Complex Contact Research Articles

Numerical Investigation and Cross‐Section Type Selection of Concrete‐Filled Double Steel Plate (CFDSP) Composite Shear Walls Under Cyclic Loading

ABSTRACTConcrete‐filled double steel plate (CFDSP) composite shear walls have excellent seismic performance and are generally used as lateral resistance for high‐rise buildings. However, the numerical simulation of such walls is complicated because of the complex contact between the concrete, the external steel plate, and the shear studs. Eighteen CFDSP walls in the present literature were numerically simulated under cyclic and constant axial loading, and the accuracy was evaluated by comparing them with the experimental results. Then, the impact of cross‐section variations on the structural performance of CFDSP walls under the same steel content ratio was numerically investigated. Designed numerical walls were evaluated under the same loading conditions with four distinct cross‐sections for comparative analysis. Finally, parametric analysis was performed to observe the influence of aspect ratio, steel thickness, and stud spacing on the seismic performance of CFDSP walls. The analysis results show that the proposed numerical model can accurately recover the hysteretic curves of CFDSP walls regarding strength reduction, energy dissipation, and pinch behavior.

Comparative analysis of fretting wear behavior of steel wire subject to tensile-torsional coupling forces in typical mining environments

The complex mining environments can significantly accelerate the fretting wear among steel wires within wire rope, thereby diminishing its service life and posing severe risks to the safety of mine hoisting operations. To explore the fretting behavior of steel wires featuring complex contact structures in typical mining environments, a customized test rig was utilized to perform fretting wear experiments of steel wire under tensile-torsional coupling forces. The findings indicate that with increasing contact force, the coefficient of friction (CoF) between steel wires in different environments decreases, whereas the frictional force and wear degree increase significantly. The wear depth and wear coefficient under peak contact structure are markedly larger than those under valley contact structure. For the same contact force, the wear of steel wire without lubrication is the largest, the wear under water lubrication is the second, and the wear under grease lubrication is the least. The primary wear mechanisms of steel wire under grease lubrication are abrasive wear and fatigue wear. The presence of mineral particles in the grease can reduce the CoF, but it will exacerbate the wear and result in adhesive wear characteristics on the wear surfaces. Under no lubrication and water lubrication conditions, the wear mechanisms encompass abrasive wear, adhesive wear and fatigue wear. Furthermore, with increasing contact force, the fatigue wear of steel wire under no lubrication intensifies, while the abrasive wear characteristics become more pronounced under water lubrication.

Simulation of homogenization behavior of compacted bentonite containing technological voids using modified penalty-based contact model

Low-density zones generated during the bentonite blocks/voids homogenization process in the repository may serve as potentially preferential paths for radionuclide leakage. More importantly, void closure during homogenization process involves complex contact problems, where the stiffness at the contact interface typically undergoes significant fluctuations. In this work, with contact interface stiffness addressed through a step function approach, a modified penal.ty-based contact model was proposed to simulate the contact behavior involved at the gap closure stage of the bentonite/gap assemblage homogenization process. Then, unsaturated infiltration swelling tests on bentonite block (1.7 Mg/m3)/gap (width: 2 mm) assemblages were performed, and the variation of dry density at different hydrated times (0, 24, 72, 168, and 720 h) in specific areas were measured. Based on the results, time-dependent swelling pressure profiles of the assemblage were acquired, while the homogenization process was evaluated. Results reveal that after approximately 40 h of hydration, the gap is completely closed, and the radial stress condition of the compacted bentonite transits progressively from the initial free swelling into a constant volume expansion state. The swelling pressure correspondingly develops quickly to a peak value at 1.8 MPa once the hydration starts, then decreases to a valley value of 1.4 MPa at the complete gap closure, and subsequently begins to increase to the final stable value of 1.8 MPa. Further examination reveals that as hydration advances, dry density of the assemblage converges to the expected final dry density with a maximum residual inhomogeneity of about 2 %. Finally, validations demonstrate that the proposed model can accurately reproduce deformations of the assemblage during the free swelling stage, and the swelling pressure profiles. A comparative analysis was made with the previous approach of identifying gaps as highly deformable materials, revealing that the proposed model overcomes the traditional limitations associated with the separation or penetration behavior occurring between the compacted bentonite and contact boundaries during the gap closure.

Progressive Failure of Water-Resistant Stratum in Karst Tunnel Construction Using an Improved Meshfree Method Considering Fluid–Solid Interaction

An improved meshfree method that considers cracking, contact behaviour and fluid–solid interaction (FSI) was developed and employed to shed light on the progressive failure of the water-resistant stratum and inrush process in a karst tunnel construction. Hydraulic fracturing tests considering different scenarios and inrush events of the field-scale Jigongling karst tunnel in three scenarios verify the feasibility of the improved meshfree method. The results indicate that the brittle fracture characteristics of the rock mass are captured accurately without grid re-meshing by improving the kernel function of the meshfree method. The complex contact behaviour of rock along the fracture surface during inrush is correctly captured through the introduction of Newton’s law-based block contact algorithms. FSI processing during inrush is accurately modelled by an improved two-phase adaptive adjacent method considering the discontinuous particles without coupling other solvers and additional artificial boundaries, which improves computational efficiency. Furthermore, the improved meshfree method simultaneously captures the fast inrush and rock failure in the Jigongling karst tunnel under varying thicknesses and strengths of water-resistant rocks and sizes of karst caves. As the thickness and strength of water-resistant rock increase, the possibility of an inrush disaster in the tunnel decreases, and a drop in the water level and an increase in the maximum flow velocity have significant delayed effects during the local inrush stage.

Mechanism analysis and prediction of bull-nose cutter wear in multi-axis milling of Ti6Al4V with TiAlN coated inserts

Cutter wear is an unavoidable issue during the milling of difficult-to-machine materials such as Ti6Al4V, which severely affects cutting performance and surface quality. Especially in multi-axis milling, the complex and irregular contact area between cutter and workpiece increases the difficulty of wear prediction. This paper proposes a flank wear prediction model of bull-nose cutter in the multi-axis milling process of Ti6Al4V with TiAlN coated inserts. The cutter workpiece engagement (CWE) zone is analyzed and the wear contact length of cutting edge is obtained, which reveals the uneven distribution characteristics of flank wear. After that, by analyzing the geometric profile properties of cutter wear in multi-axis milling, abrasive and adhesive wear, a flank wear prediction model that takes coating hardness and cutting temperature model into account is established. The proposed model is calibrated and validated by the multi-axis milling experiment of Ti6Al4V with TiAlN coated inserts. The results show that the novel wear model has high accuracy with an average percentage error of 12.76 % and can accurately and quickly predict flank wear in multi-axis milling of Ti6Al4V. Finally, the cutter wear mechanism and chip formation are analyzed, which show that the main wear mechanism is abrasive wear and adhesive wear, and there was no obvious oxidation wear.

A finite element framework for thermo‐mechanically coupled gradient‐enhanced damage formulations

AbstractThe solution of coupled multi‐field problems by means of commercially available finite element codes such as Abaqus constitutes an important part in the study of industrial processes. Against this background, a comprehensive implementation framework for a gradient‐enhanced continuum damage formulation in a thermo‐mechanically coupled finite deformation setting is proposed in this contribution. To assess the applicability of the implementation framework to industrial processes, a thermo‐mechanically coupled, gradient‐enhanced ductile damage model is exemplarily employed. The resulting three‐field problem, consisting of the balance of linear momentum, the heat equation and the balance of micromorphic momentum, is implemented based on an Abaqus user material by making use of a novel two‐instance formulation. Representative simulation results are discussed, with the specific focus lying on the application to manufacturing processes involving complex contact interactions. The Abaqus framework is made available as an open‐source code on GitHub, see Sobisch et al., Finite Elements in Analysis and Design 232 (2024) 104105.

A unified nonlinear dynamic model for bolted flange joint disk-drum structures under different interface states: Theory and experiment

Bolted flange joint disk-drum structures (BFJDDSs) are key components in aero-engines, however, bolt looseness inevitably occurs due to extreme service conditions. This can cause the bolted joint interface to exhibit complex contact behaviors, which significantly complicate the vibration characteristics of BFJDDSs. Existing dynamic models for BFJDDSs have not considered the effect of bolt looseness (slip and separation), so their vibration behaviors are not well understood. In this study, a unified nonlinear dynamic model for BFJDDSs considering different interface states (stick, slip, and separation) is proposed, which is effective under both bolt looseness and non-looseness (stick) conditions. The bi-linear hysteretic model combined with the piecewise linear model is used to simultaneously consider different interface states. The Kirchhoff plate theory, the Sanders’ shell theory, and the Euler-Bernoulli beam theory are used to derive the energy functions of the disk, drum, and flange, respectively. Then, the Lagrange equations are employed to derive the governing equations of BFJDDSs. Modal and nonlinear forced vibration experiments are carried out on a BFJDDS to prove the correctness of the proposed mathematical model. Research results show that the proposed mathematical model is able to achieve good predictions of nonlinear dynamic properties of BFJDDSs under both bolt looseness and non-looseness conditions. This model is also able to well predict the jumping phenomenon observed in the experiment.

An approach simulating interacting solid, liquid, and gas domains for dynamic seal applications

AbstractIn seal applications a solid elastic body (the seal) ensures the separation of a liquid (e.g., hydraulic oil in one chamber) from a gas (e.g., air in another chamber). In the case of a dynamic seal, the rod is moving and transports a thin liquid film from the liquid chamber into the air chamber. The seal gap consists of a converging gap, a minimum distance between seal and rod and a diverging gap, where transported liquid detaches from the seal. Between the three states of matter (gas, liquid, gas) appear the following contact conditions: liquid‐to‐solid, gas‐to‐liquid, and gas‐to‐solid. A classical fluid‐structure‐interaction is technically possible with limited effort, but is not sufficient to distinguish between the liquid and the gas. A solution can make use of the fact, that the liquid has significant dimensions only in the liquid chamber and is pressurized only there. There is a thin liquid film on the rod in the air chamber, but it has dimensions clearly lower than the air chamber and has the same pressure as the air. Therefore a simulation is possible with the “variable viscosity approach”: Liquid and gas are modeled in one single fluid domain. Differences between liquid and gas are included by pressure‐dependent fluid parameters, especially viscosity and density. The resulting violation of the mass balance is very small as the low mass flow through the seal lip is low. The presented approach allows to apply a fluid‐structure simulation with special fluid properties to model a system with three states of matter. Advantages are a less complex model with less complex contact conditions and a reduced simulation time.

Evolution of tooth surface morphology and tribological properties of helical gears during mixed lubrication sliding wear

In mixed lubrication, the interplay of lubricant flows, solid asperity contact, and material wear between tooth surfaces creates complex and unpredictable contact states on tooth surface. To comprehensively understand the interaction between the lubrication and wear characteristics of the rough tooth surfaces of helical gears, this study established a mixed lubrication sliding wear calculation model for helical gears based on the mixed elastohydrodynamic lubrication model and Archard’s model. Specifically, the study aimed to examine the effects of surface topography features on average film thickness, contact area ratio, and accumulated wear at the meshing point. The findings demonstrated that the texture and power spectral density distributions of a non-Gaussian reconstructed surface closely resembled those of the actual ground surface. Furthermore, for non-Gaussian rough surfaces, a larger wavelength ratio enhanced microwedge motion, which increased film thickness and reduced wear. Additionally, a negatively skewed surface demonstrated better lubrication performance compared to both positively skewed and Gaussian surfaces. This improved performance is evident in the smaller contact area ratio and lower accumulated wear value of the negatively skewed surface.

Digitally enhanced development of customised lubricant: Experimental and modelling studies of lubricant performance for hot stamping

Digitally enhanced technologies are transforming every aspect of the manufacturing sector towards the era of digital manufacturing. Traditional lubricant development methods involving systematic but time-consuming iterative processes is still extensively used in the metal forming industry. In the present study, a novel digitally enhanced lubricant development scheme was proposed by leveraging a mechanism-based interactive friction modelling framework and quantitative and comprehensive evaluation of lubricant performance via the data-centric lubricant limit diagrams. By predicting transient lubricant behaviour following the complex contact condition evolution experienced in actual forming operations, a close association and quantified relation between the lubricant performance and its properties such as viscosity, evaporation rate and fraction of dry matter was established. This can facilitate the optimisation efficiency of lubricant parameters and minimise the experimental cost for iterative lubricant trials. A case study was conducted in this work to develop a customised lubricant using this digitally enhance scheme for the target hot stamping process based on a benchmark lubricant as a reference. Further industrial forming tests of an automotive component were conducted to validate the ideal performance of the customised lubricant.

The point prevalence of South African male soccer players' injuries in the Gauteng province.

The ever-evolving game of soccer is a complex physical contact team sport, exposing its participants to injury. To identify the point prevalence of soccer injuries among young amateur, semi-professional, and professional South African male soccer players. The participation of male amateur (n=54), semiprofessional (n=34), and professional (n=57) players provided a cross-sectional overview of the nature of the most predominant types and anatomical sites of injuries affecting soccer players (average age 23.9±4.7 years). All participants completed the Fuller soccer injury questionnaire, ISAK somatotype profiling and knee flexion/extension isokinetic concentric peak torque (Nm) evaluations at 60°/s. Fifty per cent of the players sustained soccer injuries (X 2=0.9). Knee (20%) and ankle (19%) were the most vulnerable sites (X 2=0.00001). Knee-injured players' right quadriceps torque (199±37 vs 223±38 Nm) and percentage right quadriceps torque relative to body mass (286±54 vs 311 ±39%) was significantly weaker than the non-injured players (p<0.01). The injured players' right hamstrings/quadriceps (H/Q) torque ratio further significantly differed from the non-injured players' H/Q torque ratios (79±17 vs 70±9%) (p<0.01). Male soccer players experience neuromusculoskeletal injuries, with their knees and ankles being the most vulnerable. Knee-injured players had weaker quadriceps isokinetic strength than non-injured players.

Parameter identification of vibratory conveying systems including statistical part behavior

This work presents a complete workflow for the parameter identification of an MBS model representing a vibratory conveying system. First, the MBS model built within the multibody dynamics tool HOTINT is shown. Essential components, such as contact modeling and adaptive time step control, are explained in detail. The model includes a considerable amount of parameters that need to be identified. Altough, this model is fully deterministic, the complex contact dynamics can cause major effect on results by minor parameter variations. Thus, parameter variations usually show statistical variance, which is characteristic for real conveying processes too. For parameter identification it is important to detect parameters that significantly correlate with results. A method that allows to distinguish significant and non-significant parameters is presented. The application to the multibody system shows that stiffness, restitution and sliding friction of the contact model are the essential parameters. Next, the parameter identification is discussed with particular attention to multimodal distributions, that can occur in conveying systems. Furthermore, the integration of statistics into the deterministic simulation model is discussed. In order to demonstrate the applicability of the proposed methods, a parameter identification is performed based on measurement data of a single part on a real conveying system in the development site of STIWA Automation GmbH. Finally, the validity of the fully parametrized simulation model is shown by investigating geometric adjustments of the conveyor. In order to further verify the identified set of parameters, a conveying process with multiple parts is analyzed and compared in measurement and simulation.

Superlubricity in solid lubricated sliding and rolling contacts

Superlubricity, or near zero friction is a highly desired lubrication state for a wide range of practical applications. Although such application scenarios often involve complex contact geometries, solid lubricant technologies, including previous efforts on achieving superlubricity, are almost entirely in linear sliding test conditions. This report demonstrates an experimental pathway to yield superlubricity in rolling-sliding contact conditions using solid-lubricant materials. Ti3C2X based solid lubricant was tested under complex sliding-rolling conditions at engineering-significant contact pressures. The material's compression and inter-layer shearing result in material reconstruction to pose superlubricity. High-resolution transmission electron microscopy analysis, complemented by multi-scan Raman spectroscopy showed the formation of a robust amorphous tribolayer. This demonstration is expected to not only advance the applied aspects in the development of oil-free solid lubricants but also push the boundaries of fundamental understanding of materials’ structure-property relations across physical states.

A comprehensive isogeometric analysis of frictional Hertz contact problem

The development of computational methods has advanced the solving of complex contact problems. Despite this, reproducing the analytical solution of a classical Hertz contact problem using computational methods remains challenging. Finite element method (FEM) has gained popularity, with many studies solving frictionless Hertz contact problems. However, the more general Hertz contact problem with finite friction lacks an analytical solution and is more complex. FEM was first used for this in the 1970s. Recently, isogeometric analysis (IGA) has shown enhanced efficiency than FEM. However, comprehensive studies on the frictional Hertz contact problem using IGA are lacking. The present study aims to fill this gap by examining a benchmark example and exploring contact simulation parameters using the developed in-house MATLAB® code.

End-to-end deep reinforcement learning and control with multimodal perception for planetary robotic dual peg-in-hole assembly

The planetary construction is necessary for long-term scientific deep space exploration and resource utilization in the future. The planetary robotic assembly control is a key technology that must be broken through in future planetary surface construction. The paper focuses on the most representative dual peg-in–hole assembly, which has sufficiently complex contact interaction, wide range of applications and good method portability. To address the challenges brought by the unstructured planetary environment and the features of the construction tasks, the paper proposes an end-to-end deep reinforcement learning and control method with multimodal perception for planetary robotic assembly tasks. A staged reward function based on the visual virtual target point for policy learning is designed. The effectiveness and feasibility of the proposed control method have been verified through simulation experiments and ground real robot experiments. It provides a feasible control method of robotic operations for future planetary surface construction.

Lubrication failure mechanism of rolling‑sliding steel ball against oil-impregnated porous polyimide and bearing steel in double friction pair

Oil-impregnated Porous Polyimide (O-PPI) cages have been widely applied in aerospace bearings because of their exceptional performance and self-lubricating characteristics, where the surface blackening failure of the O-PPI cage during the operation process significantly shortens the service lifetime. However, the blackening failure mechanisms are still not fully understood due to the complex multiple contacts between steel balls, the cage, and the inner/outer rings in the bearing system. This study aims to deeply detect the surface blackening failure mechanism of PPI materials with a relevant improvement measuring method. A double-contact rolling-sliding ball holder was developed to simulate the contact and the motion in aerospace bearings with PPI cages, where the blackening phenomenon on the O-PPI surface was replicated as the bearing ball rubbed against the PPI and steel surfaces. Comparative experiments and subsequent characterization results revealed that the iron debris generated at the ball-steel sliding interface was infiltrated into the PPI surface pores along the rolling motion of the steel ball, and then the splitting reaction of PAO oil at the steel-PPI interface catalyzed by the iron (Fe) during friction resulted in the formation of blackening products and further lubrication failure. Based on these findings, effective countermeasures are proposed to prevent similar failures in the future. This analysis is expected to enhance the operational reliability and enlarge the service lifetime of the space-bearing systems.

A PCM-based train post-derailment dynamics model and its application

Understanding post-derailment behaviours is critical and fundamental to preventing derailment escalation and developing containment methods, thereby avoiding catastrophic consequences in a derailment accident. However, modelling and simulating the train post-derailment behaviours is a significant challenge because of the complexity and unpredictability of the train post-derailment contact interaction. This paper presents a novel post-derailment contact model built upon the Polygon Contact Model (PCM), aimed at enabling accurate and efficient simulation of train post-derailment contact interactions. Expanding upon the PCM-based post-derailment contact model, we introduce a framework for simulating train post-derailment behaviours and utilise it to develop a train post-derailment dynamics model that considers complex contact interactions between the bogie and the track structure. Additionally, we introduce a dynamic optimisation method to determine the essential parameters for this model. The feasibility and accuracy of the PCM-based train post-derailment dynamics model have been validated through a comparative study with an actual derailment test. Subsequently, the verified model is used to reproduce different post-derailment scenarios with varying combinations of vehicles and tracks, yielding valuable insight and understanding into the train post-derailment behaviour.

Modelling dynamic fracture and fragmentation of rocks under multiaxial coupled static and dynamic loads with a parallelised 3D FDEM

In this study, a three-dimensional (3D) combined finite-discrete element method (FDEM) based simulator, which enables the robust simulation of full-scale triaxial Hopkinson bar (Tri-HB) testing system, including the capture of fracture and fragmentation processes of rock specimens as well as the detection and analysis of generated rock fragments, is developed for investigating the dynamic responses of rocks subjected to multiaxial coupled static and dynamic loads. An innovative two-step approach is proposed to first efficiently achieve the static stress state in the entire Tri-HB system and then apply dynamic loading to the system. The proposed approach with the schemes of mass scaling and local damping can significantly reduce the run time for static computation involving cohesive elements and complex contact mechanics in the framework of explicit time-integration. The developed program is well validated by achieving dynamic stress equilibrium in the Tri-HB system and comparing the simulated stress wave profiles with those from laboratory experiments. Then, the progressive dynamic fracture and fragmentation processes of rocks under different static stress conditions in a full-scale Tri-HB system are investigated, which vividly exhibit the confinement dependence of the dynamic behaviours of rocks in the testing system. It is found that, even with the same loading rate, separate input parameter sets for rock need to be established in FDEM for different confinement conditions to capture the actual rate dependent behaviour of rock. Further studies are also conducted to investigate the effect of interfacial friction on the fracture behaviour, and the results indicate that higher interfacial frictions significantly disturb the dynamic stress variations and the true rock behaviour in the system. Through high performance computing of 3D FDEM, this study is expected to contribute to the understanding of dynamic responses of rocks subjected to multiaxial coupled static and dynamic loads in deep underground engineering.

Local connection reinforcement learning method for efficient robotic peg-in-hole assembly

Traditional robotic peg-in-hole assembly methods rely on complex contact state analysis. Reinforcement learning (RL) is gradually becoming a preferred method of controlling robotic peg-in-hole assembly tasks. However, the training process of RL is quite time-consuming because RL methods are always globally connected, which means all state components are assumed to be the input of policies for all action components, thus increasing action space and state space to be explored. In this paper, we first define continuous space serialized Shapley value (CS3) and construct a connection graph to clarify the correlativity of action components on state components. Then we propose a local connection reinforcement learning (LCRL) method based on the connection graph, which eliminates the influence of irrelevant state components on the selection of action components. The simulation and experiment results demonstrate that the LCRL method can achieve the same average reward as the traditional RL method in only 49% of episodes. In the final episode, the LCRL method's final reward is 35% higher than that of the traditional RL method, which guarantees the rapidity and stability of the assembly process.

A novel methodology for intrinsic adhesion state sensing in gecko-inspired directional dry adhesives

This paper introduces an innovative methodology designed for intrinsic sensing of the adhesion state in directional dry adhesives. Rooted in the inherent shear actuation requirements of these adhesives, the sensing framework incorporates an elastic beam model for a single seta and an equivalent spring model for setae arrays during actuation, facilitating the transformation of complex micro-scale contact issues into relatively simple mechanical measurements. Using microwedge adhesives as a representative case study, the methodology is validated by a series of quantitative experiments and an experimental robotic gripper scenario, in which a straightforward and cost-effective commercial strain gauge proves competent for complex contact state sensing. The proposed methodology indicates substantial implications for improving the operational performance and expanding the application range of gecko-inspired adhesive operations.