Search Results (310)

This study investigates the influence of the spatial distribution of specific grinding power within the contact zone on subsurface layer modification and the resulting modification depth effects. In surface grinding experiments on AISI 4140, the width of cut and depth of cut were deliberately modified to generate distinct thermal loads within the grinding contact zone, with simultaneous measurement of tangential and normal grinding forces to quantify the mechanical loading conditions. The distribution of specific grinding power was analyzed with respect to its localization along the contact length and across the width of cut. The results indicate a predominantly uniform distribution of grinding power density within the contact zone under the investigated process conditions. Subsurface integrity was characterized in terms of tempering effects in metallographic cross-sections, hardness and residual stress depth profiles. These findings were correlated with Barkhausen noise measurements to establish a non-destructive assessment methodology for thermally induced modifications. Also, roughness measurements were evaluated. The experimental results reveal a consistent relationship between specific grinding power input and subsurface modification depth. Furthermore, a uniform grinding burn threshold was identified, indicating a critical condition for thermally induced surface damage. Full article

The gradual deterioration of interfacial performance in CRTS II (China Railway Track System II) slab ballastless tracks during long-term service can significantly affect structural stability and durability. Existing studies have mainly focused on the fatigue performance of the overall track system and individual structural layers, whereas probabilistic fatigue-life modeling of the interlayer interface remains relatively limited. This study investigates the fatigue life behavior of the track slab-CA (cement-asphalt) mortar interface under cyclic loading. An exponential stress life relationship was combined with a two-parameter Weibull distribution of fatigue life at a specified stress ratio to establish a multi-parameter Weibull-based probabilistic framework that links fatigue life, stress ratio, and failure probability. Push-out and positive tensile fatigue tests were conducted on composite specimens to obtain interface fatigue lives under different stress ratios. Leveraging the multi-parameter Weibull model and experimental data, the L-BFGS-B (Limited-memory Broyden-Fletcher-Goldfarb-Shanno with Box constraints) algorithm was employed to optimize the model parameters and construct a probabilistic fatigue life model. The calibrated model was then used to analyze the fatigue behavior of the slab-CA mortar interface under tangential and vertical loading. The results show that the proposed probabilistic framework provides good agreement with the interface fatigue test data and enables the fatigue-life distribution and failure probability of the interlayer interface to be evaluated under different stress ratios. The findings provide a probabilistic basis for fatigue assessment and durability analysis of CRTS II slab ballastless track interfaces. Full article

Accurate discrete element method (DEM) modelling of mature peanut plants is essential for simulating peanut harvesting, pod detachment, and harvest-loss formation. However, existing peanut DEM models are usually simplified as isolated pods, rigid cylindrical particles, or partial stem–pod structures, which limits their ability to represent the flexible deformation of vines and pod stalks and the fracture behaviors at the pod–pod stalk junction. In this study, a DEM-based flexible plant model was developed for mature peanut plants. The geometric dimensions, contact parameters, and mechanical properties of peanut pods, pod stalks, and stems were measured through physical experiments. The Hertz–Mindlin model was used for non-bonded contacts, whereas the Hertz–Mindlin with Bonding model was adopted to represent the flexible connections among plant organs and the fracture behaviors of the pod–pod stalk junction. The main DEM parameters were calibrated using Plackett–Burman screening, steepest ascent experiments, and central composite design. The results showed that the tangential stiffness per unit area and tangential critical stress at the pod–pod stalk junction were the dominant factors affecting pod detachment force. The optimized parameter combination was a tangential stiffness per unit area of 4.738 × 10⁵ N/m³ and a tangential critical stress of 9.350 × 10⁵ Pa, corresponding to a simulated tensile force of 6.73 N. Model validation was performed by comparing peanut harvesting simulations with field trials. The relative error of pod loss rate between simulation and field measurement was less than 7.55%, and the t-test result indicated no significant difference between the two datasets (p > 0.05). These results demonstrate that the proposed flexible peanut plant model can effectively characterize pod–pod stalk separation and can provide a reliable DEM modelling basis for peanut harvesting process analysis and equipment optimization. Full article

Localized stress concentration and defect accumulation are prone to occurring during metal spinning because of the coupled effects of complex loading and interfacial friction. In this study, a molecular dynamics model of metal spinning was established to investigate the effects of process parameters and temperature on the mechanical response, material flow, contact loading, and dislocation evolution behavior within the contact zone. The results indicate that the optimal deformation coordination is achieved with an arc radius of 25 Å, an indentation depth of 8 Å, and a tangential velocity of 1.5 Å/ps. Analysis of the normal and tangential forces shows that the normal load is rapidly established during the indentation stage, whereas the tangential load continuously increases with material shear transport. Both loads decrease significantly with increasing temperature. Elevated temperature effectively suppresses dislocation accumulation and simplifies the dislocation structure, causing the plastic deformation behavior to gradually transition toward a dominant primary slip-system mode. This study reveals the local deformation and dislocation evolution mechanisms during spinning and provides theoretical guidance for the process optimization of thin-walled spinning components. Full article

Dense granular materials under low confining stress and low shear velocity—conditions relevant to low-pressure powder handling, near-surface transport, and the upper layers of stored bulk solids—remain insufficiently characterized at the microstructural level. We perform three-dimensional discrete element method (DEM) simulations of annular shear of monodisperse glass spheres at σ = 1 kPa and v = 0.01 m/s, corresponding to an inertial number I ≈ 1.06 × 10⁻³ at the quasi-static limit of the dense flow regime. The steady-state friction coefficient stabilizes at μ_ss ≈ 0.78, consistent with the quasi-static limit of the μ(I) framework. The solid volume fraction decreases monotonically from φ ≈ 0.50 at the base to φ ≈ 0.35 near the top, while the tangential velocity decays exponentially with depth (decay length δ_s ≈ 10 mm). Particle trajectory tracking reveals a sharp kinematic transition near z ≈ 5–6 mm separating a quasi-rigid basal layer (z ≲ 5 mm) from an upper shear-active zone (z ≳ 6 mm). The contact force distribution follows an exponential decay P($f$/$⟨f⟩$) ∝ exp(−β·$f$/$⟨f⟩$) with β ≈ 0.45, with strong force chains selectively concentrated in the upper zone. Together, these four microstructural descriptors co-locate within a single transition band, providing quantitative benchmarks for material characterization and constitutive modelling at the lower boundary of dense flow. Full article

Based on measured data from a shale gas well, this study develops a wellbore temperature cycle model and a temperature–pressure coupled finite element model to evaluate cement sheath stress during multi-stage fracturing. Dynamic temperature and pressure boundaries are applied to calculate radial and tangential stresses, while cumulative mechanical degradation and failure modes are assessed using the modified Mohr–Coulomb criterion. The results show that cement sheath temperature changes significantly, and stresses vary periodically with fracturing stages. The injection period is the most critical stage for cement sheath failure. Lower casing pressure and reduced fracturing fluid displacement can improve stress distribution and reduce damage. Higher initial fluid temperature increases radial stress but decreases tangential stress, while shallower horizontal well depth weakens temperature–pressure coupling. Optimizing these parameters can mitigate cement sheath damage, enhance structural integrity, and ensure safe fracturing operations. Full article

This study presents a discrete–continuous flux-guided shape-refinement framework for freeform shell geometries under self-weight. The method evaluates the directional relation between a prescribed support-directed transmission field and the shell surface normal, identifies locally underperforming regions, applies top-down geometric updates, and reconstructs a continuous surface at each step. It is intended as a transparent intermediate stage between intuitive freeform design and high-fidelity structural verification. The framework is demonstrated on nine shell cases with different geometries, support conditions, height ranges, and surface irregularities. Across all the cases, the results show reduced normal-component misalignment and increased tangential alignment relative to the prescribed transmission field. A representative finite-element comparison provides case-specific supporting evidence that under a linear-elastic gravity-load model the refined geometry can reduce deformation and stress levels over large surface regions; however, it does not prove general structural optimality or fully membrane-dominated behavior. Geometric roughness remains a key limitation requiring explicit regularization in future work. The approach is positioned as a lightweight geometric pre-optimization tool for conceptual shell design, rather than as a substitute for equilibrium-based form-finding or detailed structural optimization. Full article

This study investigates the influence of specific heat input and weld configuration on heat affected zone hardness and residual stress of S960MC high strength steel welds. In total, five types of weld samples were manufactured by Tungsten Inert Gas (TIG) autogenous welding and Metal Active Gas (MAG) butt welding to simulate the effect of increasing heat input and constraining the relative motion of welded parts during the heating and cooling phase. The obtained results show that the highest axial tensile residual stresses with magnitude above 900 MPa, combined with a hardness drop in a range from 13 up to 18%, occur mostly in the sub-critical heat affected zone, making it the critical zone of the weld. Increasing the heat input during welding does not have a simple correlation with generating more residual stresses and the trends obtained on the surface are different from results evaluated at a depth of 0.2 mm. Restraining the relative part motion during the welding affects mostly the tangential residual stresses, causing an increase in their tensile magnitude localized in the middle of the heat-affected zone while almost no influence on the axial residual stress component was recorded. Full article

Metal magnetic memory (MMM) is a promising non-destructive evaluation method for ferromagnetic materials, allowing early detection of stress concentration and micro-defects under weak geomagnetic excitation. However, current magneto-mechanical coupling models are computationally complex and insufficient to characterize the full-cycle evolution of mesoscale physically short cracks. This work proposes a magnetic dipole model and its decomposed formulation for V-shaped cracks. Combined with theoretical derivation, finite element simulation, and in situ three-point bending tests on Q345 steel, the magneto-mechanical coupling mechanism and magnetic signal evolution during crack propagation are investigated. Results show that the MMM normal component exhibits obvious peak-peak features at the crack tip, while the tangential component shows a single-peak characteristic. Two critical signal mutations are observed at crack lengths of about 100 μm and 3000 μm, corresponding to micro-meso and meso-macro crack transitions, respectively. The model is verified with relative errors of 15.2% for H_x and 17.6% for H_y. This study reveals the quantitative correlation between MMM signals and full-lifecycle crack growth, supporting damage assessment and fatigue life prediction for ferromagnetic engineering structures. Full article

The structural integrity of hydraulic structures is frequently weakened by local scour processes downstream of weirs. This study investigates the relationship between hydraulic parameters and erosion patterns to improve the predictability of bed deformation. The research methodology integrates detailed field measurements from the Radomka River in Piaseczno with laboratory experiments using a 1:30 physical scale model of the existing weir. Bed shear stress demonstrated the strongest correlation with maximum scour depth (r ≈ 0.93; RMSE ≈ 0.0032), as it directly represents the tangential force acting on sediment particles at the bed surface, which controls their entrainment, transport capacity, and ultimately the intensity of local scour development, whereas near-bed velocity showed weak and non-significant dependence (r ≈ 0.26; ${\rho }_s$ ≈ −0.11). This weak dependence reflects the dominance of turbulence-induced velocity fluctuations and localized vortical structures in the near-bed region, which obscure the relationship between mean velocity and sediment mobilization. The relationships between mean velocity, Froude number, and scour depth were moderate (r ≈ 0.63–0.73) and showed nonlinear characteristics, confirmed by HSIC values up to 9.1 × 10⁻³, due to the complex interaction between flow structures and evolving bed morphology. This nonlinearity results from the interaction between turbulent flow structures, jet-induced vortices, and the dynamically evolving bed morphology, combined with the threshold-controlled and nonlinear response of sediment transport to hydraulic forcing. Among all tested parameters, bed shear stress ranked as the dominant predictor of scour depth, outperforming velocity-based indicators. These findings imply that including bed shear stress parameters significantly improves hydraulic structure safety assessments. This study based on 11 experimental runs concludes that a combined field and laboratory approach provides a robust framework for river engineering. Finally, an improved understanding of erosion mechanisms, as presented in this work, enhances the prediction of local scour development and supports the design of more resilient hydraulic infrastructure. Full article

Robotic tactile interfaces involving artificial skins often experience sliding contact conditions. At sliding interfaces, frictional loading, tangential stress, and impending slip dominate sensing behavior. This work demonstrates three-dimensional finite element (3D-FE) and Poisson–Nernst–Planck (PNP) modeling of layered ionic polymer–metal composite (IPMC) artificial skin under finger-like reciprocating sliding contact. The layered structure consists of a Nafion-based IPMC core sandwiched between thin upper and lower electrodes. A rigid acrylic slider is used to simulate reciprocating finger motion relative to the surface of the IPMC skin. A time-dependent contact mechanics model is first utilized to simulate temporal variations in normal and tangential contact fields for various coefficients of friction. Electrochemical response is then determined in COMSOL Multiphysics by coupling ion transport and electrostatics in a PNP framework to predict the output sliding current. Parametric studies are used to investigate the dependence of sensor response on the coefficient of friction, reciprocating history, layer geometry, and transport parameters. From the results, it can be noted that the resulting parameter offers a robust and physically meaningful description of the magnitude of contact-induced shear stress under multi-mode loadings, yet retaining the capability of responding to the presence of friction-induced mechanical excitation. The current model is aimed at dynamic shear sensitivity detection in sliding contacts. It is not designed for texture discrimination or fragment identification tasks. Thus, the current study demonstrates an important coupling parameter for 3D IPMC sensor models under contact and sets up a framework for enhanced electro-chemo-mechanical modeling of soft ionic tactile sensors. Full article

To address the stability challenges of surrounding rock in large-span open-off cuts within weakly cemented strata of western China, this study investigated the 1219 open-off cut at the Shila Wusu Coal Mine. An analytical elastic model for rectangular roadway stress was developed using complex variable function theory to examine the influence of the lateral pressure coefficient on stress distribution. Furthermore, numerical simulations were employed to characterize plastic zone evolution and evaluate support effectiveness. The results demonstrate that the lateral pressure coefficient significantly dictates the stress field: circumferential stress at the ribs intensifies with the increasing lateral pressure coefficient, while stress in the roof and floor decreases accordingly. Notably, tensile stresses develop in the roof and floor when the lateral pressure coefficient is less than 1. Stress extremes are concentrated at the roadway shoulders, exhibiting a distribution pattern where the ribs experience higher concentration than the roof and floor. The circumferential stress concentration coefficient exhibits a marked positive correlation with the lateral pressure coefficient. Numerical results indicate that post-support compressive stress at the shoulders reaches 39.24 MPa, with plastic zone widths of 1.64~2.06 m at the ribs, 2.70 m at the roof, and a significant 5.33 m at the floor, highlighting a pronounced risk of floor heave. Field loosening zone measurements of 1.08 m in the roof and 2.49 m in the rib align closely with numerical findings, confirming that the implemented support effectively constrains plastic zone development. By integrating theoretical derivation, numerical modeling, and in situ observations, this study establishes a robust theoretical and technical framework for the support design of large-span roadways in similar geological settings. Full article

Adhesive quasi-static tangential contact between a rigid indenter and a linearly viscoelastic half-space is investigated numerically using the Boundary Element Method. The indenter geometry is described by a power-law profile including parabolic (n = 2), conical (n = 1), and sharp-tip (n = 1/2) indenters. Adhesion is incorporated through a stress-based detachment criterion with effective works of adhesion derived from an energetic approach for quasi-static viscoelastic contacts. During sliding, elements at the leading edge of the contact attach, while those at the trailing edge detach. Due to the viscoelastic response of the material, adhesion at the leading edge is weak, whereas adhesion at the trailing edge is significantly stronger. This asymmetry generates a tangential force acting at the contact boundary. Numerical simulations performed for different ratios of the shear moduli G₀/G₁ show that the friction force strongly depends on the indenter geometry and follows different power-law relations to the normal force: a one-third power for parabolic indenters, a square-root dependence for conical indenters, and a two-thirds power for sharp-tip indenters. Full article

Gas–liquid cyclone separators are an efficient and emerging method for air removal in hydraulic systems, yet often suffer from excessive pressure loss. A novel contracting inlet guiding structure is proposed to minimize hydraulic losses. This study adopts a comprehensive methodology combining theoretical modeling, computational fluid dynamics (CFD) using the Reynolds Stress Model (RSM), and experimental validation. A theoretical pressure-loss model incorporating the diminishing-returns effect of the contraction angle was established. Simulations revealed that increasing the contraction angle reduces energy dissipation by improving the uniformity of the tangential-velocity field. Based on the balance between pressure-loss reduction and degassing potential, a contraction angle of 11° was identified as the optimal design and experimental tests on a prototype confirmed the validity of the numerical model. The results demonstrate that, compared to the conventional straight tangential inlet, the optimized inlet reduces the pressure loss by approximately 30% under rated conditions. The experimental–numerical discrepancy decreases significantly with flow rate, achieving a relative error of approximate 10% at the design flow rate. These findings provide a theoretical basis and practical guidance for the low-energy design of hydraulic cyclone separators. Full article

A hard spot defect refers to structural defects that occur in long-distance oil and gas pipelines during the thermal processes. These defects arise from the combination of material phase changes and stress concentration, making them challenging to detect. Weak magnetic detection technology is an effective approach for identifying microscopic phase transformations and stress concentrations in materials. This study develops an ontological model linking hardness, stress, and magnetic signals at hard spots, and both simulations and real experiments are conducted to validate the model. The findings indicate a strong correlation between the model and experimental observations. The research also examined how hardness and defect shape influence magnetic signals and revealed that both the tangential and normal components of the weak magnetic signal at hard spots increase with higher hardness levels. Additionally, the peak value of the defect rises with an increasing depth-to-width ratio, and the difference between the center and peak values grows. According to the linear variation in the current constitutive model, the magnetic signal amplitude increases by approximately 35% for every 0.8% rise in hardness, with growth rates of 0.23% and 0.26% for the amplitude at the center and peak endpoint of the tangential magnetic signal, respectively. The hard spot shape parameter, H_d, is derived from the spacing of the tangential and normal peak-to-peak values, which indicates the size of the hard spot and increases consistently with the depth-to-radius ratio. Full article