Explicit Finite Element Method Research Articles

Three-dimensional train–track–bridge coupled dynamics model based on the explicit finite element method

In this paper, a train-track-bridge coupled dynamics modeling and coupling method was proposed. The coupled dynamic system was modeled separately with multiple subsystems by finite element method and the three-dimensional nonlinear wheel-rail contact relationship was used to account for non-linearity. Using explicit numerical methods and coupling the subsystems by the load term on the right end of the dynamic equations, repetitive iteration in the dynamic response solution process was avoided. Thus, a simplified the solution of nonlinear dynamic models can be achieved in limited time. In order to meet the requirement of diagonalization of the mass matrix in the algorithm, the modal superposition method was adopted. In the solution method proposed in this study, only a set of mass, damping, and stiffness matrices of the subsystem structure need to be established for solution instead of building the total matrix of the coupled dynamic system. Thus, greatly reduce the dynamic system matrix dimension for periodic train-track-bridge coupled dynamic systems. The train-track-bridge coupled dynamics model proposed in this paper is suitable to model various track and bridge structures, the wheel-rail contact relationship used is closer to reality and has more accuracy in describing the force state between wheel and rail. Besides, the unit size, number of modalities and numerical integration step size required in the calculation of each subsystem have been determined based on numerical experiments. Using the established dynamics model, the effects of the commonly used bound and separation ballastless track structures on the train operation safety was analyzed employing single-sample and multi-samples analysis. The calculation results demonstrated that the separation model is preferable for the prediction of train operation safety.

ANALYSIS OF NONLINEAR STATIC-DYNAMIC DEFORMATION OF REINFORCED CONCRETE FRAMES IN OUT-OF-LIMIT STATES

Statement of the problem. The article presents a computational model, an algorithm for computational analysis and the results of calculating the nonlinear static-dynamic deformation of reinforced concrete frames in out-of-limit states caused by the sudden removal of one of the supporting structures. Results. To design a numerical model of the static-dynamic loading mode of a structural system, the LS-DYNA software package was used that makes use of a detailed 3D model implementing an explicit finite element method. During the computational analysis, the physical and mechanical characteristics of the deformation of materials were taken in three variants: those obtained based on the experimental data by G. A. Geniev, the experimental data by N. V. Fedorova and M. D. Medyankin under the static-dynamic uniaxial testing mode of a limited number of standard samples of prisms and according to the Russian standards SP (СП) 385.1325800.2018. Conclusions. Numerical analysis of the static-dynamic deformation of the reinforced concrete framerod system of a multi-storey building has established that the differentiated accounting of the quantitative value of the concrete viscosity modulus and, accordingly, the time and level of static-dynamic loading of the structure allows one to identify the criteria for the special limit state of the elements of reinforced concrete structural systems of buildings and structures in a more rigid manner.

An improved finite element model for three-dimensional wheel–rail rolling contact

A three-dimensional wheel–rail rolling contact model (3D WRRCM) developed using the explicit finite element method (FEM) can be used to analyze the dynamic performances of wheelsets and tracks while considering the wheelset rotation and translation, as well as the real wheel–rail contact mechanism. When using the FEM with static initialisation (traditional model), the first step is to calculate the static wheel–rail displacement, strain, and stress when applying axle loading on the wheel and neglecting the wheelset rotation and translation. Then, using these results as the initial conditions, the dynamic wheel–rail displacement, strain, and stress are calculated while considering the wheelset rotation and translation by adopting the explicit dynamic solution method. However, obtaining a solution using this traditional method is time consuming, and the solution can be divergent because of the impulse produced by the suddenly increasing wheelset rotation when proceeding from the initial condition to the dynamic. The optimised method developed in this study can solve this problem. A comparison of the results from the traditional and optimised methods reveals that in the optimised method, the softer initial impulse effectively shortens the track length needed for the calculation and improves the solution efficiency.

Investigation of phase change materials (PCMs) on the heat transfer performance of building systems

The energy use of building systems contributes to a large percentage of total energy consumption, which requires consideration. Solutions of improvement to save energy are crucial. Phase change materials have been proved to be good candidates to be used in building envelopes for energy save. In this paper, an extended Explicit Finite Element Method (ex-FEM), which has been previously introduced and improved, is taken for simulation of temperatures and heat transfer in simplified multilayer wall constructions, consisting of PCM and insulation. The method has been validated against experimental data measured in a so-called Hot-Box. Temperature data are measured at different positions in a number of simplified multilayer walls. Our results show a reasonable good agreement between the simulations and the experiments, at both heating and cooling considering the temperature hysteresis effect in the PCM. The temperature stabilization ability of the PCM is clear, in both the simulations and the experiments, and particularly in the data when the transition range of the PCM is fully activated and matching the temperature variation in the wall at that particular PCM position. Our ex-FEM tool has here been proved to be able to predict the thermal performance of simplified wall constructions of multiple layers with PCMs incorporated.

Low-speed bending impact behaviour of adhesively bonded dissimilar single-lap joints

This study investigates the low-speed bending impact behaviour of adhesively bonded dissimilar single-lap joints and the effects of both strength and plastic deformation capability of adherend material on adhesive failure. Dissimilar adhesive single-lap joint specimens, such as Al 2024-T3 (top adherend)-Al 5754-0 (bottom) and Al 5754-0 (top)-Al 2024-T3 (bottom), were tested at two impact energy levels (3 and 11 J) for two overlap lengths (25 and 40 mm). The progressive failure analysis of the adhesive layer was also conducted by the non-linear explicit finite element method. The adhesive layer was modelled with a 3D cohesive layer along with the upper and lower adhesive interfaces and a non-linear continuum adhesive region between two cohesive layers. The continuum adhesive region had elasto-plastic adhesive properties whilst the cohesive layers obeyed 3D cohesive rules. The experimental and predicted contact force-time, contact force-displacement diagrams, axial separation lengths of the failed adhesive region, permanent deflection of the bonded region, fracture surfaces were in good agreement. The strength and plastic deformation capability of adherend materials and impact energy levels affected the progressive adhesive failure behaviour. The proposed finite element model was successful reasonably in predicting the initiation and propagation of the adhesive failure.

Blast Resistance of an Innovative Helmet Liner composed of an Auxetic Lattice Structure

Helmet liners are employed to prevent or reduce head injuries caused by impact or blast loads. Liners minimize the damage by shock attenuation and absorbing the dynamic energy. In order to improve blast resistance and crashworthiness characteristics of helmet liner under air-blast, in the present study, an innovative structure designed by an arrow-head auxetic lattice structure is suggested to replace the conventional EPS foams usually employed in the liner section. Explicit finite element method is employed to model the innovative helmet structure under blast loading and results are compared with the conventional case based on trend of acceleration, energy absorption, weight, and Head Injury Criteria (HIC) factor. Also, a parametric study is conducted on the effect of lattice structure’s cell size in the protective performance of helmets. Results indicate a great improvement in blast resistance of helmet when the suggested liners are employed so that the HIC number could be decreased by 71% when AH4 configuration is used while the overall energy absorption capacity of helmet is increased about 34% compared to the basic model.

An Explicit Finite Element Method for Thermal Simulations of Buildings with Phase Change Materials

The thermal performance of building envelopes is essential for building thermal comfort and the reduction of building energy requirements. Phase change materials (PCMs) implemented in building envelopes can improve thermal performance. An explicit finite element method (ex-FEM) has been developed based on a previous study to investigate the heat transfer performance through building walls with installed PCMs. For verification, we introduce an electrical circuit analogy (ECA) method. For model validation, at first, COMSOL is used. For comparison, data were collected from experiments using a small hotbox, part of the sides are covered by PCMs with different configurations. This work shows how the ex-FEM model can predict the wall’s temperature profile with and without incorporated PCM. With the implementation of PCMs, the work problematizes unpredictable influences for modeling. In addition, the study introduces results from simulations of sequencing of PCM layers in wall construction.

EXPERIMENTAL AND FINITE ELEMENT ANALYSIS OF NONAXISYMMETRIC STRETCH FLANGING PROCESS USING AA 5052

This paper deals with experimental and finite element analysis of the stretch flanging process using AA- 5052 sheets of 0.5 mm thick. A parametrical study has been done through finite element simulation to inspect the influence of procedural parametrical properties on maximum thinning (%) within the stretch flanging process. The influence of preliminary flange length of sheet metal blank, punch die clearance, and width was examined on the maximum thinning (%). An explicit dynamic finite element method was utilized using the finite element commercial package ABAQUS. Strain measurement was done after conducting stretch flanging tests. A Mesh convergence examination was carried out to ascertain the maximum percentage accuracy in FEM model. It is found through finite element simulation that the width of sheet metal blanks has a greater impact on the maximum percentage of thinning as compared to preliminary flange length, and clearance of the punch dies.

Study on unsaturated shapes of helium ballonet of rigid airship during ascent process

Airship has a good application prospect in tourism, material transportation, emergency rescue, communication relay, early warning, environmental protection and other fields. Airships can be classified into non-rigid types, semi-rigid types and rigid types. The rigid airship relies on the external skeleton to maintain its overall stiffness and shape, and the internal helium ballonet provides buoyancy. The helium ballonet is always in unsaturated state during ascent process, which will affect the center of gravity and buoyancy and the stress in wrinkle area, so it is great significance to study the unsaturated shape of the helium ballonet during ascent process. In this paper, the principal stress-principal strain principal is used to judge the stress state of the membrane. The modified constitutive matrix method and the pressure gradient method are used to obtain the shape of the helium ballonet under different saturation by the dynamic explicit FEM (Finite Element Method). When the pressure gradient method is used to apply the pressure difference internal and external of the ballonet, the change of unsaturated shape of the ballonet can be interpreted as the change of zero pressure level of the ballonet. The modified constitutive matrix method can effectively avoid the problem of non-convergence in the process of programming. The simulation results are in good agreement with the experimental results, which shows that the analysis method is reasonable and correct.

Design approach of heavy goods vehicle underrun protection using morphological analysis

One of the most harmful of two-vehicle crashes to passenger vehicle occupants is when the front of passenger vehicle hits and passes underneath the rear of truck. It resulted in 23% of total death from two-vehicle crashes with a truck in 2018 based on data from the U.S. Department of transportation’s Fatality Analysis Reporting System (FARS). To reduce the violence of such accidents, the rear underrun protective device (RUPD) is installed on the rear of heavy goods vehicle (HGV), to cause the crumple zone of the impacting passenger vehicle absorbing the impact energy and prevent the impacting passenger vehicle from getting crushed under the HGV. This article demonstrates an approach to design the RUPD based on design inputs, including the structural strength, the local RUPD builders, and the variation of commercial HGV types in Thailand. The morphological analysis is applied along with brainstorming among design team, local manufacturers, and government agency, to generate a total of 72 potential RUPD solutions. In this study, three potential RUPD designs were proposed as RUPD prototypes for different HGV types to investigate their structural strength in terms of strain, deformation, and maximum reaction force. The explicit dynamic finite element (FE) method was implemented to accurately simulate the structural strength of the RUPD prototype since its results were validated by the real test of full-scale prototype with reference to the UN R58 standard. From the results, all proposed RUPD prototypes satisfied the UN R58 standard and are not violated by test loads at all relevant positions. In addition, different designs of the protective beam, which was found to be the main load-bearing resstive component of RUPD, were proposed. Their structural strength and energy-absorbing capability were examined by FE simulation to allow local RUPD builders to have alternatives for RUPD fabrication depending on their resources and applications. Besides, the proposed design approach in this study could be further applied as a guideline design for other RUPD types in a commercial scale.

An improved continuum-based finite–discrete element method with intra-element fracturing algorithm

This work develops a continuum-based combined finite–discrete element method (FDEM) in the framework of the explicit finite element method in conjunction with fracture algorithms. To account for complex fracturing processes, both shear failure and tensile failure criteria are implemented. Furthermore, to investigate the effect of different fracture algorithms on the accuracy and computational efficiency of simulations, both the inter-element and intra-element fracture algorithms are developed in the continuum-based framework. Then, they are compared by two benchmark tests, of rock: the Brazilian tests and uniaxial tension tests. Besides, uniaxial compression tests under different loading rates are carried out to demonstrate the shear failure criterion and the corresponding fracture algorithm.The simulation results converge with the decrease of element sizes in the inter-element fracture algorithm. The intra-element fracture algorithm is proven to be more efficient and accurate in the simulation of fracturing processes compared to the inter-element fracture algorithm.

Explicit finite element method for nonlinear flutter analysis of composite panels

This work presents an efficient explicit finite element model for predicting the nonlinear aeroelastic behavior of composite panels in the supersonic regime. The first-order shear deformation plate theory in conjunction with the von Kármán nonlinear strains is used for structural modeling and the linear piston theory is used to model the aerodynamic loads. In order to reduce the computational cost of the simulations, a lumping procedure is employed in the mass and aerodynamic damping matrices of the finite element model. No modal reduction is performed and the central difference method is used for the numerical direct integration in time of the nonlinear equations. The model is verified using results from the literature and it is demonstrated that the lumping procedure drastically reduces the computational cost of the simulations.

Simulated seismic response analysis of subway tunnels under complex geological conditions of obliquely incident seismic SV waves

To investigate the seismic performance of simulated subway tunnels under complex geological conditions of obliquely incident earthquake excitations, a new input method for oblique incidence of SV waves with arbitrary incident angles in 3D space has been proposed. The method relies on explicit finite element method (EFEM) and viscous-spring artificial boundary (VSAB) condition, which simultaneously considers soil-structure interaction, surrounding soil characteristics, and seismic wave incident characteristics. It is applied and verified based on the seismic wave theory. The overall numerical model of subway tunnel and soil foundation is then established, and the dynamic response of subway tunnel in soft and hard interbedded soils under oblique incidence of SV waves is systematically analyzed. The obtained simulated results indicate that the dynamic response of each point in subway tunnel is decreased by increasing incident SV wave angle. It is also found that the dynamic responses of the site interbedded by soft and hard soils are significantly higher than that in other points of the site at the same incident angle, indicating that the mentioned zone has weak seismic resistance. In addition, the dynamic response of each point in tunnel structure tends to become closer when the bulk moduli of soft and hard soils are getting close. The displacement and moment of the site interbedded by soft and hard soils are reduced by increasing the thickness of lining structure, therefore improving the seismic resistance of the tunnel. The results of parametric study show that these factors could have significant influences on the seismic responses of tunnel structures during earthquake and should be considered during earthquake-resistant design of subway tunnels under complex geological conditions.

Modelling and experiment of gear hob tooth profile error for relief grinding

Gear hob is an important tool that is most used in gear processing. Hob accuracy directly exerts an overwhelming influence on the quality of the processed gear. Generally, the hob tooth profile accuracy is mainly determined by relief grinding process. Studies on tooth profile errors of gear hobs caused by severe friction and cutting with the high-speed rotation of the wheel during the form grinding machining of hobs are limited. Thus, a theoretical model of the tooth profile error prediction under different machining parameters was established based on the analysis of coupling influence of high temperature and high strain rate on gear hobs in the relief grinding process. The model was completed on the basis of the dynamic explicit integral finite element method of thermo-mechanical coupling. Through the prediction model, the influence of the grinding depth ap, feed speed Vw and grinding speed Vs on the tooth profile error can be analysed. In addition, an algorithm for accurately calculate the grinding wheel axial profile by combining instantaneous envelope theory and hob normal tooth profile was proposed. The hob relief grinding experiments were carried out using the proposed grinding wheel profile algorithm. The relative error of the prediction obtained by comparing the calculation results of the prediction model with the experimental results is within 10%. Results prove the validity of the prediction model. This finding is greatly important for optimising the accuracy of hob relief grinding.

Simulating Extraocular Muscle Dynamics. A Comparison between Dynamic Implicit and Explicit Finite Element Methods

The finite element method has been widely used to investigate the mechanical behavior of biological tissues. When analyzing these particular materials subjected to dynamic requests, time integration algorithms should be considered to incorporate the inertial effects. These algorithms can be classified as implicit or explicit. Although both algorithms have been used in different scenarios, a comparative study of the outcomes of both methods is important to determine the performance of a model used to simulate the active contraction of the skeletal muscle tissue. In this work, dynamic implicit and dynamic explicit solutions are presented for the movement of the eye ball induced by the extraocular muscles. Aspects such as stability, computational time and the influence of mass-scaling for the explicit formulation were assessed using ABAQUS software. Both strategies produced similar results regarding range of movement of the eye ball, total deformation and kinetic energy. Using the implicit dynamic formulation, an important amount of computational time reduction is achieved. Although mass-scaling can reduce the simulation time, the dynamic contraction of the muscle is drastically altered.

Size Effect of Shear Strength of Recycled Concrete Beam without Web Reinforcement: Testing and Explicit Finite Element Simulation

Recycled concrete is a form of low-carbon concrete with great importance. The explicit finite element method is an economical and feasible method for analyzing static concrete structures, such as those made of recycled concrete. The shear strength of regular concrete beams has size effects. In this study, a group of physical tests on the size effect of the shear strength of recycled concrete beams without web reinforcement was carried out under the condition of a constant shear span ratio. The research results show that the shear strength of the test beam generally decreases with the increase in beam section height, and a regression formula of the shear strength was obtained, which can formulate this effect. The rationale and feasibility of the explicit finite element method solving the ultimate load of concrete structures (which can derive the shear strength) were briefly demonstrated, and an explicit finite element simulation of test beams was carried out. Results showed an obvious and phenomenologically regular size effect of the shear strength of recycled concrete beams without web reinforcement, which can be simulated by the explicit finite element method. This research aims to promote the study of low-carbon recycled concrete structures to a certain extent and encourage the application of economic explicit finite element methods for the static analysis of concrete structures.

Dynamic Finite Element Analysis on Single Impact Plastic Deformation Behavior Induced by SMAT Process in 7075-T6 Aluminum Alloy

Surface mechanical attrition treatment (SMAT) is a method that enhances the mechanical properties of metallic materials by generating a thin nanostructured layer on the top surface. In this study, single-shot impact behavior was modeled for the 7075-T6 aluminum alloy to reach maximum values of equivalent stress, plastic strain, deformation depth, residual stress depth, and residual stress. Finite element simulations have been carried out to analyze the effect of selected parameters on stress and strains in the component. For simulating the SMAT process, a rigid sphere on a rectangular component is modeled using ANSYS/AUTODYN explicit dynamic solver. The plastic deformation process during SMAT was analyzed according to shot velocity and diameter with a dynamic explicit finite element method (FEM). The response surface methodology was used to evaluate the parametric results for the SMAT process. In addition, deformation behavior was evaluated after a single-shot impact according to the restitution coefficient.

Surface texture transfer in skin-pass rolling with the effect of roll surface wear

This paper presents a novel three-dimensional characterisation of the wear effects of a roll surface on the texture transfer in skin-pass rolling. The method integrates the interactions of the microscale elastic deformation of roll surface asperities with the microscale plastic deformation of strip surface asperities. An elasticity theory and a discrete fast Fourier transform were used to rationally predict the microscale elastic deformation of work roll in the rolling system. The microscale plastic deformation of the asperities on the soft strip surface was calculated by the material redistribution process. The Archard wear law was used to consider the wear effects with the random contact pressure, relative sliding and surface hardness. A multiscale analysis was carried out by the dynamic explicit finite element method (FEM), which fully coupled microscale surface contacts, macroscale elastic deformation of the work roll and the bulk plastic deformation of the metal strip. Due to the complexity associated with numerical simulation, a novel modularised approach was established to complete the calculation in a feasible and efficient manner. The study reveals that the roughness scale of a rolled metal strip decreases gradually due to the roll surface wear and that the rolling force, relative sliding and rolling speed at the roll-strip interface significantly affect the roll surface wear. It is expected that the method established can be used to control the surface texture transfer in skin-pass rolling under the continuous wear of roll surfaces.

Role of the mandrel in the variable curvature local-induction-heating bending process of B1500HS thin-walled rectangular tubes

The variable curvature local-induction-heating bending forming (VC-LIHBF) technology is commonly used in the automotive industry to lighten and stiffen the structure parts. This technology allows the simultaneously bending forming and hardening of ultrahigh strength steel tubes, and allows the tensile strength of B1500HS steel to reach 1500 MPa. By adjusting the bending curvature parameters of the experimental facility through the numerical control system, the production of the tubes with variable curvatures could be achieved without changing dies. However, the more major problem of wrinkling occurs when a small-radius bending is applied on thin-walled rectangular tubes. This paper focuses on improving of forming quality and forming limit of the thin-walled rectangular steel tube (TWRST) with mandrel supported. In this study, an analytical model of the mandrel is established and some reference formulas for the selection of the mandrel parameters are deduced. Based on the above analysis, a three-dimensional elastic-plastic finite element method (FEM) model of the LIHBF process of the B1500HS TWRST is developed using the dynamic explicit FEM code ABAQUS/Temp-disp/Explicit, and key technological problems are solved. Experiments are carried out to verify the accuracy of the analytical model and confirm the reliability of the FEM model. The influences of the mandrel on stress distribution during the local-induction-heating bending process are also investigated. The influence mechanism of the mandrel parameters on the minimum radius of the LIHBF without wrinkling and the forming quality is revealed. The appropriate process parameters for the B1500HS TWRST are obtained through experiments and simulations.

Beirut explosion 2020: A case study for a large-scale urban blast simulation

In the face of continued global urbanization, cities are challenged to satisfy increasing standards in terms of quality of life, environmental conditions, safety, security, health, economic growth and mobility. The concept of “smart cities” aims at utilising advanced technologies, artificial intelligence and high computational capacity to increase their resilience and improve the services provided to the citizens. Computation-based numerical simulations have been essentially used to estimate the effects of explosion events in urban environments in terms of both structural damage and human casualties. These provide urban planners and decision makers with valuable information for vulnerability assessment and aid developing prevention or mitigation solutions. In this article, we present a framework to generate a 3D large-scale urbanistic finite element model, where the desired geospatial data are extracted from the open-source world map OpenStreetMap. The model is used to simulate blast wave propagation effects in a wide urban area taking into account the reflections at building surfaces via a sophisticated Fluid-Structure interaction technique integrated in the EUROPLEXUS explicit finite element method software. The explosion in the Port of Beirut in Lebanon, which took place on the 4th of August 2020, was remarkable for the large amount of explosive material causing considerable damage to surrounding structures and a high number of deaths and injured. Such characteristics make the event suitable for assessing the performance of the proposed computational approach in a widely exposed (by the blast wave) urban zone.