Papers by Keyword: Elasto-Plastic Finite Element

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Authors: You Min Huang, Yi Wei Tsai
Abstract: A methodology of formulating an elasto-plastic three-dimensional finite element model, which is based on Prandtl-Reuss flow rule and von Mises yield criterion respectively, associated with an updated Lagrangian formulation. An extended r-min algorithm is proposed to formulate the boundary conditions, such as the yield of element, maximum allowable strain increment, maximum allowable rotation increment, maximum allowable equivalent stress increment, and tolerance for nodes getting out of contact with tool. In order to verify the reliability and accuracy of the FEM code, the fractured thickness of a specimen in the simple tension test is adopted as the fracture criterion of forming limit in simulation. A set of tools was designed to perform the elliptical cup drawing experiment on the hydraulic forming machine. According to the simulation and experimental results, the minimum thickness is concentrated on the contact regions between work-piece and punch major axis, because the camber radius is relatively large along the minor axis, the ones that bear are relatively small to the circular tensile stress, so the thickness does not change much. The limit drawing ratio (LDR) amounts to about 2.136 for penetration in the elliptical cup drawing process of this study. According to the definition of LDR, when the die radius is increased from R3.0mm to R9.0mm, the LDR would increase from 2.11 to 2.157. When the punch radius is increased from r3.0mm to r9.0mm, the LDR would increase from 2.07 to 2.181. This paper has provided a better understanding of the elliptical cup drawing process for improving the manufacturing processes and the design of tools.
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Authors: You Min Huang, Yi Wei Tsai
Abstract: A methodology of formulating an incremental elasto-plastic three-dimensional finite element model, which is based on Prandtl-Reuss flow rule and von Mises’s yield criterion respectively, associated with an updated Lagrangian formulation, is developed to simulate elliptical cup drawing process. An extended algorithm is proposed to formulate the boundary conditions, such as the yield of element, maximum allowable strain increment, maximum allowable rotation increment, maximum allowable equivalent stress increment, and tolerance for nodes getting out of contact with tool. In order to verify the reliability and accuracy of the FEM code, the fractured thickness of a specimen in the simple tension test is adopted as the fracture criterion of forming limit in simulation. A set of tools was designed to perform the elliptical cup drawing experiment on the hydraulic forming machine. According to the simulation and experimental results, the limit drawing ratio (LDR) amounts to about 2.136 for penetration in the elliptical cup drawing process of this study. This paper also found a comparison of the LDR of different tool radii. According to the definition of LDR, when the die radius is increased from R3.0mm to R9.0mm, the LDR would increase from 2.11 to 2.157. When the punch radius is increased from r3.0mm to r9.0mm, the LDR would increase from 2.07 to 2.181. This paper has provided a better understanding of the elliptical cup drawing process for improving the manufacturing processes and the design of tools.
116
Authors: De Wu Li
Abstract: Related to the actual project in the new Qi Daoliang tunnel between Lanzhou and Lintao highway, select 300-meter calculation range along the tunnel vertically including fault-rupture zone and effect fault-rupture zone, utilize 8 -node, 6-plane block element to scatter the calculating range, at the same time, use the deduced 8 -node, three dimensional jointed element to imitate the transformation gap of the tunnel lining, employ three-dimensional elasto-plastic static finite element program to analyze stress and transformation state of surrounding rock and lining in different construction stages of the new Qi Daoliang tunnel. Through the analysis and comparison of the calculation result of the three conditions: not placing transformation gap through, placing one transformation gap in the middle of the fault-rupture zone, placing two transformation gaps in the beginning and the end of the fault-rupture zone etc, we can get the following points: ①The gallery transformation in the fault-rupture zone and the plastic area in the surrounding rock are obviously bigger than the non-fault-rupture zone. ②Owing to the effect of fault-rupture zone, the increasing range of internal force of the initial support and twice lining is about 10% to 30%. ③Placing the transformation gap in the fault-rupture zone can obviously play a role in releasing lining internal force and transformation energy in the surrounding rock. ④In the start and end changing point of fault-rupture zone, the transformation gap should be placed in the tunnel lining.
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