Complex Contact Interactions Research Articles

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 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.

An enhanced polar-based GPGPU-parallelized contact detection algorithm for 3D FDEM and its application to cracking analysis of shield tunnel segmental linings

This study introduces the three-dimensional combined finite-discrete element method (3D FDEM) to perform cracking analysis of segmental linings under extreme conditions. Considering the complex contact interactions of segments, this study first proposes a polar-based GPGPU-parallelized contact detection algorithm to handle memory issues confronted by existing FDEM algorithms. Initially, a spatial decomposition approach based on the polar coordinate system is implemented during the broad search phase. Each tetrahedral element is positioned within suitable search cells according to the axis-aligned bounding box. Subsequently, element pairs within each search cell are iteratively traversed, and potential contact pairs are identified using the judge cell criteria. After the broad search, a narrow search phase is executed to determine all real contacts. Following the above implementation, a load-structure model encompassing soil spring and external pressure calculations is then proposed. Based on the shape functions and coordinate transformation, the formulations of soil springs and external loads are derived and parallelized in the 3D FDEM framework. Three numerical tests are presented to validate the effectiveness of the proposed approach. Simulation results confirm the suitability of the proposed method for cracking analysis of segmental linings. Compared to the existing methods, it reduces GPU memory usage by 56 ∼ 76 % without extending time, which enhances the computational scale of 3D FDEM simulations. Furthermore, the proposed method is applied to two engineering scenarios, i.e., straight and curved segmental linings, both considering the absence and presence of contact defects between segments. The results show that contact defects can significantly reduce the resistance of the structural system comprising bolts and concrete segments for straight and curved scenarios.

Impedance Optimization for Uncertain Contact Interactions Through Risk Sensitive Optimal Control

This letter addresses the problem of computing optimal impedance schedules for legged locomotion tasks involving complex contact interactions. We formulate the problem of impedance regulation as a trade-off between disturbance rejection and measurement uncertainty. We extend a stochastic optimal control algorithm known as Risk Sensitive Control to take into account measurement uncertainty and propose a formal way to include such uncertainty for unknown contact locations. The approach can efficiently generate optimal state and control trajectories along with local feedback control gains, i.e. impedance schedules. Extensive simulations demonstrate the capabilities of the approach in generating meaningful stiffness and damping modulation patterns before and after contact interaction. For example, contact forces are reduced during early contacts, damping increases to anticipate a high impact event and tracking is automatically traded-off for increased stability. In particular, we show a significant improvement in performance during jumping and trotting tasks with a simulated quadruped robot.

NUMERICAL ANALYSIS OF SQUARE HOLLOW COLUMN-BEAM CONNECTIONS BY ABAQUS

In recent years, steel or composite beam-column connections have drawn increasing praise due to the rapid development of assembled steel structures. However, limited researches have paid attention to the analytical behavior of square hollow column-beam joints. This work presents a numerical study on the static and cyclic behavior of the connections between a square hollow steel column and I-beam. Finite element analytical modeling of the joint was performed considering complex contact interactions and material models. Six different connections were evaluated by using ABAQUS. The modeling techniques used in this work, including the mesh and element types, the material properties, and the contact elements, were validated by comparing the numerical results of a through plate connection model with the experimental study results. Good agreement between the test and analytical results was observed in terms of the failure modes and the hysteretic behavior. Based on numerical results, the failure mode, moment-rotation curves for the SHS column to steel beam connections were discussed.

Experimental and Analytical Behavior of Square CFDST Column Blind Bolted to Steel Beam Connections

In recent years, steel or composite beam-column connections adopting blind fasteners have drawn increasing praise due to the rapid development of assembled steel structures. However, limited researches have paid attention to the experimental and analytical behavior of concrete filled double-skin steel tube (CFDST) column blind bolted joints. For investigating the structural performance and seismic behavior of this type of connection, cyclic tests on blind bolted joints to square CFDST columns were carried out to explore the effects of column hollow ratio and end plate type. Finite element analytical modelling of the semi-rigid joint was performed considering complex contact interactions and material models. Good agreement between the test and analytical results was observed in terms of the failure modes and the hysteretic behavior. Substantial parametric analyses were conducted on typical CFDST column connections to observe the influence of parameters including strength of steel tube, column hollow ratio and bolt pretension force. Furthermore, certain constructional measures commonly employed in engineering practice were also discussed. It was concluded that the CFDST column blind bolted to the steel beam joint has favorable seismic behavior and is feasible for application in high-intensity earthquake regions.

Moment redistribution in cold-formed steel sleeved and overlapped two-span purlin systems

Cold-formed steel purlin systems with overlapped or sleeved connections are alternatives to continuous two-span systems and exhibit different degrees of continuity. Both connection types are highly favourable in practice since they are both strategically placed over an interior support to provide additional moment resistance and rotational capacity where the corresponding demands are at their largest, thus improving the overall structural efficiency. Until recently, full-scale testing has been the most common way of investigating the structural behaviour of such systems. In this study, numerical modelling, capable of capturing the complex contact interactions and instability phenomena, is employed. The developed finite element models are first validated against data from physical tests on cold-formed steel beams featuring sleeved and overlapped connections that have been previously reported in the literature. Following their validation, the models are employed for parametric studies, based on which the structural behaviour of the examined systems is explored, while the applicability of conventional plastic design as well as of a previously proposed design approach is investigated. Finally, the efficiency of these systems in terms of load-carrying capacity is compared with their equivalent continuous two-span systems.

A modelling framework for the simulation of lubricated and dry line contacts

Abstract Complex contact interactions, which typically occur in machine elements, such as gears and bearings, require a manifold analysis methodology. This has led to the development of a large number of different simulation models throughout the last decade. The presented framework aims to incorporate the thermoelastohydrodynamic (TEHD) approach and numerical contact mechanics (NCM) into one simulation model. No analytic function of the lubrication gap is necessary, since arbitrary surfaces can be imported into the model. This leads to the possibility to analyse a wide range of different contact scenarios, considering fluid lubrication or dry contact mechanics. Example results, including a literature comparison with other models and an experimental validation of traction curves considering surface roughness, are presented to elucidate the functionalities of the developed simulation framework.

Evaluation of the Bearing Strength of Single-Shear Bolted Joint Composite Laminate Structures and Research on the Test Fixture

Abstract In this study, the test on the bearing strength of the single-shear bolted joint composite laminate structure was firstly conducted. Then a macro-micro multi-scale numerical model was developed and implemented using the general-purpose finite element code ABAQUS. In this numerical model, the complex contact interactions such as the contact at the bolt/hole and the contact at the specimen/fixture were both considered. In addition, the progressive damage and the material property degradation were also included in the numerical model. The numerical simulation results agree well with the experimental results. Based on the numerical model, the effect of the test fixture on the testing results was evaluated further. It is shown that the incomplete contact between the test fixture and the specimen and the lack of the lateral constraint on the specimen will affect the measured bearing strength of the single-shear bolted joint composite laminate structure. In addition, the lower support stiffness of the test fixture will also affect the measured stiffness of the bolted joint composite laminate structure. According to the numerical evaluation results, the test fixture was improved. Finally, the bearing strength of the single-shear bolted joint composite laminate structure was tested again using the improved test fixture. It was shown that the new testing results are improved comparing with the initial testing results.

Modeling Tsunami Induced Debris Impacts on Bridge Structures using the Material Point Method

Bridges represent a key part of infrastructure, playing a critical role in emergency response and post-event reconstruction. In this context, it is important for bridges to be able to survive both ground shaking and the effects of tsunamis. This paper focuses on numerically modeling bridge loading due to tsunamis. Although several studies have addressed the effect tsunami loads on bridges, few have examined the influence of debris carried by the tsunami. These problems involve complex contact interactions between solids and fluids that are not easily accommodated using typical fluid-oriented or solids-oriented numerical frameworks. In this paper the material point method (MPM) is used to address fluid and solid (moving and stationary) interactions with emphasis in evaluating demands on bridge superstructures by tsunami-driven debris.Two parametric studies have been conducted in this study. The first is aimed at understanding the influence of the contact area and the eccentricity of impact on the impact forces. The results show that the effect of these two factors are reduced with an increase in longitudinal length of the solid object. The second part of the study tries to evaluate the difference between tsunami driven debris impact loads and in-air debris impact loads. The results indicate that tsunami driven debris impacts tend to be larger by upto 35% compared to only in-air impact forces calculated using empirical equations.

Mechanics of chain-link wire nets with loose connections

Chain-link wire nets are used for slope stabilization, natural hazard protection systems, mine and tunnel safety and many other important applications. In rockfall protection barriers the nets are designed to withstand dynamic, impulsive loadings. As they are composed of ultra-high strength steel wires with loose three-dimensional connections, the high resistance nets are very flexible and serve to efficiently distribute loads throughout the structure. Rockfall barrier design requires accurate numerical simulations. In this work, a Finite Element model of chain-link nets is developed. To treat the complex contact interactions among chain-link elements and rockfall barrier components we develop a computational scheme relying on a general contact algorithm. The non-linear force displacement response of the net obtained in tensile quasi-static laboratory tests is successfully reproduced by the numerical model. The model parameters are obtained by optimization techniques. The calibrated chain-link model with contact is shown to successfully simulate a full-scale test of a flexible rockfall protection barrier. The computational schemes allow us to accurately model the mechanical behaviour of chain-link wire nets with loose connections.

Finite element analysis of spiral strands with different shapes subjected to axial loads

In this paper a new mathematical geometric model of spiral one or two-layered oval wire strands are proposed and an accurate computational two-layered oval strand 3D solid model, which is used for a finite element analysis, is presented. The three dimensional curve geometry of wires axes in the individual layers of the oval strand consists of straight linear and helical segments. The present geometric model fully considers the spatial configuration of individual wires in the right and left hand lay strand. Derived geometric equations were used for the generation of accurate 3D geometric and computational models for different types of strands. This study develops 3D finite element models of two-layer spiral round, triangular and oval strands subjected to axial loads using ABAQUS/Explicit software. Accurate modelling and understanding of their mechanical behaviour is complicated due to the complex contact interactions and conditions that exist between individual spirally wound wires. Comparisons of predicted responses for the strands with different shapes and constructions are presented. Resultant stress and/or deformation behaviours are discussed.

Generating Facial Expressions Using an Anatomically Accurate Biomechanical Model.

This paper presents a computational framework for modelling the biomechanics of human facial expressions. A detailed high-order (Cubic-Hermite) finite element model of the human head was constructed using anatomical data segmented from magnetic resonance images. The model includes a superficial soft-tissue continuum consisting of skin, the subcutaneous layer and the superficial Musculo-Aponeurotic system. Embedded within this continuum mesh, are 20 pairs of facial muscles which drive facial expressions. These muscles were treated as transversely-isotropic and their anatomical geometries and fibre orientations were accurately depicted. In order to capture the relative composition of muscles and fat, material heterogeneity was also introduced into the model. Complex contact interactions between the lips, eyelids, and between superficial soft tissue continuum and deep rigid skeletal bones were also computed. In addition, this paper investigates the impact of incorporating material heterogeneity and contact interactions, which are often neglected in similar studies. Four facial expressions were simulated using the developed model and the results were compared with surface data obtained from a 3D structured-light scanner. Predicted expressions showed good agreement with the experimental data.

Contact impingement in packings of elastic–plastic spheres, application to powder compaction

High-density compaction of ductile powder particles is characterized by a sharp increase of the inter-particle normal contact force. This is due to both complex contact interactions and plastic incompressibility of the particle constitutive material. A DEM model (OPEN-DEM YADE) using an interaction force-law reproducing this increase has been developed to simulate high-density compaction of ductile powders. Its formulation is derived from a Finite Element Method model (ABAQUS). Macroscopic stresses resulting from compaction tests carried out on a random assembly of spherical grains were computed with both models and then compared. A good agreement between the stress–density curves confirmed the accuracy of the DEM formulation. However, the role of the grain deformation may not be well described using DEM since it is based on an assumption of overlapping rigid particles but allows low calculation costs. To highlight the role of this deformation process, a detailed FEM-based analysis of the influence of contact impingement on the normal contact force is thus presented. It explores the mechanisms of stress transmission between contact zones and quantifies the appearance of contact interactions in terms of both indentation depth and relative density. Results show that contact impingement cannot be neglected at a relative density as low as 0.7 if a local, contact-scale analysis is aimed for (such as density distribution for instance). In such a case, previous models like the one proposed by Storåkers and co-authors, should be used with care. The local solid fraction provides a correct local description of both contact interactions and plastic incompressibility of the constitutive material of the grains up to the maximum density. This would allow the DEM to be successfully applied to large-scale simulations of high-density compaction.

Experimental and Numerical Investigation of the Tensile Behavior of Blind-Bolted T-Stub Connections to Concrete-Filled Circular Columns

This paper presents the results of two series of experimental and analytical studies on the structural behavior of an innovative moment-resisting connection to concrete-filled circular hollow sections using blind bolts. The first part of the paper presents a large-scale T-stub connection with full instrumentation tested to failure in tension, and the second part presents a series of pullout tests to explore the anchorage behavior of cogged bars within concrete-filled steel tubes. The favorable strength and stiffness characteristics of this type of connection showed that it could be an alternative to conventional welded moment-resisting connections. A 3D finite-element (FE) model was developed to simulate the behavior of blind-bolted T-stub connections when subject to tension. The FE model took into account material nonlinearities, geometrical discontinuities, and complex contact interactions among the bolt heads, tube wall, end plates, and nuts. The FE results were found to be in good quantitative agreement with the actual connection behavior. A stiffness model composed of various nonlinear springs was also developed to predict the pullout behavior of cogged bars within concrete-filled steel tubes. The cogged extensions to the blind bolts were very effective in relieving the stress concentration on the thin tube wall. The tensile load can be shared between membrane action of the tube wall and anchorage of the cogged bars. Thus, by using the blind-bolted connections with cogged extensions to connect the beam flanges to the column, moment transfer between the beam and column can be effectively achieved within a structural frame of composite construction.

Material characterization via least squares support vector machines

Analytical methods to interpret the load indentation curves are difficult to formulate and execute directly due to material and geometric nonlinearities as well as complex contact interactions. In the present study, a new approach based on the least squares support vector machines (LS-SVMs) is adopted in the characterization of materials obeying power law strain-hardening. The input data for training and verification of the LS-SVM model are obtained from 1000 large strain–large deformation finite element analyses which were carried out earlier to simulate indentation tests. The proposed LS-SVM model relates the characteristics of the indentation load-displacement curve directly to the elasto-plastic material properties without resorting to any iterative schemes. The tuned LS-SVM model is able to accurately predict the material properties when presented with new sets of load-indentation curves which were not used in the training and verification of the model.

Artificial neural network model for material characterization by indentation

Analytical methods to interpret the indentation load–displacement curves are difficult to formulate and solve due to material and geometric nonlinearities as well as complex contact interactions. In this study, large strain–large deformation finite element analyses were carried out to simulate indentation experiments. An artificial neural network model was constructed for the interpretation of indentation load–displacement curves. The data from finite element analyses were used to train and validate the artificial neural network model. The artificial neural network model was able to accurately determine the material properties when presented with the load–displacement curves that were not used in the training process. The proposed artificial neural network model is robust and directly relates the characteristics of the indentation load–displacement curve to the elasto-plastic material properties.