Energy evolution and fatigue damage of cemented coal gangue materials under triaxial stepwise cyclic loading

Recycling solid waste into artificial aggregates represents a promising approach for large-scale solid waste management and alleviating the shortage of natural construction materials. However, the preparation and curing processes play a decisive role in the performance of aggregates. To meet the requirements of early-age strength of aggregates and synergistic load-bearing behavior with hardened cement matrices, this study developed a novel solid waste-based artificial aggregate using steel slag(SS) and recycled concrete fines (RCF). Polypropylene fibers (PPF) were incorporated, and a combined process of compaction granulation and CO 2 curing was employed. The results show that the optimal performance was achieved with a mix proportion of RCF:SS = 60:40, 1% PPF content, and a compaction pressure of 89 MPa, which increased compressive and splitting tensile strengths by 152.68% and 81.81%, respectively. Energy evolution analysis further revealed that this mix proportion enhanced the total energy, elastic strain energy, and dissipated energy by 157.30%, 135.93%, and 203.72%, respectively. These improvements are attributed to the synergistic effect of fiber bridging and compaction-induced densification, which together enhance material toughness and energy dissipation capacity. Additionally, calcium carbonate crystals formed during CO 2 curing effectively filled internal pores and strengthened the fiber-matrix interface. In summary, This study introduces the incorporation of polypropylene fibers into steel slag-recycled concrete fines-based artificial aggregates, achieving synergistic regulation of their microstructure and mechanical properties through combined compaction and CO 2 curing. In perspective, this approach enables the high value integral utilization of solid wastes and provides an eco-friendly technical strategy and theoretical guidance for the production of high-performance, low-carbon artificial aggregates. • Solid wastes are integrally recycled into artificial aggregates by compact granulation and CO 2 curing. • Fibre addition into artificial aggregates improves the stress-strain properties of aggregates. • Reinforced artificial aggregates modify the stress-strain properties of cement matrix. • Energy evolution characteristics of cement specimens with reinforced aggregates are improved.

Rubber-iron interface separation using liquid nitrogen for material selective recycling and its mechanism.

Liquid crystals (LC) represent topological soft matter that spontaneously form assemblies of constituents and mesoscale textures to minimize free energy. Depending on boundary conditions, they exhibit transformable topological defects, whose study provides fundamental insights applicable to a wide array of disciplines. However, their three-dimensional (3D) structures and dynamics remain largely unexplored due to the subdiffraction limit length scales and submillisecond time scales characteristic of conventional molecular LCs. Here, we report a morphogenesis from conventional nematic tactoids to a unique flower-shaped morphology using a colloidal LC composed of Eu3+-doped LaPO4 nanorods. We demonstrate 3D orientational tomography based on polarized photoluminescence spectroscopy of the Eu3+ dopants, revealing dramatic topological and topographical modulations. We find that this morphogenesis is driven by a theoretically unexpected vertical anchoring of the nanorods on the substrate, which exerts conflicting boundary conditions and leads to a competition between elastic energy and relatively weak surface tension. Our results provide valuable insights into how energy balance in topological matter can be modulated by tuning physicochemical properties of its building blocks.

For soft robotic systems to emulate the adaptive behaviors of natural organisms, integrated systems with both high compliance and multimodal sensing are essential. However, existing soft robotic designs often struggle to simultaneously achieve large deformability, high force output, and stable real-time multimodal perception. Here, we report a precompressed flexoskeleton soft actuator integrated with a self-powered flexible bimodal sensor for enhanced actuation and multimodal perception. The developed self-powered bimodal sensor enables the simultaneous detection of distance and pressure, thereby allowing soft robots to perceive both noncontact proximity information and contact stimuli with good operational stability and durability. To further support this sensing platform, a flexoskeleton derived from a trimmed spiral surface was incorporated into the actuator and assembled in a precompressed state, thereby constraining radial expansion and promoting deformation through the release of stored elastic energy. The actuator delivered a blocking force of 17.28 N at 70 kPa while maintaining a bending angle of 30.5°, and also supported multidirectional bending and modular assembly. The integrated bimodal sensor combines noncontact triboelectric proximity sensing with contact piezoelectric pressure sensing, enabling self-powered discrimination of approach and touch events. In the proximity sensing mode, the open-circuit voltage increases from 0.24 to 0.71 V as the distance decreases from 25 to 5 mm. In the pressure sensing mode, the device produces up to 5.98 V and 325 nA under an 80 N load, together with good operational durability. Benefiting from the synergistic integration of self-powered sensing and structural actuation, the system demonstrates adaptive interaction in serial manipulators, plant-inspired predatory grasping in parallel soft grippers, and programmable gait perception in tripedal soft robots. This work provides a feasible strategy for deeply integrating self-powered multimodal sensing with soft actuation and highlights the potential of functional sensing materials for intelligent soft robotic systems.

To jump, locusts (Schistocerca gregaria) use a latch-mediated spring-actuated (LaMSA) mechanism in their metathoracic legs, which gradually stores and then rapidly releases elastic energy, propelling them into the air. This system consistently results in a head-up tail-down pitch of the body immediately after take-off, caused by a thus far unknown underlying mechanism. In this study, we aimed to test the hypothesis that head-up tail-down angular rotation is a product of the locust's centre of mass being positioned off-centre to the force vector produced by the metathoracic legs, therefore shifting the centre of mass forwards should counterbalance any torque acting around it. This was achieved experimentally by attaching a small mass, ranging from 3.4 - 13.6% of the locust's body mass, to the head of a locust, before filming it jump to a target substrate. The resultant angular velocity from these jumps decreased as the mass added increased, with a mass equivalent to 10.2% of the body mass resulting in the complete elimination of angular velocity and therefore an entirely linear jump. When mass added totalled 13.6%, negative angular velocities were recorded (head-down tail-up). This was matched with a corresponding decrease in the rotational energy percentage of each jump's total energy budget, and a slight decrease in linear velocity for the largest added mass. These findings strongly support the theory that locust's do not independently control their body pitch at take-off, and that changes to the body mass distribution can counter it.

This work investigates crack evolution in AISI 316L steel borided by powder-pack process at 1223 K for 2 and 6 h. Microscopy, X-ray diffraction (XRD), and nanoindentation confirmed the formation of FeB/Fe2B composite layers whose hardness and Young's modulus increased with treatment time. Spherical indentation tests using a 3 mm indenter produced circular cracks in both systems, with more pronounced damage in the 6 h layer due to higher elastic energy storage and stress concentration within the coating. Finite element modeling in ANSYS, using the SMART Crack technique, accurately reproduced the indentation imprint geometry and the stress fields governing the mechanical response under spherical indentation, showing good agreement with the experimentally observed surface imprint. The findings demonstrate that the thicker and stiffer layer formed after 6 h promotes deeper crack propagation toward the Fe2B/substrate interface, whereas the thinner 2 h layer confines damage mainly within the FeB phase with no evidence of interfacial failure. These results provide relevant insights for the design and performance prediction of brittle composite layers subjected to concentrated loading.

Precipitation hardening is a well-known strategy that can raise the yield strength of alloys to well over 1 GPa, including at 77 K, but is less potent in offering strain hardening than twinning/transformation-induced-plasticity (TWIP/TRIP) mechanisms, which have been essential for the high ductility and fracture toughness of established cryogenic alloys. Here we demonstrate an innovative strategy to tailor the coherent nanoprecipitates by purposely designing negative-curvature interfaces (NCIs). This morphological control uses the geometric curvature and curvature-gradient effects to generate additional local stress, high elastic energy density, and substantial strain gradients to make NCIs prolific sources of dislocation nucleation. The proliferation of partial dislocations builds up ultra-dense hierarchical stacking-faults dynamically all over the deforming volume, substantially enhancing strain-hardening and toughening. The resulting NiCoCrAlTa alloy exhibits excellent cryogenic mechanical properties, achieving a high yield strength of 1.26 GPa, a product (~90 MPa%) of ultimate tensile strength (~1.80 GPa) with tensile ductility (~50%) and a fracture toughness of 213 MPa·m1/2 at 77 K-representing a record-high combination among all reported alloys to date. Our interface design strategy may be applicable to all precipitation-hardened alloys, transforming the precipitates from merely passive strengtheners to active and tunable agents regulating the plastic flow.

SiO2 nanofluid has significant potential for weakening coal mechanical properties and improving coal seam water injection efficiency, while prewetting time critically governs its modification outcomes. Accordingly, this study systematically investigated the effects of nanofluid prewetting time on coal mechanical performance, energy dissipation, and fracture propagation. Furthermore, Langmuir adsorption theory and Young's equation were employed to elucidate the fluid dynamic mechanism underlying time-dependent structural weakening of the modified coal. Results demonstrate that nanofluid prewetting treatment significantly reduces dynamic contact angles on coal surfaces and effectively enhances hydrophilicity. Nanofluid prewetting diminishes coal resistance to deformation, with the maximum reduction rate occurring at 2 h prewetting, corresponding to the lowest elastic modulus and peak stress alongside intensified lateral expansion. Post-treatment cumulative and maximum ring-down counts decrease substantially, indicating that internal cracks slide and propagate more readily during loading, thereby alleviating instantaneous elastic energy release upon failure. Moreover, fracture development reaches its maximum at 2 h prewetting, with failure mode transitioning from tensile-dominated to shear-dominated behavior. Nanoparticle adsorption on coal surfaces initially increases and subsequently stabilizes with prolonged prewetting time. However, prolonged prewetting time leads to aggregation and deposition of the nanofluid. The channels for water infiltration become narrowed. The enhancement of wetting modification is thereby restricted. In summary, prewetting time modulates nanoparticle adsorption and aggregation behavior, thereby influencing coal water absorption and structural weakening degree, ultimately determining the failure mode transition of the modified coal. The research findings provide foundations for optimizing prewetting time in coal seam water injection.

Traditional acoustic energy-harvesting devices, constrained by their linear operating mechanisms, struggle to simultaneously achieve broadband capture of low-frequency sound waves and efficient electromechanical conversion. This study proposes a novel acoustic energy-harvesting meta-surface (AEHMS) capable of achieving acoustic energy collection through the coupling of a nonlinear Helmholtz resonator and an auxetic structure. This meta-surface exhibits subwavelength characteristics (thickness ∼ λ/12), with its core design philosophy centred on achieving physical cascading and synergy between acoustic and elastic functions: The Helmholtz resonator (HR) leverages its nonlinear acoustic response at high throat amplitudes (characterized and optimized via the Melnikov method) to broaden the acoustic energy capture bandwidth and surpass the energy input limits of linear systems; while the auxetic structure leverages its unique geometric deformation properties to convert the resonator-concentrated acoustic energy into high-density, uniformly distributed elastic strain energy, significantly enhancing the electromechanical conversion efficiency of piezoelectric materials. Experimental results demonstrate that at a centre frequency of 250 Hz and 100 dB sound pressure level, this AEHMS achieves an open-circuit voltage of 1.33 V (31 times higher than that of conventional piezoelectric beams) and an output power of 56.64 µW. This device has pioneered a novel theoretical approach for developing highly efficient, ultra-thin low-frequency acoustic energy-harvesting devices.

Conventional elastic wave metamaterials are typically constrained by fixed structural configurations, which limits their ability to achieve reconfigurable and application-specific wave manipulation. To address this challenge, this work propose a mechanical-acoustic interaction (MAI) paradigm for mechanically programmable elastic wave control, in which acoustic functionalities are reconfigured through reversible switching between bistable mechanical states. The proposed acoustic dome metamaterial (ADM) consists of modular bistable units, where the peak and valley configurations serve as two mechanically programmable states without relying on electrical, magnetic, or thermal stimuli. By spatially encoding these bistable states, the band structure and transmission characteristics of the metamaterial can be reconfigured, enabling programmable control of elastic wave propagation, attenuation, and energy localization. Numerical and experimental results demonstrate low-frequency vibration suppression, reconfigurable waveguiding, and defect-state-enabled energy localization governed by mechanically encoded state patterns. Moreover, a one-press programming strategy is introduced to improve programming efficiency and reproducibility at the system level. These findings establish MAI as a physically intuitive and scalable mechanism for elastic wave programming, offering new opportunities for reconfigurable acoustic metamaterials and intelligent acousticdevices.

Plants can move rapidly without muscles, as seen in the Venus flytrap's snapping lobes-a long-standing puzzle in plant biomechanics. Trap closure involves an elastic instability, but the active mechanical driver has remained elusive. Using in situ hydraulic and mechanical measurements, we identified the motor driving this transition. Closure occurs too quickly to be explained by water transport, revealing a distinct, nonhydraulic mechanism: a rapid (about one second) softening of the epidermal cell wall, releasing elastic energy stored in the trap. This represents the fastest modulation of wall mechanics reported in plants. Our finding reveals a mode of plant motility based on dynamic tuning of material properties, suggesting principles for muscle-free, bioinspired actuation.

Frenkel's cohesive model predicts an ideal elastic strain limit of ~10% for strong solids, a bound upheld in conventional materials. We demonstrate that such consistency breaks down in van der Waals (vdW) solids, challenging established strength theories. In situ tensile tests, combined with first-principles calculations, reveal unexpected localized decohesion failure at only ~3% strain in graphite and ~2% in h-BN along the interlayer direction-well below defect-controlled limits-defining their intrinsic elastic limits. This localization phenomenon is absent in MoS2, GaSe, and 3D crystals. We identify flexural phonon instability as the trigger for a cascade of strain localization, creating periodic nanogaps to release elastic strain energy. This dynamic instability redefines the intrinsic elastic limits of vdW crystals and opens pathways to tailor their structural/transport properties via strain engineering.

This study investigates the dynamic failure mechanisms of underground reinforced concrete (RC) dome bunkers subjected to both surface and subsurface blast loading, addressing a gap in literature regarding 3D monolithic geometries. A high-fidelity numerical model was developed using the Coupled Eulerian-Lagrangian (CEL) method in Abaqus/Explicit, incorporating the Johnson-Holmquist II (JH-2) constitutive model for concrete and the Mohr-Coulomb model for soil. The framework was validated against numerical and experimental data, achieving less than 5% deviation in near-field peak pressures. Parametric investigations assessed the influence of burial depth, charge orientation, and shell thickness. Results reveal a critical “geometric vulnerability” to lateral blast vectors, where horizontal detonations induced 75% more concrete volume loss than equivalent overhead blasts due to the bypass of the dome’s compressive arching action. Furthermore, a counter-intuitive “Stiffness-Damage Paradox” was identified: increasing shell thickness from 0.5 m to 1.25 m exacerbated damage under specific impulsive loads. Analysis of internal energy histories indicates that rigid, thicker shells trap elastic strain energy, leading to brittle comminution, whereas compliant shells facilitate soil-structure interaction and plastic dissipation. These findings suggest that ductility and geometric efficiency, rather than pure mass, govern survivability in underground protective design. However, readers are cautioned that the manifestation of this stiffness-damage paradox is subjected to the specific structural compliance, soil acoustic impedance, and explosive conditions investigated herein, highlighting the critical need for coupled SSI analysis in protective design.

To investigate the mechanical properties and damage evolution of fissure sandstone under the interaction between water and fissures, this study performed uniaxial compression tests on sandstone specimens with different water conditions (dry, natural, and saturated) and fissure angles (0°, 30°, 45°, 60°, and 90°). The experimental results indicate that peak strength decreased markedly with increasing water content, with reductions of 28.68%–53.99% under saturated conditions relative to dry conditions. In contrast, peak strength increased progressively with fissure angle. Crack initiation stress and crack damage stress exhibited similar trends. Based on the normalized ratios of characteristic stress, two damage evaluation indices, and , were proposed to characterize the weakening effect of fissures on rock bearing capacity during the crack initiation and crack propagation stages, respectively. The energy evolution results show that the strain energy corresponding to characteristic stress decreases significantly with increasing water content and generally increases with fissure angle. In addition, this study introduced a warning coefficient λ based on the ratio of elastic strain energy to dissipated strain energy to identify precursor information associated with rock failure. The results show that λ increased with water content and varied with fissure angle in an M-shaped pattern, with significant peaks at 30° and 60°. Under saturated conditions, water exerted the strongest effect on mechanical parameters at a fissure angle of 0°, while the overall effect remained relatively small at 30°. These findings provide a valuable reference for risk assessment and disaster prevention in geotechnical engineering.

Many viruses have evolved remarkably intricate polyhedral shells capable of undergoing symmetric transformations in response to external stimuli to initiate payload release. So far, such deployable auxetic nanostructures are not available in the synthetic realm. Here we present a nanoscale Jitterbug transformer realized by a DNA origami structure that can reconfigure its conformation upon chemical and optical signals while maintaining a Poisson's ratio of -1. By combining mechanical design principles with molecular dynamics simulations, we design the DNA Jitterbug to form a compact octahedron that stores elastic energy and spontaneously transitions into an expanded cuboctahedron by releasing it. DNA transformers are demonstrated to act similar to viruses that can create nanopores on lipid membranes and regulate payload release into vesicles. Integrating programmable DNA self-assembly with free-energy-guided mechanical design, this work provides a pathway toward adaptive nanomaterials with potential in synthetic organelles and stimuli-responsive nanodevices.

HighlightsWhat are the main findings?A microseismic-energy–Benioff-strain–Weibull-damage-based characterization method for hydraulic fracturing is established, which can represent the heterogeneous weakening state of the target roof in a FLAC3D finite-difference model.Numerical simulations indicate that a high-damage weakening zone forms ahead of the goaf-side working face, reducing the strength and local bearing capacity of the fractured horizon, thereby altering the mining-induced load-transfer path.What are the implication of the main findings?Hydraulic fracturing transforms continuous high stress and high energy zones into localized and dispersed distributions, weakening the high static-load and high-energy-storage state of the coal-rock mass ahead of the working face.The rockburst prevention mechanism of roof hydraulic fracturing relies on bearing-structure reconstruction and load-path adjustment under the control of the heterogeneous damage zone formed in the fractured horizon.Directional long-borehole hydraulic fracturing is an important technique for controlling rockbursts induced by hard roofs. Its effectiveness depends primarily on whether fracturing-induced damage can modify the roof-bearing structure and thereby regulate stress concentration and elastic strain energy accumulation in the coal-rock mass ahead of the working face. However, existing numerical simulations commonly rely on predefined weakened zones or empirical parameter reduction, which makes it difficult to represent the spatial heterogeneity and mechanical evolution of rock damage during field hydraulic fracturing. Taking the 2803 goaf-side working face in Hetaoyu Coal Mine as the engineering background, this study proposes a microseismic-data-driven method for characterizing hydraulic fracturing-induced damage and incorporates it into a FLAC3D finite-difference model. The stress field, elastic strain energy field, and damage distribution ahead of the working face are compared under non-fractured and hydraulically fractured conditions. In the proposed method, the energy of fracturing-induced microseismic events is converted into the Benioff strain of numerical zones according to the attenuation law of microseismic wave propagation, and the corresponding rock damage variable is then calculated using a Weibull damage model. The fracturing-damaged rock mass is further represented by weakening the elastic modulus, cohesion, and friction angle, together with the stochastic generation of strongly damaged zones. The results show that, without hydraulic fracturing, the hard roof maintains a strong, continuous bearing capacity, resulting in a continuous lateral abutment stress concentration zone and a high elastic strain energy accumulation zone ahead of the working face and near the goaf-side boundary. After hydraulic fracturing, a patchy and locally connected high-damage weakening zone forms in the target roof strata. This damaged zone cuts the original continuous load-transfer structure through which the hard roof concentrates load toward the goaf side, reduces the extent of high-stress and high-energy zones in the coal seam, and induces an asymmetric adjustment of the dominant mining-induced energy release zone from the goaf side toward the solid-coal side. These simulation results agree well with the field observation that microseismic activity is mainly concentrated near the roadway on the solid-coal side. The study indicates that the rockburst-control mechanism of directional long-borehole hydraulic fracturing is not limited to simple overall stress dissipation. A key finding is that the fracturing-induced heterogeneous damage zone effectively interrupts the continuous load-transfer and energy-storage paths on the goaf side. This induces an asymmetric spatial redistribution of the mining-induced energy field from the goaf side toward the solid-coal side, thereby mitigating the high static-load and high-energy-storage state ahead of the working face.

This study investigates the effect of single atomic vacancy defects with different random distributions on the buckling behavior of single- and double-layer graphene nanoplates. A parametric analysis was conducted to assess the influence of nanoplate dimensions, aspect ratio, defect concentration, number of layers, and boundary conditions on the critical buckling load ([Formula: see text]). To capture the discrete nature of graphene, the nanoplates were modeled using a space frame approach, where covalent bonds between carbon atoms were represented as beam elements and interlayer van der Waals forces were simulated using linear elastic springs. The atomic positions were generated using MATLAB and imported into ANSYS, where neighboring atoms were connected based on an energy-equivalent mapping between interatomic and elastic beam energies. Springs were added between atoms located within a defined cutoff distance to represent long-range interlayer interactions. A linear finite element buckling analysis was performed by solving an eigenvalue problem using beam and spring elements with linear elastic behavior. Model validation was achieved by comparing simulation results to data available in the literature. The results show that vacancy defects significantly reduce [Formula: see text]-up to 40% at 10% defect concentration. Furthermore, three distinct distributions of defects were examined for each concentration to explore spatial effects on buckling resistance.

Pathways and structural dynamics of phase transformations impact performance of materials in energy and information storage technologies. Palladium hydride (PdHx) nanocrystals are an ideal model system for studying solute-induced phase transformations, where elastic energy from lattice mismatch between α-PdHx and β-PdHx phases is often considered a key to determining the transformation pathways. α/β-PdHx interfacial elastic energy is affected by the confined geometry of a nanocrystal. However, how nanocrystal geometry influences phase transformation pathways is largely unknown. Using in situ liquid phase transmission electron microscopy, we directly visualize hydrogenation in Pd nanocrystals with two geometries, a nanocube and a hexagonal nanoplate. Both follow similar sequences of an initially curved nucleus, interface flattening, and reverse-stage nucleation; however, their evolving α/β-PdHx interfaces exhibit geometry-dependent crystallographic alignments. In nanocubes, {100}-aligned configurations conform to static elastic energy ordering, representing a pathway that maintains a local mechanical equilibrium, whereas nanoplates display both {110}- and {211}-aligned interfaces. Theoretical simulations show that geometry determines the accessibility of alternative phase transformation pathways as the system is driven far from equilibrium during hydrogenation. These findings identify geometry as a fundamental parameter for directing phase transformation pathways, offering design principles for accessing atypical configurations and improving properties of intercalation-based devices.

Dynamic mechanical response characteristics and energy evolution of sandstone under unloading subjected to low-frequency dynamic disturbance