Mineral resources on Earth are finite, but wood is renewable. Therefore, replacing limited industrial materials with modified wood remains a long-term pursuit. This study processed samples of three wood types, including balsa (Ochroma lagopus), basswood (Tilia tuan), and African blackwood (Dalbergia melanoxylon), with a large volume cubic press to compress these samples at room temperature under high pressure. The effects of high-pressure treatment on the air dry density, compressive strength, and elastic modulus of the three wood species were analyzed, and changes in their internal microstructures were observed using CT and scanning electron microscope. The results showed that the physical and mechanical properties of all three wood species improved. After high-pressure processing at 5.50 GPa, the density of balsa, basswood, and African blackwood increased by 239%, 112%, and 11%, respectively. Additionally, the surface hardness increased by 79%, 46%, and 15%, respectively, and the compressive strength increased by 33%, 9%, and 28%, respectively. Notably, the specific strength of compressed African blackwood (101.55 kJ/kg) approaches that of aluminum alloys (109.23 kJ/kg). The results demonstrate that African blackwood is lighter than ceramic materials. Furthermore, this wood offers superior electrical insulation and thermal insulation compared to aluminum alloy. Crucially, African blackwood possesses high specific strength, and this property gives it significant potential to replace aluminum alloy in numerous special environments. Such application supports sustainable development for future industries. In conclusion, this research opens new possibilities for high-value wood applications.

Multilayer sandwich composite structures have significant applications in impact protection. In particular, they demonstrate superior protective performance when subjected to impacts from explosive fragment particle clusters. Based on an analysis of the impact resistance and failure mechanisms of single-layer materials, this paper reviews the research progress regarding the dynamic mechanical response characteristics of composite structures under both single-particle and multi-particle impacts. The results indicate that metallic materials predominantly exhibit features such as plastic deformation, crack propagation, and localized thermal softening. By contrast, ceramics rapidly disperse impact energy due to their high hardness and propensity for brittle fracture. Meanwhile, fiber-reinforced composites achieve hierarchical energy dissipation through their continuous fiber network. Studies on multilayer sandwich structures show that high-speed particle impacts on the target plate have been found to induce phenomena such as localized stress wave propagation, micro-crack formation, and interfacial delamination. The mechanisms underlying impact resistance in these structures are complex. However, current research primarily focuses on the impact resistance of structures under single-impact conditions. The protective mechanisms under multi-particle impacts remain unclear, and the employed research methods are relatively limited. Experimentally, approaches such as the modified split Hopkinson pressure bar (SHPB) apparatus are predominantly utilized to achieve high-speed loading of particle clusters. Nevertheless, issues regarding secondary impacts and velocity limitations in these experiments have yet to be effectively resolved. In numerical simulations, the smoothed particle hydrodynamics-finite element method (SPH-FEM) coupling approach remains the mainstream method for investigating particle cluster impacts. However, concerns regarding the accuracy of these models still warrant further investigation.

In order to meet the high reliability requirement of velocity measurement in shock wave and detonation experiments, a new velocity measurement method named dual-wavelength laser interferometer was proposed based on wavelength division multiplexing/demultiplexing technique. A verification system was designed with 1550.0 and 1530.3 nm wavelengths, and the dynamic verification experiments under low- and high- speed conditions were carried out on the light gas gun. The dynamic experimental results show that the free surface velocity of the sample can be measured independently with a single optical fiber probe, and the velocity measurement results obtained at two wavelengths exhibit good consistency, with the relative deviation of the velocity within ±1.5%.

Aluminum alloys are widely used in aerospace, shipbuilding and high-tech fields due to their excellent mechanical properties. However, they often suffer dynamic impact loading during service. Study of their mechanical responses under dynamic loading conditions holds both theoretical and engineering significance. In this study, 6061 aluminum alloy serves as the research object. In-depth research is conducted through systematic experimental tests and numerical simulations to characterise the static and dynamic mechanical properties and the ballistic response of the alloy. The experimental results show that within the strain rate range of 0.001−3800 s⁻¹, 6061 aluminum alloy exhibits significant strain-rate strengthening effect. The flow stress increases by 18.5% with the increasing strain rate. However, its strain hardening behavior remains relatively stable under different strain rate conditions. Parameters of the Johnson-Cook constitutive model calibrated by the least square method can accurately describe the mechanical response at different strain rates. The ballistic experiment results show that the ballistic limit of a spherical projectile penetrating 6061 aluminum alloy target plate is 283 m/s, and the residual velocity has a good linear relationship with the incident velocity under the super-ballistic limit condition. The failure morphology analysis of the target plate reveals that the failure mode is related to the impact velocity. At low impact velocities, the overall deformation is dominated by composite stress. However, at high penetration velocities, it is mainly local shear failure. The finite element model established successfully reproduces the ballistic response and failure mode observed in the experiments, with an error of less than 5%, verifying the reliability of the fitted constitutive model parameters and numerical methods. Using an experimentally verified finite element model, the ballistic responses of spherical projectiles with different diameters penetrating a 6061 aluminum alloy target plate are studied. When the projectile diameters are 10, 8, and 6 mm, the ballistic limit velocities of the target plate were 283, 392, and 443 m/s, respectively. Therefore, under the condition of unchanged thickness of the target plate, the higher the projectile mass, the greater the ballistic limit velocity of the target plate. This study provides important theoretical basis and experimental data, and thus supports the engineering application of 6061 aluminum alloy under impact load conditions.

To explore the damage evolution law of gas-bearing coal under impact, a split Hopkinson pressure bar (SHPB) test system for gas-bearing coal was used to conduct dynamic compression tests on coal with gas pressures of 0, 0.5, 1.0, 1.5, and 2.0 MPa. Based on the energy theory, the deformation and failure processes of gas-bearing coal under impact were analyzed, and the influence of gas pressure on energy parameters of coal was discussed. Using the SMP strength criterion and Weibull distribution function, a dynamic damage constitutive model of gas-bearing coal considering gas-impact coupling damage was established by combining the energy consumption index. The results indicate that during the impact compression process, the energy curve of gas-bearing coal can be divided into a slow growth stage, an accelerated growth stage, and a stable stage. With the increase of gas pressure, the reflected energy of coal shows a linear increase trend, while the transmitted energy and dissipated energy show a linear decrease trend. The theoretical curve based on the gas-impact coupling damage constitutive model is highly consistent with the test curve, indicating that the model can accurately describe the damage evolution law of the entire stress-strain process of gas-bearing coal under impact.

In order to investigate the energy evolution and mechanical behavior of defective sandstone under uniaxial compression, the discrete element method (DEM) is employed. Effects of different rock bridge inclination angles and distances on the mechanical behavior of defective sandstone are systematically studied by DEM, and established a damage constitutive equation based on energy dissipation. The results indicate that the rock bridge inclination angle and distance significantly affect the mechanical response and failure modes of defective sandstone. Large inclination angles (60°, 90°) facilitate crack propagation along the direction of maximum principal stress, while small inclination angles (0°, 30°) increase the proportion of shear cracks, leading to different failure patterns. Additionally, the elastic modulus and compressive strength exhibit a “U” -shaped nonlinear characteristic with the variation of inclination angle and distance. Moreover, the energy evolution pattern depends on the rock bridge inclination angle. The total energy and dissipated energy first decrease and then increase with increasing rock bridge inclination angle, and peaking at 90°. The influence of rock bridge distance on energy varies with inclination angle. For angles less than 45°, the two types of energy decrease with increasing distance. For angles greater than 45°, the two types of energy first increase and then decrease. The three-stage characteristic of the elastic energy dissipation ratio can serve as a predictive indicator of the instability of defective sandstone. Furthermore, the energy dissipation damage constitutive model constructed based on dissipated energy can accurately describe the deformation and failure behavior of defective sandstone under different rock bridge parameters. This model has significant application potential in practical engineering, but it needs to be adjusted according to specific stress conditions to optimize prediction accuracy. The research results can provide theoretical references for disaster prevention in geotechnical engineering.

In order to effectively mitigate the destructive effects of impact ground pressure on hydraulic supports, a double-layer variable-diameter energy-absorbing component with enhanced energy absorption was proposed based on previous research on single-layer variable-diameter structures. Using the energy method, the energy dissipation theory of the expansion and reduction deformation of tubular components with different cross-sections was analyzed, and the bearing capacity formulas for stable diameter reduction processes under various combinations of corrugated and circular tubes were derived. Through numerical simulations, the energy absorption curves, bearing capacity curves, and deformation patterns of eight types of energy-absorbing components were obtained. Comparative analysis revealed that the double-layer variable-diameter energy-absorbing component structure (SBY-type), consisting of an inner corrugated tube and an outer circular tube, exhibited superior energy absorption performance. The influence of key structural parameters on the energy absorption characteristics was further investigated. Among these, inner tube thickness, outer tube thickness, corrugation radius, and inner chamfer angle of the base were found to have the most significant effects. A Latin hypercube sampling scheme was designed, and the parameters were optimized using a Kriging surrogate model coupled with a multi-objective particle swarm optimization algorithm. The optimal parameter combination was determined as follows: inner tube thickness of 6.0 mm, outer tube thickness of 2.9 mm, corrugation radius of 6.9 mm, and base chamfer angle of 40°. Subsequently, axial quasi-static compression tests were conducted to verify the accuracy and effectiveness of the numerical and optimization results. The results indicate that, the total energy absorption of the double-layer variable-diameter energy-absorbing component increased by 54.2%, the specific energy absorption increased by 55.6%, the average bearing capacity increased by 43.2%, and the load standard deviation increased by 59.5%. These enhancements demonstrate that the optimized component exhibits superior and more stable energy absorption performance, thereby improving the reliability of the yielding anti-impact process. This study provides an important theoretical basis and design reference for developing energy-absorbing components in hydraulic supports for deep roadway reinforcement.

To investigate the role of wave shapers in small-caliber shaped charges, the effects of aligning wave shaper parameters with those of center-holed liners on detonation product leakage and jet penetration performance were studied. Based on the regular oblique reflection theory of detonation waves, quantitative relationships between wave shaper parameters and detonation wave initial incident angles/pressure distributions at various positions on the liner surface were derived. Systematic analysis using LS-DYNA software was conducted to reveal the influence patterns of wave shaper diameter and height on jet formation and penetration performance. The results show that adding wave shapers to center-holed liners effectively increases the collapse pressure on the liner, suppresses detonation product leakage, enhances energy utilization efficiency, and improves jet penetration performance. Jet penetration capability initially increases and then decreases with the increasing wave shaper diameter. Wave shaper height exhibits a multi-extremum response effect on jet performance. The largest penetration depth of 158.17 mm into 45 steel targets was achieved with a wave shaper diameter of 6 mm and a height of 4 mm, representing a 17.21% improvement compared to structures without wave shapers. These findings offer valuable insights for designing small-caliber shaped charge warheads.

In view of the unclear attenuation law of shock wave in curved tunnel is unclear, the influence of radius and turning angle on shock wave propagation in curved tunnel was analyzed. It was found that its influence on the wave dissipation efficiency is limited, and the wave attenuation efficiency of curved tunnel is similar to that of direct turning tunnel with the same angle, which is basically less than 7.2%. In order to improve the wave attenuation efficiency of shock wave in curved tunnel, a new protective idea of constructing arc-shaped diffusion tunnels based on arc-shaped tunnels by setting up diffusion chambers was proposed. The influence laws of diffusion ratio and diffusion forms (inner diffusion, two-side diffusion and outer diffusion) on the wave attenuation efficiency of curved diffusion tunnels were also discussed. The calculation shows that curved diffusion tunnel can greatly improve the wave attenuation efficiency of shock wave, and the wave attenuation efficiency can reach 55.9%. Among them, the outer diffusion curved tunnel has the highest wave attenuation efficiency, followed by the inner diffusion type and the two-sided diffusion type. Moreover, the wave attenuation efficiency increases continuously with the increase of the diffusion ratio. As the peak pressure of the shock wave increases, the wave attenuation efficiency of the curved diffusion tunnel also improves, reaching up to 64.4%. When the peak pressure continues to increase, the wave attenuation efficiency of the curved diffusion tunnel slightly decreases but remains basically unchanged. The wave attenuation efficiency of the curved diffusion tunnel decreases with the increase of the positive pressure duration of the shock wave. When the positive pressure duration is 100 ms, the wave attenuation efficiency drops to 25.4%. However, as the positive pressure duration further increases, the wave attenuation efficiency of the curved diffusion tunnel remains almost unchanged.

This study addresses the challenge of excavating through heterogeneous tuffaceous sandstone formations in tunnel construction by proposing a novel energy-gathering slotting rock-breaking technique based on dynamic impact. Using self-developed geotechnical dynamic impact testing system, cylindrical tuffaceous sandstone specimens ($\varnothing $100 mm×50 mm) were prepared with 10 mm thick polyurethane pads adhered to one end. Radially arranged holes of 3, 6, and 9 mm in diameter were drilled into the pads, each fitted with six corresponding energy-gathering nails. Seven groups of tests were conducted under impact air pressures ranging from 0.35 MPa to 0.65 MPa to investigate the effects of varying impact energy and nail diameter on directional rock fracturing performance. The results show that as the impact pressure increases, the peak stress and energy absorption of the specimens rise significantly, with fracture patterns transitioning from primarily intergranular to transgranular cracking. The 3 mm nails were prone to local crushing and failed to produce effective through-cutting cracks, while the 9 mm nails caused blocky or pulverized failure under high pressure. In contrast, the 6 mm nails consistently induced stable, continuous, and directional fractures under various pressures, producing more transgranular cracks, and demonstrating excellent energy utilization efficiency. Scanning electron microscopy confirmed the strain-rate effect of impact: cracks were predominantly intergranular under low strain rates (low impact forces), and became transgranular under high strain rates. This technique leverages the compressive-reflective-tensile stress chain mechanism inherent in dynamic fracture mechanics to achieve controlled, directional rock breaking without explosives or liquid media. By properly matching impact parameters and nail diameters, this method can efficiently guide crack propagation along predetermined paths in deep, heterogeneous rock masses, offering a promising strategy for controlling over- and under-excavation in complex geological tunneling conditions.