1,721,379 research outputs found
Rate-Dependent Material Parameters of the Combined Isotropic/Kinematic Hardening Model for the TRIP980 Steel Sheet
No full textThis paper is concerned with rate-dependent hardening behaviors of the TRIP980 steel sheet. In sheet metal forming, sheet metals experiences complicated loading at various strain rates. In order to predict deformed shape in sheet metal forming, accurate material properties and an appropriate constitutive model in numerical simulation are important to consider reverse loading and various strain rates simultaneously. This paper deals with rate-dependent material parameters of the isotropic/kinematic hardening model. Tension/compression tests of the TRIP980 steel sheet are performed with a newly developed experimental technique at various strain rates ranging from 0.001 to 100 s-1. Tension/compression hardening curves of the TRIP980 steel sheet are approximated by the Chun et al. model at each strain rate condition respectively. From acquired material parameters, rate dependencies of tension/compression hardening behaviors are investigated
Prediction of fracture strains for DP980 steel sheets using a modified lou-huh ductile fracture criterion
No full textSpring-back prediction based on a rate-dependent isotropic-kinematic hardening model and its experimental verification
No full textThis paper deals with spring-back prediction with a rate-dependent isotropic-kinematic hardening model with tension/compression in high speed U-draw-bending tests. In order to verify the validity of the present model, spring-back simulation is carried out and its results are compared with experimental results. A rate-dependent isotropic-kinematic hardening model has been proposed by combining the rate-dependent function of material parameters and the Chaboche type model for the TWIP980 steel sheet under tension and compression. The proposed model can accommodate the strain rate effect on the material properties by providing rate-dependent hardening curves under loading and reverse loading condition. This change of the rate-dependent material properties is important to predict spring-back under high speed deformation in practical sheet metal forming undergoing tension and compression during the deep-drawing forming. High speed U-draw-bending tests have been performed to investigate the strain rate effect on spring-back of the TWIP980 steel sheet after draw-bending at intermediate strain rates of up to a hundred per second. The experimental results have been compared with simulation results of high speed U-draw-bending and spring-back analysis with four hardening cases: isotropic; isotropic-kinematic; rate-dependent isotropic; rate-dependent isotropic-kinematic hardening models. It is demonstrated with the comparison that the rate-dependent isotropic-kinematic hardening model proposed provides the best prediction of spring-back after U-draw-bending at intermediate strain rates among the four hardening cases
Asymmetric Hardening Behavior of AZ31B Magnesium Alloy Sheet with Large Strain at Various Strain Rates
No full textThis paper investigates asymmetric hardening behavior of the magnesium alloy sheet of AZ31B at different strain rates when deformation is large. Tensile tests are carried out at the quasi-static state of 0.001 s(-1) and the intermediate strain rate of 100 s(-1) utilizing the Instron 5583 and the high speed material testing machine (HSMTM), respectively. Compression tests are conducted at the strain rate of 0.001 s(-1) and 100 s(-1) using a jig fixture mounted on the testing machines to change the loading direction into the opposite direction. A compression testing method is developed to obtain compressive properties with large strain, which includes the attachment of a fork-type clamping device and the design of specimen dimensions to achieve large strain without buckling during the test. Experimental results reveal the asymmetric behavior showing that the tensile yield stress is much larger than the compressive one at both strain rates. The difference between the flow stress level in tension and compression becomes larger when the strain rate is higher. The compressive hardening behavior is very much different from the tensile hardening behavior showing that the compressive flow stress increases remarkably as the deformation proceeds while the tensile flow stress asymptotes to a certain value.
Evaluation of the Failure Elongation of Steel Sheets for an Auto-body at the Intermediate Strain Rate
No full textThis paper deals with the dynamic failure elongation of mild steel, SGACD and advanced high strength steel sheets such as TRIP600, DP600 and TWIP steels. The failure elongation has been obtained from the high speed tensile testing machine with various strain rates ranged from 0.003/s to 200/s. The experimental result demonstrates that the tensile elongation does not simply decrease as the strain rate increases, but it decreases from the quasi-static state to the strain rate of 0.1 or 1/s and increases again up to the strain rate of 100/s. Furthermore, some high strength steels have the tendency that the tensile elongation increases as the strain rate increases. Moreover, the localized strain rate hardening in the necking region induces the increase of elongation
Efficiency enhancement in sheet metal forming analysis With a mesh regularization method
No full textThis paper newly proposes a mesh regularization method for the enhancement of the efficiency in sheet metal forming analysis. The regularization method searches for distorted elements with appropriate searching criteria and constructs patches including the elements to be modified. Each patch is then extended to a three-dimensional surface in order to obtain the information of the continuous coordinates. In constructing the surface enclosing each patch, NURBS (non-uniform rational B-spline) surface is employed to describe a three-dimensional free surface. On the basis of the constructed surface, each node is properly arranged to form unit elements as close as to a square. The state variables calculated from its original mesh geometry are mapped into the new mesh geometry for the next stage or incremental step of a forming analysis. The analysis results with the proposed method are compared to the results from the direct forming analysis without mesh regularization in order to confirm the validity of the method. (C) 2003 Elsevier B.V. All rights reserved
Blank design and strain prediction of automobile stamping parts by an inverse finite element approach
No full textA new finite element approach is introduced for direct prediction of blank shapes and strain distributions from desired final shapes in sheet metal forming. The approach deals with the geometric compatibility of finite elements, plastic deformation theory, minimization of plastic work with constraints, and a proper initial guess. The algorithm developed is applied to automobile stamping parts such as an oil pan and a front fender in order to confirm its versatility of application by demonstrating the reasonable numerical results in stamping processes. Rapid calculation with this algorithm enables easy determination of various process variables for design of sheet metal forming process
Regression Model for Light Weight and Crashworthiness Enhancement Design of Automotive Parts in Frontal Car Crash
No full textSheet metal forming analysis of planar anisotropic materials by a modified membrane finite element method with bending effect
No full textA modified membrane finite element with proper formulation is introduced to correctly enhance the flexural rigidity not only within an element but amongst elements. A finite element formulation is derived for the incremental analysis for non-steady large deformation in sheet metal forming. The formulation employs the convective coordinates to keep the objectivity in large deformation and rotation, and considers the planar anisotropy with Hill's quadratic yield criterion. The formulation is then combined with an effective contact algorithm to deal with the contact between the material and the dies. The simulation examples demonstrate the validity and versatility of the computer code, showing the earing phenomenon in cylindrical cup deep drawing processes and the variation in deformation with different orientations of the initial blank in rectangular cup drawing. The present simulation allows the thickness variation in the flange region to redistribute the blank-holding force during deformation, which can predict a more precise contour line in the flange region and a more precise deformed shape with strain distribution than the prediction made by conventional simulation. (C) 1999 Elsevier Science S.A. All rights reserved
Three dimensional multi-step inverse analysis for the optimum blank design in sheet metal forming processes
No full textAn inverse finite element approach is employed for more capability to design the optimum blank shape from the desired final shape. Since one-step analysis is not accurate enough to calculate the initial blank shape for complicated parts, multi-step analysis is introduced to obtain more accurate blank shapes and strain distribution. Multi-step analysis deals with the sliding surface for intermediate shapes and the coordinate transformation for appropriate Newton-Raphson iterations. The present algorithm has been applied to square cup drawing and oil-pan drawing. The numerical results confirm the validity and versatility of the algorithm with the initial blank shapes calculated and comparison to experimental results. (C) 1998 Elsevier Science S.A. All rights reserved
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