Influences of D-shaped hole inclination on rock mechanical behavior and fracture evolution under uniaxial compression

The deformation modes and energy absorption of BCC (Body-Centered Cubic) lattices subjected to uniaxial compression have been widely studied. However, their mechanical behavior under complex loading conditions, such as combined compression-shear, remains unexplored. This gap limits confidence in applying BCC lattices to scenarios involving such complexities. This study investigates the mechanical behavior of BCC lattices under combined compression-shear loading conditions. The Fused Deposition Modelling (FDM) process with thermoplastic polyurethane (TPU) filaments were used to fabricate BCC lattice specimens. Quasi-static tests on lattice specimens were conducted at loading angles of 15°, 30°, and 45°, as well as under uniaxial compression at 0° for comparison. The deformation histories and force-displacement curves were examined to identify the deformation modes and analyze energy absorption characteristics. Two deformation modes distinct from those observed under uniaxial conditions were experimentally revealed at the varied loading angels. A finite element model was developed to numerically investigate the characteristics of normal and shear forces, as well as the influences of truss diameter and shear angle on the performance of BCC structures under combined compression-shear conditions. The findings presented in this study provide valuable references for the feasibility and reliability analysis of BCC lattice applications under compression-shear conditions. • BCC lattices under combined compression–shear were studied experimentally and numerically. • Two deformation modes were identified in BCC lattices under combined compression–shear. • Loading angle affects compressive and shear forces and energy absorption of BCC lattices. • The effects of truss diameter and shear angle have been investigated numerically. • The yield envelope of BCC metamaterial has been developed.

Scale effects on mechanical properties and crack propagation of single-flawed sandstone under uniaxial compression: experiments and PFC2D simulation

Uniaxial cyclic compression behaviour and constitutive model of strain-hardening cementitious composites (SHCC) with limestone and calcined clay

Experimental study on stress-strain behavior of recycled steel fiber reinforced recycled aggregate self-compacting concrete under uniaxial cyclic compression

X-ray diffraction (XRD) combined with in situ mechanical testing is a powerful, non-destructive technique that provides valuable information on structural evolution and defect formation during deformation. Unlike many other characterization methods, XRD does not impose constraints on sample dimensions, does not require a vacuum environment, and can be applied to a wide range of materials with periodic structures. However, such experiments present significant challenges due to the need for precise synchronization between independently controlled systems: one managing mechanical loading and the other handling X-ray measurements. In this work, we report on the successful software-level integration of a nanoindenter control system directly into the beamline control system. This integration enables full control of both mechanical and diffraction measurements from a single user interface, allowing real-time synchronization and automation of complex in situ experiments. We demonstrate the capabilities of this setup through uniaxial compression tests on α-Ti micropillars. Mechanical data from the nanoindenter and XRD patterns were collected simultaneously in an automated mode. Raster scans were performed on the micropillar in its pristine state, at two intermediate deformation stages, and post-mortem. This approach enabled detailed analysis of mechanical behavior and structural evolution under load, illustrating the effectiveness of the integrated system for advanced in situ studies.

Fissured limestone in the gorge-section hydro-fluctuation belt of the Three Gorges Reservoir (TGR) is continuously affected by wet-dry cycles and overburden self-weight stress, and its progressive deterioration markedly increases geohazard risk. However, the multiscale damage evolution mechanism of fissured limestone involving axial stress remains insufficiently understood. This study investigated damage evolution under coupled effects through wet-dry cycle-axial stress deterioration tests, uniaxial compression tests, and XRD, SEM, CT, and AE analyses. Based on elemental conservation, stoichiometric porosity was proposed to improve microscopic damage characterization. The results show that the deformation and failure process includes compaction, stable microcrack propagation, unstable microcrack propagation, and failure stages. With increasing wet-dry cycles and axial stress, the mass loss rate, saturated water absorption rate, and pore parameters continuously increase, while the proportion of tensile cracks decreases and the shear component increases. Under wet-dry cycle-axial stress coupling, calcite dissolution dominates mineral deterioration, grain cementation progressively weakens, the specimen surface evolves from a dense morphology to a honeycomb-like structure, and internal pore-fissure structures continue to develop. Overall, wet-dry cycling is the fundamental driver of damage deterioration, whereas axial stress promotes pore-fissure propagation and aggravates structural damage. The average difference between stoichiometric porosity and CT porosity is approximately 4.07%, indicating that the proposed index can support quantitative evaluation of microscopic damage in fractured limestone under acidic cycling. These findings deepen the understanding of damage evolution in fractured limestone within the gorge-section hydro-fluctuation belt in TGR.

Random polygonal aggregates represent the most realistic aggregate morphology in the mesostructure of concrete. Their angular characteristics and spatial distribution have a decisive influence on the stress concentration, crack initiation, and ultimate failure mode of the material under uniaxial compression. Therefore, in-depth research in this area is essential for revealing the essence of the macroscopic mechanical behavior of concrete. To this end, this paper presents an SPH-based simulation framework for uniaxial compression failure of concrete by integrating the Mohr-Coulomb criterion with tensile cutoff and an improved smoothing kernel function. A key component is the development of an in-house particle generation program for random polygonal aggregates, which achieves automatic generation satisfying geometric constraints and precise particle attribute classification based on the separating axis theorem and the ray casting method. Through three sets of comparative numerical examples, the effects of the number of aggregates (30, 40, 50), aggregate size range (1-8mm, 1-10mm, 1-12mm), and shape complexity (number of edges: 8-15, 8-20, 8-25) on the failure mode of concrete are systematically investigated. The findings reveal that an increase in aggregate density or expansion of the size range promotes a transition from localized shear failure to more distributed damage patterns, accompanied by enhanced material brittleness. In contrast, increasing the shape complexity of aggregates (i.e., a larger number of edges) shifts the failure mode from "angularity-dominated concentrated shear failure" to "interface-dominated fine diffuse failure," significantly improving material ductility. Comparison and validation with existing results show that the proposed method achieves good agreement in terms of failure morphology and crack evolution. This study provides an efficient modeling approach and theoretical support for the mesomechanical analysis of concrete with irregular aggregates.

This paper aims to explore the fracture behavior and bolt anchoring mechanism in circular tunnel under support in layered rock mass. Seven support methods, horizontal and vertical bedding planes are set up, and cubic rock-like material samples with a prefabricated circular hole and bedding planes are tested under uniaxial compression. During the compression, the failure of the hole sidewall is monitored by a camera. The fracture behavior in tunnels under support in layered rock mass is reproduced. After uniaxial compression failure, the fracture behavior of specimens is analyzed via CT scanning, and the bolt anchoring mechanism is analyzed. The results demonstrate that the system bolt and steel floral pipe provide higher improvement. The shotcrete and steel arch can provide supporting pressure for the tunnel, which effectively prevents the surrounding rock from spalling. The strength increment for the vertical bedding specimen is larger than that for the horizontal bedding specimen. CT observations combined with theoretical analysis indicate that the anchor bolt generates anchoring effect by improving the stress state and the mechanical properties of the surrounding rock in the anchorage zone where the fractures are compacted, arrested, and deflected, which could increase the bearing capacity of the surrounding rock.

Solid-state materials with actively tunable thermal conductivities can enable next-generation thermal management technologies. There is a need for materials that can be switched between high and low thermal conductivities over a large temperature window using different on and off triggers. Here, we establish that Sm1-xGdxS alloys, which undergo a pressure-induced, hysteretic, rock salt-to-rock salt metal-insulator transition, can be repeatedly cycled between high and low thermal conductivity states from 200 to 550 K due to differences in electronic contributions to thermal conductivity. Intermediate stoichiometries (0.08 ≤ x ≤ 0.14) transform from a mixed black/gold phase at ambient pressure to a metallic gold phase upon uniaxial compression at 1 GPa, leading to a 2-fold increase in thermal conductivity. The gold phase rapidly reverts to the equilibrium low thermal conductivity phase upon exposure to temperatures above 573 K. These findings establish that Sm1-xGdxS alloys hold promise for thermal switching and management applications.

The advancement of modern electronic devices toward lightweighting, high-frequency, and integrated designs has escalated the demand for multifunctional materials that can combine microwave and thermal management capabilities with mechanical load-bearing capacity. However, inherent trade-offs exist between electrical conductivity and thermal insulation, as well as between mechanical strength and lightweight properties. Herein, attempts have been made to innovatively embed lightweight, high-strength dielectric shells and highly conductive, low-infrared-emissivity metallic shells into hollow structure design. Specifically, heterogeneous dual-shell hollow microspheres (DSHM) were constructed using glass as the model dielectric material and copper as the conductive material. By optimizing the ratio of dielectric-to-conductive phases, the shell microstructure, and macroscopic structural parameters, we achieved a synergistic combination of lightweight and high strength (density: 0.4456-1.0991g cm- 3, survival rate under 2MPa uniaxial compression: 87.1%. Crucially, leveraging the distinct structural dependence of conductive and thermal networks, the integration of low thermal conductivity (0.1134-0.1478W m- 1 K- 1) with broadly tunable electrical conductivity (299.6-2625.7 S cm- 1) and infrared emissivity (0.218-0.493) in a single microsphere was achieved for the first time. These properties endow the hollow microspheres with exceptional microwave attenuation and thermal regulation performance.

Slender lattice structures offer significant advantages in mechanical applications due to their high stiffness and energy absorption capabilities; however, they are inherently prone to buckling. Although stay-based reinforcement concept have proven effective in two-dimensional lattice, extending them to three-dimensional (3D) structures presents challenges in both design and manufacturing. This study aims to develop a material-extrusion manufactured stayed 3D-lattice based on a modular design that enables non-planar stay arrangements. The goal is to improve the ultimate load capacity and energy-absorption performance of the lattice through the introduction of stays. Material-extrusion additive manufacturing was used to fabricate modular stayed lattice specimens, followed by uniaxial compression testing and digital image correlation to evaluate mechanical performance and deformation behaviour. Three types of connectors and three types of stayed unit cells were fabricated through a modular strategy and printing parameter optimisation, and assembled into six distinct lattice configurations. Buckling behaviour, relative density, relative strength, and energy absorption were studied. The results demonstrate that the stay concept can be effectively applied to 3D-lattices, increasing the ultimate load by up to a factor of 3.53 and enhancing energy-absorption capability to approximately 81%. The buckling behaviour could be tuned across five lattice configurations by varying unit cell types and additional reinforcement strategies. The connectors remained intact without observable micro-cracking, which is favourable for recyclability. Overall, the proposed modular stayed 3D-lattice framework offers a recyclable and effective strategy to enhance stability and energy absorption, providing fundamental data for selecting optimal configurations for intended applications.

ABSTRACT Driven by the global transition towards greener and more efficient mineral extraction, waste rock–cementitious tailings backfill (WRCTB) has gained prominence as an innovative solution for repurposing mining solid waste. The strength performance of WRCTB is strongly governed by the aggregate proportion of waste rock (R) to tailings (T). This study systematically evaluates the influence of R/T ratios (4:6, 5:5, 6:4, and 7:3) on mechanical behaviour and microstructural evolution using a multi-scale framework. An integrated multi-scale approach combining uniaxial compression, X-ray CT – based 3D reconstruction, and SEM was employed to evaluate mechanical properties, energy dissipation, pore architecture, and hydration characteristics. The results indicate that an equal rock-to-tailings proportion (R/T = 5:5) yields the optimal composite behaviour, maximising strength and stiffness while minimising pore volume and producing a substantially more compact microstructure. Increasing slurry concentration and prolonging age further enhance strength development. CT analysis indicates a uniform pore distribution at lower R/T ratios, whereas higher ratios lead to sedimentation stratification and pore clustering. SEM observations confirm that at R/T = 5:5, abundant C–S–H gel and ettringite (AFt) are formed, producing strong interfacial bonding and a dense microstructure. Overall, a clear ‘mix ratio–structure–property’ relationship is established, clarifying the intrinsic mechanism governing WRCTB performance.

To elucidate the influence of fracture dip angle on the mechanical response of red sandstone and the mechanism of crack evolution, this study employs the discrete element software PFC2D to construct a single-fracture sandstone model. Numerical uniaxial compression tests are conducted under varying fracture dip angles α. By integrating the 'stress field-microcrack' coupling criterion with fracture initiation displacement field characteristics, the study quantitatively derives the segmented enhancement patterns of peak strength and fracture initiation stress, systematically elucidating the mechanisms of microcrack initiation and propagation. Results indicate that as α increases, the normal clamping effect of the fracture surface intensifies, making it more difficult for the vicinity of the fracture surface to first reach the damage threshold. Microcrack activity gradually shifts from "preferential growth in the middle section of the fracture surface" to "easier triggering at the fracture tip," driving the macrocrack path from local control at low inclination angles to synchronous evolution with high-stress zones at high inclination angles (This consistency becomes more pronounced at larger inclinations). The mechanical response manifests as an overall increase in both initiation stress and peak strength with inclination angle, exhibiting a more pronounced enhancement trend within the larger inclination range. Additionally, the strain value required for the first AE signal increases, the strain range where AE events occur narrows, and the peak ringing count rises.The crack initiation stress increased from 11.5MPa (α = 0°) to 25.0MPa (α = 90°), representing an approximately 117% increase; the peak stress rose from 24.2MPa to 33.6MPa, an increase of approximately 39%. Microcrack counts exhibited exponential growth with accumulated strain, dominated by tensile cracks, indicating a tensile-dominated brittle failure mechanism in the rock specimens.The research findings provide an interpretive framework based on stress thresholds for identifying failure modes under controlled joint dip angles and for engineering stability assessments.

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.

Prediction of compressive strength of vertebral body with metastatic lesions based on quantitative computed tomography-based subject-specific finite element models.

ABSTRACT During CO₂ sequestration in abandoned mines, concrete isolation walls or lining layers and surrounding rock may suffer damage or failure during CO₂ injection and long-term storage, increasing leakage risk. To investigate the damage–failure behaviour, crack evolution and sequestration prediction of sandstone–concrete composites under Sc-CO₂ conditions, specimens with interface inclinations of 0°, 30°, 45°, 60° and 90° were immersed in Sc-CO₂ for 0, 12 and 24 h. Uniaxial compression and acoustic emission (AE) tests were conducted, and constitutive and sequestration prediction models were established. Results show that: (1) at the same immersion time, specimens with a 60° interface inclination exhibited the lowest peak strength (15.82–18.53 MPa) and cumulative AE ringing counts (1.8×10³–4.1×10³); (2) for a given inclination, peak strength increased while cumulative AE ringing counts decreased with immersion time; (3) permeability first decreased and then increased with interface inclination, reaching a minimum at 60°, which was 31.2%–69.9% lower than that of other inclinations; and (4) CO₂ sequestration states were classified into steady, controllable, warning and critical levels. Based on strain and cumulative AE ringing counts, crack constitutive and sequestration prediction models were developed, with prediction errors within ±8%. These findings provide theoretical guidance for safe CO₂ sequestration in abandoned mines.

Incomplete grout filling in natural rough fractures is common in grouting practices and alters the mechanical behavior of rock masses. This study numerically simulates slurry diffusion in fractures with different joint roughness coefficients (JRC). Rock models with varying roughness and filling degrees are tested under uniaxial compression and constant normal stiffness (CNS) direct shear. Results show that uniaxial compressive strength depends weakly on filling level but strongly on roughness. Higher roughness intensifies stress concentration, accelerates grout damage, and reduces stress transfer, lowering compressive strength. Incomplete filling only induces local stress behind the grout front, slightly reducing bearing capacity. Under CNS direct shear, peak shear strength increases with both filling level and roughness, with filling showing a more linear effect. Residual shear strength is mainly controlled by roughness and can exceed peak strength at high roughness due to asperity interlocking and grout dilation. These findings highlight the key role of fracture roughness in partially grouted rock masses and aid strength evaluation in real grouting conditions.

Osteonecrosis of the femoral head (ONFH) is a progressive disorder characterized by regional trabecular bone deterioration that ultimately results in collapse. While elastic property changes in diseased bones are well documented, the contribution of region-specific viscoelastic behavior and its relationship to multiscale microarchitecture and composition remain insufficiently defined. Eighteen femoral heads (mean age: 40.8 ± 7.1 years; 15 males, 3 females; diagnosis: Ficat Stage III/IV) were retrieved during total hip arthroplasty. Patient-matched trabecular cores were harvested from three distinct zones: necrotic (NCZ), sclerotic (SCZ), and healthy (HZ). Bone quality was evaluated using micro-CT, uniaxial compression, nanoindentation, FTIR, and XRD. Viscoelasticity was characterized via stress relaxation and dynamic mechanical analysis (DMA) tests. The NCZ demonstrated microarchitectural decay (bone volume/total volume reduced by 54.54%, p < 0.001) and lower elastic modulus (reduced by 60.25%, p < 0.001) compared to SCZ. DMA revealed that while the NCZ exhibited the lowest storage modulus (E'), it showed a trend toward greater matrix-dominated stress relaxation (~ 25% increase). Conversely, the SCZ exhibited a 60% increase in E' (p < 0.01) but significantly reduced damping and post-yield energy than NCZ, consistent with a stiff yet brittle phenotype. Stress relaxation correlated strongly with mineral/matrix ratio (r = - 0.71) and collagen maturity (r = - 0.64), with collagen spectral markers significantly predicting microscale mechanical properties. ONFH induces profound viscoelastic and structural heterogeneity. This zonal mismatch between the compliant necrotic core and the stiff, brittle sclerotic rim likely promotes stress concentrations, driving structural instability and subchondral failure.

Floatable chitosan-based cryogels embedded with copper nanoparticles as efficient and reusable heterogeneous catalysts for hydrogenation of 4-nitrophenol.