Search Results (157)

Metastructures, waveguides composed of multiple unit cells (meta-atoms), have gained significant attention for controlling wave propagation in engineering applications, especially in the context of elastic and acoustic waves. However, existing metastructures often lack sufficient tunable functionality to dynamically control both elastic vibration and acoustic wave transmission using a single external parameter. This study introduces a phase-change material (PCM)-embedded meta-atom, where a core mass is connected to an outer shell by Archimedean spiral bridges. The solid–liquid phase transition of PCM induces a notable change in the effective shear modulus, enabling dynamic wave control. The mechanism for bandgap formation transitions from Bragg scattering in the solid PCM state to local resonance in the liquid state. Core rotation, driven by the phase transition, is key to generating flat bands and low-frequency locally resonant bandgaps at high temperatures. Temperature-dependent, mode-selective transmission behavior is observed, with transverse vibrations and acoustic waves exhibiting opposite blocking and transmission characteristics at the same frequency. This design provides a promising approach for decoupling sound and vibration management, using temperature control driven by the PCM phase transition. The work contributes to multifunctional metastructures with applications in adaptive noise control, structural health monitoring, and tunable vibration isolation systems. Full article

Carbonate reservoirs in the Shunbei area develop pronounced fracture networks after acidized hydraulic fracturing and thus have the potential to be repurposed as underground gas storage (UGS) after hydrocarbon depletion. Characterizing their mechanical behavior is essential for safe UGS operation; however, deep to ultra-deep natural cores are difficult to obtain, and conventional macroscopic tests often cannot provide parameters that meet engineering requirements. To address this issue, nanoindentation combined with QEMSCAN (Quantitative Evaluation of Minerals by Scanning Electron Microscopy) was employed to quantify microscale mineral distributions and the mechanical properties of the major constituents. The investigated rock is calcite-dominated (89.62%), with minor quartz (9.89%) and trace feldspar-group minerals (1.89%). Minerals are randomly embedded, and soft–hard phase boundaries are widely distributed. A finite–discrete element method (FDEM) model was then constructed and calibrated in ABAQUS. The discrepancies in uniaxial compressive strength and elastic modulus relative to laboratory results were 6.51% and 9.91%, respectively, indicating good agreement in both mechanical response and failure mode. Parametric analyses using three additional models with different mineral proportions show that damage preferentially initiates at mineral phase boundaries and stress concentration zones induced by end constraints. Microcracks then propagate and coalesce into a dominant compressive–shear band, and final failure is mainly governed by slip along the shear band with localized tensile cracking. With increasing quartz and feldspar contents, enhanced heterogeneity and a higher density of phase boundaries lead to a higher density of crack nucleation sites and increased crack branching, and the failure pattern transitions from a single shear-band–controlled mode to a more network-like fracture system. Moreover, macroscopic strength is not determined solely by the intrinsic strength of individual minerals; heterogeneity and phase-boundary characteristics strongly govern microcrack behavior, such that higher hard-phase contents may result in a lower peak strength. Full article

The mechanical behavior of metallic core–shell nanoparticles is critical for their use as reinforcement particles and additive manufacturing feedstocks, yet their deformation mechanisms remain incompletely understood. This study employs molecular dynamics simulations to investigate the compressive response of a Cu-core/Al-shell nanoparticle and compares it with solid Cu, solid Al, and a hollow Al shell of the same size under uniaxial loading along ⟨100⟩, ⟨110⟩, ⟨111⟩, and ⟨112⟩ directions. The single-material nanoparticles show strong anisotropy: solid Cu exhibits orientation-dependent transitions from dislocation slip to deformation twinning, while introducing a void to form a hollow Al shell reduces stiffness and strength, confines plasticity to the shell wall, and suppresses extended load-bearing twins. The Cu–Al core–shell nanoparticle combines these behaviors in an orientation-dependent manner. Under ⟨110⟩ and ⟨112⟩ loading, deformation is largely shell-dominated, whereas ⟨100⟩ and ⟨111⟩ loading more strongly activates the Cu core. Mechanistically, ⟨100⟩ is characterized by Shockley partial activity and junction/lock formation in the Al shell coupled with twinning in the Cu core; ⟨110⟩ shows primarily shell partials with limited core involvement; ⟨111⟩ promotes partial-dislocation activity in both shell and core; and ⟨112⟩ produces localized, twin-dominated bands in the Al shell with shell-thickness-dependent twin extension into the Cu core. These trends are rationalized using Schmid factor considerations for $\left\{111\right\}⟨110⟩$ slip and $\left\{111\right\}⟨112⟩$ partial/twinning shear, together with the effects of faceted free surfaces and the Cu–Al interface. The core–shell geometry enables two concurrent interface-mediated pathways, i.e., (i) stress transfer and reduced cross-interface transmission and (ii) circumferential bypass within the shell, which together yield only slight flow-stress increases over solid Al while markedly reducing stress serrations compared with both solid Cu and solid Al. Across all orientations, the core–shell structures also exhibit delayed yielding (higher yield strain) relative to solid Cu, indicating enhanced ductility. The results provide an atomistic basis for designing Cu–Al core–shell nanoparticles for robust particle-based processing and additive manufacturing feedstock, and for informing multiscale models with mechanism-resolved, orientation-dependent inputs. Full article

Al/TiB₂ aluminum alloy laminates were fabricated using a combination of accumulative roll bonding (ARB) and cold rolling processes. The Al/TiB₂ interface and microstructure were meticulously characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The mechanical properties of the laminates were assessed through tensile testing. The experimental results demonstrate that with an increasing cold rolling reduction, a laminated composite sheet with a nanocrystalline structure was successfully produced. The critical strain for the onset of plastic instability was also investigated. The findings indicate that as the cold rolling reduction increases, severe necking occurs in the Al12Zn2.2Mg1.7Cu3TiB₂ layer. At a reduction of 80%, the necking region approaches fracture. Tensile results reveal that this pronounced necking has a detrimental effect on the strength of the laminate. It is proposed that the plastic instability originates from shear bands, and the mechanical property mismatch between the constituent layers is identified as the primary reason for the localized preferential deformation. Full article

Bulk metallic glasses exhibit unique viscoplastic flow behavior within their supercooled liquid region. Their high-temperature deformation mechanisms diverge markedly from the highly localized deformation at room temperature. This contrast offers a critical window for investigating their compressive flow models and assessing their forming potential. This study aims to systematically reveal the high-temperature compressive flow behavior of bulk metallic glasses within the supercooled liquid region and to establish a corresponding flow model. Through constant strain rate high-temperature compression experiments conducted on Zr₅₆Co₂₈Al₁₆ bulk metallic glass within its supercooled liquid region, the variations in flow stress, crystallinity, and surface deformation characteristics with temperature were systematically investigated. The results indicate that the compressive behavior of the bulk metallic glass exhibits significant temperature dependence within this temperature range. The compressive strength decreased from 689 MPa at 487 °C to 330 MPa at 507 °C, and then increased to 435 MPa at 527 °C. The angle between the fracture/bulging direction and the loading direction increased from 45° at 487 °C to 88° at 507 °C, and then decreased to 60° at 527 °C. The shear band average spacing increased from 1.797 μm at 487 °C to 2.060 μm at 507 °C, and then decreased to 1.189 μm at 527 °C. These results consistently indicate that the plastic deformability is optimal at a compression temperature of around 510 °C. By integrating the analysis of mechanical curves and morphological characteristics, the applicability of three deformation mechanisms was evaluated: highly localized shear banding, homogeneous viscoplastic flow, and dynamic structural relaxation hardening. A constitutive relationship between compressive strength and temperature was established, which accurately describes their correlation. Simultaneously, it reveals that the dominant deformation mechanism evolves through highly localized shear banding and homogeneous viscoplastic flow, ultimately transforming into dynamic structural relaxation hardening as the temperature increases. This study provides theoretical guidance for predicting the compressive flow behavior of bulk metallic glasses in the supercooled liquid region and offers critical model support for precisely controlling their thermoplastic forming processes. Full article

Adiabatic shear banding (ASB) is a critical failure mechanism in titanium alloys subjected to high-strain-rate deformation, and its initiation is strongly influenced by the initial crystallographic texture. The dynamic response and ASB sensitivity of extruded and annealed Ti-6Al-4V (TC4) alloy rods were investigated under dynamic compression of cubic specimens along the extrusion direction (ED) and the transverse direction (TD) at a strain rate of 2500 s⁻¹. Split Hopkinson pressure bar (SHPB) tests combined with digital image correlation (DIC) were employed to obtain the stress–strain response and the evolution of strain localization. A dislocation density-based crystal plasticity finite element model (CPFEM), incorporating the measured texture, was established to elucidate the correlation between texture and ASB behavior. The experimental results show that TD specimens exhibit a yield strength approximately 100 MPa higher than that of ED specimens, while both orientations display comparable post-yield hardening behavior. ASB initiation occurs earlier in TD (compressive strain ~0.13) than in ED (~0.23), indicating greater ASB sensitivity in the TD orientation. The CPFEM successfully reproduces the directional stress–strain responses and the observed localization morphology, enabling mechanistic interpretation in terms of slip activity and thermomechanical coupling. The simulations indicate that ED loading is dominated by prismatic ⟨a⟩ slip, resulting in lower flow stress and more dispersed strain localization. In contrast, TD loading is governed primarily by pyramidal ⟨c + a⟩ slip, leading to elevated flow stress and intensified localization. The higher ASB sensitivity in the TD orientation is therefore attributed to texture-controlled slip-mode partitioning, enhanced thermomechanical coupling, and a more concentrated crystallographic orientation distribution that facilitates intergranular slip transfer. These findings provide guidance for tailoring microtexture to mitigate dynamic failure in titanium alloys subjected to high-strain-rate loading. Full article

Transverse shear deformation plays a non-negligible role in lightweight periodic-core structures and motivates the use of shear-corrected reduced-order plate and beam models. However, the shear correction factor $k_s$ is often treated as a constant despite its strong dependence on cross-sectional heterogeneity and geometry. This work quantifies the global sensitivity of $k_s$ in corrugated paperboard by combining an energy-consistent pixel-based identification of the effective shear stiffness $\left(GA{)}_{\mathrm{e}\mathrm{f}\mathrm{f}}\right.$ with a space-filling exploration of the parameter domain. Representative three-ply (single-wall) and five-ply (double-wall) configurations are generated directly in the pixel domain using sinusoidal fluting descriptions and non-overlapping liner bands. The effective shear stiffness is obtained from a heterogeneous shear-energy equivalence, where a normalized two-dimensional shear-stress shape function is computed from pixel-based sectional descriptors and integrated with spatially varying shear moduli. Latin Hypercube Sampling is employed to explore wide ranges of flute period, height, and thickness, liner thicknesses, and liner–flute shear-modulus contrasts. Global sensitivity is reported using unit-free normalized indices, including log-elasticities (based on the slope of $\ln k_s$ versus $\ln x$) and partial rank correlation coefficients. The results demonstrate that flute geometry is the primary driver of $k_s$ variability, while material contrast significantly modulates shear-energy localization, particularly in double-wall boards with two distinct flutings. The proposed framework enables high-throughput shear correction assessment and supports robust parameterized reduced-order models for corrugated structures. Full article

Reinforced-soil structures in rainfall-prone regions may deform or fail when infiltration weakens the geogrid–soil interface. This study quantifies the degradation of unsaturated shear strength at a geogrid–sandy-soil interface during rainfall infiltration. A large-scale direct shear apparatus was retrofitted with a controllable rainfall system and real-time water-content monitoring. Interface shear tests were conducted under different normal stresses, rainfall intensities, infiltration durations, and shear rates. Peak interface shear strength increased approximately linearly with normal stress and remained about 50% higher than that of unreinforced sand. Rainfall infiltration caused pronounced strength loss; at 120 mm·h⁻¹, extending infiltration from 10 to 30 min reduced apparent cohesion by ~56% and friction angle by ~23%. Cohesion decayed exponentially, whereas friction angle decreased nearly linearly, and faster shearing intensified both reductions. Response-surface regression further indicates that degradation is most severe under low normal stress, high rainfall intensity, and long infiltration duration. Water-content profiles reveal a persistent moisture-enriched zone adjacent to the shear plane (~3.4% higher than at 30 mm depth), implying reduced matric suction and promoting shear-band localization that accelerates interface weakening. These findings provide quantitative input for evaluating rainfall-induced performance loss of geogrid-reinforced soil structures. Full article

The coupling mechanism involving high-pressure seepage and soil degradation regarding the face stability in water-rich silty sand environment remains to be comprehensively elucidated. This paper employs 3D fluid–solid coupling simulations to investigate these interactions taking the Jingu-Haihe Tunnel as a case study, and the dry and saturated hydraulic environments alongside three softening scenarios are set. Results indicate that hydro-mechanical coupling significantly compromises face stability, elevating the limit support pressure from 140 kPa in dry mechanical state to 231 kPa. The failure mechanism transitions from localized “horn-like” shear bands in dry states to global quasi-symmetric “bulb-like” visco-plastic diffusion in saturated seepage field scenarios. Softening effects cause stress-dependent stiffness degradation, increasing the deformation rate by 53.8% under low support pressure, and inducing uneven deformation where the crown displacement increases by 32.8 times, exceeding the 11.8-fold increase at the center as the support pressure drops from 600 kPa to 100 kPa. Moreover, the fluid–solid coupling effect amplifies the stratum’s sensitivity to shear strength parameters by up to 26 times at the face center compared to the dry condition. These findings may offer theoretical insights for optimizing support pressure determination in deep-buried saturated excavations. Full article

The microstructure and properties of a cobalt-free, cost-effective Al_0.4CrFe₂Ni₂ medium-entropy alloy (MEA) after multi-stage thermomechanical processing, including annealing, rolling over a wide temperature range from hot to cryogenic conditions, and subsequent precipitation strengthening, were investigated in the present study. The initially cast microstructure was effectively homogenized through hot rolling with an 80% thickness reduction followed by homogenization annealing, resulting in the formation of a single-phase supersaturated solid solution and enhanced stability of plastic deformation. Strengthening of the MEA was achieved by rolling under both ambient and cryogenic conditions, with the deformation process predominantly governed by shear band formation. However, rolling under cryogenic conditions led to a more pronounced localization of plastic deformation, promoting the formation of deformation nanotwins and resulting in significantly higher strengthening compared to ambient rolling, with the alloy reaching a yield strength of 1040 MPa and an ultimate tensile strength of 1235 MPa. Precipitation hardening was governed by the formation of B2-type (ordered body-centered cubic, BCC) precipitates, which preferentially nucleated along deformation bands, thereby effectively strengthening the alloy to a yield strength of 1420 MPa and an ultimate tensile strength of 1465 MPa. Our results demonstrate that the investigated MEA offers a wide range of tunable mechanical properties, which can be effectively tailored through appropriate combinations of thermomechanical processing routes. Full article

To address the depletion of shallow coal resources, mining activities have progressed to greater depths, where rock masses contain numerous fractures due to complex geological conditions, making grouting reinforcement essential for ensuring stability. Using digital image correlation, this study investigated the strain evolution characteristics of grouted fractured specimens of three rock types—mudstone, coal–rock, and sandstone—under uniaxial compression. Analysis of the strain evolution process focused on two typical fracture inclinations of 0° and 60°, while examination of the peak strain characteristics covered five inclinations, namely 0°, 15°, 30°, 45°, and 60°. The findings indicate that the mechanical response varies systematically with lithology and fracture inclination. The post-peak curves differ significantly among rock types: coal–rock shows a gentle descent, mudstone exhibits a rapid strength drop but higher residual strength, and sandstone is characterized by “serrated” fluctuations. The failure mode transitions from tensile splitting at a horizontal inclination of 0° to shear failure at inclinations of 15°, 30°, 45°, and 60°. Strain nephograms corresponding to the peak stress point D reveal sharp, band-shaped zones of strain localization. The maximum principal strain exhibits a non-monotonic trend, first increasing and then decreasing with increasing inclination angle. For grouted coal–rock and sandstone, the peak values of 47.47 and 45.00 occur at α = 45°. In contrast, grouted mudstone reaches a maximum value of 26.80 at α = 30°, indicating its lower susceptibility to damage. The study systematically clarifies the strain evolution behavior of grouted fractured rock masses, providing a theoretical basis for evaluating the effectiveness of reinforcement and predicting failure mechanisms. Crucially, the findings highlight mudstone’s role as a high-integrity medium and the particular vulnerability of horizontal fractures, offering direct guidance for the targeted grouting design in stratified rock formations. Full article

High rock slopes are extensively distributed in areas of major engineering constructions, such as transportation infrastructure, hydraulic projects, and mining operations. The stability and failure evolution mechanism during their multi-stage excavation process have consistently been a crucial research topic in geotechnical engineering. In this paper, a series of two-dimensional rock slope models, incorporating various combinations of slope height and slope angle, were established utilizing the Discrete Element Method (DEM) software PFC2D. This systematic investigation delves into the meso-mechanical response of the slopes during multi-stage excavation. The Parallel Bond Model (PBM) was employed to simulate the contact and fracture behavior between particles. Parameter calibration was performed to ensure that the simulation results align with the actual mechanical properties of the rock mass. The research primarily focuses on analyzing the evolution of displacement, the failure modes, and the changing characteristics of the force chain structure under different geometric conditions. The results indicate that as both the slope height and slope angle increase, the inter-particle deformation of the slope intensifies significantly, and the shear band progressively extends deeper into the slope mass. The failure mode transitions from shallow localized sliding to deep-seated overall failure. Prior to instability, the force chain system exhibits an evolutionary pattern characterized by “bundling–reconfiguration–fracturing,” serving as a critical indicator for characterizing the micro-scale failure mechanism of the slope body. Full article

This study presents a novel experimental methodology enabling the synchronous observation of strain and stress evolution in granular backfill subjected to active earth pressure. A physical model of plane deformation was used in which a rigid retaining wall was gradually moved away from the ground while simultaneously recording, at each step, both displacement-based images for digital image correlation (DIC) and photoelastic pictures of the force-chain rearrangements. The results show that active failure develops gradually through narrow shear bands, initiated near the wall base and propagating towards the ground surface. A consistent inverse relationship between shear-strain location and photoelastic stress concentration was identified: low-strain zones within the shear wedge in the shear and volumetric strain images correspond to strong force-chain development, whereas high-strain zones (strain localization) correspond to local stress release. These findings provide new experimental evidence regarding the micromechanics of active pressure and offer comparative data for calibrating DEM (discrete element method) models and interpreting the reduced active pressures reported in confined granular backfills. Full article

This study investigates the development of adiabatic shear bands (ASBs) in AISI 1045 carbon steel under high-strain-rate uniaxial compression, emphasizing the conditions governing their onset and growth. Split Hopkinson pressure bar (SHPB) experiments were carried out at strain rates of 1000, 2000 and 4000 s⁻¹ with controlled displacement/strain interruption to capture gradual ASB formation throughout the process. Stress–strain data were analyzed alongside optical microscopy to determine the critical strain for ASB initiation, document ASB morphology, dimensions and type, and connect ASB formulating stages to material macroscopic mechanical behavior. The observations clarify how deformation evolves from homogenous plastic flow to localized shear instability as the strain and strain rate increase, linking mechanical response to microstructural features. Integrating these results, the effects of strain rate and strain progress on ASB formation and evolution characteristics are investigated. These findings enhance our understanding of shear localization phenomena under dynamic loading and provide a basis for predicting failure modes in structural applications. Full article

Deformation bands provide a microscale record of strain localisation within sandstones and offer key insights into deformation mechanisms and conditions. This study integrates detailed field observations with optical microscopy and three-dimensional X-ray microtomography (µCT) to characterise deformation bands in thick-bedded sandstones of the Krosno Formation (Silesian Nappe, Outer Carpathians). Two sections within a regional first-order fold were examined: an upper, mudstone-rich and mechanically weak unit, and an underlying sandstone-dominated competent unit. The contrasting kinematics of the deformation bands reflect layer-parallel strain partitioning during the onset of folding. Normal-shear bands developed in the weaker upper unit, whereas compaction bands formed pervasively in the competent unit. Microstructurally, shear bands are sharply bounded, organised in arrays, and dominated by grain rearrangement with local cataclasis, while compaction bands exhibit diffuse margins, tight grain packing, and disaggregation through progressive cataclasis. These features indicate that the bands formed under shallow-burial (<500 m) conditions. µCT imaging reveals the bands as darker, low-attenuation zones relative to the host rock, reflecting post-deformational cementation and the absence of cement within the bands. This diagenetic contrast enhanced mechanical heterogeneity and promoted later reactivation and fracture development. The study provides a three-dimensional microstructural assessment of early strain localisation in mechanically layered rocks in the buckle fold limb. Full article