler equations are used as the governing equations and two-step induction-reaction rate law is considered. The numerical results indicate that the disturbance with lower wavelength and amplitude can induce more transverse waves and enhance the cellular instabilities, facilitating the detonation initiation.

Cylindrical quasi-isentropic compression driven by explosive magnetic flux compression generator (MFCG) enables ultra-high pressure loading of low-density materials. To obtain the optical properties of the compressed sample, a new vacuum light-guide probe structure using metal vacuum tube as the optical transmission channel is proposed to avoid the influence of loading pressure on the optical measurement path. In order to evaluate whether the optical diagnostic channel of the vacuum light-guide probe is closed in the MFCG quasi-isentropic loading experiment, the compression characteristics and light transmission characteristics of the cavity of the high-density metal vacuum tube under cylindrical implosion quasi-isentropic loading were analyzed and experimentally tested. In the experiment of compressing water conducted on the single-stage MFCG device CJS-100, through the comparative analysis of the measurement results of the inner shell velocity of the Ta tube and the theoretical calculation results, the inner diameter of the Ta tube with an outer diameter of 3 mm and an inner diameter of 2 mm is compressed to 1.28 mm when the water is quasi-isentropic loaded to about 485 GPa. During this time, the optical signal transmission channels of the Ta tube cavity and the optical fiber and fiber probe inside the Ta tube remain open. The optical signal remains present for about 50 ns after the inner diameter of the Ta tube is compressed to 1.28 mm. The results show that the measurement of optical characteristics of cylindrical implosion loading samples is feasible by using vacuum light-guide tube made of high-density metal materials such as Ta, which provides a new technical way for the measurement of optical properties of high-pressure samples in MFCG driven quasi-isentropic loading experiments.

In order to study the mechanism for disk containment of high-energy rotor, with test rotor manufactured with precast cracks, containment tests are carried out using a high-speed spin tester, and the nonlinear explicit dynamics commercial software is used to simulate the containment process of the high-energy rotor. It is found that the impacted area and the edge material in the containment case are compressed and sheared respectively after the impact of the disk fragments by test and simulation results. If the local perforation failure does not occur, the penetration of the fragment is determined by the tensile strain energy of the impacted area and the circumferential extension of the case. Then taking some turbine starter disk an example, the thickness and material analysis of the containment ring are discussed. The design method of determining the allowable thickness of the containment ring by the critical containment thickness 1.15 times of the safety factor is proved. By comparing the containment capacity of different materials, it is concluded that using higher ultimate strength and elongation material to achieve significant weight reduction. This study has some significance to the design of the containment structure of the high energy rotor.

To reveal the fracture evolution mechanism and crack propagation law of water-bearing granite, uniaxial compression, Brazilian splitting and direct shear tests of granite with different water-bearing states were carried out. The mechanical and acoustic information of rock during deformation and failure were obtained. Combined with acoustic emission ringing count and the relationship between RA (ratio of rise time to amplitude) and AF (average frequency), the microscopic fracture characteristics of water-bearing granite under different test conditions were clarified. The results show that water has obvious weakening effect on the compressive strength, tensile strength, shear strength and elastic modulus of rock. There are significant differences in acoustic emission activities of granite under different test conditions. Under uniaxial compression, the ringing count of acoustic emission surges near the peak stress point and the signal activity mainly occurs after the peak stress point. Under Brazilian splitting condition, the overall fluctuation of the ringing count of acoustic emission is relatively small. Under direct shear test, the ringing count surges significantly earlier than that of uniaxial compression and increases in a stepwise manner. The influence mechanism of water on shear cracks and tensile cracks of granite under different test conditions is similar, that is, the presence of water increases the number of tensile cracks in the rock and reduces the number of shear cracks. In uniaxial compression, tensile cracks show a trend of decreasing first and then increasing, while shear cracks are always decreasing. Shear cracks play a leading role in the direct shear test, and tensile cracks play a leading role in the Brazilian splitting. The research results provide some reference for further study on the fracture characteristics of engineering surrounding rock under different stress conditions.

The liquid silicon cement sheath samples were prepared, and the mechanical property testing experiments were carried out. Aiming at the problem of downhole failure of porous cement sheath, the porous “single-layer cement sheath” and “cement sheath-casing-cement sheath” models were established by using Flac 3D self-programming program to simulate the cement sheath fracturing process under the action of deep in-situ stress, and the deformation and failure laws of cement sheath under the coupling action of hydraulic pressure and in-situ stress were proved. The research shows that the single-layer cement sheath exhibits brittle failure under the action of stress, while under the protection of the outer casing and the cement sheath, the peak load of the cement sheath can be effectively increased. The research results provide a theoretical basis for revealing the failure mechanism of cement ring seal failure.

In this paper, the deformation behavior and energy absorption performance of the hierarchical structure were investigated based on the face-centered cubic hierarchical structure to change the amplitude and distance of the hierarchical structure’s straight beams and introduce the honeycomb structure layer. The quasi-static compression behavior of the proposed hierarchical structure was carried out through finite element methods (FEM) and experimental tests. Thermoplastic polyurethanes (TPU) as the raw material was used to prepare the experimental samples. The force-displacement curves obtained from the FEM and experimental tests are consistent with each other. Compared with the original face-centered cubic layered structure, the conclusion can be obtained: the new hierarchical structure has better energy absorption performance than the face-centered cubic hierarchical structure. The introduction of sinusoidal beams, the increase of plastic hinges, the adjustment of the angle between layers, and the introduction of honeycomb structure layers can enhance the energy absorption ability.

Sinusoidal corrugated thin-walled tubes are introduced as a core layer into polygonal thin-walled tubes, and quadrilateral, pentagonal and hexagonal sandwich tubes with corrugated cores are then obtained. First of all, their mechanical responses including energy absorption performance under quasi-static axial compression are studied by a combination of experiment, numerical simulation and theoretical analysis. Effects of the structural wall thickness and the wave amplitude of the core layer on the compression performance of the sandwich tube are analyzed, and the numerical simulation results agree well with the experimental ones. Then, the analytical solution for the mean compression force of the sandwich tube with corrugated cores under quasi-static compression is derived based on the simplified super folding element theory. The hexagonal sandwich tube subjected to quasi-static axial compression exhibits a deformation mode of progressive folding collapse. The theoretical mean compression force of the hexagonal sandwich tube agrees approximately with the experimental results with a relative error of 6.1%, while at a relative error within 9.8% compared to the simulation results. The specific energy absorption of the sandwich tubes with corrugated cores increases with increasing structure wall thickness and core-layer wave amplitude. For the same wave amplitude and wall thickness, the energy absorption capacity of the hexagonal sandwich tube is better than those of the quadrilateral and pentagonal sandwich tubes. Finally, with the objectives of maximum specific energy absorption and minimum initial peak force, multi-objective optimization is carried out on the core wave amplitude and structure wall thickness of the three types of sandwich tubes. The compromise and balance scheme for the maximum specific energy absorption and minimum peak crushing force is given, and the corresponding Pareto front is obtained.

In blasting excavation of deep rock mass engineering, the blasting effect is closely related to ground stress. Based on the rock mass-air fluid-solid coupling model, the blasting damage effect of rock mass under different in-situ stress and lateral pressure coefficient, and the variation rule of energy and peak particle velocity (PPV) threshold at inelastic boundary of rock mass were studied by combining theoretical analysis and LS-DYNA finite element numerical simulation. The results show that the damage range and crack propagation of rock mass are restrained by in-situ stress to a certain extent. The larger the in-situ stress is, the smaller the damage range and crack length will be. Under different ground stresses, the energy difference between the inelastic zone and the elastic zone decreases with the increase of the lateral pressure coefficient. When the lateral pressure coefficient is constant, the energy increases with the increase of ground stress. Under the condition of high in-situ stress, it is inaccurate to use the PPV threshold to determine the safety control of rock blasting.

In polycrystalline materials, the grain boundaries between grains with different orientations have a great influence on the dynamic response of material under shock loading. On the basis of the single crystal plasticity model, a polycrystal plasticity model containing grain boundary obstacle, geometrically necessary dislocations (GND) and back-stress is established by considering the microscopic mechanism of the interaction between grain boundaries and dislocations. Based on this model, the mechanical response of polycrystalline aluminum with Voronoi geometry under shock loading was studied through simulations. The results show that: (1) the grain boundary elements after the shock loading have a very high residual shear stress, while the shear stress of the element within the grain tends to be zero; (2) a large plastic deformation gradient is found near the grain boundary, resulting in a large number of GND and back stress distributed along the grain boundary; (3) the grain boundary obstacle caused by the slip discontinuity is the main factor causing the large amount of residual shear stress, while the GND and back stress have little influence on the extent of shear stress relaxation.

In order to explore the influence of projectile geometry on the dynamic mechanical response of graphene, two projectile designs with different shapes and different structural size ratios under the same shape have been considered using molecular dynamics simulation. The mechanical response of single/multi-layer graphene under impact was studied by characterizing the residual velocity of the projectile, kinetic energy consumption, the damage state of graphene and the propagation state of stress wave. The results show that the residual velocity and kinetic energy consumption of different shapes of projectiles impacting graphene can be roughly divided into three regions with the change of impact velocity. The impact of spherical and hemispherical projectiles is similar, but cylindrical projectiles exhibits large difference. The damage of graphene by cylindrical projectiles is stronger than those by spherical and hemispherical projectiles, and the fractal theory model can quantitatively describe the morphology of graphene holes. The “barrier effect” generated by the flat head of cylindrical projectiles can better explain the ballistic limit velocities of penetrating monolayer and bilayer graphene, which are lower than or close to those of spherical and hemispherical impact, respectively. For the same shape of hemispherical projectile, the penetration capability increases with the increase of the size ratio, but the enhancing effect brought about by the increase of the size ratio does not last continuously.

To realize the effect of the near-field shock wave enhancement of low collateral damage ammunition, this study proposes to add reactive material into the embedding layer of heavy metal particle in the sub-package low collateral damage ammunition to enhance the near-field overpressure and specific impulse. Static explosion experiments with different contents of reactive material were carried out, and the pressure curves of the near field and the mid-far field shock wave after the explosion were measured by the free field pressure test system. The results show that: after adding a certain content of reactive material into the heavy metal particle intercalation, the peak value of the overpressure and the specific impulse of shock wave at 37.5 times charge diameter are increased by 31.6% and 21.3%, respectively. According to the experimental results, the parameters of the Miller reaction rate model were determined by numerical simulation, and the law of energy release after-combustion reaction of the active element and the time-dependent change of the reactivity of the reactive material components were discussed. The duration of the secondary combustion can reach 300 ms under the ideal situation of sufficient combustion, and an optimal proportion of the range of reactive material content is likely exist. This research provides considerable development direction and application prospects for the regional enhancement effect of near-field shock wave and its engineering design of sub-packaged low collateral damage weapons.

In order to reveal the inhibition effect of solid explosion suppressors on acetylene-air premixed gas explosion, a 20 L spherical explosion test system was used to study the impact of typical solid explosion suppressors of SiO₂, Al(OH)₃ and NaHCO₃ on the explosion characteristics of premixed acetylene-air gas. The results showed that the low-concentration SiO₂ (less than 300 g/m³) can promote the explosion intensity of acetylene-air, while the high-concentration SiO₂ has a significant explosion inhibition effect. The explosion inhibition effect of SiO₂, Al(OH)₃ and NaHCO₃ on acetylene-air explosion increases in turn. The explosion inhibition effects of SiO₂ and Al(OH)₃ are dependent on the heat absorption and decomposition of particles (generating Al₂O₃ and H₂O). By contrast, the explosion inhibition effect of NaHCO₃ is dependent on the gas-solid-liquid three-phase suppression characteristics as the decomposition of NaHCO₃ produced Na₂CO₃, H₂O and CO₂. Therefore, the NaHCO₃ possessed the optimal effect of explosion inhibition.

Basis on a self-built gas explosion platform, the influence of hydrogen on methane-air explosion pressure is studied when the hydrogen doping ratio is 0%, 5%, and 10%, and the explosion suppression performance of single spherical and combined spherical porous non-metallic materials for methane-hydrogen-doped syngas is explored. The experimental results show that the explosion intensity can be effectively increased after the methane-air is mixed with hydrogen, and the maximum explosion pressure and pressure rise rate increase with the increase of hydrogen volume fraction, when the hydrogen doping ratio is 10%, the maximum explosion pressure (p_max) is 245 kPa and the maximum explosion pressure rising rate (dp/dt)_max is 3250 kPa/s. Spherical porous non-metallic materials can reduce the maximum explosion pressure and rising rate of syngas, and with the increase of filling length, the inhibition effect becomes more and more obvious. Compared with a single spherical porous non-metallic material, the combined spherical porous non-metallic material has a more remarkable effect on the explosion suppression of methane-hydrogen-doped syngas, and the explosion suppression effect is affected by the filling length. When the filling length is 40 cm, the maximum explosion pressure decreases by 51.02%, and the maximum explosion pressure rising rate decreases by 53.85%, and therefore its explosion suppression performance is increased by 78.58% compared with the single spherical porous non-metallic materials.

To ensure the construction stability of rectangular pipe jacking shield tunnel, taking the underground passage project on the east side of a railway station as the case study, the refined model of rectangular pipe jacking shield tunnel under high-speed railway in composite stratum was established using the finite element software ABAQUS. The effects of hard rock ratio, buried depth and pipe joint factors on surface displacement, track deformation, pipe joint convergence and safety factor were analyzed. The results show that with the increase of hard rock ratio in composite stratum, the decrease of buried depth factor and the increase of pipe joint factor, the extreme value of stratum displacement, surface settlement, the overlying high-speed rail track deformation and pipe joint convergence gradually decrease, the safety factor of pipe joint gradually increases, and the construction stability of rectangular pipe jacking shield in composite stratum becomes better and better. The research conclusion can provide reference for similar projects.