Search Results (156)

To enhance critical infrastructure protection against low-cost UAV impacts, this study proposes a novel ring lattice sandwich structure (RLSS) fabricated via an economical interlocking-assembly-brazing method. Its quasi-static compressive behavior is systematically investigated through experiments, numerical simulations, and theoretical analysis. Theoretical models for relative density and initial yield stress are validated against experiments, with errors of 7.1% and 6.6%, respectively. Quasi-static tests show that the one-layer RLSS exhibits a specific energy absorption (SEA) of 8.67 J/g, while the two-layer structure drops to 5.66 J/g due to inter-layer torsional instability. SHPB impact tests at strain rates of 750–1369 s⁻¹ demonstrate a pronounced strain-rate effect, with dynamic increase factors ranging from 1.14 to 1.43. Numerical simulations accurately reproduce the experimental deformation modes and reveal that multi-layer (2–5 layers) RLSSs reduce SEA by 46.9% compared with the one-layer simulated value of 9.43 J/g. Adding a 0.3-mm inner panel in simulations restores the crushing mode and raises the SEA of the two-layer structure to 7.19 J/g, surpassing the non-panel counterpart (6.03 J/g). Hybrid core configurations provide additional advantages: Mode I (ring–pyramid with inner panel) enhances total energy absorption with a limited ring-layer count, while Mode II (alternating layers) achieves minimal plateau stress fluctuation (PSF = 0.09). These findings confirm that the proposed RLSS, especially when optimized with thin inner panels or hybrid designs, offers great potential as protective cladding against impact and blast threats. Full article

This paper mainly investigates the ice-impact resistance of PVC foam sandwich beams for polar ship protective structures through low-velocity impact experiments and nonlinear finite element simulations. An experimentally validated elastic–plastic coupled model, accounting for ice crushing and large structural deformation, was used to examine the effects of core density and face-sheet thickness distribution on the ice-impact response of sandwich beams. Results show that the upper face sheet undergoes local indentation and global bending, the lower face sheet mainly bends globally, and the foam core exhibits local compression and overall bending, while compressive deformation accompanied by ice crushing and spalling occurs at the front part of the ice impactor. Moreover, the effective structural stiffness decreased during plastic loading as local indentation and core compression developed, whereas the unloading stiffness was higher than the effective stiffness during plastic loading. Energy dissipation primarily comes from ice crushing, face-sheet plasticity, and core compression. Increasing core density reduces deflection and core compression but increases peak force. Among the three face-sheet configurations examined at a constant total thickness, the configuration with a thinner upper face sheet and a thicker lower face sheet produced a smaller final deformation of the lower face sheet. This study provides a useful reference for ice-resistant design of sandwich structures in polar ships. Full article

Owing to transportation, installation, grid-connection, and maintenance requirements, nearshore offshore wind farms are often located close to busy shipping routes, substantially increasing the risk of ship–offshore wind turbine (OWT) collisions. To enhance the impact resilience of OWT support structures against ship collisions, a novel honeycomb sandwich fender is proposed for tower protection. Nonlinear transient analyses were performed using ANSYS/LS-DYNA to simulate a 5000 t ship traveling at 2 m/s and colliding with a 4 MW OWT supported by a single-column tripod foundation. The effects of rubber and aluminum foam cores on the crashworthiness and protective performance of the fender were compared. The results show that the rubber core stores collision energy through recoverable large deformation and releases most of the stored energy during unloading, resulting in pronounced energy restitution and prolonged structural excitation. By contrast, the aluminum foam core dissipates 7.5 MJ through cell-wall buckling, progressive crushing, and plastic collapse, corresponding to 75% of the initial kinetic energy of the ship. Compared with the rubber-core fender, the higher initial stiffness of the aluminum foam increases the peak contact force by 23.1%, from 13.0 to 16.0 MN. However, its irreversible energy-dissipation mechanism reduces the maximum tower-top displacement by 40.0%, from 1.25 to 0.75 m, and decreases the residual tower stress after three successive collisions by 25.0%, from 200 to 150 MPa. These results demonstrate that, despite transmitting a higher peak contact force, the aluminum foam fender provides more effective overall protection under the collision conditions considered because of its greater irreversible energy-dissipation capacity. Full article

Polymer-based sandwich structures have garnered significant interest as energy-absorbing protective materials. However, common damage modes in composite sandwich panels include matrix cracking, delamination, core crushing or core fracture, and debonding between the face sheets and the core. Among these, face–core debonding is one of the most prevalent failure mechanisms. This paper investigates a sandwich configuration designed to enhance blast resistance by incorporating a self-adhesive, stiffened polyimide foam (ASPI) into a steel–foam–steel architecture. The thermogravimetric analysis exhibits that ASPI foam obtained excellent thermal stability, and the residual mass retention at 800 °C was more than 36.2%. Experimental results show that at scaled distances of 1.077 m/kg^1/3 and 1.292 m/kg^1/3, the ASPI foam-based sandwich panels exhibited mid-span displacements as low as 8.5 mm and 6.7 mm, respectively. Under a scaled distance of 1.077 m/kg^1/3, the mid-span displacement of the ASPI foam-based sandwich structure decreased from 15.0 mm to 8.5 mm, representing a 43.3% reduction compared with that of the neat polyimide foam-based sandwich structure. Moreover, compared with neat PI foam, the ASPI foam exhibited superior adhesion to steel face sheets, and no interfacial debonding was observed after blast loading. To further elucidate the underlying damage mechanisms under blast loading, a well-validated finite element model was developed and employed. Complementary scanning electron microscopy (SEM) analyses were conducted to examine the microstructural morphology of the ASPI foam core’s cross-section and surface after blast exposure. This study presents an investigation of a lightweight, self-adhesive, high-thermal stability, blast-resistant polymer-based composite foam. Full article

Ensuring the sustainability of deep coal mining requires a comprehensive understanding of hydrogeological risks, particularly fault-induced water inrush, which threatens human safety, depletes freshwater resources, and causes irreversible ecological damage. This study addresses the sustainability gap in managing heterogeneous fault fracture zones by conducting coupled loading–seepage experiments on representative limestone, sandstone, coal, and coal–rock mixtures from the Zhaogu No. 2 Mine. Results demonstrate that seepage behavior follows the Forchheimer non-linear regime (E = 0.2–0.95), deviating significantly from Darcy’s law. We quantified that effective stress induces particle crushing and rearrangement, leading to a drastic porosity reduction (up to 97.52% in coal). Crucially, lithology dictates permeability evolution: coal and mixtures exhibit exponential decay, whereas sandstone and limestone follow quadratic functions. The fractal dimension of particles correlates negatively with permeability (R² > 0.95). These findings provide a quantitative framework for predicting water inrush channels, enabling proactive strategies to prevent catastrophic groundwater loss and ensure the long-term viability of mining operations. This research supports SDG 6 (Clean Water) and SDG 12 (Responsible Consumption and Production) by offering scientific guidance for balancing resource extraction with hydrogeological integrity. Full article

This study aims to clarify the mesoscopic damage evolution mechanisms of concrete subjected to rigid projectile penetration and provide support for the optimal design of high-performance protective structures. Based on the ABAQUS/Explicit finite element framework, a three-phase mesoscopic numerical model of concrete considering aggregate, mortar matrix, and interfacial transition zone (ITZ) is constructed. By combining the random convex polygon algorithm with the background mesh mapping technique, the intrinsic geometric features of stochastic materials such as crushed stone and pebble are accurately characterized. The effects of aggregate geometric characteristics, volume fraction, and projectile motion/geometry parameters (velocity, length–diameter ratio, curvature radius of the warhead CRH) on the damage evolution of the target, penetration depth, and velocity attenuation law are systematically investigated. The results reveal that increased aggregate angularity substantially enlarges both tensile and compressive damage zones and promotes crack bifurcation, which collectively enhances kinetic energy dissipation, reduces penetration depth, and accelerates projectile deceleration. Increasing the aggregate volume fraction can significantly enhance the anti-penetration resistance of the target. A high proportion of aggregate grains effectively enhances the structural toughness by blocking the crack propagation path. Penetration velocity, length–diameter ratio, and CRH are the core elements determining the penetration efficiency, and the increase in their values will lead to a significant increase in penetration depth and induce a change in the damage mode from local failure to large-scale cracking. The mesoscopic model and related conclusions established in this study can provide a theoretical foundation and numerical benchmark for the impact resistance design, optimization, and damage assessment of high-strength concrete protective structures. Full article

The development of potash deposits under complex mining and geological conditions requires the implementation of efficient geotechnologies, including backfilling of mined-out voids. Preserving the water-protective strata and preventing mining-induced accidents are impossible without accurate prediction of the stress–strain state of the backfill mass. Traditional models, based on the Mohr–Coulomb criterion, are unable to properly describe physical and mechanical processes occurring in crushed salt rock, including the transition from dilatancy to compaction and nonlinear hardening. This requires the application of specialized models such as the SRP model. The aim of this study is to investigate the mechanical response of crushed salt rock backfill material under complex loading conditions and to calibrate the parameters of the SRP model in order to improve the accuracy of geomechanical calculations. The shape of the plastic flow surface in the deviatoric plane was established, including both shear and cap components. A nonlinear dependence of the friction angle on mean stress was identified and described by a logarithmic function. The law of plastic hardening was determined, and a non-associated plastic flow rule was confirmed in the shear domain. The calibrated SRP model allows for predicting the backfill mass behavior with high reliability, which is a necessary condition for substantiating the parameters of safe potash mining. Full article

In this study, a hierarchical aluminum foam-filled thin-walled structure is proposed and its performance under axial impact is subsequently investigated. Two primary configurations are studied, namely, a hierarchical unit-cell structure (HUCS) and hierarchical multi-cell structure (HMS), respectively. Meanwhile, based on the experimental results, models are established to further investigate the effect of geometries, foam densities and impact velocities on the impact performance of the proposed structure. Finally, an improved simplified super folding element (SSFE) theoretical model which accounts for the constraint-induced strengthening effect of the foam filler is derived and a closed-form expression for the mean crushing force (MCF) is obtained. Compared with non-hierarchical counterparts (NHUCS and NHMS), the hierarchical designs exhibited superiority in reducing deformations and enhancing specific energy absorption (SEA). Compared to non-hierarchical structures, under an impact with identical energy, the HUCS shows a 12.7% reduction in maximum deformation and a 15.4% increase in SEA at the same deformation level. Meanwhile, the HMS reduces MCF by 17.2% and initial peak force (IPF) by 20.2% compared to the NHMS. Parametric studies reveal that wall thickness has a greater influence on final deformation than foam density. Numerical results are in good agreement with the proposed SSFE model within the baseline parameter range, with typical deviations below 10%, though larger discrepancies up to 23% are observed for certain extreme combinations of wall thickness and foam density. The hierarchical multi-cell collaborative design and the MCF prediction method presented here can provide practical guidance for designing high-efficiency impact-protective structures. Full article

Logging causes damage on residual trees, with differing characteristics and severities. The causal agent, as well as the size and type of injury, is influenced by the type of machines, the harvesting technology adopted, and the machine operator. This study descriptively documents residual tree damage observed in two sledge-yarding operations conducted under contrasting stand and operational conditions: a beech stand managed with a full-tree system and a Scots pine stand managed with a cut-to-length system. Two stands were selected: the harvesting intensity was 50% in the coniferous stand (salvage logging) and 20% in the deciduous stand (thinning). In each stand, six 20 × 20 m plots (0.04 ha) were delineated to assess residual tree damage. In the two observed cases, the beech operation showed a higher proportion of damaged residual trees, 32.2%, than the Scots pine operation, 5.3%. In the deciduous stand, bark injuries were mainly slight wood exposure (75%), whereas in the coniferous stand, crushed bark (42.9%) was most frequent, followed by slight wood exposure (35.7%). No concerning damage to seedlings was detected. In general, the number of damaged trees and the severity of injuries were considerably lower than those typically observed when extracting with a cable skidder, and especially with an adapted farm tractor. To reduce mechanical damage to residual trees, protective devices can be deployed around trees at risk of root and stem injury. Another effective measure is to financially motivate workers to implement environmentally sound forest operations. Full article

Auxetic cellular materials attract increasing attention for crashworthiness and impact protection due to their negative Poisson’s ratio (NPR). However, conventional double-arrowhead auxetic honeycombs (DAHs) with straight ligaments often exhibit limited energy absorption and unstable collapse under large deformation. In this study, a curvilinear hybrid auxetic honeycomb (CHAH) is proposed by replacing straight walls with smoothly curved ligaments and embedding a circular positive Poisson’s ratio subcell to provide symmetric support. The mechanical behavior of the CHAH is investigated through a combined experimental–numerical approach. Finite element simulations are validated by quasi-static compression experiments, and a parametric study is conducted to evaluate the influence of key geometric variables on specific energy absorption (SEA) and peak crushing force (PCF). Based on the validated simulations, a multi-objective optimization framework integrating optimal Latin hypercube sampling, radial basis function surrogate modeling, and NSGA-II is employed to optimize the structural parameters. Compared with the conventional DAH under identical material and volume conditions, the CHAH exhibits significantly improved deformation stability and energy absorption capability, with SEA increasing by up to 67.06% and a more stable plateau response. In addition, SEA and PCF can be effectively tuned by varying the geometric angles (θ₁, θ₂). Full article

Broken gangue in goafs exhibits complex mechanical deformation and seepage evolution under coupled loading and hydraulic action, which directly affects the hydraulic stability and water-hazard prevention of mining engineering. In this study, a systematic investigation was carried out to elucidate the evolution of seepage characteristics in a granular broken-rock assemblage under coupled hydraulic–mechanical loading. Four mono-sized specimen groups with particle-size ranges of 5–10 mm, 10–15 mm, 15–20 mm, and 20–25 mm were prepared. Using a modified rock triaxial–hydraulic testing system, nominal uniaxial compression tests, triaxial compression tests under different moisture conditions, and staged axial loading–seepage coupling tests were conducted. The results indicated pronounced particle-size effects: with increasing particle size, the nominal uniaxial compressive strength decreased (maximum reduction of 41.26%), while the crushing ratio increased (from 0.99% to 28.89%). The compression–densification process exhibited a staged evolution characterized by “slow increase–rapid increase–stable increase.” Water-induced deterioration intensified with increasing water content, and the compressive strength reduction reached 29.8% under saturated conditions. The evolution of seepage behavior was jointly governed by loading rate and particle size. Both pore pressure and pore-pressure gradient increased with loading rate. The permeability–porosity relationship was nonmonotonic, with an inflection occurring at a porosity of approximately 0.30–0.32, accompanied by an order-of-magnitude variation in the Darcy-flow deviation factor, indicating a progressive nonlinear deviation from Darcy behavior. These observations reflected a competitive mechanism involving “compaction-induced flow resistance increase–fragmentation and rearrangement–local channel regeneration.” Numerical simulations performed in COMSOL6.2 further confirmed, at the microscopic level, that the development of preferential local seepage channels and the expansion of stagnant-water zones were the fundamental causes of locally enhanced seepage capacity under an overall compaction background. The findings provide a theoretical basis for understanding water–rock interaction mechanisms in goafs and offer reference for mine water-hazard mitigation and groundwater resource protection. Full article

Due to high specific energy absorption, composite/metal hybrid multi-cell thin-walled tubes hold significant potential in the field of automotive passive safety. However, the material coupling effect enhancing SEA often elevated the initial peak crushing force, reducing crushing force efficiency and compromising occupant protection. To balance SEA and CFE, trigger holes were introduced as an induced deformation mechanism for hybrid tubes to reduce IPCF while preserving SEA, with the optimized perforated configuration yielding higher CFE than the non-perforated counterpart. A high-fidelity finite element model of the hybrid tube was developed and experimentally validated, and the influences of induced structural parameters on SEA and CFE were investigated. Given the strong nonlinear coupling between trigger parameters and crashworthiness, a multilayer perceptron surrogate model was constructed using 200 optimal Latin hypercube sampling samples (20 for validation). A Q-learning enhanced particle swarm optimization (QL-PSO) algorithm was adopted for optimization, with reinforcement learning dynamically adjusting PSO parameters to balance global exploration and local exploitation. Finite element simulations validated that the proposed method achieved a favorable SEA-CFE trade-off, with SEA and CFE improved by 12.02% and 16.39% respectively, outperforming reported configurations. Compared with standard PSO, QL-PSO exhibited superior search efficiency and inverse mapping accuracy, with 22% higher optimization efficiency and full compliance with inverse design performance targets. This study provided valuable guidance for the design of thin-walled energy-absorbing structures in multi-material vehicle bodies. Full article

Lightweight design and crashworthiness of protective structures are critical for battery safety in electric vehicles (EVs). This study addresses the limited research on cross-sectional shape design of high-strength steel double-cell roll-formed tubes (DCRFTs), widely used in EV bumper beams, battery boxes, and electric bus frames. A parametric design method is proposed based on three parameters: middle flange offset (o), upper deflection angle (α), and lower deflection angle (β). Under the constraints of constant cross-sectional height and enclosed area, this method systematically generates diverse shapes, including square, trapezoid, hexagon, re-entrant hexagon, and various hybrid shapes. Validated finite element models were employed to analyze the deformation modes and crashworthiness of DP980 steel DCRFTs under idealized lateral three-point bending with simple supports. The results indicated that the re-entrant hexagon section reduced maximum deformation (Disp) by 2.95%, peak crushing force (PCF) by 9.53%, and improved crushing force efficiency (CFE) by 13.88% compared to the baseline square section. The parametric study and sensitivity analysis confirmed that the offset (o) was the most critical parameter, contributing over 80% of the variance in Disp, PCF, and CFE. Multi-objective optimization using an RBF surrogate model and the NSGA-II algorithm yielded Pareto optimal solutions. Compared to the baseline, three representative solutions achieved Disp reductions of 11.83–25.10% and CFE improvements of 15.63–22.26%, each with distinct trade-offs among objectives. This work establishes a methodological framework for parametric cross-section design of roll-formed profiles; its extension to realistic boundary conditions will further facilitate practical EV protective structure design. Full article

Driven by the requirements of lightweight design and efficient impact protection, biomimetic hexagonal honeycomb structures have been widely used for energy absorption. However, their dynamic response and energy absorption behavior in underwater environments remain insufficiently understood. To address this gap, this study investigates the impact response and deformation mechanisms of aluminum honeycomb structures under fully submerged conditions relevant to marine engineering. We fabricated honeycomb cores from 5052-H18 aluminum alloy and developed a custom fixture for fluid–structure interaction tests under underwater drop hammer impact conditions. Using force sensors and high-speed photography, we characterized the dynamic impact behavior through load–time and velocity–time responses. Results demonstrate that drainage holes in the support plate serve a dual function: they enable the structure to maintain stable deformation and absorb energy underwater while also significantly enhancing energy absorption capacity. Specifically, the mean crushing force increases by 156.5%, and the energy absorption capacity increases by 333% compared to performance in air. This enhancement arises from the plastic deformation of cell walls and the additional energy dissipation induced by fluid–structure interaction. Overall, this study clarifies the dynamic compression behavior of aluminum honeycombs in underwater environments and demonstrates their potential for marine energy-absorption applications. Full article

As an effective technical approach for ecological environment protection in mining areas and coal resource recovery under buildings, railways and water bodies, solid backfill coal mining technology has been widely applied. When gangue was used as backfill material and placed into the goaf, its compression characteristics and crushing behavior were found to directly affect the control effect of overlying strata deformation. In this study, combined with the compression characteristics of gangue solid waste backfill materials, eight kinds of gangue solid waste backfill materials with different particle size gradations were adopted as research objects. From the perspectives of stress–strain compaction characteristics, the coupling relationship between internal crushing and acoustic emission (AE), relative density in the compacted state and particle size distribution, the hierarchical crushing behavior, and the AE response characteristics of gangue solid waste backfill materials under different gradation schemes were systematically revealed, and the optimal gradation parameters for different layers were determined. The results showed that the compaction process of gangue solid waste backfill materials could be divided into three stages: initial compression, rapid compaction and plastic compaction. During the compaction process, internal crushing was mainly concentrated in the middle layer. In the initial stage of the test, the AE intensity of the middle layer was measured to be higher than 78%, and the AE intensity remained above 50% in the compacted state. When the specimen was compressed to 220 mm, all eight gradation schemes exhibited the characteristic that the proportion of locating points and energy level in the middle layer were much higher than those in the upper and lower layers. With the continuous increase in axial pressure, the intensive area of crushing events was observed to migrate in the order of middle layer → upper layer → lower layer. With the continuous increase in axial pressure, the intensive area of crushing events was observed to migrate in the order of middle layer → upper layer → lower layer. The findings obtained in this study have provided a theoretical basis and experimental support for the gradation optimization of gangue solid waste backfill materials and roof deformation control in solid backfill coal mining engineering. Full article