Search Results (65)

This paper focuses on mixed seeds of Vicia villosa and Avena sativa, with their discrete element model and contact parameters being systematically calibrated and validated to provide reliable theoretical support for the structural design and parameter optimization of the air-assisted seed delivery system. The physical properties of both seed types, including triaxial dimensions, density, moisture content, Poisson’s ratio, and shear modulus, were first measured. The Hertz–Mindlin (no slip) contact model and the multi-sphere aggregation method were employed to construct the discrete element models of Vicia villosa and Avena sativa, with preliminary calibration of the intrinsic model parameters. Poisson’s ratio, elastic modulus, collision restitution coefficient, static friction coefficient, and rolling friction coefficient between the seeds and PLA plastic plate were determined through uniaxial compression, free fall, inclined sliding, and inclined rolling tests. Each test was repeated five times, and the calibration criterion for contact parameters was based on minimizing the relative error between simulation and experimental results. Based on this, experiments on the packing angle of mixed seeds, steepest slope, and a three-factor quadratic rotational orthogonal combination were conducted. The inter-seed collision restitution coefficient, static friction coefficient, and rolling friction coefficient were set as the experimental factors. A total of 23 treatments were designed with repetitions at the center point, and a regression model was established for the relative error of the packing angle with respect to each factor. Based on the measured packing angle of 28.01° for the mixed seeds, the optimal contact parameter combination for the mixed seed pile was determined to be: inter-seed collision restitution coefficient of 0.312, static friction coefficient of 0.328, and rolling friction coefficient of 0.032. The relative error between the simulated packing angle and the measured value was 1.32%. The calibrated inter-seed contact parameters were further coupled into the EDEM–Fluent gas–solid two-phase flow model. Simulations and bench verification tests were carried out under nine treatment combinations, corresponding to three fan speeds (20, 25, and 30 m·s⁻¹) and three total transport efficiencies (12.5, 17.5, and 22.5 g·s⁻¹), with the consistency coefficient of seed distribution in each row being the main evaluation variable. The results showed that the deviation in the consistency coefficient of seed distribution between the simulation and experimental measurements ranged from 1.24% to 3.94%. This indicates that the calibrated discrete element model for mixed seeds and the EDEM–Fluent coupled simulation can effectively reproduce the air-assisted seed delivery process under the conditions of Vicia villosa and Avena sativa mixed sowing, providing reliable parameters and methodological support for the structural design of seeders and DEM-CFD coupled simulations in legume–grass mixed sowing systems. Full article

Large-area membrane spacecraft, such as solar sails, must be tightly stowed before launch. However, excessive folding readily induces plastic creases that impede full on-orbit deployment and degrade membrane surface accuracy. To overcome this challenge, this study aims to quantify the mechanical response of Kapton films during folding and to establish a reliable welding process for post-fold sail membranes. Based on the theory of linear elastic engineering, an S-shaped folding model was theoretically simplified to obtain the relationship between the rebound force P of adjacent contact thin films and the thin-film spacing h. Then, the Kapton film folding process was numerically simulated based on the implicit static method by using ABAQUS. The stress–strain curves and mechanical parameters of the thin films measured through uniaxial tensile tests are applied to theoretical and numerical results. It is found that the P-h curves obtained by the theoretical, numerical, and experimental method have good consistency. Step-loaded creep tests show that, after 6 h, the mean spacing reductions Δh are 0.43 mm for 50 µm thin films and 1.05 mm for 125 µm thin films, matching simulation results within 3%. Finally, uniaxial tensile tests are conducted on the welded thin films to measure the strength of the thin-film welds under different welding temperatures and pressures. The tensile force and elongation required to eliminate weld wrinkles are also measured to explore the welding connection of Kapton film. Further, for 50 µm thin films with a 10 mm weld width, eliminating welding-induced wrinkles requires a tensile force of 9.61 N and an elongation of 0.43%. Full article

In response to issues of long construction cycles, high pollution, and labor shortages in traditional cast in situ subway station construction, a refined 3D model of a large-segment prefabricated subway station was established using ABAQUS software 2024, with mechanical behavior throughout the construction process studied based on the Shenzhen Huaxia Station project case. The model incorporates a concrete inelastic damage constitutive model and a steel elastic–plastic model, accurately simulates key components, including dry joints of mortise–tenon grooves, prestressed reinforcement, and bolted connections, and implements a seven-phase construction sequence. Research findings indicate the following: (1) During component assembly, the roof vault settlement remains ≤3.8 mm, but backfilling significantly increases displacements (roof settlement reaches 45 mm, middle slab deflection measures 66.91 mm). (2) Longitudinal mortise–tenon joints develop stress concentrations due to stiffness disparities, with mid-column installation slots identified as vulnerable zones exhibiting maximum Von Mises stress of 32 MPa. (3) Mid-column eccentricity induces structural asymmetry, causing increased deflection in longer-span middle slabs, corbel contact stress differentials up to 6 MPa, and bolt tensile stresses exceeding 1.1 GPa. (4) The arched roof effectively transfers loads via three-hinged arch mechanisms, though spandrel horizontal displacement triggers 5 cm rebound in diaphragm wall displacement. Conclusions confirm overall the stability of the prefabricated structure while recommending the optimization of member stiffness matching, avoidance of asymmetric designs, and localized reinforcement for mortise–tenon edges and mid-column joints. Results provide valuable references for analogous projects. Full article

The present study aims to investigate the orientation-dependent mechanical behaviors of ZnO single crystals under nanoindentation by molecular dynamics simulation. The load–indentation depth curves, atomic displacement, shear strain and dislocations for the c-plane, m-plane and a-plane ZnO single crystals were analyzed in detail. The simulation results showed that the elastic deformation stage of the loading curves for the three oriented ZnO single crystals can be described well by the Herz elastic contact model. The Young modulus values for the c-plane, m-plane and a-plane ZnO were calculated to be 122.5 GPa, 158.3 GPa and 170.5 GPa, respectively. The onset of plastic deformation occurred first in a-plane ZnO, then in m-plane ZnO, and lastly in c-planeZnO. The atomic displacement vectors in the three oriented ZnO single crystals were in good agreement with the primary activated slip systems predicted by the maximum Schmid factor. For the c-plane ZnO, the activated pyramidal {$11\overline{2}2$}<$11\overline{2}3$> slip system led to a complex dislocation pattern surrounding the indenter. A U-shaped prismatic half-loop was formed in the [$2\overline{11}0$] direction, confirming the activation of the prismatic {$10\overline{1}0$}<$11\overline{2}0$> slip system. For the m-plane ZnO, the activated prismatic {$10\overline{1}0$}<$11\overline{2}0$> slip system led to the preferential nucleation of dislocations along the $\left[\overline{11}20\right]$ and [$\overline{2}110$] directions. A prismatic loop was formed and emitted along the [$\overline{2}110$] direction, governed by a confined glide on {$10\overline{1}0$} planes. For the a-plane ZnO, the activated prismatic {$10\overline{1}0$}<$11\overline{2}0$> slip system led to dislocations concentrated in the [$\overline{1}\overline{1}20$] direction beneath the indentation pit, emitting a prismatic loop along this direction. Perfect dislocation (with a Burgers vector of 1/3 <$1\overline{2}10$>) is the dominant dislocation in the three oriented ZnO single crystals. The findings are expected to deepen insights into the anisotropic mechanical properties of ZnO single crystals, offering guidance for the development and applications of ZnO-based devices. Full article

As critical components in offshore wind turbine (OWT) systems, pitch bearings require exceptional fatigue resistance to ensure the extended operational lifespan and structural reliability demanded by marine environments. Failure of these bearings due to rolling contact fatigue (RCF) can severely affect the economic efficiency of offshore wind turbines and potentially lead to safety accidents involving both humans and machinery. A simulation model for pitch bearings used in a 3 MW OWT is established to study the RCF behavior under operational conditions based on continuum damage mechanics. Both the elastic and plastic damage are considered in the damage process through a Python script. A user subroutine UMAT is programmed to depict the gradual deterioration of mechanical properties. The results indicate that the fatigue damage of the raceway exhibits significant nonlinear characteristics, with elastic damage playing a predominant role in determining its fatigue life under operational conditions. Full article

The primary objective of this study is to establish an innovative theoretical framework for analyzing the behavior of an end-bearing pile-supported embankment. This proposed methodology extensively investigates various aspects, including the characteristics of relative slip at the interface between the pile and soil, the distinctive non-uniform deformation patterns typically observed in soft soils, and the substantial influence of pile–soil interaction on the evolution of soil arching phenomena. To precisely capture the frictional relationship and relative displacement within the pile–soil system, we introduce an enhanced ideal elastic-plastic model. Additionally, a deformation function is incorporated to simulate the non-uniform deformation of soft soils, and an improved soil arching model is developed to assess its impact on the overall behavior. The analytical solution is derived through the implementation of a stress and volume deformation continuity condition, and its validity is effectively demonstrated through numerical simulations. The results indicate that under the load of the embankment, relative slip at the pile–soil contact surface is a significant phenomenon and should not be neglected in theoretical calculations. The relative displacement between the pile and soil initially exhibits a linear relationship with depth, and later follows a quadratic function as depth increases. Full article

At the microscale, the three-dimensional morphological features of contact surfaces have a significant impact on the performance of electrical contacts. This paper aims to reconstruct the microscopic contact state of contact groups and to deeply study the effect of contact morphological features on electrical contact performance. To fully obtain multimodal data such as the three-dimensional micro-morphological features and chemical composition distribution of contact surfaces, this paper proposes a contact surface feature-matching method based on entropy rate superpixel seed point adaptive morphological reconstruction. This method can adaptively retain meaningful seed points while filtering out invalid seed points, effectively solving the problem of over-segmentation in traditional superpixel segmentation method. Experimental results show that the proposed method achieves a segmentation accuracy of 92% and reduces over-segmentation by 30% compared to traditional methods. Subsequently, on the basis of the moving and static contact group difference plane model and the W-M model, this paper constructs a three-dimensional surface fractal contact model with an irregular base. This model has the ability to layer simulate multi-parameter elastic and plastic and to extract fractal parameter point cloud height, which can more accurately reflect the actual contact state of the contact group. The model demonstrates a 15% improvement in contact area prediction accuracy and a 20% reduction in contact resistance estimation error compared to existing models. Finally, this paper compares and verifies the theoretical feasibility of the model, providing a new theoretical contact model for the study of the impact of three-dimensional micro-morphology on the electrical contact reliability. Full article

Current designs of sealing systems for non-adhesive flexible pipe end-fittings primarily address short-term loading conditions, often overlooking the creep behavior of polyvinylidene fluoride (PVDF) and the material used in the sealing layer. Over time, the creep of PVDF, particularly at elevated temperatures, can lead to excessive reduction in the sealing layer’s thickness, thereby compromising the sealing performance of the end-fittings. In this study, to address the creep-related issues in the sealing layer, the compression and compression creep tests of PVDF were conducted at different temperatures to establish the material’s elastic-plastic constitutive relationship and develop a creep constitutive model based on the time hardening model. Using the pressure penetration method within ABAQUS software, a two-dimensional axisymmetric finite element model of the end-fitting sealing system was constructed, incorporating the effects of internal fluid pressure. This model was employed to analyze the sealing performance while accounting for the materials’ creep behavior across varying temperature conditions. The results demonstrate that creep in the sealing layer occurs predominantly in the early stages post-installation. Furthermore, the API 17J standard, which stipulates that reduction in sealing layer thickness should not exceed 30%, is found to be conservative at high temperatures. In these conditions, although the thickness reduction exceeds 30% before the maximum contact pressure drops below the fluid pressure, no fluid leakage is observed. Thus, in the initial phase following installation, especially at elevated temperatures, monitoring for potential leakage is critical. This research is the first to quantify the long-term impact of PVDF creep behavior on the sealing performance of flexible pipe end-fittings through comprehensive experiments and simulation analysis. The findings provide both a theoretical foundation and practical guidance for enhancing the long-term sealing performance of flexible pipe end-fittings. Full article

Rupture discs, also known as bursting discs, are indispensable components in fluid-operated systems providing effective protection against hazardous over-pressure or partial vacuum. They belong to a special class of safety devices and are found in a variety of technical applications including pressure vessels, piping systems, reactors and boilers. In all application scenarios, rupture discs act as sacrificial parts that have to fail precisely at a predetermined differential pressure, opening a relief flow path for the working fluid. The membrane employed within rupture discs is usually made out of specific metal alloys or different material layers depending on the particular application. However, for many manufacturers of rupture discs, the production process is characterized by a lack of systematic procedures, relying instead on trial and error as well as empirical values. By means of thorough finite-element-based modeling and simulation of the bulge-forming process of rupture discs, including an elastic–plastic material law, large deformation, as well as contact mechanics, it is possible to accurately predict the resulting stress–strain behavior. All simulation results are rigorously validated through corresponding experiments conducted during the bulge-forming process. Therefore, this contribution provides a reliable basis for the parameter set-up during the manufacturing process of rupture discs. Full article

We aimed to investigate the fluid–solid–ice coupling mechanism as structures break through ice into water. Using LS–DYNA finite element software, a numerical simulation method is established, based on the ALE flow–solid coupling method, and the penalty function contact algorithm, which describes the structure–ice–water coupling interaction. The Eulerian algorithm is used to describe the air and water domains, while the Lagrange method is applied to the wedge and ice structure. The mechanical properties of ice are characterized using the elastic–plastic failure strain model. The feasibility of simulating the entry of structures into water via the ALE method is demonstrated by comparing the experimental and simulation results of wedges entering into water. The applicability of the ice material model in simulating collision–induced breakup is verified by comparing a simulation of a rigid plate hitting a spherical head of ice, with results from the ISO standard. The effects of water during icebreaking are assessed by simulating a wedge breaking through ice into water, as well as through ice without water. Additionally, the ice breakup and motion response of the wedge under different working conditions are compared by varying the wedge mass and icebreaking speed. Full article

A new unloading contact model of an elastic–perfectly plastic half-space indented by an elastic spherical indenter is presented analytically. The recovered deformation of the elastic indenter and the indented half-space has been found to be dependent on the elastic modulus ratio after fully unloading. The recovered deformation of the indented half-space can be calculated based on the deformation of the purely elastic indenter. The unloading process is assumed to be entirely elastic, and then the relationship of contact force and indentation can be determined based on the solved recovered deformation and conforms to Hertzian-type. The model can accurately predict the residual indentation and residual curvature radius after fully unloading. Numerical simulations are performed to demonstrate the assumptions and the unloading model. The proposed unloading model can cover a wide range of indentations and material properties and is compared with existing unloading models. The cyclic behavior including loading and unloading can be predicted by combining the proposed unloading law with the existing contact loading model. The combined model can be employed for low-velocity impact and nanoindentation tests and the comparison results are in good agreement. Full article

It is essential and convenient to use accurate and validated numerical models to simulate the seismic performance of post-tensioned (PT) rocking bridge piers, with a particular emphasis on accurately capturing rocking behavior. The primary contribution of this study is a comparison of the effectiveness of four commonly used numerical base rocking models (namely, the lumped plasticity (LP) model and the multi-contact spring (MCS) models with linear elastic (MCS-LE), bilinear elastic–plastic (MCS-EP) and nonlinear plastic (MCS-NP) material behavior, respectively) in modeling both the cyclic and seismic responses of PT rocking bridge piers. Also, this study validates the 3D contact stiffness equation for numerical models and assesses the differences between the dynamic and static stiffness values of the contact springs. Both quasi-static and shaking table tests of typical PT rocking piers are adopted to calibrate/validate these numerical models. These models describing the PT rocking piers’ seismic performance are formulated and calibrated, showing good agreement with test results for test specimens. Additionally, the suggested values of model spring stiffness for dynamic and quasi-static analyses are identified by parametric analysis. All base rocking models can predict the pier’s cyclic and seismic behavior after the calibration of contact spring stiffness values. The recommended contact stiffness for the dynamic analysis of PT rocking piers is smaller than that used for the quasi-static analysis. The results and findings provide a valuable reference and solution for the numerical simulation of PT rocking piers. Full article

The impact of contact between two elastic–plastic bodies is highly complex, with no established theoretical contact model currently available. This study investigates the problem of an elastic–plastic sphere impacting an elastic–plastic half-space at low speed and low energy using the finite element method (FEM). Existing linear contact loading laws exhibit significant discrepancies as they fail to consider the impact of elasticity and yield strength on the elastic–plastic sphere. To address this limitation, a novel linear contact loading law is proposed in this research, which utilizes the concept of equivalent contact stiffness rather than the conventional linear contact stiffness. The theoretical expressions of this new linear contact loading law are derived through FEM simulations of 150 sphere and half-space impact cases. The segmental linear characteristics of the equivalent contact stiffness are identified and fitted to establish the segmental expressions of the equivalent contact stiffness. The new linear contact loading law is dependent on various factors, including the yield strain of the half-space, the ratio of elastic moduli between the half-space and sphere, and the ratio of yield strengths between the half-space and sphere. The accuracy of the proposed linear contact loading law is validated through extensive Finite Element Method simulations, which involve an elastic–plastic half-space being struck by elastic–plastic spheres with varying impact energies, sizes, and material combinations. Full article

The azimuth track is an important component of the radio telescope wheel–rail system. During operation, the azimuth track is inevitably subject to phenomena such as track wear, track fatigue cracks, and impact damage to welded joints, which can affect observation accuracy. The 110 m QiTai radio telescope (QTT) studied in this paper is the world’s largest fully steerable radio telescope at present, and its track will bear the largest load ever. Since the welded joint of an azimuth track is the weakest part, an innovative welding method (multi-layer and multi-pass weld) is adopted for the thick welding section. Therefore, it is necessary to study the contact mechanical properties between the wheel and the azimuth track in this welded joint. In this study, tensile tests based on digital image correlation technology (DIC) and Vickers hardness tests are carried out in the metal zone (BM), heat-affected zone (HAZ), modified layer, and weld zone (WZ) of the welded joint, and the measured data are used to fit the elastic–plastic constitutive model for the different zones of the welded joint in the azimuth track. Based on the constitutive model established, a nonlinear finite element model is built and used to simulate the rolling mechanical performance between the wheel and azimuth track. Through the analysis of simulated data, we obtained the stress distribution of the track under different pre-designed loads and identified the locations most susceptible to damage during ordinary working conditions, braking conditions, and start-up conditions. The result can provide a significant theoretical basis for future research and for the monitoring of large track damage. Full article

Poisson’s ratio is one of the fundamental characteristics in the material models that are used. In engineering practice, its values are assumed to be constant in the elastic and in the plastic region. In this paper, the conventionally used values of this number for steel materials and aluminum alloys are confronted with experimental results. By using non-contact strain measurements with the DIC (digital image correlation) method, the evolution of the Poisson ratio value in the regions of transition from the elastic to the plastic region as well as in the regions of large plastic deformations was documented. The obtained experimental results are graphically compared using the proposed strain scaling. The gradient of the Poisson ratio changes in the vicinity of the yield stress is significant, indicating the need for a refinement of the material models in this region. Deviations from the conventionally used value of this number were found in the large plastic deformation region. In conclusion, a possible approach for improving the accuracy of simulations in FEM softwares was formulated. Full article