Rigid-viscoplastic Finite Element Research Articles

Numerical simulation of extrusion of FeMnSiCrNi/NiTiNb dissimilar shape memory alloy composite tube based on finite element method and cellular automaton

FeMnSiCrNi/NiTiNb dissimilar shape memory alloy composite tube is firstly put forward and it can be fabricated by means of isothermal extrusion. Based on Arrhenius constitutive model of FeMnSiCrNi and NiTiNb shape memory alloys, isothermal extrusion of FeMnSiCrNi/NiTiNb dissimilar shape memory alloy composite tube is simulated by rigid viscoplastic finite element method. It can be found that the deformation zone of the dissimilar shape memory alloy composite tube is always in a three-dimensional compressive stress state during extrusion, and the deformation of the inner tube is obviously higher than that of the outer tube. It is necessary to guarantee the interface compatibility between the inner tube and the outer tube during isothermal extrusion of FeMnSiCrNi/NiTiNb dissimilar shape memory alloy composite tube. The relationship between macroscopic process variables and microscopic variables during plastic deformation of FeMnSiCrNi shape memory alloy tube at high temperature is established by coupling finite element simulation and cellular automaton simulation. The microstructural evolution of FeMnSiCrNi shape memory alloy in different deformation zones during isothermal extrusion of dissimilar shape memory alloy composite tube is simulated. It can be concluded that the grain size of dynamic recrystallization is reduced with the increase of plastic strain in the deformation zone.

Numerical investigation on thermo-mechanical and material flow characteristics in friction stir welding for aluminum profile joint

Friction stir welding (FSW) technology has been applied for aluminum profiles which are widely used in rail vehicles, while process and flow behavior investigations by numerical simulation technology are still insufficient as the geometric complexity of profile joint. In this study, a fully coupled thermo-mechanical model is presented for the FSW process of AA6082-T6 profile. The numerical modeling scheme is executed on the basis of rigid-viscoplastic finite element theory with adaptive re-meshing technology, which is validated firstly by experimental measured temperatures for a sheet case in literature. The temperature field and material deformation are investigated for two different rotational directions of welding tool. The material flow around the tool is visualized and elaborated using a material trajectory demonstration manner based on the point tracking method. The material flow behavior in the three-dimensional space is clearly captured, which shows that the material flow along both the horizontal and vertical directions on the advancing side is more complicated and essentially different with that on the retreating side. Especially, a “sparse material area” is found at the rear of the pin which explains the formation mechanism of void or groove defects. Furthermore, the material stir zone is also presented by the material flow characteristics and analyzed at different welding process.

An evolution model for elliptic-cylindrical void in viscous materials considering the evolvements of void shape and orientation

The evolution behavior of the internal voids influences the mechanical property of the materials significantly. Considering the void deformation and rotation, the evolution behavior of the elliptic-cylindrical void in power-law viscous materials was investigated by using the representative volume element (RVE) model. The rigid visco-plastic finite element (FE) method was applied to calculate the velocity field in the RVE under different loading conditions, and the instantaneous changing rate of the void radius and orientation were determined by evaluating the evolving of the void profiles at the instant. The calculated results show the deviatoric stress takes an important role in the void radius evolution, and the shear stress influences the change of the void orientation significantly. Based on the investigation, a void evolution model was established to relate the changing rates of the void radius and orientation to the void aspect ratio and the macroscopic stress/strain conditions. This model was incorporated into the FE code to predict the evolvements of void radius and orientation in each step of the deformation history. The predictions agree well with the results of the numerical simulations containing embedded void geometries in the mesh, which demonstrates that this model is capable to evaluate the void evolution behavior under large deformation. As an application, this model was used to predict the closure behavior of the void defects in the large ingot during the hot forging process.

Finite Element Analysis of Cross Rolling on AISI 304 Stainless Steel: Prediction of Stress and Strain Fields

Studies on the effect of strain path during rolling has been carried out for a long time, but the same has not been done using Finite Element Analysis (FEA). Change in strain path affects the state variables in the rolled plate like stress, strain, temperature etc. In the current work, Finite Element Analysis for cross rolling of AISI 304 austenitic stainless steel has been carried out by rotating the plate by 90° in between the passes. To analyze stress and strain fields in the material for cross rolling, a full 3D model of work-roll and plate has been developed using rigid-viscoplastic finite element method. The stress and strain fields, considering von-Mises yield criteria, are calculated by using updated Lagrangian method. In addition to these, the model also calculates the normal pressure and strain rate distribution in the plate during cross rolling. The nature of the variations of stress and strain fields in the plate, predicted by the model, is in good agreement with the previously published works for unidirectional rolling.

Parameter Optimization During Forging Process of a Novel High-Speed-Steel Cold Work Roll

The forging of high-speed-steel (HSS) roll has always been a technical problem in manufacturing industry. In this study, the forging process of a novel HSS cold work roll was simulated by deform-3D on the basis of rigid-viscoplastic finite element model. The effect of heating temperature and forging speed on temperature and stress fields during forging process was simulated too. The results show that during forging process, the temperature of the contact region with anvils increases. The stress of the forging region increases and distributes un-uniformly, while that of the non-forging region is almost zero. With increasing forging time, Z load on anvil increases gradually. With increasing heating temperature or decreasing forging speed, the temperature of the whole billet increases, while the stress and Z load on anvil decrease. In order to ensure the high efficiency and safety of the forging process, the heating temperature and the forging speed are chosen as 1160 °C and 16.667 mm/s, respectively.

Simulation of dynamic recrystallization process during friction stir welding of AZ91 magnesium alloy

In the present research, a continuum-based thermo-mechanically coupled rigid-viscoplastic finite element model is proposed in Deform-3D software to simulate the friction stir welding (FSW) of AZ91 magnesium alloy. Then, to consider the microstructure evolution of the weld zone, a model is established based on the combination of cellular automaton and Laasraoui-Jonas models. The simulated microstructure of the weld zone is compared with the experiment one. Furthermore, the ability of presented model in demonstrating the nucleation and grain growth stages during dynamic recrystallization (DRX) is considered.

A 3-D model for void evolution in viscous materials under large compressive deformation

The paper presents a study on the evolution of dilute ellipsoidal voids in power-law viscous materials under triaxial loading condition. Firstly, referring to the work of Eshelby (1957), a semi-analytical expression is deduced to evaluate the deformation of ellipsoidal void in linear viscous material. Then, for the non-linear viscous materials, the concept of mesoscopic representative volume element (RVE) is applied to study the voids deformation under different stress states, and a rigid visco-plastic finite element (FE) procedure is applied to solve the RVE model. For the condition of stress triaxiality ranging from −1 to +1, it is found that the voids deformation behaves similarly in both linear and non-linear viscous materials. Due to this fact, the framework of the expression of void deformation in linear viscous material is inferred to describe the void evolution in non-linear viscous materials, while the parameters of the expression are re-evaluated for the specific materials. The results show that the void shapes and loading conditions take important roles in the void evolution. Therefore, for an ellipsoidal void, the void radius strain rate is expressed as a function of the void shape index, the macroscopic stress and strain-rate. Meanwhile, the void volume strain rate is obtained as a function of the void radius strain rate. This void evolution model is integrated into FE code and applied to study the void closure problem in the metal forming process. The FE simulation provides the evolution of macroscopic stress, strain and strain-rate, and then the model is used to calculate the changes of void shape and volume in each step of the deformation history. It can be found that the results predicted by this model agree well with the analytical solution, experiment measurements and numerical simulations with embedded void shapes, which demonstrates that this method can be appropriately used to predict the void evolution during the large compressive deformation process.

Finite element simulation of plate or sheet metal forming processes using tetrahedral MINI-elements

In this paper, finite element prediction of sheet metal forming process is investigated using solid elements. A three-dimensional rigidviscoplastic finite element method with linear tetrahedral MINI-elements is employed. This technique has traditionally been used for bulk metal forming simulations. The solid element approach with remeshing capability is applied to simulating a plate metal forming process to reveal its possible problems. The similar approach is also applied to a typical sheet forming process. Both single- and double-layer finite element mesh systems are studied, with particular attention to their effect on the deformed shape of the workpiece and thickness variation of a cold sheet forming process. The procedure is applied to the well-known problem of the NUMISHEET93 international benchmark. The resulting predictions are compared with experimental observations found in the literature, and good agreement is noted.

Parameters Optimization of Fan-Shaped AZ31 Magnesium Alloy in Extrusion Process

It was simulated with rigid viscoplastic finite element theory for fan-shaped profile extrusion process of AZ31 magnesium alloy, and analyzed the distortion mesh of the various stages of the extrusion process and obtained the speed field, stress field and strain field in inner workpiece during the deformation course. Appiying to orthogonal experimental method, we carried out nine simulations with the different extrusion ratio, extrusion temperature and extrusion speed. The above three main factors impacted the organization of the extrusion products, designed into three levels respectively. It was used the mean-square deviation of effective stress at the die orifice during the extrusion forming to determine the best technical parameters. With the best technical parameters and normal technical parameters obtained above, we had a extrusion test and observed the microstructure of extrusion products.

Forging limit of a novel high-speed-steel cold work roll based on ductile fracture criteria by finite element model

In this study, the temperature field, stress field and strain field of a novel high-speed-steel (HSS) cold work roll during forging process were simulated by Deform-3D software on the basis of rigid–viscoplastic finite element (FE) model. The effects of forging temperature, speed and position on the maximum effective stress (MES) of the billet, maximum reduction (MR) and maximum Z load (MZL) of the anvil before cracking were analyzed based on Normalized C&L ductile fracture criterion. Finally, the forging limit diagram was drawn. The results show that seven passes are carried out during the forging process. The temperature field, stress field and strain field of the forging zone distribute un-uniformly, but the billet has been penetrated before cracking. The MES and MR are insensitive to the forging speed, and the MZL is in the safe range consistently at 1000–1140°C. When the surface temperature of the billet is below 1000°C, some parameters have exceeded the measured limit, which indicates that it is not suitable to go on forging.

Finite element simulation of ball spinning of NiTi shape memory alloy tube based on variable temperature field

As a new attempt, ball spinning was used to manufacture the nickel-titanium shape memory alloy (NiTi SMA) tube at elevated temperature. The NiTi bar with a nominal composition of Ni50.9Ti49.1 (mole fraction, %) was solution treated and was used as the original tube blank for ball spinning. Based on the variable temperature field and the constitutive equation, rigid-viscoplastic finite element method (FEM) was applied in order to simulate the ball spinning of NiTi SMA tube. The temperature field, the stress field, the strain field and the load prediction were obtained by means of FEM. FEM results reveal that there is a temperature increase of about 160 °C in the principal deformation zone of the spun part. It can be found from the stress fields and the strain fields that the outer wall of NiTi SMA tube is easier to meet the plastic yield criterion than the inner wall, and the plastic deformation zone is caused to be in a three-dimensional compressive stress state. The radial strain and the tangential strain are characterized by the compressive strain, while the axial strain belongs to the tensile strain. The variation of spinning loads with the progression of the ball is of great importance in predicting the stable flow of the spun part.

Simulation and Optimization of Die Forging Process for High Pressure Valve Bonnet

In this paper, the multi-stage die forging process of a high pressure valve bonnet was simulated by 3D coupled thermal-mechanical rigid-viscoplastic finite element (FE) method. The deformation and the metal flow field of billet were obtained. Based on the simulation, two optimized schemes were put forward for improving the yield. Both of them can save material and ensure the stability of billet during the forging process. The study can provide scientific theory foundation for practical engineering applications.

The Numerical Simulation of Multi-Directional Forging 6700 Steering Knuckle

The numerical simulation of multi-directional precise contour forging of 6700 steering knuckle was studied in this paper. A 3D thermodynamic coupling finite element method (FEM) was established for each process of the deformation, based on the rigid-viscoplastic finite element method FEM. The results showed that the shape and size of the blanking billet can be optimized and the materials utilization ratio and the dimensional accuracy can be increased dramatically by using multi-directional precise contour forging

Numerical Simulation for Precision Roll-Forging of Automobile Front Axle

Roll forging process for automobile front axle has been simulated by using a rigid viscoplastic finite element method, force-time curve have been obtained and analyzed. On the basis of simulation result, typical characteristics of roll forging process have been explained. It concluded that simulation results could guide the development of roll forging and die design for automobile front axle.

Prediction of the effects of hardening and texture heterogeneities by finite element analysis based on the Taylor model

The main objective of this study is to simulate deformation induced anisotropy during the upsetting of commercially available pure aluminum AA1050 after being processed by the equal channel angular extrusion (ECAE) process including the friction effect. A Taylor-type polycrystalline constitutive model was adopted to investigate the effects of texture evolution and deformation heterogeneity during the ECAE and upsetting. In order to save computation time, a decoupled analysis between the crystal plasticity model and finite element method for the multi-pass ECAE and a fully coupled analysis for the subsequent upsetting process were conducted. The rigid-viscoplastic finite element analysis of the ECAE was carried out to determine the history of velocity gradient during the ECAE process in order to identify the effects of the processing routes A and C on texture evolution. The calculated history was applied to the crystal plasticity model to obtain the crystallographic texture distribution. Then, a finite element analysis based on the Taylor model was conducted for prediction of the anisotropic behavior of the three-pass ECAEed specimens which was obtained by applying the ECAE of the aluminum alloy AA1050 with routes A and C, respectively. For this analysis, algorithms for the data transfer of Euler angles and hardness were developed and implemented into the program. The good agreement between the measured and simulated deformed shapes indicates that the proposed simulation technique with the data transfer algorithms can be used effectively to simulate deformation induced heterogeneity during the bulk forming process.

Deformation mechanism of hot spinning of NiTi shape memory alloy tube based on FEM

As a successively and locally plastic deformation process, ball spinning is applied to manufacturing thin-walled Nickel-Titanium shape memory alloy (NiTi SMA) tube at high temperature. NiTi SMA tube blank belongs to the as-cast state which consists of a lot of dendritic grains and a few equiaxed grains. The compression tests of NiTi SMA were carried out at various strain rates at high temperature in order to obtain the constitutive model of NiTi SMA. Because NiTi SMA is sensitive to the strain rates at high temperature, rigid-viscoplastic finite element method (FEM) is used to simulate ball spinning of thin-walled NiTi SMA tube in order to analyze the deformation behavior of ball spinning of NiTi SMA tube. Stress fields, strain fields as well as velocity fields is obtained by means of rigid-viscoplastic FEM, which lays the profound foundations for studying the metal flow rule in ball spinning and forming perfect spun NiTi SMA tube.

FE analysis on Deformation and Temperature Nonuniformity in Forming of AISI-5140 Triple Valve by Multi-Way Loading

In triple valve forming process by multi-way loading severely nonuniform deformation and temperature distributions are prone to occur, which may lead to poor forming quality and macro-micro defects. A 3D coupled thermo-mechanical rigid-viscoplastic finite element (FE) model for multi-way loading forming of AISI-5140 steel equal diameter triple valve was developed based on DEFORM-3D. Through comprehensive simulation and analysis, the influences of main process parameters on the forming process and nonuniformity of deformation and temperature were studied. The results showed that: (1) the degree of deformation nonuniformity decreased with the increase of the punch loading speed, initial temperature of billet, or the decrease of the friction factor; (2) the average temperature of forming body increased as the punch loading speed, initial temperature of billet and the friction increased, while the degree of temperature nonuniformity decreased with the increase of punch loading speed or decrease of initial billet temperature.

Comparative Study of the Two Bar Billets for Bevel Gear Based on Multi-Objective Comprehensive Assessment

The two bar billets with different height-diameter ratio in enterprise were studied on the process of gear blank thermal forming. The rigid-viscoplastic finite element simulations in multifactor coupling condition of stress ,heat and wear were established. The metal flow in the process was simulated. The temperature distribution and varying of the mold and blank was forecast. The single-step wear depth and distribution of the die in forging was analysed based on Archard ,which provided sufficient data to evaluate life of the die. The reasonable aspect ratio for blank can be obtained upon the results, which will offer basis to the product.

Numerical Simulation and Technology Research on the Precision Forging for Inner Ring Gear

Rigid-viscoplastic finite element method was used to analysis the cold extrusion of the external boss and ring gear. Some groups of numerical models were built with different design parameters of die, geometric parameters of gear, processing conditions, and the service loads were investigated. Form the investigation; we predicted the forming defects occurring in the practice. Based on Archard model the lives of dies were predicted. The conclusion above has more guidance to the production.

Effects of stretching processing parameters on the mean elongation ratio and maximum spread ratio of heavy forgings

Heavy forgings are the essential parts of some nuclear, electrical power generation, rolling mill equipments. The rigid-viscoplastic finite element models (FEM) were established to study the effects of processing parameters (deformation degree, tool width ratio, blank width ratio, strain rate, friction, and forming temperature) on the mean elongation ratio and maximum spread ratio of heavy forgings during stretching process. A new formula (LD model) is proposed to predict the mean elongation ratio for stretched heavy forgings. The predicting capabilities of LD model were verified by experiments. Results show that: (1) The mean elongation ratio and maximum spread ratio increase with the increase of deformation degree; (2) When the tool width ratio is decreased, the mean elongation ratio increases and the maximum spread ratio decreases; (3) When the blank width ratio is increased, the mean elongation ratio increase and the maximum spread ratio decrease; (4) The mean elongation ratio is not affected by strain rate, friction, and forming temperature. However, the effects of these three process parameters on the maximum spread ratio of deformed block are significant; (5) There is a good agreement between the experimental results and predictions by LD model, which confirms that the proposed LD model is valid for the practical industrial productions.