Contact Parameters Research Articles

Lessons learned from matching 3D DEM and experiments at macro, meso and fabric scales for triaxial compression tests on lentils

A series of discrete element method (DEM) triaxial compression simulations on specimens of an anisometric granular material starting from distinct initial fabric anisotropy states are conducted and compared with physical experiments on lentils at different scales, assisted by operando X-ray tomography measurements. A quantitative reproduction of the group of experimental results is achieved by appropriate idealization and determination of particle shape, boundary conditions, contact parameters, and initial state. The reliability of DEM in quantitative representation of macro scale stress–strain response, meso scale strain localization, and micro scale fabric anisotropy evolution is thus comprehensively validated against measurements from physical experiments, which is a step forward from comparisons only at the macro or particle kinematics level. Several key factors that govern realistic DEM simulations are also identified. The friction coefficient between particles during specimen generation, particle shape, and specimen preparation method can significantly affect the initial state of DEM specimens. Differences in initial state at macro and micro scales and boundary conditions can strongly influence the stress–strain response. However, the evolution of fabric anisotropy appears to be insensitive to changes in initial state and boundary conditions.

Contact parameters calibration of mixtures in different aerobic composting period: Focusing on establishment of particle model and its flow properties

In order to calibrate the contact parameters, particle models for mixtures of each period were established by simulation of repose angle using combined models in EDEM software, and then the flow properties of mixtures in different aerobic composting periods were clarified. Results showed that compared with the six-sphere model, the use of the double-sphere model to represent the compost mixtures of each period was not only closer to the ellipsoid of the actual particles but also simplified the calculation process. The contact parameters that mostly affected the repose angle were Poisson's ratio and shear modulus of mixture in the mesophilic period and JKR surface energy in thermophilic and cooling periods. The relative errors between the simulated repose angle using the optimal parameter combination and the actual measured value were less than 2.5% indicating the reliability of the regression models at each period representing the relationship among the repose angle and significant contact parameters. In addition, the flow properties of mixtures at the mesophilic period were better than those at the thermophilic and the cooling period of its smaller repose angle, the larger mass transformation, and the smaller Ek max value. Meanwhile, mixtures in thermophilic and cooling periods had similar flow properties. Hence, these could provide information for the further application of simulation to optimize the composting process (e.g., stirring frequency and ventilation time) to promote compost maturity.

Nano-Y2O3 effects on the electrical contact properties of Al2O3-Cu/35Cr3TiB2 composites

Al2O3-Cu/35Cr3TiB2 and 0.5Y2O3/Al2O3-Cu/35Cr3TiB2 electrical contact composites were prepared by vacuum hot pressing sintering endo-oxidation method. Both composites were over 98% dense with tensile strengths of 395 MPa and 413 MPa and compressive strengths of 839 MPa and 898 MPa, respectively. The TEM results showed that Cr and TiB2 particles along with Al2O3 nanoparticles generated by internal oxidation were uniformly distributed in the Cu matrix. The addition of Y2O3 had almost no negative effects on the electrical conductivity and hardness of the composites. The electrical contact parameters such as arc energy, arc duration, and weld force between pairs of contacts were analyzed. The material transfer direction of both composite contacts was from cathode to anode. The average welding force of the contacts decreased by 24.6% after the addition of Y2O3, and the material transfer and loss decreased by 28.6% and 42% at 35 A current, respectively. The addition of Y2O3 reduced the arc energy and duration by 43.7% and 55.9% at 25 A and 35 A, respectively, and improved the stability of the contacts during disconnect and closure.

A novel test apparatus to study the mechanism of harmonic normal force on fretting wear

Fretting wear significantly affects the hysteresis behavior of the contact surface and leads to joint degradation due to material removal. Although numerous tests have been conducted to investigate fretting wear under constant normal force, the applied mechanical load on the contract surface more or less deviates from that in the operational condition. The normal force is typically time-varying due to the coupling of tangential and normal vibration, rather than remaining constant. The time-varying normal force can be regarded as the superposition of harmonics for steady-state vibration which is widely encountered in engineering. In this paper, we investigate how would the harmonic component of the normal force affect the evolution of interface morphology and contact parameters with fretting wear. To do that, we design a novel fretting wear test apparatus that generates the stable harmonic normal force. The normal force is controlled by a closed-loop control system, ensuring its consistency throughout the entire wear test. In addition, we develop various subsystems to realize different functions like support, constraint and measurement, enabling the acquisition of hysteresis loops under different normal forces. The critical performances of the test apparatus (e.g. force transfer, closed-loop control and repeatability) are also demonstrated. Results indicate that the harmonic normal force can significantly influence the hysteresis loop and the energy dissipation distribution on the contact surface. In comparison to the constant normal force, the worn surface has a higher degree of non-uniformity, characterized by alternating pits and prominences. Furthermore, the friction coefficient exhibits an outstanding upward trend after reaching a steady state, while the tangential contact stiffness continuously weakens as fretting wear progresses. These unique evolution characteristics could be attributed to the non-uniform energy dissipation caused by the harmonic normal force acting across the fretting space. This viewpoint can be partly validated through observing the interesting hysteresis loops, which are captured by the test apparatus.

Proper Orthogonal Decomposition-Based Surrogate Modeling Approximation for Aeroengines Nonlinear Unbalance Responses

Abstract Finite element (FE) models to simulate aeroengines rotordynamics become more and more complex thanks to the improvement of computational resources. Numerical simulations for industrial scale applications are nevertheless expensive in terms of computational effort because of their size and the presence of nonlinearities. In many-query frameworks (sensitivity or reliability analysis, model calibration, etc.), parametric studies have to be performed and the FE models are generally simplified or strongly reduced with a consequent loss of accuracy. Recent machine learning methods can be employed to build faster-to-evaluate surrogates of the original model. Nevertheless, this type of offline approach can be very demanding in terms of number of full order evaluations to reach a sufficient accuracy. The challenge is therefore to control the burden associated with the evaluation of the design of experiments (DoE) and the surrogate model training phase. This work presents a surrogate modeling technique to quickly and accurately reproduce the nonlinear unbalance responses of industrial scale rotor-dynamical models submitted to rotor–stator contact. About 20DOFs of the industrial FEM are considered in this work and a proper orthogonal decomposition (POD)-based approximation (surrogate modeling technique known as POD-SM or nonintrusive POD in the literature) of their frequency dependent unbalance response are presented. In order to analyze the modeling uncertainties of a specific shaft's support of a modern aeroengine, its dynamical parameters (stiffness, damping, nonlinear contact parameters) are studied within a specific variation range, defining the design space covered by this study.

A Modified Model for Identifying the Characteristic Parameters of Machine Joint Interfaces

The contact parameters of joint interfaces have a great influence on the dynamic performance of the machine tool, and the dynamic performance determines the machining precision of the machine tool. Therefore, it is important to accurately identify the contact parameters of joint interfaces to improve the machining precision of the machine tool. In this paper, a method of identifying the joint interface stiffness parameters based on a joint simulation in Matlab and Ansys is first proposed, and then stiffness parameters of joint interfaces between the bed and column of the precision grinding machine are identified by applying the method. Finally, the feasibility and high efficiency of the proposed method are proved by comparing the natural frequencies of the simulation and the experiment. In order to further analyze the influence of joint contact parameters on the performance of the joint interfaces, the theoretical model of the normal stiffness of the joint interfaces based on fractal geometry is amended and verified by taking into account the asperity interaction and elastic–plastic deformation. Then, the modified model is extended to a three-dimensional model, which is more in line with the actual situation. Finally, the influencing factors of the joint interface stiffness are analyzed. The conclusions of this paper are of great significance in the dynamic performance analysis and structural design of machine tools.

Calibration of Small-Grain Seed Parameters Based on a BP Neural Network: A Case Study with Red Clover Seeds

In order to enhance the accuracy of discrete element numerical simulations in the processing of small-seed particles, it is essential to calibrate the parameters of seeds within the discrete element software. This study employs a series of physical tests to obtain the physical and contact parameters of red clover seeds. A discrete element model of red clover seeds is established. Plackett–Burman Design, steepest ascent, and Central Composite Design experiments are sequentially conducted. The simulation deviation of the resting angle of red clover seeds is employed as the evaluation criterion for parameter optimization. The results indicate that the coefficients of static friction between red clover seeds, the coefficients of rolling friction between red clover seeds, and the coefficients of static friction between red clover seeds and the steel plates significantly influence the resting angle. Modeling was performed using a backpropagation neural network, a genetic algorithm–optimized BP network, particle swarm optimization, and simulated annealing. It was found that GA-BP ensured both accuracy and stability. Compared to the traditional response surface methodology, GA-BP showed better fitting performance. For the optimized red clover seed simulation, the error between the angle of repose and the physical experiment was 0.98%. This research provides new insights into the calibration of small-grain seed parameters, demonstrating the value of GA-BP for precision modeling.

Calibration of Model Parameters for Soda Saline Soil-Subsoiling Component Interaction Based on DEM

To apply the discrete element method (DEM) to simulate the interaction process between soda saline–alkali soil and subsoiling component in Northeast China, establishing the soda saline–alkali soil particle model and selecting more accurate simulation parameters are important. In this paper, we studied the soda saline–alkali soil of the Songnen Plain in China. First, we studied the geometric shape of soda saline–alkali soil particles and proposed a modeling method for single soil particles based on the multisphere combination method. Considering the cohesion of soda saline–alkali soil particles, the Hertz–Mindlin with JKR (JKR) model was used as the contact model between soil particles. Then, the calibration method was used to obtain simulation parameters of soils that are difficult to obtain experimentally. We conducted soil angle of repose (AoR) tests, the Plackett–Burman (PB) tests, and steepest ascent (SA) tests in turn to perform a sensitivity analysis for microscopic contact parameters and select the parameters that have a significant effect on the response value (static AoR), i.e., soil surface energy, soil–soil static friction coefficient, and soil–soil rolling friction coefficient. Then, the optimal combination of simulation parameters was obtained via the Box–Behnken (BB) tests, using ANOVA to optimize the multiple regression equation. Finally, the optimal parameter combination was verified by the AoR test and the direct shear (DS) test. The results showed that the parameters had good adaptability for the AoR test. However, the simulation results of the DS test were significantly different from the experimental values. Therefore, the contact model needs to be further modified by adding Bonding bonds between soil particles based on the JKR model and further correcting for Rayleigh time step, shear modulus, and surface energy. By comparing the simulation and the experimental results, it was found that the simulation results obtained from both the DS test and AoR test had relatively small errors relative to physical tests, the two trends are the same, and the values are similar. This verified the feasibility and effectiveness of the soda saline–alkali soil particle modeling method and parameter selection proposed in this paper.

Optimisation design of grinding rail profile of metro lines for small radius curved track based on the GFC method: a case study

The rail side wear in small radius curved track of metro lines is a serious problem in railway maintenance, which reduces the curve passing performance and shortens the service life of the wheel and rail. To improve the vehicle's curve passing performance and reduce rail wear, a localized grinding profile design method for sharp curves was developed. The GFC profile generation method was used to generate the profiles for the curved track of the metro line. Then a metro vehicle-track dynamic model was established to calculate the wheel rail contact parameters, objectives and constraints. The profiles are optimized by the KSM-PSO optimization algorithm. Finally, a simulation analysis of the curve passing performance and wheel-rail wear of the optimized profile was carried out. When the metro vehicle passes through the curved track with a curve radius of 450m, the optimized rail profile can effectively reduce the wear of the rail, the wear of the high rail in the curved track is reduced by 20.18%. The localized rail grinding of the curved track can effectively reduce the rail side wear, the GQI index is also significantly improved. This study can guide the design of rail grinding profiles for the metro lines.

Phase separation in binary Bose mixtures at finite temperature

We investigate the magnetic behavior of finite-temperature repulsive two-component Bose mixtures by means of exact path-integral Monte-Carlo simulations. Novel algorithms are implemented for the free energy and the chemical potential of the two components. Results on the magnetic susceptibility suggest that the conditions for phase separation are not modified from the zero temperature case. This contradicts previous predictions based on approximate theories. We also determine the temperature dependence of the chemical potential and the contact parameters for experimentally relevant balanced mixtures.

Discrete element contact model and parameter calibration for clayey soil particles in the Southwest hill and mountain region

Distinct physical properties of red clay soil in hilly and mountainous regions of southwest China, including high adhesiveness and density, challenge the operation of agricultural machinery. A scarcity of accurate discrete element simulation parameters for this soil type restricts computational modeling. The study was focused on red clay soil with a moisture content of 12.50% ± 1% and a measured repose angle of 35.54°. The soil's inherent physical properties were identified through experimental assessments. Soil contact mechanical parameters were obtained from the GEMM database, and optimal contact parameter ranges were determined using Steepest Ascent Experiments, with the simulated soil particle repose angle serving as the response value. A second-order regression model was developed using a quadratic regression rotation orthogonal combination test. By taking the actual repose angle as the optimization criterion, parameters were optimized. The optimal contact mechanical parameters in EDEM simulations were identified as: JKR surface energy at 8.981 J/m2, recovery coefficient at 0.474, dynamic friction coefficient at 0.196, and static friction coefficient at 0.45. The model yielded a repose angle of 36.21°, closely corresponding with the observed value, with a relative error of 1.80%. The parameters calibrated in this study offer a valuable reference for future soil-tool interaction studies and tillage implement optimization in these regions.

Calibration and verification of DEM parameters for particles in transfer chute from rapid flow to stable accumulation

The discrete element method (DEM) is conducive to optimizing bulk material conveying equipment. Calibration experiments are essential in DEM simulation, requiring particles to accurately replicate the flow behavior from rapid motion (up to a maximum of 6 m/s) to stable accumulation in bulk material handling. In typical calibration experiments, excessively high particle velocities will affect the stability of the characterization data in stable accumulation. The paper presents an innovative calibration approach that enables reliable prediction of both impact forces during rapid flow and bulk density during stable accumulation. A single-factor numerical test determines the sensitivity of simulation parameters to calibration experiments, and comprehensive testing methods ensure that equivalent DEM contact parameters align with experimental particle behavior. Finally, verification experiments indicate that the proposed calibration experiments in this study can successfully replicate the particle flow behavior during bulk material handling.

Multi-level coarse-grained discrete element method modeling of cylinder particle flow in a rotating drum

The coarse-grained discrete element method (DEM) is probably a feasible option for simulating an actual drum-type biomass boiler, which contains over 10 million cylinder particles. A multi-level study was conducted based on particle and coarse-grained level data to evaluate the adequacy of the coarse-grained approach in terms of geometrical characteristics, kinematic features, and dynamic properties. Two scaling laws for contact parameters were used and compared during the simulations. The results show that the coarse-grained approach can accurately predict the positions of the free surface and active-passive interface, the mixing index, and the orientation properties. Deviations in the velocity fields may occur due to the worse flowability of coarse-grained particles near the free surface. The efficiency is significantly improved by the coarse-grained model compared with the corresponding original case (the same DEM code without a coarse-grained model was used for the original simulations).

Simulation model of contact interaction during surface strengthening of steel parts

In the processes of surface strengthening of steel parts, the stress-strain state is decisive for explaining the physical processes of strengthening, forming the dimensions of the contact area. Analytical dependences of contact parameters are quite approximate. In this work, based on the Ansys software complex, a simulated model of the contact of a truncated torus with a cylinder is proposed, which demonstrates the kinetics of the process of pressing a hard alloy tool into a steel workpiece - a cylinder. The experiment was conducted for 4 seconds in order to determine the maximum level of stresses, the distribution of stresses and the amount of residual stresses after removing the load. The clamping force was applied mainly in the zone of elastic deformations. The results showed an uneven stress distribution with a maximum in the center of the contact spot of 1082 MPa. After changing the load direction, small residual deformations at the level of 0.00311 μm were observed in the center of the contact patch. This indicates a violation of the elastic region on a small contact area, which does not affect the general nature of the stress distribution and can be removed during the finishing process. The results of simulation of the stressed state are used for the correlation with the observed structural changes of the material during the action of thermal and power stresses. The stress peak was formed at a distance of 200 μm, which contributes to the formation of maximum values of microhardness at this depth.

Study on transmission and reflection characteristics of plane S1 wave at the interface between saturated frozen soil and elastic solid bedrock

Based on the propagation theory of elastic waves in frozen poroelastic media and elastic media, a theoretical model of saturated frozen soil and elastic solid bedrock is established. The saturated frozen soil is lying on an elastic solid bedrock and is modeled as a porous material containing a three-phase medium that contains two solids (soil skeleton and ice particles) and a compressible viscous fluid. Based on the Helmholtz vector decomposition and the boundary conditions on the interface, the theoretical expressions of the amplitude ratio and displacement of the plane S1 wave incident from the saturated frozen soil to the elastic solid bedrock interface are obtained. The effects of incidence angle, frequency, cementation parameters, saturation, and contact parameters on amplitude ratio and displacement were investigated. The results indicate that only S wave and horizontal displacement exist when the incident angle [Formula: see text] = 0°. As cementation parameters, saturation, porosity, and contact parameters increase, the critical angle appears earlier. Each wave has different degrees of pulses when reaching the critical angle, among which the transmitted P wave and the reflected S2 wave are the most significant. At higher saturation, it is observed that the amplitude ratio of the reflected S2 wave decreases significantly. The horizontal and vertical displacements increase significantly with increasing frequency.

Research on the macro- and meso-mechanical properties of frozen sand mold based on Hertz-Mindlin with Bonding model

In this study, macro- and meso-mechanical properties of frozen sand molds were discussed based on the Hertz-Mindlin with Bonding (HMB) model. Plackett-Burman, steepest ascent, and central composite designs were utilized to propose a parameter calibration methodology. The effects of mesoscopic parameter variations on the compressive strength and average gradient of stress-strain were investigated through response surface method analysis. Results showed that the relative error between the simulated and measured repose angle is 3.1% under calibrated intrinsic contact parameters. The compressive strength and average stress-strain gradient primarily depend on the normal and shear stiffness per unit area, as well as the particle size and porosity of the silica sand. Furthermore, taking load-displacement curves of three frozen sand molds with different geometric characteristics as the target value, the reliability and effectiveness of the frozen sand mold HMB model were verified through uniaxial compression tests and discrete element simulations.

Audiogenic Seizures and Social Deficits: No Aggravation Found in Krushinsky-Molodkina Rats.

Epilepsy or epileptic syndromes affect more than 70 million people, often comorbid with autism spectrum disorders (ASD). Seizures are concerned as a factor for social regression in ASD. A stepwise experimental approach to this problem requires an animal model to provoke seizures and monitor subsequent behavior. We used rats of the Krushinsky-Molodkina (KM) strain as a validated inbred genetic model for human temporal lobe epilepsy, with recently described social deficiency and hypolocomotion. Generalized tonic-clonic seizures in KM rats are sound-triggered, thus being controlled events in drug-naïve animals. We studied whether seizure experience would aggravate contact deficits in these animals. Locomotor and contact parameters were registered in "the elevated plus maze", "socially enriched open field", and "social novelty/social preference tests" before and after sound-provoked seizures. The triple seizure provocations minimally affected the contact behavior. The lack of social drive in KM rats was not accompanied by a submissive phenotype, as tested in "the tube dominance test", but featured with a poor contact repertoire. Here, we confirmed our previous findings on social deficits in KM rats. The contact deficiency was dissociated from hypolocomotion and anxiety and did not correlate with seizure experience. It was established that experience of rare, generalized tonic-clonic convulsions did not lead to an impending regress in contact motivation, as seen in an animal model of genetic epilepsy and comorbid social deficiency. One of the oldest animal models for epilepsy has a translational potential to study mechanisms of social behavioral deficits in future neurophysiological and pharmacological research.

Modeling of time-dependent elliptic contact parameters for biological nanoparticles with common geometries: Human red blood cell

Extracting mechanical properties of living cells by Atomic Force Microscope (AFM) can cause cell destruction due to uncontrolled forces. In this regard, the reaction of healthy (MCF-7) and cancerous (MCF-10A) breast cells and human Red Blood Cells (RBCs) to contact force was simulated by using different contact theories and applying time-dependent mechanical models. To validate the simulation results, the topography test and nanomanipulation of MCF-7 and MCF-10A using AFM was implemented. Experimental data showed that the average maximum diameter of MCF-7 and MCF-10A is 25.24 and 12.06 μm, respectively. Furthermore, the elastic modulus of the MCF-7 and MCF-10A cells was calculated in the range of 1.23 ± 0.02 kPa, and 1.17 ± 0.02 kPa, respectively. In addition, the contact theories were developed for application in the case of different geometries, and utilized for modeling the contact mechanics of human RBCs. The results showed that Hertz and DMT theories accurately calculate the contact behavior of living cells in small deformations; However, in case of large contact deformations, Tatara and Chang's theories provide more accurate results. Furthermore, the effect of RBC geometry on the contact parameters is negligible due to the significant difference in the dimensions of RBCs in comparison with AFM-tip.

Overview of the Metallization Approaches for Carbyne-Based Devices.

Metallization for contacts in organic electronic nanodevices is of great importance for their performance. A lot of effects can appear at the contact/organic interface and modify the contact parameters, such as contact resistance, adhesive strength, and bonding ability. For novel materials, it is important to study the interactions with metal atoms to develop a suitable technology for contacts, fulfilling to the greatest extent the above-mentioned parameters. A novel material is carbyne, which is still under intensive research because of its great potential in electronics, especially for sensing applications. However, the most appropriate metallization strategy for carbyne-based devices is still unknown, so the interactions between carbyne and metal films should be studied to more precisely direct the development of the metallization technology, and to form contacts that are not limiting factors for device performance.

On the robust experimental multi-degree-of-freedom identification of bolted joints using frequency-based substructuring

Modeling joint dynamics is the bottleneck for precise predictive models of machines. Bolted joints are especially relevant due to their common use in mechanical engineering. Stiffness and damping properties of bolted joints are highly influenced by contact parameters (geometry, surface treatment, preload, …). For high amplitude vibrations, when non-appropriate joint closure is present, even frictional effects can play a role.Substructuring techniques offer a lean solution for isolating dynamical or quasi-static components of joint dynamics. It may be used for an identification of linearized contact parameters for multiple degrees of freedom (dofs). The main limitation of the method is finding a robust workflow to guarantee a proper controllability and observability of the desired joint dynamics, as well as dealing with disturbance/noise in the measurements.In this contribution a robust procedure for the identification of a bolted joint using frequency-based substructuring is presented for a contact in an experimental scenario. The dynamics of the joint are isolated from the assembled system using different substructuring techniques treating the joint as a quasi-static or dynamic component. A simple physical model of the joint is parametrized from the experimental joint dynamics. A validation of the methodology is given by using the identified joint parameters on a modified assembled system.