Search Results (810)

To reveal the mechanism of the load transfer of drilling shaft lining under the influence of filter cake, this study establishes a mechanical interaction model that integrates the surrounding rock, filter cake, backfill layer, and shaft lining system based on elastoplastic theory. The analytical solution of this system was derived; this was followed by the systematic examination of the impact of the key parameters (thickness of filter cake, elastic modulus of surrounding rock, cohesion, and internal friction angle) on stress field evolution and load distribution. The operational mechanisms of filter cake and load formation principles in drilling shaft linings were elucidated. The results show that the filter cake induces stress concentration in surrounding rock by delaying stress transmission, effectively mobilizing the bearing capacity of surrounding rock and improving the stress state of the lining. An increase in the elastic modulus of the surrounding rock enhances the load-bearing proportion of the surrounding rock, thereby reducing the load transferred to the backfill layer and shaft lining. Higher cohesion and a higher internal friction angle of the surrounding rock strengthen the bearing capacity of the surrounding rock, which decreases the load transmitted to the backfill layer and shaft lining. The increased stiffness of the backfill layer raises the load-bearing proportion of the backfill layer, while diminishing loads on both the shaft lining and surrounding rock. The above research provides a theoretical basis for promoting the application of drilling technology in deep, water-rich, and weakly cemented bedrock formations in western China. Full article

This study investigates the relationship between microscale indentation creep and macroscale tensile creep of immiscible polymer blends. Micro- and macroscale creep were measured across the full composition range of model poly(lactic acid)/poly(caprolactone) blends (PLA/PCL), using indentation loadings of 50 and 300 gf and a tensile loading of 2 kg. The creep data were fitted with the empirical power law (PL) model and three phenomenological elasto-visco-plastic (EVP) models implemented in our open-source Python package MCREEP (version 1.1.6). Traditional creep descriptors, such as indentation creep (C_IT) defined by ISO standard or the creep exponent (n) from the well-established empirical PL model (deformation = C·tⁿ), yielded inconsistent or even misleading results. However, detailed analysis of the creep curves showed that alternative creep descriptors, such as the total deformation corrected for the initial deformation, exhibited the same trends at the micro- and macroscale and strong linear correlations (R² > 0.97). These findings demonstrate that short-term microindentation creep can predict the ranking of macroscale creep behavior in polymer blends, provided that suitable creep descriptors are employed. Full article

Grouted connection segments are key load-transfer components in offshore wind jacket structures, and their axial compressive performance is essential for the safety and reliability of the foundation system. This paper develops a finite element model of a grouted connection segment incorporating steel-fiber-reinforced high-strength grout to investigate its mechanical behavior and parametric effects under axial compression. A 1:7-scale model test is conducted to verify the numerical model through comparisons of the load–displacement response and strain responses at key locations. The steel tubes are simulated using a trilinear hardening elastoplastic model, while the steel-fiber-reinforced high-strength grout is represented using the concrete damaged plasticity model with corresponding tensile and compressive constitutive relationships and damage parameters to characterize its nonlinear response. Based on the validated model, a full-scale numerical model is established to analyze the effects of steel tube thickness, shear key spacing, shear key height, and shear key width using the control variable method. The results indicate that steel tube thickness has the most significant influence on the ultimate bearing capacity and can improve the load-bearing capacity and ductility of the structure. Shear key spacing mainly affects axial stiffness and deformation compatibility, while shear key height and width have limited effects on the ultimate bearing capacity but contribute to local deformation control and stiffness enhancement. The findings provide a validated numerical basis for evaluating the axial compressive behavior of steel-fiber-reinforced grouted connections and offer a useful reference for the design and parameter optimization of grouted connection segments in deep-water offshore wind jacket structures. Full article

An active vibration-based methodology for structural health monitoring of polymer-matrix composites is presented, in which piezoelectric actuators excite resonant vibrations and the diagnostic information is carried by two nonlinear characteristics: the backbone curve and the amplitude-dependent logarithmic decrement. Both are described by a single elastoplastic model of the Iwan (microplasticity) type with a power-law distribution of yield thresholds. The two characteristics share a common power-law exponent, and the model predicts a parameter-free ratio between the modulus defect and the hysteretic intensity. The four parameters are identified by a joint Bayesian fit. The methodology is applied to two carbon-fiber-reinforced polymer objects: a cantilever beam with a symmetric stacking sequence (three modes, 87 to 1431 Hz) and a plate strip with an unsymmetric one (two modes near 34 and 203 Hz), each tested intact and after controlled local damage. The measured ratio reproduces the prediction within 4 to 12%; whereas, the fundamental plate mode reveals a non-frictional, matrix-dominated dissipation. Local damage increases the hysteretic intensity 1.4 to 2.3 times and the modulus defect up to 2.7 times, while the resonant frequency changes by less than 0.8% and the background decrement remains nearly unchanged, giving a compact damage signature with minimal baseline requirements. Full article

Steel moment-resisting frames are widely used in seismic regions, but conventional beam–column connections often suffer from concentrated damage and difficult post-earthquake repair. To address these issues, this study proposes a novel replaceable energy-dissipating slit beam–column joint for steel frames. To enhance structural energy dissipation efficiency, mitigate seismic damage, and enable rapid post-earthquake repair, the joint utilizes connectors as energy-dissipating elements such that plastic deformation is confined to these connectors while main beams and columns remain elastic throughout the loading history. A quasi-static test was conducted on the proposed joint. The test results indicate that the hysteresis loops are full and fusiform, demonstrating excellent energy dissipation capacity. The joint exhibits ductility coefficients of 6.30 and 5.27 under positive and negative loading, respectively, and the equivalent viscous damping coefficient remains above 0.30 after a rotation of 0.025 rad. Furthermore, plastic damage is primarily sustained by the connectors, with no evident yielding observed in other structural members. To further investigate the joint, it was applied to a three-story, four-bay, three-span steel frame for finite element analyses. Compared with a conventional rigid joint frame, the proposed joint frame under rare earthquakes reduces roof displacements by 20.97% (with the X-direction as the primary direction) and 16.23% (with the Y-direction as the primary direction), and maximum interstory drift ratios by 18.06% (with the X-direction as the primary direction) and 15.55% (with the Y-direction as the primary direction), while satisfying the code-specified limits of 1/250 for elastic and 1/50 for elastoplastic interstory drift ratios, thereby indicating its superior seismic performance. Full article

Steel wire ropes (SWRs) are exceptional load-bearing elements. However, conventional designs often treat them as passive structures, lacking strategies to actively program their ultimate load-bearing capacity and failure behaviors. To address this gap, this study systematically investigates the tunable load capacity and fracture characteristics of SWRs by developing a simplified power-law hardening elastoplastic constitutive model and a finite element framework integrated with a ductile-damage criterion. Following material parameter calibration via single-wire tests and independent experimental validation of the baseline model using 1 × 7 strand tensile tests, comprehensive numerical parametric studies were conducted to evaluate the simulation-based influence of core diameter (d_core), overall rope diameter (D), layer count (F), and strand configuration (S) on mechanical responses. The numerical results reveal that these geometric parameters act as effective tuning knobs that govern internal stress transfer pathways and ultimate load-bearing capacity. Specifically, simulations predict that increasing the $d_{\mathrm{core}}$ to 1.00 mm elevates the peak tensile force by 9.6% while maintaining a 90.07% tensile force efficiency (TFE, defined as the ratio of mean to peak tensile force). Furthermore, implementing a hybrid multi-strand architecture (SWR-S3) achieves an optimized TFE of 99.76%. These structural modifications facilitate internal strain synchronization, which effectively buffers localized stress peaks and dictates the progressive fracture sequence. Ultimately, this study demonstrates the potential of complementing traditional material enhancement strategies with active geometric parametrization. Rather than offering immediate industrial design rules, it provides a conceptual theoretical framework for exploring custom-tailored tensile strength profiles and predictable failure behaviors. However, because these advanced structural configurations are evaluated using idealized quasi-static finite element models, further experimental validation addressing real-world manufacturing constraints, residual stresses, and dynamic loading is required before practical engineering deployment. Full article

High-frequency induction hardening enhances the surface wear resistance and contact fatigue life of high-speed linear guides, but simultaneously produces an inhomogeneous, layered cross-sectional structure comprising a high-strength, low-ductility outer hardened layer and a low-strength, high-ductility inner core. This structural heterogeneity renders conventional straightening stroke prediction models—predicated on homogeneous material assumptions—fundamentally inadequate. Moreover, the iterative trial-bending operations ubiquitous in industrial practice progressively accumulate plastic strain, causing guide rails to exhibit erratic positive-to-negative deflection reversal during sequential straightening passes. To address these critical challenges, this study proposes a novel two-stage hybrid straightening strategy based on inverse finite element analysis (FEA) and closed-loop experimental feedback. An equivalent hardened layer depth (HD₀) is introduced as a parametric descriptor to construct a layered elastoplastic finite element model, and an inverse simulation strategy is developed to generate a comprehensive three-dimensional stroke–residual deflection prediction dataset encompassing both vertical and lateral straightening conditions across multiple support spans. Displacement-controlled three-point bending experiments validate the layered model and elucidate the mechanism by which cumulative plasticity progressively amplifies cross-sectional plastic sensitivity under repeated loading. Grounded in this physical insight, a hybrid straightening algorithm is formulated, combining dataset-driven initial stroke prediction for rapid large-deformation elimination with an upper-bound constraint and a measurement-feedback-driven sequential reduction compensation scheme for fine-tuning. Comparative experiments demonstrate that the proposed strategy effectively suppresses the oscillatory over-straightening characteristic of conventional empirical trial-and-error approaches, consistently reducing residual deflection below 0.05 mm within two to three loading cycles. This work bridges the gap between theoretical simulation and the complex physical state of actual machining, substantially improving both the efficiency and precision of straightening for guide rails with induction-hardened layers. Full article

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

High-speed permanent magnet motors, due to their high speed, compact size, and light weight, are increasingly widely used in renewable energy systems, electric pump drives, fuel cell air compressors, and other fields. As a core component of high-speed permanent magnet motors, the reasonable design of the rotor system structure directly affects motor stability. To ensure the safe and reliable operation of high-speed permanent magnet motors, this paper designs the structure of a certain type of high-speed electric pump rotor. First, the actual interference amount between the rotor permanent magnet and the high-temperature alloy sleeve under high-speed and high-temperature conditions is considered, and radial and tangential stress analyses are performed on both the rotor and high-temperature alloy sleeve to determine the optimal interference amount. Second, based on rotor dynamics and fluid–structure coupling theory, the natural frequency and critical speed of rotors under wet and dry modals are studied; on this basis, harmonic response analysis and fatigue assessment were conducted; furthermore, an elastoplastic mechanical model of the rotor sleeve is introduced to analyze the effects of interference amount and rotational speed on the sleeve’s yield failure; finally, the dynamic safety of the high-speed rotor structure is verified through modal tests and overspeed operation tests. The results show that the optimal interference amount for the rotor is 0.02 mm; the first-order critical speeds in both dry and wet modals are well above the rated speed of 40,000 rpm, with no risk of resonance; the minimum cycle for fatigue life is 6.9 × 10⁵, meeting usage requirements; the equivalent force on the rotor sleeve increases with speed and interference amount; when the speed exceeds 44,000 rpm, the sleeve undergoes plastic deformation and failure; modal test error is less than 5%. This paper provides theoretical basis and experimental support for the rotor structure design and strength evaluation of high-speed permanent magnet motor drive equipment. Full article

This study demonstrates that supercritical carbon dioxide phase-change fracturing technology can reduce acute pressure-related injury potential compared to conventional explosives in underwater reef clearance operations along the Yangtze River. Employing a stepwise “pipe test, numerical simulation and engineering application” framework, a novel rock–water–fish coupled HJC–Gruneisen elastoplastic model was established to simulate cross-medium shock wave attenuation processes. The supercritical CO₂ shock wave exhibits characteristics of “low peak overpressure (13% of equivalent explosives) and long duration (6–7 times longer than conventional explosives),” attenuating in water with a power-law index α = 0.717. A dual-parameter “resistance line (intact rock buffer between the fracturing tube and the rock–water interface)–water depth” correction model indicates that the resistance line reduces peak overpressure by 18.6%, while each 10 m increase in water depth enhances attenuation by 60.6%. The preliminary engineering critical safety threshold for 30 cm silver carp (indicated by swim bladder rupture) is 0.20 MPa. Based on the representative engineering scale of the Chaofu Waterway Regulation Project, characterized by water depths of approximately 6–16 m and a resistance-line-controlled buffer condition, a theoretical safety distance model R_safe was also derived. Under these engineering constraints, the application results indicate that the lethal zone was confined to 7.5–9.9 m, enabling precise lethal-injury-safe zoning. This work establishes a fish injury threshold and safety assessment system for supercritical CO₂ subaquatic fracturing, providing direct green guidelines for Yangtze River navigation projects. Full article

To address the structural deformation and mechanism jamming frequently observed in critical linkages during retraction and extension of door-coupled landing gear systems, this study proposes a rigid–flexible coupled dynamic modeling approach. A representative landing gear system was studied, and a high-fidelity rigid–flexible multibody dynamics model was developed based on a conventional rigid-body framework. The left linkage, which was prone to failure, was modeled as a flexible finite element component, while the remaining parts were treated as rigid bodies. A multibody dynamics method based on nonlinear finite element was adopted, incorporating elastoplastic constitutive relations and Lagrange constraint equations. Two materials, ultra-high-strength 300M steel and high-strength 7075-T6 aluminum alloy, were evaluated to investigate the influence of structural stiffness on critical linkage stress and door kinematics during deployment. Results showed that maximum stress occurred at the hinge joint, identified as the critical region for strength assessment. The peak stress for 300M reached approximately 168 MPa, about 8.4% higher than that of 7075-T6. However, 7075-T6 exhibited lower stress oscillation frequency and superior damping performance, which helped suppress high-frequency vibration. Material selection had negligible influence on door centroid displacement, velocity, and opening angle, and the motion trajectories remained highly consistent. Full article

This study investigates the tribological performance of three commercial PTFE-based Xylan^® coatings—Xylan^® 1425, Xylan^® 1052, and Xylan^® 1010—applied to 18CrNiMo7-6 steel under dry sliding conditions. Ball-on-Disk tests were conducted at normal loads of 5, 7.5, and 10 N, wear-track radii of 12, 16, and 20 mm, and corresponding sliding velocities of 0.31–0.52 m·s⁻¹. The tribological evaluation was complemented by measurements of coating thickness, surface roughness, nanoindentation, wear-track profilometry, scanning electron microscopy, EDS mapping, and post-test cross-sectional microscopy. All coatings reduced the coefficient of friction from approximately 0.49–0.64 for the uncoated steel to 0.09–0.13, corresponding to an average reduction of 78–80%. Xylan^® 1425 exhibited the highest nanohardness of 57.02 MPa, the highest reduced elastic modulus of 3.33 GPa, and the most favorable elastoplastic indices. It also achieved the lowest wear, with a volumetric loss of approximately 0.03 mm³ under the most severe conditions, representing a reduction of more than 99% compared with the substrate. Xylan^® 1010 provided the lowest friction but showed pronounced plastic deformation, whereas Xylan^® 1052 exhibited fragmentation and increased wear. Post-test cross-sectional microscopy confirmed local exposure of the steel substrate in both coatings. Overall, Xylan^® 1425 provided the best balance of low friction, mechanical stability, coating continuity, and wear resistance. Full article

Classic elastic–plastic models for concrete do not fully account for either the material properties of shotcrete or the influence of environmental factors, resulting in significant limitations in the research and application of shotcrete in tunnels. This paper comprehensively considers the early-age strength of tunnel shotcrete and the physical and chemical attack effects of a sulfate environment, to investigate the mechanical degradation mechanisms of tunnel shotcrete under sulfate conditions and establish a corresponding nonlinear elastoplastic model. This study carried out sulfate attack tests on tunnel shotcrete and systematically revealed the stress–strain evolution characteristics of shotcrete under sulfate attack. Based on experimental data on both chemical and physical attack, this paper improves the classical elastoplastic constitutive model and constructs an elastoplastic constitutive model applicable to both the early and hardening stages of shotcrete. Overall, the improved model can describe the stress–strain response of shotcrete reasonably well; however, due to the high inherent discreteness of the shotcrete material itself, some fitting deviations still exist near points of sudden change in strain or stress. Under sulfate chemical attack conditions, the cracking stress of shotcrete exhibits a nonlinear trend of first increasing and then decreasing as corrosion time progresses. Under physical attack conditions, the cracking stress shows a clear linear decrease. Furthermore, in high-concentration sulfate environments, the influence of sulfate concentration on cracking stress is moderately reduced. The results of this study provide theoretical support for the durability assessment and constitutive modeling of tunnel shotcrete in sulfate-corrosive environments. Full article

Cast irons are extensively used in high-temperature applications such as cylinder heads of heavy-duty diesel engines, where sustained exposure to high stresses and temperatures can initiate creep-related failure mechanisms, impacting their long-term durability and efficiency. Our previous experimental research demonstrated significant differences in creep mechanisms and behaviour of compacted graphite iron (CGI) under tensile and compressive loading. In situ analysis of the microstructural effects defining these differences during long-term high-temperature experiments is hardly possible. An alternative way to study these effects is to develop advanced micromechanical models using a finite-element method. The aim of this paper is to study the local responses at microscale (considering local distributions of stresses and strains) to macroscale long-term loading at high temperature employing direct introduction of microstructural features into numerical models. The models consider elasto-visco-plastic behaviour of the CGI material under tensile and compressive loading regimes. The novel results presented in this paper are applicable to cast irons as well as other heterogeneous materials such as metal matrix composites and the models presented can be used as a tool in the development of materials with microstructures customised for high-temperature applications. Full article

A critical research gap persists in modular steel construction regarding the seismic behavior of inter-module connections between square steel tubular columns and H-shaped steel beams. While numerous connection systems have been proposed, two fundamental challenges remain unresolved: the inherent conflict between construction efficiency and mechanical performance, and the insufficiency of restoring force models that systematically describe hysteretic characteristics and stiffness degradation under cyclic loading. To address these issues, a novel box-type modular connection between square steel tubular columns and H-shaped steel beams is proposed. A finite element model was established using ABAQUS, and the modeling methodology was validated against experimental results from the literature. The seismic behavior was systematically investigated, and a restoring force model with theoretical saturation and linear degradation was developed. Results show that the novel joint is a semi-rigid connection that satisfies the “strong column–weak beam” design principle. The outer ring plate shifts the plastic hinge away from the vulnerable beam end region, preventing failure at the beam–column connection. Among the detrimental factors identified, the insert-to-column gap has the most severe impact, causing up to a 49.5% reduction in energy dissipation and a 6.5% reduction in initial stiffness; the outer ring plate thickness below the beam flange thickness causes a 44.6% drop in energy dissipation. The proposed restoring force model, validated against nine calibration specimens and one independent specimen, predicts peak load with a deviation of only 1.14% and the equivalent viscous damping coefficient with a relative error of 14.7%, confirming its reliability in capturing the cyclic behavior of the joint. This study provides both design recommendations for engineering practice and a theoretical foundation for elasto-plastic analysis of modular frames with this connection type. Full article