The coexistence and interplay between spin, charge, orbital and lattice in electron correlated systems give rise to many interesting quantum phenomena, including unconventional superconductivity, colossal magnetoresistance, metal-insulator transition, topological phase transition, etc. While, as one of the most important issues in condensed matter physics, the mechanism of the unconventional high temperature superconductivity is still unclear up to now. In this paper, we report some new phenomena/physics obtained from our high pressure studies on three typically unconventional superconductors—heavy fermion superconductor, cuprate high temperature superconductor and iron-based superconductor, which include the correlation between magnetism and superconductivity, the influence of valence change on superconductivity, the discovery of superconductivity reemerging, the bi-critical points, and the universal transition from superconducting to insulating-like states, etc. These high-pressure experimental results on the unconventional superconductors are expected to provide useful information for a better understanding on the unconventional superconducting mechanism.

The quantum material GaTa₄Se₈ has attracted a substantial amount of attention because it exhibits a variety of interesting physical properties, such as metallization, J_eff quantum state, and topological superconductivity, and moreover, it is a medium for resistive switch and electric storage. However, controversies still exist on its insulating ground state, which hinders from understanding its various physical properties. The insulating ground state of GaTa₄Se₈ has been considered over a long period of time as a cubic symmetric structure with space group $ F\bar{4}3m $, and as a Mott-type energy gap driven by the combination of the spin-orbit coupling and the electronic correlation interaction. However, recent first-principles phonon calculations have shown that the cubic structure is mechanically unstable due to the presence of imaginary frequencies, and have predicted to be stabilized into the trigonal structure ($ R3m $) or the tetragonal structure ($ F\bar{4}{2}_{1}m $) through lattice distortion. In order to further investigate the ground state structure of GaTa₄Se₈, here we combine multiple experimental techniques such as Raman spectroscopy, X-ray diffraction, and resistance measurement to adjust its energy gap by pressure, and compare the experimental results with first-principles calculations. Our results show that the trigonal symmetric structure ($ R3m $) is more consistent with our experimental observations.

In many thermoelectric materials, SnTe has the same crystal structure as PbTe, but does not contain heavy metal Pb, which has attracted extensive attention in recent years. At present, the thermoelectric properties of intrinsic SnTe are not particularly excellent. There are some disadvantages: a large number of intrinsic Sn vacancies lead to high carrier concentration, which worsens the electrical transport performance; the energy splitting between the light band and the heavy band in the valence band is large and the band gap is too narrow, which is not conducive to the Seebeck coefficient participating in the electrical transport through the heavy band; the lattice thermal conductivity is large. In this study, SnTe doped with Ge was prepared under high pressure and high temperature conditions. The results show that the band structure and the electrical transport properties of SnTe can be tuned effectively by Ge doping. At the same time, Ge doping can modulate the microstructure of the SnTe, which induced the formation of fine grains and second nanophases then reduced the thermal conductivity. The maximum figure-of-merit is 0.35 at 700 K for Ge_0.2Sn_0.8Te.

Using diamond anvil cell (DAC) technique and Raman spectroscopy, we have studied the stability of PbCO₃ at high pressure. Solid NaCl, mixture of methanol-ethanol-water (16∶3∶1) and methanol-ethanol (4∶1) were used as pressure transmitting medium. The highest pressure in this study reached up to 24.5, 25.0 and 67.0 GPa, respectively. It is found that PbCO₃ undergoes three phase transitions at around 10, 15 and 30 GPa, respectively. In addition, the softening of the out of bending vibration mode belonging to ${\rm{CO}}_3^{2-} $ group was observed. By comparison with the Grüneisen parameters ($\gamma $) of PbCO₃ in different pressure-transfer media, the phase transition mechanism is slightly different, and the influence of pressure on lattice vibration is greater than that of ${\rm{CO}}_3^{2-} $ group, which is attributed to the larger distance of the Pb²⁺—O bond. PbCO₃ did not decompose or amorphized in the pressure range of 67.0 GPa, the highest pressure reached in this study. The observed PbCO₃-Ⅳ phase above 30.0 GPa is stable up to 67.0 GPa.

The structural stability of gibbsite $\gamma $-Al(OH)₃ was investigated under high pressure and shear stress conditions by using a rotating diamond anvil cell (RDAC) combining with micro-laser Raman spectroscopy and micro-beam X-ray diffraction. As increasing pressure to 1.5 GPa and rotating to 180°, gibbsite triggers a new structural change at room temperature. In the range of high-wavenumbers, the four peaks of hydroxyl vibration (3363, 3434, 3524 and 3618 cm⁻¹) disappear gradually, and two new peaks with different intensities appear at 3303 and 3560 cm⁻¹. In the range of low-wavenumbers, the intensities of Raman spectra are getting weaker and weaker, but the broad peaks of amorphism are not observed. Both of the double peaks (568, 539 cm⁻¹) of Al-O-Al deformation vibration and the shoulder peaks (321 and 307 cm⁻¹) of Al-O stretching vibration merge into one peak, respectively. However, the four vibration peaks of hydroxyl deformation vibration (1052, 1018, 981 and 922 cm⁻¹) still remain. In addition, further increasing pressure to 3.5 GPa and rotating to 360°, and finally decreasing to ambient pressure, two new peaks of hydroxyl stretching vibration in high-wavenumbers, and the peaks of Al-O-Al deformation vibration and Al-O stretching vibration in low-wavenumbers are still observed. Compared to the phase transition of $\gamma $-Al(OH)₃ under quasi-hydrostatic pressure conditions, the Raman spectra and phase transition pressure in this study reveal that the $\gamma $-Al(OH)₃ take place another new structure change under high pressure and shear stress conditions. The micro-beam X-ray diffraction spectrum of the quenched product reveals that the framework of (OH)-Al-(OH) octahedra of this new phase is still remain, but has a shorter distance between the layers of (OH)-Al-(OH) and a higher symmetry. This newfound structure change of gibbsite in this study mainly due to the inhomogeneous pressure distribution in the sample chamber (from 0.5 to 4.5 GPa). The investigation on structural stability of $\gamma $-Al(OH)₃ under high pressure and shear stress conditions is vital for us to identify the stability of hydrous minerals in the cold subduction slabs, and to derive the physical and chemical properties of slab and its subduction rates.

Plate tectonic activity is closely related to the lithosphere and is the physical source of major geological activities such as earthquakes, but its dynamic mechanism is not clear. This paper will explore the force source mechanism of plate movement by analyzing the influence of magma solidification in a high-pressure environment inside the Earth on the mechanical state of the lithosphere. The Earth as a whole is constantly radiating heat into outer space, and its interior is in a state of liquid-solid coexistence under high pressure and high temperature. The solidification process of molten magma has continued since the formation of the Earth, and this liquid-solid transition will result in density changes and latent heat release in the Earth’s interior, reducing the pressure and supporting force at the bottom of the rigid lithosphere. We found that the lithosphere is not strong enough to support its dead weight, and any pressure fluctuations at the bottom destabilize its mechanical structure. Due to the constraint of rigid and brittle lithosphere, the solidification of magma under high pressure in the Earth will inevitably lead to the change of the mechanical state of the lithosphere. Under the action of gravity, the interaction between plates intensifies, and local stress accumulation exceeds the strength limit of rocks, leading to fracture in the lithosphere. The accumulated stress is released in the weak zone of the lithosphere through geological activities such as earthquakes and adjusts itself to reach a new mechanical equilibrium. And plate boundaries are the weakest parts of the lithosphere, so there’s a lot of seismic activity. The above process is repeated over and over again, and this is where the driving force of plate movement comes from.

Py-FeO₂, Py-FeOOH and ε-FeOOH are important components of mantle and core-mantle boundary. Their physical evolution characteristics at high temperature and high pressure are important for understanding the composition, structure and dynamic process of mantle. The crystal structures and elastic properties of Py-FeO₂ and Py-FeOOH at 0−350 GPa and ε-FeOOH at 0−170 GPa were calculated by first principles in this study. The Py-FeO₂ and Py-FeOOH belong to the cubic crystal system, their lattice constants decrease gradually with increasing pressure. The ε-FeOOH belongs to orthorhombic crystal system, and its lattice constants decrease with increasing pressure, however, a and b axes bump up at 33 GPa, while c axis swoop at 33 GPa. The cell densities of Py-FeO₂, Py-FeOOH and ε-FeOOH increase with pressure, and the relative cell density among these three phases is Py-FeO₂ > Py-FeOOH > ε-FeOOH. The bulk moduli of Py-FeO₂, Py-FeOOH and ε-FeOOH increase linearly with pressure, and the shear moduli of Py-FeO₂ and Py-FeOOH increase linearly with pressure, but the shear modulus of ε-FeOOH mutates at 33 GPa. Py-FeO₂ has the highest bulk modulus, and Py-FeOOH and ε-FeOOH have almost the same bulk modulus at high pressures. In addition, Py-FeO₂ has the largest shear modulus, and ε-FeOOH has the smallest shear modulus. The compression wave velocities of Py-FeO₂, Py-FeOOH and ε-FeOOH decrease gradually with the increasing pressure, while the shear wave velocities of Py-FeO₂ increase gradually with the increasing pressure. The shear wave velocity of Py-FeOOH decreases with the increasing depth in the range of 0−2000 km, and the variation is small in the range of 2000−6000 km (5.8 km/s < v_s < 6.0 km/s). The shear wave velocities of ε-FeOOH mutate at 33 GPa (about 900 km depth). The wave velocity of ε-FeOOH is the lowest, while that of Py-FeO₂ is the highest. Based on comprehensive theoretical calculations, it is found that Py-FeO₂ and Py-FeOOH have the high density and low wave velocity characteristics, which are consistent with the properties of the mantle ultra-low velocity zone (ULVZs). Py-FeO₂ and Py-FeOOH may enrich and sink to the core-mantle boundary after formation, becoming the source of the ULVZs. The hydrogen bond symmetry of ε-FeOOH under 33 GPa may affect the crystal structure of ε-FeOOH, the atomic interactions of ε-FeOOH, and then the elastic properties and seismic wave velocity of ε-FeOOH.

In the high-temperature and high-pressure experiments, it is essential to know the pressure and temperature of sample as well as the temperature distribution inside sample chamber. Therefore, it is necessary to calibrate the pressure and temperature of the experimental assembly before using the high-temperature and high-pressure experimental device. Here we carried out the pressure and temperature calibrations experiments on 19 mm outer diameter sample assembly of the end-loaded piston-cylinder apparatus. We calibrated the pressure of sample chamber by using the melting curve of sodium chloride (NaCl) under high pressure. When the oil pressure of the oil cylinder drops significantly, the NaCl in the sample chamber melts; according to the temperature measured by the thermocouple at this time and the comparison of the melting curve of NaCl under high pressure published by the predecessors, the real pressure in the sample chamber was determined. The pressure calibration results show that there is a linear relationship between the real pressure and the nominal pressure. The double thermocouple method was used to measure the temperature in the center and upper part of the 19 mm outer diameter sample assembly chamber. It was found that the temperature in the center of the sample chamber was higher than the temperature in the upper part of the sample chamber. In addition, the temperature gradient in the sample chamber increases with increasing temperature and decreases with increasing pressure. The temperature gradient in the sample chamber during the second stage pressurization and heating is higher than the temperature gradient in the sample chamber of the first stage pressurization and heating experiment. The pressure and temperature calibration results obtained in this study are of reference value and guiding significance for future high-temperature and high-pressure experimental study using 19 mm outer diameter sample assembly.

The dynamic fracture toughness of branch staggered laminated biomimetic composites was studied by three-point bending dynamic impact experiments and numerical simulations. Firstly, the branched staggered laminated shell-like composite specimens were designed and prepared. A brittle rigid material and a rubber material were selected as the hard and soft phases of the composite, respectively. Next, the three-point bending impact experiments were carried out by the improved split Hopkinson bar device, then the effects of initial impact velocity, hard material aspect ratio and soft material layer thickness on the dynamic fracture behavior of composite specimens were discussed. Finally, the effects of different widths and impact directions on the dynamic fracture toughness and crack propagation of composite specimens were studied by numerical simulation using finite element software ABAQUS. The experimental results show that with the increase of the impact velocity and the ratio of length to width of hard material, the thickness of the soft rubber layer decreases, the crack tends to propagate along a straight line, and vice versa. With the increase of the impact velocity, the peak dynamic load and initiation time of the specimen also increase. The finite element simulation results show that the fracture toughness of the specimen increases with the increase of the width, and the crack tends to bypass the hard material and propagate along the soft rubber layer; using the impact direction designed by the experiment, the fracture toughness of the sample is higher than that in other directions.

The high-velocity impact tests were carried out on the basalt fiber cloth/Al-plate composite shields, the ballistic limit velocity was obtained in the range of ballistic impact velocity. The diameter of 2017 Al-sphere projectile was 3.97 mm, and the impact velocity of Al-spheres was varied between 1.49 and 3.65 km/s. The residual velocity of Al-sphere projectile penetrating thin Al-plate and basalt fiber cloth bumper was analyzed. Furthermore, the shielding performance of the basalt fiber cloth/Al-plate composite shields was studied based on the critical impact kinetic energy for the failure of the single Al-plate. The results show that the velocity reduction of the constant diameter projectile penetrating the same basalt fiber cloth bumper at different velocities is a constant when the projectile is not broken. The velocity reduction of the projectile decrease with increasing diameter. For the same areal density, the shielding performance of composite shield with aluminum plate as the first wall is better than that of composite shield with basalt fiber cloth as the first wall.

The dynamic response of unreacted solid TATB-based explosive PBX-14 under ramp wave compression up to 20 GPa was obtained with the magnetically driven loading technique and laser interferometry technique. The pressure-relative specific volume relationship and dynamic parameters, such as the high-pressure sound velocity and particle velocity relationship c_L=2.53+3.12u_p of PBX-14 under ramp wave compression from 0 to 20 GPa were calculated by the iterative Lagrange data processing method based on impedance matching modification. The one-dimensional hydrodynamic numerical simulation of this experimental process was carried out with the isentropic equation of state and dynamic parameters obtained from the experiment. The calculation results agree well with the experimental results, which verifies the correctness of the experimental method, data processing method, and selected physical models in this work.

Based on the Hashin 3D failure criteria, both stiffness degradation and interface delamination are adopted to model the damage evolution of the composites, a numerical study on the composite lattice sandwich and its foam-reinforce sandwich beams subjected to local impulsive load is performed to identify the effects of impulsive intensity and foam reinforcement on the dynamic response, failure modes, and energy absorption mechanisms. The numerical result is confirmed to have a great agreement with the previously experimental results. The results show the impact strength has a significant influence on the dynamic response, failure mode, and energy dissipation mechanisms of the beams. With the reinforcement of the foam, the composite sandwich beam undergoes a slower deformed response than the lattice sandwich beam, especially for the intensive loads. The compression and cracking of the foam core reduces the degree of failure and keeps the structural integrity, and at the same time effectively decreases the energy absorption ratio of other components, indicating a noticeable improvement of impact resistance of the foam-reinforce composite lattice sandwich beam to concentrated impact load.

As a typical impact resistant bio-material, shell shows excellent properties such as light weight, high strength and high toughness. In this paper, the finite element model of nacre-like brick and mortar structure is constructed and its dynamic response under the impact load of drop hammer is numerically simulated. The effects of the number of stacked layers, impact velocity and hammer type on the energy absorption performance of nacre-like brick and mortar structure are analyzed. The results show that the specific energy absorption of nacre-like brick and mortar structures under the five types of stacked layers increases first and then decreases; and the three-layer nacre-like brick and mortar structure has the largest ratio among the five types of stacked layer structures designed, the value of the specific energy absorption is increased by 10.8% compared with the single-layer structure. With the increase of impact velocity, the peak load and energy absorption of the structure increase slightly. Under the same hammer diameter, the cylindrical hammer is easier to penetrate the model than the hemispherical hammer.

Investigation of the influence of helium bubbles on the dynamic strength has drawn continuous attention. In this article, the phase field method (PFM) is applied to investigate the evolution of helium bubbles at an early stage in shock-loaded aluminum based on its advantage to describe the interface evolution. PFM is coupled with the crystal plasticity finite element method (CPFEM), which makes it possible to investigate the interaction between the helium bubbles and the collective behaviors of dislocation assembles. It is found that the heterogeneity of helium bubbles induces a local concentration of plastic deformation, which leads to a rarefaction wave along the propagation direction of the shock wave. From an energy perspective, it is inferred that both the growth of helium bubbles and the plastic deformation are driven by the strain energy, which indicates that these two processes may compete with each other.

Inspired by the microstructures of bamboo in nature, two new bionic honeycomb structures were designed based on topological derivation method by introducing inner tube and double diamond ribs on the basis of traditional round tube and hexagonal tube. The performances of the bionic honeycomb structures and the traditional honeycomb structures under quasi-static compression are compared, and the theoretical analysis model of the bionic honeycomb structures is established based on the simplified super folding element theory. On this basis, ABAQUS finite element software is used to simulate the crashworthiness of the new bionic honeycombs. The influences of the single cell configuration, the wall thickness and the angle of the double diamond ribs of the honeycomb on the crashworthiness of the bionic honeycombs are studied. The results show that the crashworthiness of the bionic honeycombs is better than that of the traditional circular honeycomb and the traditional hexagonal honeycomb. Compared with the traditional hexagonal honeycomb, the specific energy absorption and compression force efficiency of the new bionic hexagonal honeycomb are increased by 51.18% and 53.14%, respectively. The theoretical predictions on the average compression forces of the bionic honeycomb structures are consistent with the numerical simulation results, and the errors are less than 10%. The crashworthiness of the hexagonal bionic honeycomb is better than that of the circular bionic honeycomb. Moreover, the crashworthiness of the bionic honeycomb structure can be improved by increasing the wall thickness appropriately, or by increasing the angle of the double diamond ribs.

Fiber reinforced thermoplastic and metal laminates have received wide attention in the field of naval protection, due to the excellent impact resistance performance. Numerical study on the fiber reinforced thermoplastic and metal laminate was carried out, based on the dynamic response test data of the laminate subjected to blast load in a confined space and the mechanical performance parameters of fiber reinforced thermoplastic calculated by the representative volume element (RVE) method. The validity of the numerical method was verified by comparing the test results with simulation one, and the response law of the laminate was further analyzed by the simulation results. The numerical simulation method of the fiber-reinforced thermoplastic and metal laminates adopted in this paper has a certain significance for the study of the impact resistance of laminates, and provides a feasible idea for the further development of related research.

Inspired by the metal crystal structures, the improved face centered cubic (FCC) lattice material was designed. The finite element simulations were carried out through ABAQUS, both for body centered cubic (BCC) and FCC lattice materials subjected to quasi-static compression and dynamic impact (10−100 m/s), respectively. The energy absorption characteristic of these two lattice materials were quantitatively analyzed and compared. Moreover, the semi-empirical formulae for plateau stress and plastic energy dissipation under dynamic loading were proposed. The results show that when undergoing quasi-static compression, the energy absorption capability of FCC lattice is better than that of BCC lattice with the same relative density, while the normalized specific energy absorption is 2.6 times larger than that of BCC lattice when the relative density is 10.5%−10.6%. In addition, maintaining the same relative density, FCC lattice performs larger specific stiffness, higher energy absorption efficiency and better compression force efficiency compared with most of the common negative Poisson’s ratio materials and truss lattice materials.

Based on the detonation product state equation and the Rayleigh-Plesset equation, this paper proposed a numerical method for calculating the bubble pulsation period of underwater explosions. We can quickly calculate the bubble pulsation period of underwater explosions of different explosives. Compared with the bubble period calculation method using the JWL equation of state and the γ equation of state, the former has a smaller error (less than 3%) for TNT explosives. Additionally, by comparing the results of the RS211 explosive underwater explosion experiment, it is further verified that the numerical calculation method has good applicability for aluminum-containing explosives.

To address the problem of the after-effect of the enhanced shaped charge jet penetrating armor, the cone-shaped flat-topped conical copper-aluminum double-layer composite charge structure was designed. Numerical simulation of the jet forming and penetration process of the steel-aluminum interval target with this structure was performed using Euler dynamics software SPEED. And the influence rules of parameters such as the height ratio $\varepsilon $ of the inner and outer liner, the cone angle α of the liner on the compound jet forming and the penetration of the interval target plate were analyzed. The research results show that the head velocity of the compound jet declined first and then rose with the increase of $\varepsilon $. When $\varepsilon $=1/2, a coaxial copper and aluminum compound jet element with similar velocity can be formed, which is conductive to strengthening the after-effect after the interaction between the aluminum jet and the target. When $\varepsilon $ is 55°～60°, the middle section of the compound jet is a concentrated aluminum jet element, which is more conducive to the intensified explosive reaction after penetration. It is found that the simulation results of the optimized parameters of the compound liner structure are perfectly consistent with the experimental results published in the literature. This research results have a certain reference value for the enhanced after-effect shaped charge design.

In order to study the effect of charge decoupling coefficients on the extent of granite blasting damage, a particle flow code (PFC) blasting simulation method with mixed “dynamic” and “quasi-static” loads is proposed based on the joint action of blast shock wave and detonation gas, and then the numerical simulation of granite blasting process under six decoupling coefficients was carried out. The results show that the extent of granite blasting damage increases and then decreases as the decoupling coefficients increases; the number of blasting induced cracks under coupled charge is 9367, which increases to 24975 when the decoupling coefficient is 1.2, and then decreases to 292 when the decoupling coefficient is 2.0. Comparing to the damage pattern under coupled charge, the extension distance of blasting induced crack is obviously shorter when the decoupling coefficient is 1.4, which indicates that the quasi-static pressure of blast gas plays an important role in crack extension. According to the number of blasting cracks, the prediction model of rock blasting damage under different decoupling coefficients greater than or equal to 1.2 was established, and the fitting degree reaches 0.9808. The prediction model presented in this paper is of certain reference significance for practical blasting design.