Rigid-plastic Finite Element Analysis Research Articles

Microstructure and properties of Mg–Al–Mn magnesium alloy under shear deformation coupled tension rolling

Shear coupling tension rolling is based on equal diameter angle rolling, which meets the requirements of modern industrial development with high production efficiency and short process. It is of great significance to improve the defects of uneven texture distribution and insufficient grain refinement in continuous casting billet rolling process. In this study, the effects of different reduction rate, circular arc radius and tensile angle of shearing roll on the stress and strain of sheet metal were studied by means of high precision constitutive model and rigid plastic finite element analysis software. At the same time, the effects of different process parameters on the microstructure and mechanical properties of rolled magnesium plate were analyzed. The results show that the larger the single pass reduction rate is, the smaller the arc radius of the shear roll is and the smaller the tensile angle is, the greater the equivalent strain and equivalent stress at the corner are. The higher the reduction rate is, the greater the tensile strength and yield strength are and the smaller the extension is. The smaller the arc radius and tensile angle of the shear roll are, the greater the tensile strength and extension are, the smaller the yield strength is, and the easier it is to form dynamic recrystallization.

Finite element analysis of strain gradients in aluminium alloy sheets processed by asymmetric rolling

Gradient microstructures can be achieved due to creating of strain gradient, which can be considered as a mechanism to simultaneous improves the ductility and strength of metallic materials. Asymmetric rolling is one of the methods of severe plastic deformation and this process can be used to fabricate metallic materials with gradient microstructures. Searching the process parameters which provide predetermined strain gradient is very important. This paper presents the distributions of the effective strain through strip thickness of aluminum alloy Al-6.2Mg-0.7Mn processed by a single-pass asymmetric rolling. Effects of thickness reduction per pass (10…60%), rolls speed ratio (1…60%), diameters of the rolls (50…500 mm), contact friction coefficient (0.1…0.4) and initial strip thickness (1…8 mm) were investigated by the rigid-plastic finite-element analysis. The non-linear effect of rolls speed ratio on the strain gradient during asymmetric rolling was found. Extremely high predetermined strain gradient up to e ≈ 3…6 was reached during a single-pass asymmetric rolling. Finite element analysis of the deformation characteristics, presented in this study, can be used for development of the asymmetric rolling process as a method of fabrication of metallic materials with gradient microstructures.

Finite element simulation of extremely high shear strain during a single-pass asymmetric warm rolling of Al-6.2Mg-0.7Mn alloy sheets

Abstract Shear strain and accumulated strain plays a critical role in the grain refinement of aluminium alloys processed by asymmetric rolling, when circumferential speeds of the top and bottom rolls are different. Asymmetric rolling induces larger grain refinement in the mode of severe plastic deformation, when accumulated strain with dominant shear strain is more than 3. Searching the optimal process parameters which provide such extremely high deformation characteristics is very important. This paper presents the distributions of the accumulated strain through strip thickness of Al-6.2Mg-0.7Mn alloy processed by a single-pass asymmetric warm rolling. Effects of thickness reduction per pass (10…60%), rolls speed ratio (1…60%), diameters of the rolls (50…500 mm), contact friction coefficient (0.1…0.4), initial strip thickness (1…8 mm) and ratio of contact arc length to average thickness of strip were investigated by the rigid-plastic finite-element analysis with taking into account the heat generation due to work of plastic deformation and friction. The non-linear effect of rolls speed ratio on the deformation characteristics during asymmetric warm rolling was found. Extremely high shear strain and accumulated strain up to e=3.8...4.8 were reached during a single-pass asymmetric warm rolling. Finite element analysis of the deformation characteristics, presented in this study, can be used for optimization of the asymmetric rolling process as a method of severe plastic deformation.

Effect of Shear Deformation on Closure of a Central Void in Thin-Strip Rolling

Central voids or voids at the middle layer are often found in thin strips produced by twin-roll casting. These strips are in general so thin that they are unable to take a required reduction in thickness to close the voids. In the present investigation, equal-speed rolling and differential-speed rolling were compared to assess the effect of differential speed on closure of the voids by the rigid-plastic finite-element analysis. As a result, shear deformation developed in differential-speed rolling was found to reduce the reduction in thickness required for void closure. An increase in speed ratio, length of deformation zone, or friction coefficient at the interface expedited the progress in void closure. However, as the speed ratio exceeded thickness ratio, a portion of rolling power was dissipated extensively by excessive slip at the interface. Moreover, tensile stress developed which would cause cracks in the strip.

Multi-stage forging process design of steering system output shaft for reduction of energy consumption

The purpose of this study is to propose a method for reducing carbon emissions produced during the manufacture of output shafts by increasing productivity and reducing energy consumption. To this end, the existing machining process was redesigned as a multistage cold forging process, using a computer-aided engineering technique. The critical parameters considered for the redesigning were material deformation, metal flow, and load. Rigid plastic finite element analysis software DEFORM-2D3D was utilized to identify and analyze these parameters. The derived multi-stage cold forging process was designed on the basis of the test results. It was also verified that the new process substantially increased productivity. A carbon life cycle assessment (LCA) was performed to compare the amounts of carbon emission, material loss and energy consumption of the existing machining process and derived multistage cold forging processes. The comparison results indicated considerably lower carbon emissions, material loss and energy consumption in case of the latter.

The Research on the Generated Mechanism about the End Concavity of Shaft in the Closed Type of Cross Wedge Rolling

To further improve the material utilization in cross wedge rolling, the paper simulated the forming of closed cross wedge rolling through DEFORM-3D, a rigid-plastic finite element analysis software, and analyzed the distribution and changing rule on the fields of strain and displacement in the parts rolling. Then the paper clarified the generated mechanism about the end concavity of shaft in the closed type of cross wedge rolling, which has great theoretical significance and engineering applied value in controlling and decreasing the end concavity in closed type cross wedge rolling and improving the parts’ end quality.

Finite element analysis of advanced bicycle precision brake disk forming technology

In recent years, the bicycle has become an environmentally friendly transportation. The bicycle can be divided into mountain bicycle and highway bicycle. Safe driving is the prior consideration. The bicycle braking system can be divided into oil pressure disk brakes and mechanical disk brakes. The brake disk system is one indispensable component of the safe system. In accordance to overall weight consideration of the bike, the brake disk should also focus on the lightweight design. This paper discussed an innovative brake disk forming technology for 6061 aluminum alloy by the rigid-plastic finite element analysis. The simulation parameters include geometric shapes of the brake disk and mold, die temperature, and friction factors. The stress and strain in forming, brake deformation and vibration modal analysis of brake disk in riding were studied. The paper is expected to offer some precision bicycle brake disk manufacture knowledge for industry.

Finite-element analysis of severe plastic deformation in differential-speed rolling

Differential-speed rolling can impose severe plastic deformation on a metallic sheet by developing extensive shear strain. Plastic deformation by a single pass with a speed ratio of 3 was found to be as high as 3.5 in terms of the effective strain. Although the speed ratio, the friction coefficient and the length of deformation zone are important parameters in controlling the differential-speed rolling, their effects on plastic deformation are yet unknown. In the present study, these effects were investigated by the rigid-plastic finite-element analysis, and as a result logics in dissipation of power, mechanisms in development of plastic deformation and an upper limit of the speed ratio were found. Moreover, a double-pass differential-speed rolling was introduced to achieve a symmetric distribution of the effective strain through thickness of a sheet. An excessive speed ratio would waste unnecessarily a portion of the power through friction at the interface between the sheet and rolls, and also exert a tensile stress in the sheet, which could result in fracture if the material of the sheet is as brittle as a magnesium alloy.

Optimization Analysis of A7075 Bicycle Stem Forging Process

This research analyzes an innovative forging mold design for the various bicycle stem. The paper used the rigid-plastic finite element analysis software and structural analysis to investigate the plastic deformation behavior of aluminum alloy A7075 workpiece for forging process. Under various forging conditions, it analyses the effective strain, the effective stress, the temperature changing, surface pressure, mold radius load distribution, stress analysis of billet and mold. Moreover the paper used the Taguchi method combine the algorithm method of artificial neural network to find out the best design parameters. The paper hoped to offer some tolerance um precision forging manufacture knowledge for industry.

地下水圧および飽和度による粘着力の変化を考慮した切羽安定評価法

A ground water has a great influence on the tunnel face stability. This paper describes an evaluation method of tunnel face stability affected by ground water pressure and variation of sandy layer's cohesion due to a degree of saturation. A rigid plastic finite element analysis (RPFEA) was applied to simulate the face collapse in the study. The method pays attention only to the plastic state and uses the upper bound theorem. Body forces in the analysis were self-weight of soil and water-pressure. The subject is a railway tunnel of Tohoku-Shinkansen, constructed in soft ground by the shotcrete tunneling method, or the currently so-called NATM. At the construction site, the ground water level is high throughout the whole section, and the ground near the tunnel face is sandy soils with a clayey layer, whose position at the face varies by the face advance. The ground water flows both in the lower and upper sandy layers separated by the clayey layer. Therefore, deep well method was applied to lower the ground water level, since the ground water level normally has significant influence on the stability of the tunnel face. However, it is difficult to lower the ground water level in the upper sandy layer. Therefore, the authors analyzed the tunnel face stability by measurements of the groundwater level, results of face observation and RPFEA. As a result, it has been known that the face stability is affected strongly by value of soil cohesion c and it is necessary to estimate strictly the value of soil cohesion c. For this reason, the authors studied on the relation between degree of saturation and cohesion of sandy layer, and applied this relation to the evaluation of tunnel face stability. Furthermore, they developed the indicator for selection of auxiliary method to stabilize the tunnel face by the evaluation method.

Simulation of static softening behavior of an aluminum alloy after cold strip rolling

In this work, softening kinetics after cold rolling has been simulated using a coupled finite element-cellular automata model. Firstly, a two-dimensional rigid plastic finite element analysis has been developed to assess strain field and the stored energy accumulation during cold rolling as well as the initial condition of the mesoscopic model. Then, the cellular automata scheme has been employed to calculate the progress of static recrystallization at a given temperature while a dislocation-base model was simultaneously utilized to consider the effect of recovery on static softening process and final microstructures. The model has been examined on isothermal annealing of cold rolled AA5052 and a good agreement was found between the experimental observations and the predicted results.

Solving the Simulations Equations Arising in the Rigid-Plastic Finite Element Analysis by a Modified Cholesky Factorization Method

Solving the Simulations Equations Arising in the Rigid-Plastic Finite Element Analysis by a Modified Cholesky Factorization Method

Solving the Simulations Equations Arising in the Rigid-Plastic Finite Element Analysis by a Modified Cholesky Factorization Method

Solving the Simulations Equations Arising in the Rigid-Plastic Finite Element Analysis by a Modified Cholesky Factorization Method

Application of an Improved Trust-Region Method to Rigid-Plastic Finite Element Analysis in Strip Rolling

Rigid-plastic finite element analysis (RPFEA) is an efficient and practical method to calculate rolling parameters in the strip rolling process. To solve the system of simulations equations involved in the RPFEA, a numerous of numerical methods, including the standard Newton-Raphson method, the modified Newton-Raphson method, and etc., have been proposed by different researchers. However, the computational time of the existed numerical methods can not meet the requirement of the online application. By tracking the computational time consumption for the main components in the standard Newton-Raphson method used in finite element analysis, it was found that linear search of damping factor occupies the most of the computational time. Thus, more efforts should be put on the linear search of damping factor to speed up the solving procedure, so that the online application of RPFEA is possible. In this paper, an improved trust-region method is developed to speed up the solving procedure, in which the Hessian matrix is forced to positive definite so as to improve the condition number of matrix. The numerical experiments are carried out to compare the proposed method with the standard Newton-Raphson method based on the practical data collected from a steel company in China. The numerical results demonstrate that the computational time of the proposed method outperforms that of the standard Newton-Raphson method and can meet the requirement of online application. Meanwhile the computational values of rolling force obtained by the proposed method are in good agreement with experimental values, which verifies the validity and stability of the proposed method.

Finite Element Analysis of High Pressure Torsion Processing

Considerable interest has recently been developed in processing bulk materials through the application of severe plastic deformation (SPD). High pressure torsion(HPT) is one of severe plastic deformation methods. By this method, the material grain size can be refined to 20~200nm, which are nanometer level, and the micro-hardness and mechanical properties of materials can be improved. So the nanometer material can be got through this method. In this paper, the results of the rigid-plastic finite element analysis of the plastic deformation behavior of bulk materials during the HPT processing are presented. The torque and strain patterns of the sample as well as the relationship between the slippage time and pressure are also investigated.

Permeation of Lubricant Trapped Within Pocket Into Real Contact Area on the End Surface of Cylinder

Knowledge on the behavior of lubricant trapped in a surface pocket is important for improving metal forming technology, since the trapped lubricant affects friction and surface finishing. The permeation phenomena at higher reduction in height were quantitatively observed during the upsetting of cylinders with a central conical dent using the new fluorescence direct observation apparatus developed by the authors. Moreover, the permeation phenomena were estimated using a rigid-plastic finite element analysis model incorporating the compressibility of the lubricant. From the experimental results, it was quantitatively observed that over a reduction in height of 37%, the outline of the central conical dent became blurred, and the lubricant trapped within the conical dent permeated into the peripheral real contact area. It was also quantitatively observed that the volume of the lubricant trapped within the conical dent decreased gradually and abruptly with increasing reduction in height up to and above 36%, respectively. From the numerical results, it was estimated that the trapped lubricant permeated when the hydrostatic pressure generated within the lubricant pocket exceeded the die pressure at higher reduction in height.

Investigation of the Drawing Process of a Square Rod from a Round Bar by Using 3-D Finite Element Analysis

Wire and rod drawing is widely used in metal forming processes to obtain products such as rods and wires. Rods having shaped sections such as square, rectangle and irregular section are necessary to produce connecting pins and components of transformers. Important characteristics of the shaped drawing process are the corner filling and inhomogenious factor of strain that influence the dimensional accuracy and the good quality of the product. In this paper, a three-dimensional rigid-plastic finite element analysis is used to simulate the drawing process of a square rod from a round bar. A finite element method is also used to investigate the corner filling, forming load, stress distribution and inhomogenious factor of effective strain under various process parameter conditions, including the reduction of area, the die semi-angle, and the friction factor

Physical Modeling of Cylinder Upsetting with Plasticine for Validation of FEM

Physical simulation was conducted on the process of upsetting cylinder between flat platens by using colorful plasticine. The results of the physical simulation are basically consistent with rigid-plastic finite element analysis, which supports the rigid-plastic mechanical model for the cylindrical billets whose height-diameter ratio are greater than 1. Further physical simulation is conducted on cylinders upsetting between platen and supporting ring. The experimental method provides a reference for physical simulation of large deformation.

Slide-Bend Forming of Very Thin Metal Sheet Using Slide-Ironing Tool

Characteristics of slide-bend forming were investigated. In this process, foil specimens can be bent to various shaped products by indenting and sliding a tool. The effects of the tool indentation load, the foil thickness and the number of slide repetition on the bending angle were examined experimentally for three kinds of foil materials. In addition, the deformation of bent region was examined using a rigid-plastic finite element analysis. Bending angle increased with increasing the indentation load or decreasing the foil thickness. When the number of slide repetition increased, the bending angle increased slightly. The slide repetition can be effective for adjusting bending angle slightly. By sliding a thin edge-shaped tool relative to the foil specimen, bending angle and radius of curvature of specimens can be controlled freely.

Rigid-plastic and elastic-plastic finite element analysis on the clinching joint process of thin metal sheets

This article describes the joining of thin metal sheets by a single stroke clinching process. Elastic-plastic and rigid-plastic finite element analysis were applied by employing Coulomb friction and constant shear friction in order to investigate the behavior of the clinch joint formation process. Four process variables, such as die diameter, die depth, groove width, and groove corner radius were selected to investigate the parametric effect on the clinch joint. The strength of clinch joints were evaluated by examining the separation strengths, such as peel strength and tensile shear strength, respectively. A failure diagram was constructed that summarizes the analysis results. The simulation results showed that die diameter and depth were the most decisive parameters for controlling the quality of the clinch joint, while the bottom’s thickness was the most important evaluation parameter to determine the separation strengths.