Search Results (51)

Tamarindus indica L., a key economic tree species in tropical regions, suffers severely from postharvest decay. From 2023 to 2025, disease fruits exhibiting pericarp softening, pulp browning, and sticky exudates were collected in Yunnan, China. Pathogenicity tests following Koch’s postulates, combined with morphological characterization and phylogenetic analyses of the internal transcribed spacer (ITS), translation elongation factor 1-alpha (TEF 1α), and beta-tubulin (TUB) gene regions, identified the causal pathogen as Botryosphaeria fabicerciana (isolates ZWML-06, ZWML-44, ZWML-17). This is the first report of this postharvest disease on tamarind in Yunnan, filling an etiological gap. Additionally, an endophytic bacterium, designated BV-1, was isolated from asymptomatic pulp tissues. Whole-genome sequencing and phylogenetic analysis identified it as Bacillus velezensis. Strain BV-1 exhibited strong in vitro antagonistic activity against the pathogen, indicating promising biocontrol potential. Functional annotation revealed that BV-1 possesses a complex genetic system with developed transporter systems; its core metabolic network is dominated by nitrogen metabolism and redox processes, suggesting a potential “multi-target” antimicrobial mechanism. This study provides a theoretical basis and novel resources for the green control of postharvest diseases in tamarind. Full article

Uranium dioxide (UO₂) is the standard fuel in light water reactors, but improving its mechanical performance is essential for achieving higher burnups. This study employs first-principles density functional theory with the DFT + U approach to investigate the effect of molybdenum (Mo) substitution on the elastic properties of UO₂. Supercell models with Mo concentrations from 3.125 to 9.375 at.% are constructed, and elastic constants are calculated using the stress–strain method, complemented by Bader charge and charge density analyses. The results reveal a non-monotonic concentration-dependent behavior: at 3.125 at.% Mo, the shear and Young’s moduli increase by ~16% and ~14%, respectively, indicating significant stiffening; at higher concentrations (6.25 and 9.375 at.%), both moduli decrease, leading to softening of UO₂ lattice. Bader charge analysis shows that Mo loses only 0.13 electrons (vs. 2.56 for U) and the Mo–O bond is much shorter than the U–O bond; this is evidence of covalent bonding between Mo and O atoms that acts as local strengthening centers at low doping. The softening at higher concentrations is attributed to increased lattice distortion and enhanced bond delocalization, supported by changes in Cauchy pressure, Debye temperature, and Vickers hardness. The calculated elastic modulus and hardness of pure UO₂ are in good agreement with previously reported experimental data. For Mo-doped UO₂ systems, this work establishes a quantitative composition–property relationship, providing a theoretical reference for future experimental investigations. Full article

The nonlinear dynamic response of aerospace thin-walled structures in a post-buckling state under thermo-acoustic loads is critical for their design. This study investigates this phenomenon through integrated experimental and numerical approaches. Acoustic tests on thermally stressed flat plates yielded results in close agreement with finite element and reduced-order modal (FEM/ROM) simulations, with first-order frequency deviations within ±2 Hz and strain values of the same order of magnitude (10.7 µε vs. 9.5 µε at 50 °C). A key observation is the non-monotonic variation in the thermal modal frequency, which initially decreases then increases with the buckling coefficient, while dynamic strain data further validate the computational model. Comparative analysis of three Haynes 188 alloy geometries—flat plates, cylindrical shells, and spherical shells—reveals distinct behaviors rooted in their critical buckling temperatures (68.46 °C, 151.20 °C, and 698.28 °C, respectively): flat plates exhibit softening–hardening transitions with a frequency range of 491–624 Hz; cylindrical shells show irregular responses with a dramatic frequency drop from 1120 Hz to 360 Hz; and spherical shells maintain the highest stability and frequency range (1913–2109 Hz), governed by the buckling coefficient’s linear effect. Time-domain and probability density function (PDF) analyses elucidate the snap-through phenomena and the modulating roles of the buckling coefficient and sound pressure level (SPL). These findings underscore that geometric configuration and inherent stiffness are critical to post-buckling performance, providing a theoretical basis for designing aerospace components in extreme environments. Full article

Squeezed branch piles, originally developed for building and bridge foundations, have been downsized and deployed at larger pile spacing for reinforcing embankments over soft soils. However, the working mechanism of squeezed branch pile-supported embankments remains unclear. In this study, a three-dimensional numerical model of this embankment was established based on field tests. The analyses consider different pile types (squeezed branch piles and straight piles) and pile-head structures (beam-type cap and plate-type cap). These concrete components were modeled utilizing an advanced concrete model, which captures the strain-softening/hardening and yielding behavior. Simulation results show that squeezed branch piles provide better settlement control in the subsoil beneath the embankment than straight piles for the studied cases. The beam-type cap with squeezed branch piles behaves as a pile-beam foundation that reduces maximum settlement by around 38% compared to that of the plate-type cap, while the plate-type cap system functions as a composite foundation that enhances surcharge capacity by about 35–40%. The instability of the embankment is driven by tensile failure in concrete: The beam-type cap leads to a localized failure along the ground beam, and the plate-type cap system induces a progressive failure centered on the squeezed branch piles. Within the plate-type cap, the dimensions of the pile-head plate significantly influence settlement control and the stability of the embankment in soft soil. Full article

Standard compatibility-based truss models, including the Disturbed Stress Field Model (DSFM), often underestimate the shear strength and deformation capacity of reinforced-concrete (RC) beam-column joints. This study investigates the origin of this bias through a systematic inverse identification framework and derives joint-core constitutive relationships tailored to the highly confined, nonuniform stress states of joints. Inverse analyses show that improving confinement effectiveness alone leads to unrealistic parameter saturation and cannot reproduce the measured energy absorption, indicating that conventional compression-softening formulations remain excessively punitive for joint cores. When confinement activation and softening are identified simultaneously, a clear mechanism shift emerges: unlike panel-based theories that link softening to tensile-cracking measures (principal strain ratio), joint softening is overwhelmingly governed by the principal compressive strain, consistent with crushing-dominated damage accumulation. Based on these trends, unified power-law expressions are proposed for both passive confinement activation and damage-induced softening as functions of principal compressive strain only, adhering to a parsimonious formulation without auxiliary variables such as concrete strength or reinforcement ratio ($R^2\approx 0.89$). The model is validated on an independent database of 113 specimens, including high-strength concrete and exterior joints, eliminating the systematic conservatism of the standard DSFM and improving the mean experimental-to-predicted strength ratio from 0.85 to 1.01 while reducing the coefficient of variation from 34.5% to 13%. The proposed formulation supports more reliable joint shear backbone predictions for seismic assessment of RC frame buildings. Full article

The mechanical response of geomembranes in hydraulic structures is strongly influenced by temperature variations, which alter both material stiffness and interface shear strength behavior. This study develops a non-linear, temperature-dependent tensile behavior constitutive model for a polyvinyl chloride (PVC) geomembrane and evaluates its implications for the stability of geomembrane-lined reservoir slopes. The empirical relationship was calibrated using tensile tests reported in literature for temperatures between 10 °C and 60 °C, reproducing the observed non-linear softening and modulus reduction with increasing temperature. A classical thermal dilation formulation was incorporated to simulate cyclic thermal expansion and contraction. The constitutive and thermal formulations were implemented in FLAC2D and applied to a 2H:1V covered geomembrane slope representative of dam lining systems. The results show that temperature-induced softening significantly increases tensile strain within the geomembrane. The model also shows that the lower surface interface friction angle of the geomembrane plays a significant role in the slope stability. Thermal cycle analysis demonstrates the accumulation of efforts resulting from the fatigue of the geomembrane. The proposed model provides a practical framework for incorporating thermo-mechanical coupling in design analyses and highlights the necessity of accounting for realistic thermal conditions in assessing the long-term stability of geomembrane-lined reservoirs. Full article

A knowledge of the process–structure–property correlation and underlying deformation mechanisms of material under a coupled electro-thermal–mechanical field is crucial for developing novel electrically assisted forming techniques. In this work, numerical simulation and experimental analyses were carried out to study the non-uniform deformation behaviors and microstructure evolution of Ti₂AlNb-based alloy stiffened panels in different characteristic deformation regions during electrically assisted press bending (EAPB). The quantitative relationships between electro-thermal–mechanical routes, microstructural features, and mechanical properties of EAPBed stiffened panels were initially established, and the underlying mechanisms of electrically induced phase transformation and morphological transformation were unveiled. Results show that the temperature of the panel first increases then deceases with forming time in most regions, but it increases monotonically and reaches its peak value of 720.1 °C in the web region close to the central transverse rib. The higher accumulated strain and precipitation of the acicular O phase at mild temperature leads to strengthening of the longitudinal ribs at near blank holder regions, resulting in an ideal microstructure of 3~4% blocky α₂ phase + a dual-scale O structure in a B2 matrix with a maximal hardness of 389.4 ± 7.2 HV_0.3. While the dissolution of the α₂ phase and the spheroidization and coarsening of the O phase bring about softening (up to 9.29%) of the lateral ribs and web near the center region, the differentiated evolution of microstructure and the mechanical property in EAPB results in better deformation coordination and resistance to wrinkling and thickness variation in the rib–web structure. The present work will provide valuable references for achieving shape-performance coordinated manufacturing of Ti₂AlNb-based stiffened panels. Full article

This paper concerns the issue of selecting appropriate stress field parameters for predicting the stability of headings driven under the geological and mining conditions of Polish underground copper mines. The problem is of key importance due to strict safety requirements in mine workings that serve ventilation and transport functions. Numerical analyses were carried out for four stress field variants: the stress state determined based on Bulin’s formulas (variant 1), the hydrostatic stress state (variant 2), and stress states determined from in situ measurements conducted in the Rudna mine (variant 3 and variant 4). Numerical simulations were performed for a group of four headings, supported with fully grouted rock bolts, in the geological and mining conditions of the Rudna mine. Stability assessment was performed using the finite element method (FEM). Rock mass input parameters for the modeling were obtained with RocLab 1.0, applying the Hoek–Brown classification, while numerical analyses employed the Mohr–Coulomb failure criterion. The elastic–plastic model with softening was used to describe the rock mass behaviour. Numerical calculations were conducted in the RS2 computer program in a triaxial stress state and in a plane strain state. The range of the yielded rock mass zone in the roof of the headings was assumed as the optimal measure of the headings stability. The obtained simulation results provided a basis for recommending suitable rock bolting systems to protect the stability of headings developed under various initial stress field conditions. Full article

As concrete exhibits localized strain softening, for example, under tension, fracture-energy consistency is essential for obtaining mesh-insensitive results of finite-element (FE) analyses. Accordingly, element- and structural-level parametric studies of uniaxial tensile behavior are performed within an FE framework coupling the Concrete Damaged Plasticity (CDP) model, the Crack Band Theory, and the Newton–Raphson solver in Abaqus. The effects of several CDP parameters and the mesh size are quantified using a sensitivity index ($SI$). A damage evolution law with several tensile parameters is proposed for energy consistency in addition to scaling of the softening strain. Besides tensile strength, elastic modulus, and an estimated uniaxial stress–strain curve, three key parameters are validated: the ratio between fracture energy from pure tension in the crack band and that from direct-tension tests, and two mesh-independent damage evolution parameters. An inverse calibration is proposed, in which the damage parameters and the fracture-energy ratio are identified in one-element ($SI\le 5\%$) and multi-element models, respectively. With these calibrations, the tensile response of the crack band is obtained, and multi-element analyses achieve mesh insensitivity when meshes are not smaller than the crack-band width. For finer meshes violating continuum assumptions, the initial damage rate parameter is reduced to preserve energy consistency. Full article

Microorganisms present in asphalt pavement service environments can alter the composition of asphalt through metabolic activities, thereby affecting its rheological properties. To investigate this influence and compare performance variations across asphalt types, two asphalt-degrading bacterial strains were isolated from in-service pavements. Following 16S rRNA gene sequencing and phylogenetic analysis, the strains were identified as Pseudomonas putida and a putative novel species within the Citrobacter genus. Using a custom-designed thin-film inoculation system, the performance evolution of base asphalt and styrene-butadiene-styrene (SBS) modified asphalt was systematically evaluated after microbial activity periods of 5, 10, and 15 days. Conventional property tests and multi-temperature rheological analyses (temperature sweep, multiple stress creep recovery test, linear amplitude sweep, 4 mm DSR) were conducted. Results demonstrated that microbial action reduced penetration, elevated softening point, and decreased ductility in both asphalt types, with more pronounced changes observed in base asphalt. High-temperature rheological parameters (G*/sinδ), recovery rate, and non-recoverable creep compliance indicated compromised resistance to permanent deformation. SBS-modified asphalt substantially mitigated these detrimental effects. Fatigue life of base asphalt decreased overall with periodic fluctuations, whereas SBS-modified asphalt exhibited superior fatigue stability: after an initial decline at 5 days, performance recovered and stabilized between 10 and 15 days. Low-temperature performance showed slight improvement in base asphalt, while SBS-modified asphalt demonstrated significant enhancement during later activity stages. Full article

Recent tailing dam failures in Brazil have been attributed to liquefaction. Chemical stabilization offers a promising solution to enhance the strength and stiffness of tailings and mitigate liquefaction potential. This study investigated the mechanical and microstructural behavior of gold mine tailings (GMTs) stabilized using (i) an alkali-activated binder composed of sugar cane bagasse ash (SCBA), hydrated eggshell lime (HEL), and sodium hydroxide (NaOH) and (ii) Portland cement (PC). Drained and undrained triaxial shear tests and scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS) analyses were performed. Specimens stabilized with Portland cement exhibited a strong strain-softening behavior and the highest strength, with 5.3 MPa under 200 kPa confining pressure compared to 2.3 MPa for alkali-activated samples and 740 kPa for untreated GMTs. The addition of either binder also increased both the peak effective friction angle and the critical state stress ratio, confirming an enhanced shear strength. SEM-EDS analyses confirmed the formation of cementitious reaction products, explaining these improvements. This research validates both binders as viable solutions for tailing stabilization, with the novel alkali-activated binder offering a sustainable alternative for large-scale applications. Full article

Micro-pillar compression is a popular experimental technique used for characterizing the mechanical behavior of nano- and micro-laminates. The compressive stress–strain response of the column-shaped thin-film composite can be measured, and the deformation and damage features can be revealed by post-test cross-section microscopy. The development of plastic instability in the form of localized strain concentration (shear bands), leading to eventual failure, is frequently observed. In the present study, a computational approach is used to illustrate the commonality of shear band formation from a continuum standpoint. Systematic finite element analyses are conducted, showing that the strain field tends to become localized once plastic yielding commences. Distinct shear offsets of the layered structure can be revealed from the numerical model, which is similar to those observed in experiments. The actual appearance of shear bands depends on the materials’ constitutive behavior and precise geometries. Post-yield strain hardening reduces the propensity of shear band formation, while strain softening enhances it. Imperfections such as the undulated layer geometry, as well as the frictional characteristics between the specimen and test apparatus, can also influence the shear band morphology and overall stress–strain response. Full article

Crack initiation, propagation, and slippage serve as the key mesoscopic mechanisms contributing to the deterioration of deep tunnel surrounding rocks. In this study, a secondary anisotropy of deep tunnels surrounding rocks was proposed: The axial-displacement constraint of deep tunnels forces cracks in the surrounding rock to initiate, propagate, and slip in planes parallel to the tunnel axial direction. These cracks have no significant effect on the axial strength of the surrounding rock but significantly reduce the tangential strength, resulting in the secondary anisotropy. First, the secondary anisotropy was verified by a hybrid stress–strain controlled true triaxial test of sandstone specimens, a CT 3D (computed tomography three-dimensional) reconstruction of a fractured sandstone specimen, a numerical simulation of heterogeneous rock specimens, and field borehole TV (television) images. Subsequently, a novel SSA (strain-softening and secondary anisotropy) constitutive model was developed to characterise the secondary anisotropy of the surrounding rock and developed using C++ into a numerical form that can be called by FLAC^3D (Fast Lagrangian Analysis of Continua in 3 Dimensions). Finally, effects of secondary anisotropy on a deep tunnel surrounding rock were analysed by comparing the results calculated by the SSA model and a uniform strain-softening model. The results show that considering the secondary anisotropy, the extent of strain-softening of the surrounding rock was mitigated, particularly the axial strain-softening. Moreover, it reduced the surface displacement, plastic zone, and dissipated plastic strain energy of the surrounding rock. The proposed SSA model can precisely characterise the objectively existent secondary anisotropy, enhancing the accuracy of numerical simulations for tunnels, particularly for deep tunnels. Full article

Coral sand is characterized by unique particle morphology and pore structure, which result in pronounced dilatancy and a high internal friction angle during shear. The dilatancy angle is a critical parameter for finite element analyses of sand foundation bearing capacity; the inappropriate selection of this parameter can lead to significant computational errors. In this research, a series of consolidated drained triaxial tests were conducted on coral sand samples from the South China Sea to investigate the dilatancy behavior and its effect on shear strength parameters. A dilatancy equation for coral sand was proposed, incorporating the dilatancy index, relative density, and mean effective stress. The results indicate the following: (1) Within the confining pressure range of 25–400 kPa, the stress–strain curves exhibit varying degrees of strain softening. When the effective confining pressure reaches 400 kPa, the dilatant behavior is nearly suppressed, resulting in a transition from dilatancy to contraction; (2) The peak internal friction angle decreases significantly with increasing effective confining pressure. However, the sensitivity to confining pressure varies for samples with different relative densities (Dr = 30–90%), with denser samples showing a more rapid reduction in peak friction angle; (3) At a confining pressure of 25 kPa, the maximum dilatancy angle of coral sand samples reaches 44.2°, significantly exceeding the typical range observed in terrestrial quartz sands. This difference may be attributed to the irregular and angular characteristics of the coral sand particles; (4) Based on Bolton’s dilatancy theory, a dilatancy equation applicable to coral sand was developed, demonstrating a strong linear relationship among the dilatancy index (I_R), relative density (Dr), and peak mean effective stress (p′_f). These findings provide valuable guidance for the selection of strength parameters for engineering applications involving coral sand. Full article

Calcareous sands are widely distributed across the South China Sea’s continental shelf and coastlines. Understanding their mechanical behavior and microstructural evolution under cementation is critical for coastal engineering applications. While previous studies have investigated cemented calcareous sands, the comparative analyses of particle breakage and microstructural characteristics between cemented and pure sands remain limited. This study combines triaxial compression tests with X-ray CT scanning and Digital Volume Correlation analysis to systematically examine both material types. Pre- and post-loading CT scans enabled the detailed tracking of microstructural transformations. Results demonstrate that cemented specimens exhibit higher strength–stiffness properties with strain-softening behavior compared to pure sand under 200 kPa confining pressures. A quantitative analysis revealed greater particle breakage in cemented sand, while pure sand showed more pronounced increases in particle sphericity and the aspect ratio during deformation, accompanied by reduced porosity variation along specimen height (coefficient of variation decreased from 15.2% to 12.8% for pure sand. Microstructural analysis indicated moderate increases in pore sphericity and reduced anisotropy in both materials. Fractal dimension analysis demonstrated more significant structural reorganization in cemented sands. Both materials exhibited increases in key morphological parameters, including the throat equivalent radius, channel length, pore equivalent radius, and coordination number, with changes being more substantial in cemented sands. Within shear band regions, cemented sands displayed marked reductions in pore and throat quantities. These findings elucidate fundamental relationships between cementation effects and micro–macro mechanical responses, providing theoretical support for geotechnical applications involving calcareous sands. Full article