Search Results (445)

This paper addresses the elastoplastic torsion and tension of a prismatic bar with a multiply connected circular cross-section containing one central and four symmetrically arranged lateral holes. The relevance of this problem stems from the fact that internal contours alter the shear-stress flow, amplify local gradients, and cause non-uniform development of plastic zones. The study considers a two-parameter loading scenario. It is demonstrated that for the same final combination of axial force and torque under different strain trajectories, the equivalent-stress fields and effective torsional stiffness significantly depend on the loading sequence. The obtained results confirm the necessity of simultaneously considering hole geometry, plastic flow, and loading history when analyzing multiply connected bars. Full article

The flexural behaviour of body-centred cubic (BCC) lattice beams fabricated by stereolithography remains supported by limited experimental evidence, and available homogenized beam models are rarely confronted with data in the combined regime of high relative density, non-slender struts, and low span-to-depth ratios. This work presents an experimental campaign on polymeric BCC lattice beams with three unit-cell edge lengths ($L=3$, 4, and 5 mm) and a constant strut-to-cell ratio $R/L=1/6$, yielding a relative density ${\rho }^{*}\approx 0.423$. Specimens were tested under uniaxial compression and three-point bending for nine combinations of geometry. The experimental data are compared with three analytical frameworks: a classical Euler–Bernoulli homogenized beam model and a BCC-specific shear-corrected formulation at the structural level, both evaluated without calibration to the bending tests, together with a strain-gradient extension whose intrinsic length scale is calibrated against them. For the effective Young’s modulus, the closed-form expression of Lee et al. reproduces the compression data within 10%, whereas the Tancogne-Dejean and Mohr model remains markedly stiffer even after the strut-level Timoshenko correction is included. In bending, none of the models proves adequate over the full geometric range: the Euler–Bernoulli model is accurate for several configurations (errors below 16% in five of nine cases) but overestimates the stiffness by up to 108% for the deepest specimen; the shear-corrected model reduces the global root mean square error from 97.94 to 24.44 N/mm (approximately a factor of four), but introduces excessive flexibility in some slender and intermediate configurations; and the strain-gradient correction, being strictly stiffening, yields no appreciable improvement. To avoid assigning the discrepancy to a single mechanism, the bending data are further analysed through an experimental compliance decomposition. The additional compliance relative to Euler–Bernoulli theory is small or negative in several cases, showing that shear flexibility alone cannot explain the full dataset, but becomes dominant for the deepest beams. The results therefore delineate the range of validity of simple homogenized beam models for dense finite BCC lattice structures and identify the combined influence of structural shear, non-slender struts, nodal-region morphology, finite-cell and boundary effects, local roller-contact compliance, and the discrete distribution of struts across the cross-section as the main mechanisms requiring more refined descriptions. These findings correspond to a single relative density (${\rho }^{*}\approx 0.423$) and a single strut-to-cell ratio ($R/L=1/6$), so the resulting span-to-depth indicator ($L_0/h\approx 2.5$) should be regarded as indicative for this class of dense lattices rather than as a general design rule. Full article

Frozen soil on alpine slopes is influenced by inclination and aspect-induced differential solar radiation effects, resulting in non-uniform temperature fields and inclined layered ice lenses that enhance anisotropy and degrade mechanical properties. This study investigates the deformation and strength responses of frozen soil under different temperature-gradient magnitudes and orientations and ice-lens conditions. A stress–strain constitutive model incorporating the magnitude and orientation of the temperature gradient is established. In addition, an equal-scale discrete element model based on the parallel-bond contact model is developed and calibrated against the laboratory results. The numerical specimen is divided into 13 layers, and temperature-dependent interparticle bond properties are assigned layer by layer to reproduce the prescribed magnitude and orientation of the temperature gradient. Results show that the orientation of the temperature gradient significantly alters the mechanical response and failure mode. As the inclination angle increases, the failure mode transitions from compressive dilatancy to combined dilatancy–shear failure and ultimately to shear-dominated failure. At −10 °C, increasing the inclination angle from 0° to 30° reduces the compressive strength by 44.48%. The elastic modulus also decreases with increasing inclination, with a maximum inclination-induced difference of 111.98 kPa. Moreover, the presence of an ice lens further reduces specimen stiffness, and the elastic-modulus difference between ice-lens-bearing and ice-lens-free specimens increases from 5.57 kPa at −1 °C to 75.72 kPa at −10 °C. The DEM results show that particles at the top and bottom of the specimen primarily undergo vertical displacement, whereas particles in the middle region exhibit dominant horizontal displacement, forming an X-shaped shear band. The inclined temperature gradient produces a heterogeneous distribution of interparticle bond strength within each horizontal layer. As inclination increases, the shear band evolves from symmetric to asymmetric; particle displacements on the side toward which the temperature gradient points are larger than those on the opposite side, revealing the microscopic origins of macroscopic mechanical behavior. Full article

Metal additive manufacturing (MAM) enables the fabrication of geometrically complex and high-performance components but is accompanied by steep thermal gradients, repeated thermal cycling, phase transformation, residual stress, and deformation. These effects can reduce dimensional accuracy, manufacturing stability, fatigue resistance, and service reliability. This review systematically examines residual-stress and deformation behavior in MAM from the perspectives of formation mechanisms, influencing factors, measurement and prediction methods, mitigation strategies, and service-related consequences. The temperature gradient, mechanical constraint, and phase transition mechanisms are discussed as quantitatively coupled rather than independent processes. Comparative attention is given to process-specific differences, alloy-dependent thermophysical and metallurgical behavior, multi-track and multi-material interactions, and complex geometries. Destructive and non-destructive measurement techniques are compared in terms of penetration depth, spatial resolution, uncertainty, and cross-validation. Thermo-mechanical finite element, inherent strain, analytical, reduced-order, machine-learning, physics-informed, and digital-twin approaches are evaluated according to accuracy, efficiency, transferability, and applicability. Mitigation strategies are further compared considering residual-stress reduction, deformation control, manufacturing cost, and mechanical-property retention. Finally, challenges associated with uncertainty quantification, service environments, post-machining stress redistribution, and closed-loop control are identified. This review provides an integrated framework for selecting measurement, prediction, and mitigation approaches for reliable and high-precision MAM. Full article

High-purity quartz is a critical raw material for high-tech industries such as semiconductors and photovoltaics, yet its purity is severely constrained by gas–liquid inclusions within quartz crystals that are difficult to eliminate. The calcination–water quenching process is a key pretreatment step for removing inclusions and achieving deep purification, but its underlying mechanisms and the influence of process parameters on removal efficiency remain insufficiently understood. In this study, systematic calcination–water quenching experiments at different temperature gradients (500 °C, 700 °C, 900 °C, and 1100 °C) were conducted on high-purity quartz samples from Inner Mongolia and Angola. Comprehensive analytical techniques, including X-ray diffraction (XRD), major and trace element analyses, and polarizing microscopy, were employed to investigate the microstructural evolution, inclusion morphology, impurity element concentration changes, and phase transformation behavior before and after treatment. With increasing temperature, the quartz samples exhibited pronounced whitening and pulverization, accompanied by a significant reduction in the number of internal linear inclusions. Elemental analysis revealed that calcination–water quenching effectively removed certain alkali metals, alkaline-earth metals, and iron impurities, with 900 °C identified as the optimal calcination temperature; moreover, the sand-sized samples consistently showed better impurity removal efficiency than the lump-sized counterparts. XRD analysis was used to verify the phase transformation of quartz during calcination. Excessive temperatures (e.g., 1100 °C) led to a rebound in the content of some impurity elements. The calcination–water quenching process promotes inclusion decrepitation, exposure, and subsequent removal through the combined effects of volumetric strain induced by quartz phase transitions, thermal pressurization of inclusions, and thermal-shock stress from water quenching. This study establishes the optimal process window (hold at 900 °C for 2 h, sand-sized morphology) for the specific ore samples, elucidates the multi-factor synergistic mechanism of inclusion rupture, and provides both experimental and theoretical bases for the industrial purification of high-purity quartz. Full article

Carbon fiber-reinforced polymer (CFRP) composites are increasingly used in aerospace, rail transportation, and energy engineering owing to their high specific strength and corrosion resistance. However, their complex and interacting damage mechanisms, including delamination and matrix cracking, present significant challenges for reliable structural health monitoring. Fiber Bragg grating (FBG) sensors offer distinct advantages for monitoring composite structures because of their compact size, immunity to electromagnetic interference, embeddability, and capability for distributed strain measurement. Nevertheless, the effectiveness of an FBG sensing network depends strongly on the spatial distribution of the sensing points. This study proposes a finite-element-assisted framework for evaluating and improving FBG sensor layouts for strain-field reconstruction and structural feature characterization of composite plates. The framework first reconstructs the spatial strain field from limited sensing data using interpolation and least-squares fitting methods, and then evaluates the performance of existing and candidate sensor layouts based on reconstruction errors and spatial coverage of structurally important regions. A strain-gradient-informed heuristic strategy is subsequently developed to improve sensor placement by combining high-gradient region identification, spatially uniform coverage, minimum-distance constraints, and predefined support-region monitoring requirements. The Fourier least-squares fitting method provides the lowest reconstruction error among the investigated approaches and is therefore adopted for subsequent layout evaluation and improvement. Finite-element simulations and experimental measurements are used to assess the reconstruction performance and identify the advantages and limitations of different sensor layouts under static and dynamic loading conditions. The results demonstrate that the proposed framework can effectively evaluate existing FBG layouts and provide a systematic basis for their improvement, while also revealing the trade-off between local strain-gradient resolution and global spatial coverage. The proposed framework provides practical guidance for the performance-oriented design and improvement of FBG sensor networks for structural health monitoring of composite structures. Full article

Fused deposition modeling (FDM) is one of the most widely deployed additive manufacturing methods, and the mechanical performance of FDM-printed parts is governed by a small set of strongly coupled process parameters. Silk PLA, a PLA-based filament engineered to deliver a high-gloss finish with improved mechanical performance, has received far less attention than commodity PLA, and its parameter–property relationships remain incompletely characterized. In this work, the effects of three FDM printing parameters: (i) layer height (0.10, 0.15, and 0.20 mm), (ii) extrusion temperature (200, 210, and 220 °C), and (iii) print speed (100, 120, and 140 mm/s) on the tensile characteristic of Silk PLA were investigated through a full-factorial design consisting of 27 parameter combinations and 135 ASTM D638 Type-I specimens. Tensile tests were performed on an MTS E42 universal testing frame, while Digital Image Correlation (DIC) was employed to obtain full-field longitudinal and transverse strain distributions and to identify the onset and location of necking. Analysis of variance (ANOVA) was used to assess the statistical significance, while an interpretable machine learning (ML) pipeline combining extreme gradient boosting (XGBoost), Shapley additive explanations (SHAP) values, and partial dependence plots (PDPs) was employed to quantify the relative influence of each parameter and elucidate its effect on the tensile response. Both analyses identified extrusion temperature as the dominant factor governing ultimate tensile strength and Young’s modulus. Partial dependence analysis further revealed that strength gains saturate above 210 °C and are maximized at an intermediate print speed of 120 mm/s, providing actionable guidance for process optimization. The highest tensile strength, 40.68 MPa, was achieved at a layer height of 0.20 mm, an extrusion temperature of 220 °C, and a print speed of 120 mm/s. DIC measurements showed that thinner layers (0.10 mm) produced higher breaking strains and necking that initiated at the gauge-section edges, whereas thicker layers (0.20 mm) shifted necking toward the mid-gauge. Together, the experimental, statistical, and ML results provide a consistent, mechanistically interpretable framework for optimizing FDM process parameters for Silk PLA functional parts. Full article

Cover cracking induced by steel corrosion is a critical issue governing the durability degradation of reinforced concrete structures in marine environments. The crack initiation and propagation processes dominated by non-uniform rust expansion stress fields urgently require high-resolution continuous monitoring techniques. In this study, based on the principle of Rayleigh backscattering, distributed optical fibers were embedded along the upper surface of specimens to conduct in situ monitoring of surface strain in concrete. The effects of specimen length, biochar content, cover thickness, and rebar diameter were systematically investigated. The results indicate that the surface strain evolution follows a two-stage pattern—a slow growth stage followed by a rapid rise stage—corresponding respectively to the early-stage filling of interfacial pores and stress accumulation, and the later-stage propagation of macroscopic cracks. Increasing specimen length significantly amplifies the spatiotemporal non-uniformity of strain, characterized by “locally high peak strains but low overall mean values,” with the onset time of strain surges differing by more than 50 h across different cross-sections. The incorporation of 0.5% biochar reduces the average strain by approximately 17% and delays crack initiation to 260 h. Increasing cover thickness from 25 mm to 40 mm exhibits the most pronounced inhibitory effect, achieving a 39% reduction in strain and delaying crack initiation to 320 h, primarily attributed to the extended chloride transport path and enhanced hoop confinement stiffness. Reducing rebar diameter from 20 mm to 12 mm decreases the peak strain to 79% of that of the standard specimen, owing to reduced rust product volume and increased relative cover thickness. The macro-cell effect driven by chloride concentration gradient transition zones is identified as a key factor governing crack initiation locations. Theoretical crack widths derived from strain integration of optical fiber data are slightly lower than measured values, yet the overall trends remain consistent. This study provides a quantitative basis for continuous monitoring and durability assessment of corrosion-induced cracking in marine environments. Full article

Concrete shrinkage is significantly influenced by the restraint level, and cracking often occurs under specific restraint conditions, thereby adversely affecting structural performance. Investigating the effect of restraint on shrinkage cracking is of great significance for enhancing early-age durability and ensuring structural safety. In this study, four distinct restraint levels (0%, 35%, 55%, and 75%) were established by varying the thickness of the inner steel ring. The influence of varying degrees of restraint on the shrinkage behavior was investigated, with digital image correlation (DIC) and internal strain gauge measurement employed to observe the strain and predict the risk of cracking. As the degree of restraint increases, the inner steel ring inhibits the free radial shrinkage of concrete more significantly, thereby inducing greater tensile strains at both the outer circumferential surface and the interior. The surface strain accumulation far exceeds the interior response due to the drying gradient. During the first 60 h, the shrinkage strain measured by both methods exhibited the most rapid evolution, indicating a critical high-risk period for cracking. These results advance the understanding of restraint effects in concrete and comprehensively clarify the relationship between the degree of restraint and the shrinkage, which accurately captures the evolution of shrinkage, facilitates the transition from empirical to quantitative design for crack-resistant materials and supports their customized optimization under practical engineering loading conditions. Full article

This study presents a comprehensive analysis and predictive modeling framework for the axial compressive strength (f_cc) and ultimate axial strain (ε_cu) of concrete columns confined within fiber-reinforced polymer (FRP) systems. Large databases comprising 3312 samples for f_cc and 3319 for ε_cu were compiled from the literature, encompassing a wide range of key variables, including unconfined concrete strength from 7 MPa to 204 MPa and diverse FRP confinement configurations. The datasets were subjected to extensive statistical and multivariate analyses to identify the primary factors influencing axial behavior and guide feature selection for predictive modeling. Three groups of machine learning (ML) algorithms were subsequently considered: (i) artificial neural networks (including multilayer perceptrons with one and two hidden layers), (ii) kernel-based models (Gaussian process regression and support vector regression), and (iii) tree-based ensemble models (gradient boosting machine, eXtreme gradient boosting, and light gradient boosting machine). Hyperparameters were optimized using grid search cross-validation, while feature importance analyses were performed to quantify the contribution of each input variable. Among all ML models, eXtreme gradient boosting demonstrated superior predictive performance, effectively capturing the nonlinear and multivariate interactions governing confinement effectiveness. Comparative analysis with the top performing regression-based formulations further highlighted the accuracy, robustness, and generalization capability of the eXtreme gradient boosting model. The findings provide a data-driven and interpretable framework for the design and prediction of FRP-confined concrete columns. Full article

Fe-Mn-Al-C lightweight high-strength steels are promising for aerospace and defense applications, but selective laser melting (SLM) introduces steep thermal gradients and rapid solidification, causing directional grain growth, crystallographic texture, and the non-uniform precipitation of κ-carbides and B2 phase at grain boundaries. This results in pronounced mechanical anisotropy between XY and YZ planes, limiting engineering use. To eliminate this anisotropy, we investigate the post-SLM solution treatment of an SLM-fabricated Fe-Mn-Al-C steel at 1050–1150 °C for 0.5–1.5 h followed by oil quenching, and characterize microstructures and tensile properties on both planes. At 1050 °C, the XY plane remained equiaxed γ-austenite, while the YZ plane transformed to α and became equiaxed over time, causing strength–ductility anisotropy. At 1100 °C for 1 h, anisotropy was effectively removed: XY and YZ planes exhibited tensile strengths of ~1159 and 1154 MPa and elongations of ~40% and 41%. TEM revealed that uniform fine κ-carbides and coarsened B2 at grain boundaries suppressed direction-dependent strain. At 1150 °C, dissolved boundary phases and diffuse intragranular κ-carbides severely reduced ductility. The optimal treatment is 1100 °C for 1 h, yielding a homogeneous microstructure and excellent isotropic properties. Full article

Laser-welded stainless steel joints usually suffer from strain localization and premature failure in the weld metal (WM) due to microstructural heterogeneity introduced during welding. In this work, surface mechanical rolling treatment (SMRT) was applied to laser-welded 304 stainless steel plates to enhance the mechanical performance of the welded joints. Laser welding introduced multiple heterogeneous features in the WM, including local Ni compositional fluctuations, nanoscale oxide particles and heterogeneous grain structures. Among them, the local fluctuation of Ni concentration is considered to play a dominant role by locally modifying the stability of γ-austenite and promoting strain-induced martensitic transformation during SMRT. As a result, the WM exhibited more severe grain refinement and a stronger gradient nanostructure than base metal (BM) under identical processing conditions. The near-surface hardness of the WM reached ~500 Hv, which was noticeably higher than that of the BM. Uniaxial tensile tests revealed that the yield strength increased from ~350 MPa to ~700 MPa, while the ultimate tensile strength reached ~1000 MPa with ~40% elongation. More importantly, the fracture location shifted from the WM to the BM after SMRT. The enhanced martensitic transformation and gradient nanostructure effectively suppressed strain localization and improved the mechanical reliability of the welded joint. Full article

Extensometers housed in vaults are capable of resolving strain changes of less than a nanostrain; however, they are differently distorted by variations in barometric pressure at different frequencies, which may result in complicated strain noise. Therefore, how to quantify the barometric effects in different frequency bands is a perennial challenge in extensometric observation and research. Since the first strain observations at the Geodynamical Observatory Jingyuan (NW China) in 2007, the barometric effect has proven significant. Nevertheless, the frequency dependence and underlying mechanism of this effect remain unknown. With targeted research lacking at present, this study attempts to adopt the transfer function method to provide a systematic diagnosis. The results indicate that (1) the North–South (NS) component responds significantly to low-frequency pressure waves, with a slight phase shift leading the phenomenon; (2) the East–West (EW) component responds well to pressure waves in high-, medium-, and low-frequency bands, and the frequency dependence of the barometric coefficient spectrum and phase shift spectrum is strong; (3) the frequency-dependent response effect of the EW component may be related to factors such as horizontal pressure gradient force, topography, and fracture medium. These findings not only contribute to sub-frequency band correction of the barometric effect at the Geodynamical Observatory Jingyuan but also deepen our understanding of the ground–atmosphere coupling mechanism in the fault zone. Full article

Flow forming has emerged as an effective route for manufacturing thick-walled Cu–Ni alloy tubes, particularly for producing gradient microstructures. To clarify the evolution of microstructure during deformation and to elucidate the mechanism governing ultrafine-grain formation, flow forming experiments were conducted on BFe10-1-1 thick-walled tubes. Finite element (FE) simulations and electron backscatter diffraction (EBSD) characterization were performed in parallel. On this basis, a coupled finite element analysis–cellular automaton (FEA-CA) microstructure evolution model was established, in which the local equivalent plastic strain (PEEQ) gradient was introduced to modify the geometrically necessary dislocation (GND) distribution at grain boundaries. The results reveal that the microstructural transformation during flow forming proceeds through a continuous high-angle boundary development pathway resembling continuous dynamic recrystallization. A marked through-thickness gradient in grain size is observed. Owing to the higher accumulated strain and stronger strain-gradient effects, the outer surface layer undergoes accelerated refinement and forms a stable banded ultrafine-grained structure with an average grain size of approximately 0.39 μm. The governing mechanism of ultrafine-grain formation exhibits a distinct pass-dependent response. During Pass 1, rapid substructure establishment dominates. In Pass 2, substantial grain refinement is driven by progressive grain-boundary misorientation increase and high-angle transformation. By Pass 3, the refinement rate decreases noticeably, and the microstructure approaches a saturated and relatively stable state. Full article

Understanding the absorption and desorption behavior of superabsorbent polymers (SAPs) in ionic environments is critical for their practical applications. Ion exchange between monovalent counterions within the SAP and multivalent cations (e.g., Ca²⁺) in solution not only induces macroscopic desorption but also generates non-uniform internal strain, creating a complex feedback loop with ion transport. This study establishes a phenomenological coupled model that integrates Fickian diffusion for ion transport with an elastic wave equation for SAP deformation. The coupling is realized through deformation-dependent diffusion coefficients and an ion-concentration-modulated elastic modulus, with the latter described by a first-order linear relationship over a limited range. Taking Ca²⁺ as a representative divalent cation, we systematically investigate the effects of solution concentration, SAP particle size, and ion dissociation degree. The model predicts several non-intuitive phenomena, including transient internal free Ca²⁺ concentrations exceeding the boundary concentration by up to ~15% and concentration gradient inversions for small SAP particles (radius 75 μm) at later times. Characteristic absorption time constants τ_a range from 98 s to 179 s depending on particle size and Ca²⁺ level. Simulated total Ca²⁺ uptake agrees with experimental data within an 8% mean relative error. The model is validated against macroscopic absorption/desorption curves and total Ca²⁺ uptake, while the predicted internal concentration and strain fields remain to be confirmed by spatially resolved experiments. These findings provide new mechanistic insights into the chemo-mechanical coupling in SAPs and offer guidance for their tailored design. Full article