Elasto-plastic Finite Element Model Research Articles

The Evolution of Stress and Strain around the Bayan Har Block in the Tibetan Plateau

With the constraint of GPS observation, the tectonic deformation of the Bayan Har block and its periphery faults is investigated based on an elastoplastic plane-stress finite element model. The results show that the elastic model cannot explain the current GPS observation in the Bayan Har block. When East Kunlun fault and Yushu-Xianshuihe fault are under plastic yield state or high strain localization, the calculated velocities fit well with the observation values. It indicates that most of the current shear deformations or strain localizations are absorbed by these two large strike-slip faults. In addition, if the recurrence intervals of large earthquakes are used to limit the relative yield strength of major faults, the order of entering the plastic yield state of the major faults around Bayan Har block is as follows. The first faults to enter the yield state are Yushu-Xianshuihe faults and the middle segment of East Kunlun faults. Then, Margaichaka-RolaKangri faults (Mani segment) and Heishibeihu faults would enter the yield state. The last faults to enter the yield state are the eastern segment of East Kunlun faults and Longmenshan faults, respectively. These results help us to understand the slip properties of faults around the southeastward moving Bayan Har block.

Finite element modelling of stress field perturbations and interseismic crustal deformation in the Val d'Agri region, southern Apennines, Italy

The Val d'Agri area provides the opportunity to analyse active structures in a seismic region for which a large amount of subsurface data is available. This area, which was struck in 1857 by one of the most destructive earthquakes in Italy (MW=7.03), represents a unique natural laboratory to gain new insights into geometry, modes and rates of faulting controlling crustal deformation in an actively extending orogen. In this study, a crustal geological section through the southern Apennines is discretized into a finite element model (FEM). We present a 2D elastoplastic FEM that reproduces stress perturbations and strain field around the Val d'Agri active fault system. The influence of fault strand activity on interseismic crustal deformation is tested by a series of computer models, whose predictions are compared with the horizontal velocity components of continuous GPS sites in the region and with stress directions and geological data. The best fit with available geological and geophysical constraints is obtained with a 300km long, 29km deep model formed by a multilayer including three components having different rheological characteristics and including several shallow, locked fault segments, which branch into a freely slipping major basement fault at depth. Finite element modelling provides new insights into the controversial and widely debated active tectonic setting of the study area, pointing out the fundamental role played by a structural reactivation process involving inherited, long-lived, mature fault systems at depth. Our FEM, reconciling apparently contrasting geological and geophysical constraints from the study area, points to maximum stress build up and strain accumulation at a depth of 15±5km. Such a depth range is suggested as the most likely one for the nucleation of large events such as the 1857 Val d'Agri earthquake.

Influence of Variable Blank Holding Pressure on Impeller Sheets in Deep Drawing Process

In this research paper, a three dimensional elasto-plastic finite element (FE) model for mild steel material as blank has been developed to study the behavior of wrinkling on the impeller flange surface and parameters of deep drawing under different blank-holder pressure from 2.5 to 7.6 MPa. For modeling and simulation, commercially available FE software ANSYS 14.0 has been used. In industry, an experimental setup was built accordingly with a half cone angle of 36°. Experiments were carried out on a hydraulic press machine. The experimental results were compared with numerical results.

Stress and deformation characteristics of transmission tower foundations in permafrost regions along the Qinghai–Tibet Power Transmission Line

A transmission tower foundation embedded in frozen soil is subject to both the wind-induced uplift and frost heave forces. The frost heave results in an upward force acting on the foundation, while additional stress induced by the structure load may compress the underlying soils. The freezing- and thawing-induced deformations tend to cause further structural loads and lead to instability problems within the structure. To evaluate the engineering risk and ensure the safety of the Qinghai–Tibet Power Transmission Line (QTPTL) system, stress sensors were installed at the bases of two test tower foundations to investigate the stress state of the tower foundations. Using data on air and ground temperatures, and the deformation of tower foundations, we analyzed the stress variation, and the causes were discussed here. The results showed that the stresses at the bases of tower foundations had a close relationship with air and ground temperatures. The cooling of the underlying soils led to the occurrence of frost heave, which pushed the foundations upward and caused a significant stress bulb under the bases of tower foundations. Seasonal variations in the contact stress depended on the seasonal freezing and thawing of foundation soil. The contact stress increased with the cooling of the underlying soils and decreased with the warming of the underlying soils. The results also showed that the contact stress was free of the wind influence, i.e., the wind-induced uplift force was minor for the contact stress. To fully understand the influences of freezing and thawing on the stress state of tower foundations, a thermal–elasto-plastic finite element model for the tower foundation–soil system was established, and the stresses and deformations of a tower foundation subject to frost heave and thaw settlement were simulated. The results showed that the frost heave force induced by soil freezing potentially threatens the safety and normal operation of the QTPTL. Thaw settlement may lead to harmful deformation of tower foundations if global warming is considered in the numerical model. The remedial measure with thermosyphons only can reduce the settlement of the foundation and will increase the frost jacking risk of the foundation.

The influence of high temperature due to high adhesion condition on rail damage

In wheel–rail contact, the locomotive adhesion variable characterizes the capability of the locomotive to convert available friction into traction at the interface. Recently developed AC (Alternating Current) drive induces a higher adhesion level compared to DC (Direct Current) drive. This can significantly affect the wheel–rail contact conditions such as high contact temperature due to the frictional rolling, wear and damage initiation of the rails.The aims of this paper are to determine the temperature rise due to high adhesion contact and the thermal influence on the wear and rail life. Three-dimensional (3D) elasto-plastic finite element model was applied to evaluate the growth of temperature, residual stress and strain. The numerical model employed the moving heat source code developed by Goldak within ANSYS/LS-DYNA. The mechanical and thermal properties of the rail material were governed by temperature. The influence of multi-passes from multiple wheels attached to the locomotives on one point of the rail was also taken into account.The results indicated that after six wheel passes, the temperature due to the high adhesion condition was sufficiently high (723°C) to form the white etching layer (WEL) known to be associated to the rolling contact fatigue (RCF) on the rail surface. Moreover the rail material would be softened by high temperature, which resulted in the acceleration of wear process. Finally the results of thermal stress and strain from FE model were used as input to Kapoor׳s ratcheting model to determine the number of wheel rolling cycles leading to rail damage.

Blending Glowworm Swarm Optimization Algorithm with Thermal-Mechanical Coupling Finite Element Model for Optimization Method of Box Structure Welding Technology

Welding sequence is the important influence factor of the temperature field and residual stress and deformation in welding structure, At present, determining the welding sequence is usually based on experience and test method. For complex structure it is very difficult to get the optimum welding sequence. This study is aiming to settle the problem of solving the optimum welding sequence of complex box welding structure. In our study, we take the welding deformation as objective function, and then, associate glowworm swarm optimization algorithm with thermal-mechanical coupling and nonlinear thermal elastoplastic finite element model to optimize numerical simulation, eventually the optimum welding sequence is determined. Optimization results demonstrate that the optimum welding sequence obtained by our method has small welding deformation and little change rate. At the same time, our method is faster, more accurate, more effective than the traditional experience or test method.

Insight into Failure Mechanism of Large-Diameter Monopile for Offshore Wind Turbines Subjected to Wave-Induced Loading

Wu, K.; Fan, Q., and Zheng, J., 2015. Insight into failure mechanism of large-diameter monopile for offshore wind turbines subjected to wave-induced loading.In this paper, the refined elasto-plastic finite element model based on effective stress method is developed for the large-diameter monopile for offshore wind turbines subjected to cyclic wave-induced loading. An improved dynamic Cam-clay constitutive model is utilized to simulate the behavior of seabed soil under cyclic loading. The finite element package is used for analyses in plane strain case and its capability in simulating the wave-induced seabed responses is successfully verified using the analytical solution available. Then the contact pairs algorithm is employed to simulate nonlinear interaction behavior of the contact between the monopile and soil. The lateral boundary in the finite element model is considered according to repeatability principle. By using the refined finite element model established, the failure mechanism and distribution of skin friction acting on the outer wall of monopile is evaluated.

Numerical Validation of Experimental Result in Deep-Drawing

Deep drawing process is an important sheet metal forming process used in domestic and automotive components. In this process blank material is converted into the desired complicated shape by punch. In this research paper, a 3- Dimensional elasto-plastic Finite Element (FE) model for Mild Steel IS 2062 material as blank has been developed to study the behaviour of the flange wrinkling and deep drawing parameters under different Blank-Holder Pressure (BHP = 2.5 to 9.5MPa). This paper is discussing about the technology window for acceptable product. The present process successfully produces shape with drawing ratio of 2.0. For this, commercially available Finite Element software ANSYS 14.0 has been used. Simulation results are critically studied and salient conclusions have been drawn. An experimental setup is built accordingly with a half cone angle of 40°. The outputs of finite element simulation are used to investigate the effect of blank-holder pressure on product integrity and mechanical properties. The experimental results were compared with FE results.

Sheet Metals Forming Die Design Using Finite Element Analysis and the Taguchi Method

Sheet metal deep-draw die is primarily constructed with draw bead, which is then modified based on trial and error to obtain a successful forming without splitting. This work aims at a robust design of forming die using numerical analysis and the Taguchi method. A three dimensional elastoplastic finite element model of a sheet metal forming process of SPCEN steel has been successfully developed using the material flow stress obtained from the modified Erichsen cup test. The model was validated with the actual forming experiment and the results agreed well. The influence of draw bead parameters on splitting and thinning distributions were examined using the Taguchi method. Four parameters, namely the friction coefficient, draw bead height, radius and shoulder radius were investigated. The Taguchi main effect analysis and ANOVA results show that the height and shoulder radius of the draw bead are the most important factor influencing the thinning distribution. Applying the Taguchi method and using the minimum thinning percentage as the design criteria, the optimum die design was identified as height, radius, shoulder radius and the friction coefficient of 4, 8, 8 mm and 0.125 respectively. The verified finite element model using the optimum die design was conducted. The predicted Taguchi response was within 5.9% from finite element analysis prediction. The improvement in the reduction of thinning percentage was 22.35%.

Modeling of elastoplastic behavior of stainless-steel/bronze interpenetrating phase composites with damage evolution

In this paper an elastoplastic finite element model for stainless-steel/bronze interpenetrating phase composites (IPCs) is proposed. 3D representative volume elements (RVEs) are created based on the microstructures of the stainless-steel/bronze IPCs and the corresponding finite element models are used to study the mechanical and thermal expansion properties. The predicted effective elastic moduli and coefficient of thermal expansion are compared with those obtained from micromechanics based homogenization methods. The Gurson–Tvergaard–Needleman (GTN) constitutive model is adopted to investigate the influence of voids located in the bronze phase on elastoplastic and evolutionary damage behavior of the IPCs under uniaxial tension. The FE results have very good correlation with the experimental data, and the effects of thermal residual stress, void growth and nucleation on the flow properties of the IPCs are discussed.

Computing Flatness Defects in Sheet Rolling by Arlequin and Asymptotic Numerical Methods

Rolling of thin sheets generally induces flatness defects due to thermo-elastic deformation of rolls. This leads to heterogeneous plastic deformations throughout the strip width and then to out of plane displacements to relax residual stresses. In this work we present a new numerical technique to model the buckling phenomena under residual stresses induced by rolling process. This technique consists in coupling two finite element models: the first one consists in a three dimensional model based on 8-node tri-linear hexahedron which is used to model the three dimensional behaviour of the sheet in the roll bite; we introduce in this model, residual stresses from a full simulation of rolling (a plane-strain elastoplastic finite element model) or from an analytical profile. The second model is based on a shell formulation well adapted to large displacements and rotations; it will be used to compute buckling of the strip out of the roll bite. We propose to couple these two models by using Arlequin method. The originality of the proposed algorithm is that in the context of Arlequin method, the coupling area varies during the rolling process. Furthermore we use the asymptotic numerical method (ANM) to perform the buckling computations taking into account geometrical nonlinearities in the shell model. This technique allows one to solve nonlinear problems using high order algorithms well adapted to problems in the presence of instabilities. The proposed algorithm is applied to some rolling cases where “edges-waves” and “center-waves” defects of the sheet are observed.

Interpreting the interseismic deformation of the Altotiberina Fault (central Italy) through 2D modelling

The Altotiberina low-angle normal fault in central Italy has been a focus of many recent studies. Although the existence of this fault has long been known, its seismicity and relationship to other faults are still debated. We present a 2D elastoplastic finite-element model that reproduces the interseismic deformation of the Altotiberina Fault. The model predictions are compared to observed geodetic velocities, stress orientations and geological data. The influence of the Altotiberina Fault on interseismic evolution is tested by building several models with different boundary conditions. The best model is 180 km long, 40 km deep and contains two layers with different rheological parameters, two ramps, two faults and four freely slipping segments. The main factors contributing to the large-scale interseismic deformation include basal traction, rheology and the Altotiberina Fault itself, whereas the local, small-scale variations are due to two secondary high-angle faults.

Basal Heave Stability Analysis of Deep Foundation Pit in Soft Soil

In order to avoid the limitations in traditional methods of basal heave stability analysis for deep foundation pit, numerical analysis was adopted by establishing a two-dimensional elasto-plastic finite element model. Resistant heave stability safety factor was calculated using the fitting formula acquired from the simulated results, and then the upheaval value and plastic range under critical conditions were studied. The results show that the soil stress will be redistributed with the increasing of excavation depth until upheaval damage taken place. The upheaval value will be larger, the plastic range will be greater, and the basal heave stability will be worse with the decreasing of plastic parameters. Meanwhile, the basal upheaval peak position will transform gradually from excavation center to diaphragm neighborhood with the decreasing of plastic parameters. There is a critical value associated with supporting parameters for soil plastic parameters and the possibility of upheaval destruction increases significantly if the plastic parameters are less than the critical value.

A Study on Gear Tooth Metal Flowing Law and Process Optimization of Spiral Bevel Gear Forging

Insufficient gear tooth corner filling and high forming load are the main problems in spiral bevel gear forging. In this study, three different preforms were proposed. According to the analysis of the forging spiral bevel gear process using the semi-closed die, which was based on elastoplastic finite element model, the metal flowing law of tooth along tooth alignment and profile are revealed. From the simulation results, the arc face shape preform and the finish die with divided flow cavity are good for forging gear, and an optimized process was presented. Experiments were carried out using electric drive screw press with the rated forming load of 2500 Tons. By analyzing numerical simulations and experimental results, the process mentioned in this paper improves the tooth corner filling and reduces the forming load effectively.

The effect of contact edge geometry on fretting fatigue behavior in complete contacts

The effect of contact edge geometry on the fretting fatigue behavior of a complete contact was studied with 34CrNiMo6 quenched and tempered steel. The contact geometries employed were sharp and rounded square-ended pads against a plane surface. A 2D elasto-plastic finite element model of the contact setup was used to calculate fretting cracking risk for these geometries using the Findley multi-axial fatigue criterion and the theory of critical distances. A series of experimental fretting fatigue tests was carried out with two corresponding geometries and loadings using an in-house complete contact fretting test device. It was found that the slightly rounded contact edge has a somewhat higher risk of cracking than the sharp contact edge. This agrees with the experimental results. The effect of the friction coefficient on the cracking risk was also studied. In addition, fretting wear scars from the experimental test specimens were evaluated.

Pull-out forces in shear connectors in composite beams with large web openings

Composite beams with large web openings are often used, and their design is controlled by Vierendeel bending at the four corners of each opening, which is assisted by local composite action with the floor slab. Development of this Vierendeel bending resistance may be limited by pull-out failure of the shear connectors.In this paper, a non-linear elasto-plastic finite element model of a composite beam with web openings was used to investigate this mode of pull-out failure. A test was performed on a typical composite slab in which the shear connectors were subject to pure tension and the failure load was 67kN, which is approximately 70% of the longitudinal shear resistance. The results of the finite element model are compared against those obtained using the established design theory, that does not limit the vertical pull-out resistance of the shear connectors.It is shown that the local bending resistance due to composite action should be reduced when limited by pull-out of the shear connectors. A parametric study investigated the effect of openings of 600 to 1200mm length. A simple model is developed to establish the Vierendeel bending resistance, when limited by pull-out of the shear connectors.

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.

Relationship of forces acting on implant rods and degree of scoliosis correction

BackgroundAdolescent idiopathic scoliosis is a complex spinal pathology characterized as a three-dimensional spine deformity combined with vertebral rotation. Various surgical techniques for correction of severe scoliotic deformity have evolved and became more advanced in applying the corrective forces. The objective of this study was to investigate the relationship between corrective forces acting on deformed rods and degree of scoliosis correction. MethodsImplant rod geometries of six adolescent idiopathic scoliosis patients were measured before and after surgery. An elasto-plastic finite element model of the implant rod before surgery was reconstructed for each patient. An inverse method based on Finite Element Analysis was used to apply forces to the implant rod model such that it was deformed the same after surgery. Relationship between the magnitude of corrective forces and degree of correction expressed as change of Cobb angle was evaluated. The effects of screw configuration on the corrective forces were also investigated. FindingsCorrective forces acting on rods and degree of correction were not correlated. Increase in number of implant screws tended to decrease the magnitude of corrective forces but did not provide higher degree of correction. Although greater correction was achieved with higher screw density, the forces increased at some level. InterpretationThe biomechanics of scoliosis correction is not only dependent to the corrective forces acting on implant rods but also associated with various parameters such as screw placement configuration and spine stiffness. Considering the magnitude of forces, increasing screw density is not guaranteed as the safest surgical strategy.

Ultimate Compressive Strength of Cold-Formed Steel Angle Struts Loaded through a Single Bolt

In cold-formed steel trusses and space frames, angles are commonly used for the members, the load being transferred to the members at both ends through a connection to a gusset plate. Such connections are typically formed through bolts or screws. Since this connection is made through one of the angle legs, the load is therefore eccentric to the centroid of the section. On the other hand, owing to contact with the gusset plate and the bolt-head, the ends of the connection possess partial torsional restraint. When designing cold-formed steel angle sections, an engineer would typically take into account the eccentricity of the connection but ignore the beneficial effect of the partial torsional restraint. This paper describes a non-linear elasto-plastic finite element model of angle sections connected to a gusset plate through a single bolt at each end subjected to axial compressive load. The results of the finite element model are validated against previously published full-scale laboratory test results. A parametric study of both equal and unequal angle sections is presented. From the results of the parametric study, simple design recommendations are proposed.

The association of cone–sheets and radial dykes: Data from the Isle of Skye (UK), numerical modelling, and implications for shallow magma chambers

We present field data and numerical models that aid understanding of fundamental volcano-tectonic processes of inclined sheet and dyke propagation, and more in general of volcano internal growth, under a stress field resulting from the inflation of a shallow magma chamber. Structural field data from the classical Cuillins cone–sheet complex (Isle of Skye) show that sheets have a constant average dip angle (45°), with pure dilational or hybrid shear-dilational kinematics. Our elasto-plastic finite element models, which consider the total stress field including gravity, tectonics and magma overpressure, suggest that only in the case of an inflating oblate shallow magma chamber cone–sheets can be predicted. They do not develop with spherical or prolate magma chambers and/or under deflation. Radial dykes dominate beyond a critical distance of 1–1.2 diameters of the magma chamber, whilst cone–sheets are confined immediately above it. These results may be used to infer, from observations on the sheet and dyke pattern at surface, the geometry and tensional state of magma chambers under active volcanoes.