Helium (He), the second element in the periodic table, is the most abundant element in the universe apart from hydrogen. It is widely accepted that He exists in the interiors of gas giant planets which holds the high-pressure conditions. Helium is extremely difficult to react with other elements to form compounds owing to its strong chemical inertness determined by the full-shell electronic structure. However, in recent years, several studies have shown that physical behavior of helium is not that simple under extremely high pressure, such as the predicted stable helium compound FeO₂He and the predicted water helium compound He-H₂O with anomalous atomic diffusion under high pressure. These results not only play a leading role in the discovery of new paradigm on chemical bonding, but also make a substantial step for the relevant researches in the fields of high-pressure physics, geoscience, and planetary science. This paper mainly introduces the progress on helium compounds at high pressure, focuses on discussing the physical mechanism of their stability, and provides prospects for future research on the design and discovery of new helium compounds under high pressure.

It has great importance for the blast-resistant design of the structures to study the dynamic response and damage failure of structural components under explosion loads. This work focused on analyzing the influences of the shock tube’s parameters on the loads at the end of the driven section. Based on the ANSYS/LS-DYNA, the numerical simulation of the shock tube is conducted. The accuracy of the finite element model, parameters values, and the numerical simulation method are verified by comparing the numerical simulation results, such as overpressure-time histories and the deflection response of the reinforced concrete slabs, with the experimental results. Furthermore, a shock tube with a size of 3 m×3 m at the end of the driven section is designed. The influences of the shock tube’s geometric parameters and its inner overpressure on the loads at the end of the driven section are analyzed. The results show that the peak overpressure and positive time duration increased with the increase of the length, diameter, and pressure of the driver section. The results also show that the peak overpressure and positive time duration increased with the decrease of the angle of the expansion section. Finally, the design method of the shock tube based on peak overpressure and positive time duration is given, which was verified by the designed examples.

To analyze the strain rate effect and its influence on the dynamic response of ultra-high molecular weight polyethylene (UHMWPE) subjected to hypervelocity impact, the stress-strain relation of UHMWPE at different strain rates loading were obtained through universal material testing machine and Hopkinson bar experimental system. Furthermore, strain rate effect on the hypervelocity impact response was analyzed by numerical simulation. The results show that the tensile modulus and strength increase with the rise of strain rate. With the increase of the strain rate sensitivity index, the energy absorption ratio of the protective structure against the projectile decreases at the beginning followed by an increasing trend.

To systematically study the mechanical properties of glass fiber reinforced plastics, the stress-strain curves and corresponding mechanical parameters of glass fiber reinforced plastic with strain rates of 0.001–0.1 s⁻¹ and 1128–1840 s⁻¹ were obtained by material testing system (MTS) and split Hopkinson tensile bar (SHTB). The results show that the glass fiber reinforced plastic exhibits significant strain rate strengthening effect under dynamic loading. Therefore, the dynamic increasing factor was introduced to describe the strengthening effect of strain rate on mechanical properties of glass fiber reinforced plastics. Scanning electron microscopy (SEM) was used to observe and analyze the damaged section, and it was found that the fiber bundle was flatly fracture under dynamic loading, rather than failed by pulling out under static loading. In addition, the results show that the fracture toughness of the fiber-matrix interface under dynamic tensile loading is higher than that under static loading. Finally, based on the dynamic tensile mechanical response of glass fiber reinforced plastic, a nonlinear tensile constitutive model considering damage was established by introducing the macroscopic damage accumulation. Compared with the experimental results, the model as a whole can be used to characterize the dynamic tensile mechanical response of glass fiber reinforced plastic.

To explore the relationship between energy release and failure mode of pegmatite gabbro under confining pressure, the dynamic mechanical properties under different confining pressures and different impact velocities were studied using split Hopkinson pressure bar and LS-DYNA simulation software, and the energy release characteristics and the failure laws under different confining pressures and strain rates were analyzed. The results show that there is no obvious plastic deformation stage under high confining pressure, and the confining pressure restrains the dynamic compressive strength under high strain rate, and the growth trend of the dynamic compressive strength slows down when the impact pressure is greater than 0.4 MPa in the specimen. The strain rate and the confining pressure have great significance for the energy and the failure mode of the specimen. With the increment of the confining pressure, the proportion of the reflected energy of the specimen gradually increases, while the proportion of the transmitted energy decreases. The energy consumption density increases with the increment of the strain rate, and there is an inflection point at the strain rate of 95 s^–1 (corresponding to 0.4 MPa of impact pressure). The energy consumption density under high confining pressure is greater than that under low confining pressure. The specimen under confining pressure usually has a certain angle on the failure section. LS-DYNA simulations showed the dynamic failure process of the specimen under confining pressure from microscopic point of view. The specimen is mostly shear failure under medium and low confining pressures, while under high confining pressure, the specimen has multiple shear cracks developed and penetrated, showing a composite failure mode.

Aviation aircraft inevitably encounter threat of hail impact during flight, which seriously endangers flight safety of aircraft. At present, impact characteristics of natural ice materials are still unclear, this paper studies mechanical properties of natural ice materials under different strain rates. However, natural ice has the characteristics of low density and high strength compared with artificial hail. According to the hail preparation standard ASTM F320-21 “Ice Impact Testing of Transparent Shells for Aviation and Aerospace”, icicle specimens containing cotton fiber with mass fractions of 0, 3%, 6% and 12% were prepared. The icicle specimens were subjected to compression experiments with strain rates of 10⁻⁴, 10⁻³, and 10⁻² s⁻¹ using a universal testing machine, and effects of cotton fiber mass fraction and strain rate on their compressive mechanical properties, as well as a relation between damage form and critical strain energy density change, were analyzed. The results show that the transparent icicles without cotton fiber transforms from ductility to brittleness at a strain rate of about 10⁻³ s⁻¹, and that the addition of cotton fiber increases the compressive yield strength of ice, resulting a phenomenon of “cracking but not breaking” during the compression process. Under quasi-static compression, less energy is required to convert to crack surface energy than to plastic energy.

To study the effect of water content on mechanical properties and energy damage of hard rock materials, the uniaxial compression tests were carried out on sandstone samples under different water contents. The test results show that with the increase of water content, the peak stress, brittleness index and elastic modulus of sandstone samples decrease, and the peak strain of sandstone increases. In the dry state, there is no obvious plastic deformation before failure, showing a significant brittle failure, while in the saturated state, there is a significant plastic deformation in the pre-peak stage, and a yield plateau before failure. The larger the water content of sandstone samples is, the stronger the energy absorption capacity is, the smaller the energy absorption rate is, but the more significant the energy dissipation phenomenon is. The smaller the water content of sandstone samples is, the larger the damage variable is at the time of failure, and the sandstone samples have a strong impact tendency at the time of failure in the dry state. The conclusions provide a theoretical reference for the stability control of surrounding rock in deep underground engineering.

To achieve the tunable plateau stress and energy absorption in porous grid structures, a design method for star-shaped structures with double stress plateaus was proposed. Three kinds of star-shaped structures with double stress plateaus were designed and fabricated. The mechanical behavior and energy absorption properties under in-plane compressive load were investigated through experimental tests, theoretical analysis and numerical simulations. It was shown that the star-shaped structures with double stress plateaus exhibit two distinct plateau steps in the load-displacement curves. The geometric parameters of the structure and the number of ribs have a significant effect on the structural deformation stability and the plateau stress. The theoretical predictions, experimental results and numerical simulations were in good agreement with each other. The plateau stress and energy absorption capacity of star-shaped structures can be effectively controlled by tuning the corresponding design parameters. To further improve the energy absorption capacity of the star-shaped structure with double stress plateaus, a multi-objective optimization method was performed using the mass and specific absorption energy of the structure as design variables. The radial basis coupling polynomial function proxy model and genetic algorithm (NSGA-Ⅱ) were used to maximize the specific energy absorption and minimize the mass of the structure. Compared to the original structure, the optimized structure has a 6.0% reduction in mass and a 21.5% increase in specific energy absorption.

A new type of circular chiral multicellular tube with different geometric structures was proposed, and its crashworthiness was analyzed under the condition of the same wall thickness and mass. The results show that the circular chiral multicellular tube has better crashworthiness than the traditional circular tube. Under the same wall thickness, the specific energy absorption and crush force efficiency of the present structure are 66.19% and 49.11% higher than the traditional circular tube, respectively. The circular chiral multicellular tube of CCMT7-20 (7 ribs, 20 mm inner circle diameter) has the best crashworthiness. Compared to the circular chiral multicellular tube of CCMT4-40 (4 ribs, 40 mm inner circle diameter) with the worst crashworthiness, the energy absorption of CCMT7-20 is 795.35 J higher, and its specific energy absorption and crush force efficiency are 30.83% and 22.87% higher, respectively. The parametric study of the effects of the number of ribs, diameter of inner circle and wall thickness on the crashworthiness of the structure shows that the energy absorption and initial peak force increase with the increase of the number of ribs, but the specific energy absorption does not change significantly with the increase of the number of ribs. The energy absorption, specific energy absorption and crush force efficiency all decrease with the increase of inner circle diameter. The increase of wall thickness will increase the energy absorption of the structure, but the initial peak force will also increase.

Additive manufacturing technology has promoted the development of composite materials and broadened the design space of composite structures. However, the dynamic mechanical properties of composite materials based on additive manufacturing still face problems such as lack of research methods and complex design processes. The split Hopkinson pressure bar (SHPB) experimental technique and ABAQUS finite element simulation were used to study the dynamic mechanical behavior of two-phase composites printed by light-cured 3D, combined with the principal component analysis (PCA) to establish composite structure datasets, and the relationship between the composite structures and the stress-strain curves were learned through a high-performance convolutional neural network (CNN). The research results showed that the finite element model containing interface elements was more suitable for simulating the dynamic mechanical response of composites, and the predictive performance of CNN could be improved by setting hyperparameters. Based on the structure, the trained CNN could quickly predict the dynamic stress-strain curve of the composites. This study provides a reference for the design and application of machine learning in the dynamic performance of composites.

Numerical simulations of polyurea/aluminum structures under blast loading were carried out to study the blast resistant performance of polyurea/aluminum composite (PAC) structures. The accuracy of the numerical models was verified by the test results in related literature. Under the condition of equal masses, the effects of structural layer number, volume fraction of metal aluminum in the structure, and position of polyurea layer on the blast resistant performance of PAC structures were investigated. Meanwhile, the energy absorption characteristics of PAC structures were analyzed. The results show that the PAC hierarchical structure is the best structure design under the same mass. Except for the four-layer structure with 90% aluminum volume fraction, the other structures exhibit better performance than the homogeneous aluminum counterpart. The single-layer structure with 10% aluminum volume fraction presents the most excellent blast resistance. For polyurea-coated structures, the shock resistance of polyurea coating on the rear surface of the structure opposite to explosion is superior. Internal energy absorption of aluminum plates provide the most contribution to the overall energy absorption. The proportion of internal energy absorption of aluminum layers first decreases, and then increases with the enhancement of aluminum volume fraction. The research results can provide a reference for the anti-explosion design of PAC structures.

In order to improve the in-plane mechanical properties of honeycomb structure, a hexagonal hierarchical structure is established based on the conventional hexagonal honeycomb structure. The presented hierarchical one is used to replace part of the cell layer of the conventional hexagonal honeycomb, thus form a new type of multi-order hierarchical gradient honeycomb structure. The impact response characteristics and energy absorption capacity of the in-plane hierarchical gradient honeycomb under different impact velocities are studied through explicit dynamic finite element method. The results show that the deformation mode of the hierarchical gradient honeycomb is related to the plastic collapse strength and impact velocity; the nominal stress-strain curves at the impact end and the fixed end are related to its deformation mode under different impact velocities. Different composite methods will lead to different plateau stress and specific energy absorption of hierarchical gradient honeycomb. Its plateau stress is 45.4%–63.8% higher and energy absorption is 10.8%–34.1% higher than that of the conventional hexagonal honeycomb under high-speed impact. The relative density will affect the energy absorption capacity of hierarchical gradient honeycomb.

Based on the hybrid cross-section design, 10 kinds of cross-section design of star-shaped hybrid multi-cell tube (SHMT) were proposed. The crashworthiness of SHMT under multiple impact angles was studied by numerical simulation. It is found that the connection mode of hybrid cross-section and the number of polygonal edges N have important influences on the energy absorption of SHMT. Under axial impact, SHMT with vertex connection (SHMT-V) is more sensitive to N. The specific absorption energy of octagonal SHMT-V (SHMT-V8) reaches 24.31 J/g, which is 71.86% higher than that of quadrangular SHMT-V (SHMT-V4). SHMT with midpoint connection (SHMT-M) has stronger mechanical response, and its crushing force is more than 30% higher than that of SHMT-V. Under oblique impact, the load-carrying capacity of SHMT decreases with the increase of the impact angle, and the crashworthiness of SHMT shows great uncertainty. Technique for order preference by similarity to ideal solution method (TOPSIS) was used to evaluate the crashworthiness of SHMT. The results show that SHMT-M8 is the optimal cross-section design. The research results of this paper can provide guidance for practical application and crashworthiness optimization design of thin-walled structures.

In order to reduce the waste of residual top and bottom pillars resources in the recovery process of Chaihulanzi gold mine, a numerical model of extrusion blasting was established based on LS-DYNA finite element software. According to the three minimum burden of 0.7, 0.8 and 1.0 m, and the three hole spacings of 0.8, 0.9 and 1.0 m, nine cases were designed. And the evaluation indicators of each case were obtained by analyzing the blasting crack propagation and pressure evolution, effective stress and effective plastic strain varying with time and ore damage during the blasting process. The fuzzy analytic hierarchy process (F-AHP) was used to construct the target relative superiority matrix and fuzzy judgment matrix, and the best blasting case was selected by a comprehensive evaluation. The results show that the minimum burden is 0.7 m and the hole spacing is 0.9 m, which is the optimal blasting parameter combination for extrusion blasting. The field test results show that the blasting effect is better with the optimized blasting parameters.

The net side bushing is an important part of the transformer. During operation, the cooling oil inside the bushing will explode due to insulation breakdown, which will cause great potential safety hazard to the transformer. Therefore, it is of great significance to carry out quantitative evaluation of the net side bushing explosion accident. In this paper, a two-dimensional transformer bushing model was established by nonlinear finite element software ANSYS/LS-DYNA with smooth particle hydrodynamics (SPH) method. The dynamic response of transformer bushing under internal explosion was simulated. And the influence of different parameters on the failure characteristics of bushing was analyzed. The instability time of bushing was evaluated by the stability judgment method based on the curves of radial particle velocity. The results show that under the action of internal explosion, the middle part of the bushing is first damaged under the combined action of tension and compression of the inner and outer surfaces, and the overall damage of the bushing shows a convex trend during the propagation of the shock wave. The high explosion equivalent, the existence of cooling oil and initial crack defects have a greater influence on the stability of bushing. The decrease of explosion equivalent can change the failure mode of bushing from bidirectional shear failure to tensile failure, and the influence on overall stability is also reduced. When the explosion source is located on the outer wall of the conductive rod, the shock wave radiated by the cooling oil not only makes the bushing instability time advance, but also causes the outer wall expansion damage range to become wider. The stress concentration and the decrease of effective wall thickness make the shear failure instability of bushing with initial crack defects develop rapidly.

In order to study the evolution mechanism of shale permeability under thermal-fluid-solid coupling, the effective stress-permeability model of shale is developed considering the impact of thermal desorption and effective stress and thermal expansion on shale permeability. The proposed model is capable of revealing the influence mechanism of sorption strain and thermal expansion strain on shale permeability. Based on the model and the elastic theory of porous media, the thermal induced desorption permeability model of shale gas reservoirs under uniaxial strain condition was established. The model can discuss the evolution mechanism of shale permeability with temperature and pore pressure. The validity and accuracy of the model was verified against the laboratory measurements of shale core permeability. The following results were obtained: (1) The thermal induced desorption permeability model can fit the permeability of Marcellus shale under constant pressure and variable temperature. (2) The evolution mechanism of shale permeability with pore pressure under constant temperature is explored. The evolution law of permeability under constant temperature is U-shaped. The rebound of permeability with pore pressure decrease is less obvious with the increase of temperature. (3) The evolution mechanism of shale permeability with temperature under constant pressure condition is analyzed. The evolution law of permeability with temperature under constant pressure condition presents an inverted “U” shape. The influence of temperature on permeability is less with the increase of pore pressure. (4) The sensitivity analysis of thermal desorption permeability model under constant temperature and pressure was carried out. The larger the Poisson’s ratio is, the larger the permeability ratio gradient is. The larger the pore volume modulus, the smaller the permeability ratio gradient. At constant pore pressure, when the linear expansion coefficient is larger than the critical value or the Langmuir bulk strain is smaller than the critical value, the permeability evolution does not show an inverted “U” shape. At constant temperature, when Langmuir strain is less than critical value, permeability evolution does not show “U” shape.