Large Deformation Elastic-plastic Finite Element Research Articles

Residual stresses and strains analysis in press-braking bending parts considering multi-step forming effect

Press-braking bending is a multi-step bending process and widely applied in the aerospace industry. Residual stresses and strains generated during the forming process play an important role in determining its forming parameters and bending path. This work aims to analyze the residual stresses and strains in press-braking bending parts using both the theoretical method and numerical method. First, the analytical model of residual stress and strain is established based on the elastic–plastic bending theory. Second, a fully finite element model of press-braking bending has been developed, and a procedure to simulate the multi-step bending process is presented by using the elastic–plastic large deformation finite element method. The simulation results are then compared with three-point bending experiments in terms of forming force and final shapes of the bent specimens, and excellent agreement is achieved. Finally, the results calculated from the analytical model are compared with the numerical results. The distributions of residual stresses and strains on the finished plate along the length and thickness direction, and particularly the multi-step forming effect on residual stresses and strains, are discussed. It is found that the residual stresses and strains decrease at the initial loading position along the thickness direction during the forming process of subsequent loading positions. With the same punch displacement, the residual stresses and strains at the initial loading position are less than those at the subsequent bending position.

Ultimate compressive strength of deteriorated steel web plate with pitting and uniform corrosion wastage

Steel structural members are likely exposed to corrosive environments, and thus corrosion is one of the dominant life-limiting factors of steel structures. Extensive studies on the effectsof pitting and uniform corrosion on the strength performance of steel structural members under a wide variety of loading conditions have been undertaken to assess the relationship between pitting corrosion intensity and residual strength. The aim of this study is to investigate the ultimate compressive strength characteristics of steel web plate elements with pit and uniform corrosion wastage. A series of ABAQUSnonlinear elastic-plastic large deformation finite element analyses are carried out on I-shapedsection steel girder models with varying pittingcorrosion intensities. Artificial pitting of different intensities is considered on the web plates and a uniform loading applied vertically on the upper flange section. The ultimate load-carrying capacity of deteriorated models with different levels of uniform thickness loss is also studied. The results are applied to assessing the ultimate compressive strength of web plates with different pitting corrosion intensities and a uniform loss thicknessby developing design formulae that represent the average loss thickness versus the ultimate load-carrying capacity.

Multiscale Hot-working Simulations Using Multi-phase-field and Finite Element Dynamic Recrystallization Model

In this study, we simulated non-uniform compression of a cylinder under various temperatures and deformation rates using a multi-phase-field and finite element dynamic recrystallization (MPFFE-DRX) model, which couples the multi-phase-field dynamic recrystallization (MPF-DRX) model with a large-deformation elastic-plastic finite element (FE) method using J2 flow theory for DRX microstructure evolution and macroscopic mechanical behavior, respectively. Detailed examination of the results confirmed that microstructure evolution and macroscopic mechanical behavior were accurately coupled over a wide range of temperature and deformation rate conditions. We also concluded that the MPFFE-DRX model can be used with a wide variety of temperatures and deformation rates.

Multiscale modeling of hot-working with dynamic recrystallization by coupling microstructure evolution and macroscopic mechanical behavior

Dynamic recrystallization (DRX) occurs during the hot-working of a metallic material with low-to-medium stacking-fault energy. The macroscopic mechanical behavior during hot-working is largely affected by the microstructure evolution due to DRX. In this study, a novel multiscale hot-working model was developed by coupling the multi-phase-field dynamic recrystallization (MPF-DRX) model and large deformation elastic–plastic finite element (FE) method using J2 flow theory to evaluate the microstructure evolution and macroscopic mechanical behavior, respectively. We call this model the multi-phase-field and finite element dynamic recrystallization (MPFFE-DRX) model. Compression simulations with nonuniform deformation of a cylinder confirmed that the newly developed MPFFE-DRX model can be used to evaluate the macroscopic mechanical behavior during hot-working by considering the DRX microstructure evolution, which differs depending on the area. We also confirmed that the MPFFE-DRX model can be used to simulate macroscopic mechanical behavior depending on the initial microstructure by varying the initial grain size.

FEM Simulation of Main Deformation during Cage Roll-Forming Process

Cage roll-forming is an advanced roll-forming technique widely used in high frequency welding (HFW) pipes production. However, to the authors' knowledge, the real cage roll-forming production is mainly on experience rather than science. Few publications can be found on cage roll-forming for its complexity. In order to improve the understanding of the technique, a large deformation elastic-plastic finite element model for the HFW660 cage roll-forming mill was established and simulated through adopting the dynamic explicit algorithm. The distribution of effective plastic strain and the deformed geometry of the strip at the pre-forming and linear section were obtained. The simulation results were validated with the measurements. The results show that the biggest effective plastic strain (EPS) occurs at the center of strip. The distribution of EPS is far from uniform on the cross-section of the strip. This may owe to the uneven distribution of down-hill amount.

W012004 Phase-field法によるLPSO型マグネシウム合金の動的再結晶シミュレーション(【W01200】シンクロ型LPSO構造の力学特性と高強度Mg合金の変形機構(その2),計算力学部門企画,ワークショップ)

By using our multi-phase-field and finite element dynamic recrystallization (MPFFE-DRX) model, where a multi-phase-field dynamic recrystallization (MPF-DRX) model to simulate the DRX microstructure evolution and large deformation elastic-plastic finite element (FE) method using J2 flow theory to evaluate macroscopic mechanical behavior are coupled, we performed nonuniform compression simulations of a cylinder with LPSO type alloy.

FE Analysis on Rolls Deformation in Rolling Process of 4100 Heavy Plate Mill

Against 4100 heavy plate miller, a 3-D rolling model involving rolls’ elastic deformation and workpiece’s elastic-plastic deformation is established using large deformation elastic-plastic finite element method. The distributions of the rolls’ bending deformation and the roll gap shape by simulation under the different processes. The results can provide the practical referential value for equipment design and processing setup of heavy plate mill. The FE model may be used to analyze skinning process on off-line.

Stability Analysis of Slope Based on Finite Element Method

Based on the finite element software as calculation tool, Mohr-Coulomb yield criterion and Drucker-Prager yield criterion were converted to equivalent area circle yield criterion, the elastic-plastic large deformation finite element method (FEM) was adopted, at the same time strength reduction technology combined with convergence criterion, catastrophe criterion and plastic zone penetrability criterion was used, and the problem of 2-D slope stability was analysed. Then based on finite element reduction strength method and three criterions, the homogeneous slope safety factors were calculated. The results showed that equivalent area circle D - P yield criterion was suitable for slope stability analysis and that strength reduction technology could be applied in simple homogeneous side slope stability analysis.

A Finite Element Model of Roll-Over Protective Structures for Wheel Loader Frame

ROPS is an effective way to reduce casualty rate in the rolling accident. This paper introduces the design of a cab to strengthen safety-ROPS large wheel loader method. The finite element model, it's a ROPS rear, absorbers and supporting structure frame of the safety-cabs, was created. Force and displacement boundary conditions obtained in accordance with the international standard ISO3471:2008-The large deformation elastic-plastic finite element analysis, horizontal, vertical and ROPS vertical load cases of performance testing and the corresponding lab for investigation. The test results show that the design can meet the requirements of ISO3471 ROPS: 2008. Test results differences and simulation and welded joint of the fracture analysis on the reason.

Simulation of cold roll forming using elastic-plastic finite element method

Based on large deformation elastic-plastic finite element method, utilising MARC software for 3D simulation of the tube while being out of shape, this paper analyses longitudinal strain of the tube in the course of roll shaping. Influence of different forming parameters such as the forming speed, the material properties and the friction coefficient have also been parametrically studied. The simulation results show that increasing the roll velocity, the material yield limit the longitudinal strain reduces. But increasing the friction coefficient, work-hardened material, inter-stand distances increase the longitudinal strain. This leads to a better insight and an efficient design for the complicated technological roll-forming process. The simulation of the tube shows that the method is suitable for the whole process simulation of cold roll forming.

Normalizing the influence of flaw length on failure pressure of straight pipe with wall-thinning

Burst tests using wall-thinned pipe of carbon steel for high-temperature use were conducted in order to examine the influence of length of wall-thinning on burst pressure. Then, three-dimensional elastic-plastic large deformation finite element analyses (EP-FEA) were performed to accurately predict the burst pressure obtained by the tests. The failure pressure corresponding to the burst pressure in tests was defined as the maximum pressure during the analysis including the instability condition after the peak of pressure. The results showed that the failure pressure obtained by EP-FEA agreed well with the experimental results. Finally, failure pressures of wall-thinned pipes with various sizes, thicknesses, flaw lengths and depths were examined by EP-FEA with the same procedure of analysis as validated in this paper. The results showed that, from the standpoint of influence of flaw length on failure pressure, it is preferable to normalize flaw length by pipe mean radius of the unflawed section R rather than by shell parameter ( Rt) 0.5, where t is the thickness of the unflawed section.

Influence of crack tip constraint on void growth in pressure sensitive plastic solids – I: 2D analysis

In this work, the effect of constraint on void growth near a notch tip under mode-I loading is investigated in materials exhibiting pressure sensitive yielding and plastic dilatancy. To this end, large deformation elastic–plastic finite element analyses are performed using a two-dimensional (2D) plane strain, modified boundary layer formulation by prescribing the elastic K − T field as remote boundary conditions. The analyses are conducted for different values of K (or J) and T-stress. The material is assumed to obey a finite strain, Extended Drucker–Prager yield condition. The roles of pressure sensitivity, plastic dilatancy and yield locus shape on the interaction between the notch and a nearby void are studied by examining the distribution of hydrostatic stress and plastic strain in the ligament connecting them as well as the growth of notch and the void. The results show that void growth with respect to J is enhanced due to pressure sensitivity, and more so when the plastic flow is non-dilatational. By contrast, irrespective of pressure sensitivity, loss of crack tip constraint can significantly retard void growth.

FEM Simulation of Large Diameter Pipe Bending Using Local Heating

With the aid of elastic-plastic large deformation finite element method (FEM), an elastic-plastic and coupling thermo-mechanical model was built to calculate the bending process of the bent pipe, combining with local heating or cooling of the bent pipe. Based on the FEM simulation, the metal deformation during the bending process was analyzed in detail. The thinning and thickening ratio of the pipe wall thickness, the ovality of the cross-section of the pipe and the spring-back angle, etc., are presented.

Friction coefficient of upsetting with a procedure of combining the inverse model and the Tikhonov method

The purpose of this paper is to develop an inverse procedure, which is used to obtain the history of the Coulomb's friction coefficient on the contact surfaces between the workpiece and the die during the AA1050 aluminum upsetting process. This procedure is based on the experimental upsetting normal loadings and combines the matrix-presentation linear least-squares errors method of inverse elastic–plastic large deformation finite element model developed in this paper with the regularization of Tikhonov method. The square of the difference of the friction coefficients between successive stages is adopted as the stabilizing function of the regularization of Tikhonov method. In this paper, the Coulomb's friction model is adopted before the sticking effect occurs. After the sticking effect occurrence, the shear strength friction model is adopted. From the results of this paper, it can be shown and demonstrated that the inverse procedure proposed in this paper can make the history of the Coulomb's friction coefficient more stable and reasonable.

Matrix-presentation linear least square error method of inverse elastic-plastic large deformation finite element model for upsetting

The main purpose of this paper is to develop the matrix presentation linear least square error method of inverse elastic-plastic large deformation finite element model for upsetting to obtain the friction coefficients during the upsetting process. This inverse model assumed the linear material and based on the modified experimental loading increments using the linear modified experimental upsetting loading standard proposed in this paper. Then the friction coefficients of contact boundary between the workpiece and the die at specific finite element analysis stages can be derived. Finally, using the cubic spline fitting, the history of friction coefficient during the upsetting process can be obtained. It is demonstrated that the workpiece profile of upsetting experiment is quite identical to the workpiece profile of simulation using the result obtained in this paper as the history of friction coefficient of contact boundary, and furthermore the distribution of stress and strain of the workpiece during upsetting process can be understood.

A finite element analysis of the flange earrings of strong anisotropic sheet metals in deep-drawing processes

Flange earrings of strong anisotropic sheet metals in deep-drawing process are numerically analyzed by the elastic-plastic large deformation finite element formulation based on a discrete Kirchhoff triangle plate shell element model. A Barlat-Lian anisotropic yield function and a quasi-flow corner theory are used in the present formulation. The numerical results are compared with the experimental ones of cylindrical cup drawing process. The focus of the present researches is on the numerical analysis and the constraining scheme of the flange earring of circular sheets with strong anisotropy in square cup drawing process.

The numerical analysis of anisotropic sheet metals in deep-drawing processes

Flange earing of strong anisotropic sheet metals in the deep-drawing process is analyzed numerically by the elastic–plastic large deformation finite element formulation based on the discrete Kirchhoff triangle plate shell element model. A Barlat–Lian anisotropy yield function and a quasi-flow corner theory are introduced in the present formulation. The numerical results are compared with the experimental results of the cylindrical cup drawing process. The focus of the present research is on the numerical analysis and the constraining scheme of the flange earing of circular sheets with strong anisotropy in the square cup drawing process.

Numerical study of the flange earring of deep-drawing sheets with stronger anisotropy

A Barlat–Lian anisotropy yield function is introduced into a quasi-flow corner theory of elastic–plastic finite deformation and the elastic–plastic large deformation finite element formulation based on the principle of virtual velocity and the discrete Kirchhoff triangle plate shell element model. The focus of the present researches is on the numerical simulation of the flange earring of deep-drawing process of circular sheets with stronger anisotropy, based on which, the schemes for controlling the flange earring are proposed.

A continuum damage mechanics model for ductile fracture

Continuum damage mechanics theory together with large deformation elastic–plastic finite element analysis has been used to predict crack growth initiation in ductile materials. The damage growth law is based on experimental observations reported in the literature. A local crack growth initiation criterion is proposed. The criterion makes use of the critical damage as the continuum parameter and the average austenite grain size as the characteristic length. To test the validity of this criterion, experiments have been conducted on standard specimens and have also been simulated numerically. The proposed criterion has been used to predict the values of the critical load at crack growth initiation and the fracture toughness. The numerically predicted values compare favourably with the experimental values.

Die entry pressure drops in paste extrusion

Pressure drops for the extrusion of a perfectly plastic material through smoothwalled dies with various reduction ratios and conical entry angles have been calculated by the large deformation elastic–plastic finite element method. They are found to agree well with extrusion pressures obtained from slipline field analyses for plane strain problems, and lie within the limits set by upper- and lower-bound solutions in axisymmetric cases. The results for axisymmetric dies are compared with the die entry pressure drop term in the Benbow– Bridgwater equation, used to describe the flow of pastes in a ram extruder.