Three-dimensional Elasto-plastic Finite Element Model Research Articles

Study on Damage Evolution of Tunnel Lining under Strike-Slip Fault Movements

For the purpose of investigating the damage mechanism and failure characteristics of tunnel lining under the strike-slip fault movements, a three-dimensional elastoplastic finite element model was established in the present study including a railway tunnel across an active strike-slip fault. With the assistance of this numerical model, the tensile and compressive damage, plastic strain development process, and shear failure of the secondary lining at different fault plane positions were analyzed, and further, the damage laws of the secondary lining at different fault displacement and tunnel-fault intersection angles were summarized. The simulation results showed that when the maximum imposed fault displacement is 30 cm, the most unfavorable fault plane appears at the junction between the moving block and the fracture zone, and serious tensile cracks and shear failures occur on each fault rupture plane. Besides, the maximum plastic strain and compressive damage are distributed in the vault and invert. In addition, with the increase of the fault displacement, the axial strain of the secondary lining increases as well, of which the main part shows the tensile strain. Interestingly, with the decrease of the crossing angle, the axial strain gradually changes from the tensile strain to the compressive strain, which is consistent with the direction of the fault angle. Furthermore, the tensile and compressive damage of the secondary lining increases with the increase of movement distance. At the same time, the tensile damage along the tunnel ring develops, and the compressive damage propagates mainly in tunnel vault and invert. With the decrease of the crossing angle, the degree of the tensile damage in the lining reduces, as well as its range. The compressive damage area of the lining develops from the vault and inverted arch to the tunnel wall on both sides, which has a trend of penetrating the side walls on both sides. The distribution area and maximum value of the overall lining damage indices in tensile (OLDT) and overall lining damage indices in compressive (OLDC) increase with the increase of fault movement distance. With the decrease of the crossing angle, the distribution range and maximum value of OLDT decrease, and the distribution range of OLDC increases, while the maximum value basically remains the same. The research results of the present work can provide reference for the antidislocation design of railway tunnels crossing strike-slip faults.

Dynamic mechanical behaviour and energy absorption of aluminium honeycomb sandwich panels under repeated impact loads

Sandwich structures are widely applied in the field of marine structure lightweight design and impact protection due to their excellent mechanical properties. In this paper, the dynamic mechanical behaviour and energy absorption characteristics of aluminium honeycomb sandwich panels (AHSPs) under repeated impact loadings are investigated. A three-dimensional elastoplastic finite element model of AHSP under repeated impact loadings is established by using the commercial software ABAQUS Explicit. The accumulation processes of plastic deformation, the impact force-displacement curves as well as the energy absorption performances are numerically calculated. Besides, the repeated impact experiments of AHSPs were conducted by using the drop-weight impact testing machine INSTRON CEAST 9350. Furthermore, the influences of geometrical parameters on the dynamic behaviours of AHSPs under repeated impact loadings are further performed. Results show that the numerical calculated results are in good agreement with the experimental results. With the increase of the repeated impact numbers, the bending deflections of both top and bottom face sheets of AHPSs accumulate gradually, the compressive deformations of the honeycomb cores enlarge gradually and finally the densification phenomenon appears. The deformation mode of bottom face sheet experiences the mode transition from the global bending deformation model to the coupling deformation mode of the global bending deformations and the local indentations.

Thermomechanical analysis of the wheel-rail contact using a coupled modelling procedure

Abstract This research presents a coupled thermomechanical modelling procedure for the wheel-rail contact problem and computes the flash-temperature and stress-strain responses when thermal effects are present. A three-dimensional elasto-plastic finite element model was built considering the wheel-track interaction. When the wheel is running on rail, frictional energy is generated and converted into heat. To evaluate the contribution of thermal effects and plasticity, five different material models were studied among them TEPS was nonlinear and temperature-dependent including thermal softening. Discussions were made on the effect of solution type and material type. The rail temperature, calculated for a critical creepage case, confirmed the potential of martensitic phase transformation. Thermal effects were also important at lower creepages, where a synchronization effect causes earlier damage.

Through-Thickness Deformation Gradient in a Part-Pilgered Zirconium Tube: Experimental Measurements and Numerical Validation

Through-thickness microstructure development and residual stress evolution were explored in a part-pilgered Zircaloy-4 tube. Clear gradients in microstructure and residual stress were experimentally established at different locations. Such locations were considered along the axial length and also across the wall thickness. These were naturally subjected to different von Mises effective strains and were reflected on strain/microstructural gradients. The deformation gradients were also simulated with a three-dimensional elastoplastic finite element model. The model used both isotropic and anisotropic yielding. Though deformation gradients were similar with both yielding criteria, the anisotropic yielding provided a better match with experimental residual stress gradients.

Springback prediction for incremental sheet forming based on FEM-PSONN technology

In the incremental sheet forming (ISF) process, springback is a very important factor that affects the quality of parts. Predicting and controlling springback accurately is essential for the design of the toolpath for ISF. A three-dimensional elasto-plastic finite element model (FEM) was developed to simulate the process and the simulated results were compared with those from the experiment. The springback angle was found to be in accordance with the experimental result, proving the FEM to be effective. A coupled artificial neural networks (ANN) and finite element method technique was developed to simulate and predict springback responses to changes in the processing parameters. A particle swarm optimization (PSO) algorithm was used to optimize the weights and thresholds of the neural network model. The neural network was trained using available FEM simulation data. The results showed that a more accurate prediction of springback can be acquired using the FEM-PSONN model.

Studies on the Springback Mechanism of Incremental Sheet Forming Based on FEM Simulation

Incremental sheet forming (ISF) is an innovative and highly flexible sheet metal forming process for small batch production and prototyping, but springback is a very important factor to influence the quality of incremental sheet forming. This paper investigates the springback mechanism of incremental sheet forming using numerical method. A three-dimensional elasto-plastic finite element model was established for the simulation of the incremental sheet forming process. In this model, the combination of dynamic explicit algorithm and the static implicit algorithm was proposed to calculate the whole forming process including springback. The results of numerical simulation, such as, the strain history and distribution, the stress state and distribution, etc., are discussed in details. Moreover, the results confirm that residual stress has been releasing during forming process, which reveal the peculiar springback characteristic of incremental sheet forming process.

Numerical simulation and experimental investigation of incremental sheet forming process

In order to investigate the process of incremental sheet forming (ISF) through both experimental and numerical approaches, a three-dimensional elasto-plastic finite element model (FEM) was developed to simulate the process and the simulated results were compared with those of experiment. The results of numerical simulations, such as the strain history and distribution, the stress state and distribution, sheet thickness distribution, etc, were discussed in details, and the influences of process parameters on these results were also analyzed. The simulated results of the radial strain and the thickness distribution are in good agreement with experimental results. The simulations reveal that the deformation is localized around the tool and constantly remains close to a plane strain state. With decreasing depth step, increasing tool diameter and wall inclination angle, the axial stress reduces, leading to less thinning and more homogeneous plastic strain and thickness distribution. During ISF, the plastic strain increases stepwise under the action of the tool. Each increase in plastic strain is accompanied by hydrostatic pressure, which explains why obtainable deformation using ISF exceeds the forming limits of conventional sheet forming.

Influence of thickness and number of dielectric layers on residual stresses in micromultilayer ceramic capacitors

The residual stresses due to high-temperature processing in micromultilayer ceramic capacitors (MLCCs) with various thicknesses and numbers of dielectric ceramic layers were investigated by using a three-dimensional elastoplastic finite element model with temperature-dependent material properties taken into account. For comparison, an explicit analytical solution for the in-plane residual stress in the dielectric ceramic layer was derived. Both the numerical results and the analytical model showed that the thickness ratio of the dielectric layer to electrode layer has a dominant impact on the residual stress states. There exists a critical thickness for the dielectric ceramic layer in MLCCs in the case of a given thickness of the electrode layer, below which both high tensile out-of-plane stresses and high compressive in-plane stresses could cause the cracking of the brittle dielectric layers near the electrode tips and/or the debonding of the electrode/dielectric interface.

An analysis of forming limit in the elliptic hole-flanging process of sheet metal

Abstract A methodology for formulating a three-dimensional elasto-plastic finite element model, which is based on Prandtl-Reuss flow rule and Hill's yield criterion, respectively, associates with an updated Lagrangian formulation, is developed to simulate the elliptic hole-flanging process. An extended r-minimum algorithm is proposed to formulate the boundary condition, such as the yield of element, maximum allowable strain increment, maximum allowable rotation increment, maximum allowable equivalent stress increment, and tolerance for nodes getting out of contact with tool. The fractured thickness of a specimen in simple tension test is adopted as the fracture criterion in simulation. The numerical simulation results include relationship between punch load and punch displacement, variation of the workpiece thickness, distribution of stress, distribution of strain, and limit forming ratio. The finite element model is developed to simulate anisotropic of the elliptic hole-flanging process. The accuracy of the finite element program is based on a comparison between the simulation and experiment outcomes. According to the experimental data, the prediction of the phenomenon of necking of the elliptic hole-flanging process occurs at the inner periphery of elliptic hole is studied. The simulation dearly demonstrates the efficiency of the model to simulate the elliptic hole-flanging process. This study has provided an improved understanding of the elliptic hole-flanging process for improving the manufacturing processes and the design of tools.

Analysis of subsurface crack propagation under rolling contact loading in railroad wheels using FEM

A general subsurface crack propagation analysis methodology for the wheel/rail rolling contact fatigue problem is developed in this paper. A three-dimensional elasto-plastic finite element model is used to calculate stress intensity factors in wheels, in which a sub-modeling technique is used to achieve both computational efficiency and accuracy. Then the fatigue damage in the wheel is calculated using a previously developed mixed-mode fatigue crack propagation model. The advantages of the proposed methodology are that it can accurately represent the contact stress of complex mechanical components and can consider the effect of loading non-proportionality. The effects of wheel diameter, vertical loading amplitude, initial crack size, location and orientation on stress intensity factor range are investigated using the proposed model. The prediction results of the proposed methodology are compared with in-field observations.

3D finite element investigation on the plastic flows of rolling contacts—correlation with railhead microstructural observations

In this work, a three-dimensional elasto-plastic finite element model is used to simulate the rail mechanical response to the action of a rolling wheel. Plastic flows in the near-surface layer are computed as a function of the traction coefficient. The depth and the distortion of the plastically deformed layer are analysed versus this traction coefficient and correlated qualitatively to the microstructural observations of plastic flows in real railheads and existing theoretical studies. The deviations of the numerical results with reality are discussed in terms of the presence of a solid third body layer, neglected in the simulations.

Three-dimensional elastoplastic finite element model for residual stresses in the shot peening process

The fatigue life of mechanical components subjected to variable loading conditions is a crucial parameter in the design of automotive and aerospace mechanical components. The fatigue strength of the component can be improved by inducing compressive residual stress in the surface and subsurface layers by the shot peening process. This increases the failure strain magnitude for crack nucleation and propagation. Extensive experimental results have been published on the effect of shot peening process parameters on residual stress distributions and subsequently on fatigue performance. Numerical simulation of residual stres induced by the shot peening process is important for understanding and optimization of the process in terms of the residual stress profile and maximum shot coverage in the shortest time. In this paper, an elastoplastic finite element (FE) model will be presented to simulate the shot peening process in three-dimensional configuration. The FE model takes into account numerical and material damping, thermal elastic—plastic material behaviour, a rigid or deformable body for the shot and the effects of multiple shot impacts. The workpiece material modelled was AISI 4340 steel at HRC 52 ± 2. The effects of strain hardening, strain rate and temperature were considered in the non-linear material model. Results show that the predicted residual stress profile agreed well with that acquired from published experimental results provided the shot was modelled as a deformable body and material damping was considered.

Thermo-mechanical finite element analysis of a rail wheel

The rail wheel, which is acted upon by mechanical forces also experiences thermal stresses due to braking, during service. The coupled nature of these forces is analysed using a three-dimensional elasto-plastic finite element model. Contact stresses at the rail–wheel interaction location are analysed using a global– local approach on a three-dimensional elasto-plastic finite element model. The paper also brings out the size and shape of the plastic zone at the contact region. Commercial finite element code ABAQUS has been used for the analysis and SDRC’s I-DEAS has been used for modelling. American Association of Railroad’s standards, available for the purpose of analytical evaluation of the rail wheel, has also been critically evaluated in this work.

Elastoplastic Finite Element Analysis of Three-Dimensional, Pure Rolling Contact at the Shakedown Limit

This paper describes a three-dimensional elastoplastic finite element model of repeated, frictionless rolling contact. The model treats a sphere rolling on an elastic-perfectly plastic and an elastic-linear-kinematic-hardening plastic, semi-infinite half space. The calculations are for a relative peak pressure (po/k) = 4.68 (the theoretical shakedown limit for perfect plasticity). Three-dimensional rolling contact is simulated by repeatedly translating a hemispherical (Hertzian) pressure distribution across an elastoplastic semi-infinite half space. The semi-infinite half space is represented by a finite mesh with elastic boundaries. The calculations describe the distortion of the rim, the residual stress-strain distributions, stress-strain histories, and the cyclic plastic strain ranges in the vicinity of the contact.