[求助]翻译：用有限元法研究在精密冲压加工中的塑性破坏

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<p>Investigation on ductile fracture in fine-blanking process by finite element method`<br/></p><p>[Abstract]&nbsp; In order to continuously analyze the whole fine-blankinn process, from the beginning of the operation up to the total rupture of the sheet-metal,&nbsp; without computational divergence,&nbsp; a 3-D rigid visco-plastic finite element method based on Gurson void model was developed.&nbsp; The void volume fraction was introduced into the finite element method to document the ductile fracture of the sheet-metal.&nbsp; A formulation of variation of the rigid visco-plastic material was presented according to the virtual work theory in which both the effects of equivalent stress and hydrostatic pressure in the deformation process were considered. The crack initiation of the sheet was predicted and the crack propagation was geometrical1y fulfilled in the simulation by separating the nodes according to the stress state.&nbsp; Furthermore, the influences of different state variables on the deformation process were also studied.<br/>[Key words] fine-blanking;&nbsp; ductile fracture; <br/>finite element method;&nbsp; Gurson plastic potential<br/>[CLC numbers]T G 38&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; [ Document code] A<br/>————————————————————</p><p>1&nbsp; INTRODUCTION<br/>&nbsp;&nbsp;&nbsp; Sheet metal forming is a widely used process in manufacturing industries,&nbsp; among which fine-blanking process is the most advanced technique that offers an effective and economical metal cutting.&nbsp; Similar as all other blanking processes,&nbsp; fine-blanking process ends in total rupture of the sheet metal as opposed at other processes such as stamping and drawing which are aimed at deforming the sheet plastically without ruptune.&nbsp; At the same time,&nbsp; fine-blanking process is implemented with triple action tools[1]:a punch,&nbsp; an indented&nbsp; V-ring,&nbsp; and an ejector to generate a concentrating compressive stress state and nearly pure shearing forces to perform a bulk deformation of the blank in the narrow clearance zone between the punch and the die.&nbsp; Comparing with the conventional blanking process and other metal forming processes,&nbsp; the material behavior in fine-blanking process is submitted to more complex stress and strain state, and is subject to ductile fracture and crack propagation phenomena[2].<br/>&nbsp;&nbsp;&nbsp; The ductile fracture phenomena exist&nbsp; in many metal-forming processes,&nbsp; and the ductile fracture occurs when the material is subject to too large plastic deformation and stresses beyond the yield point. A lot of researches have been done on the ductile fracture by both experimental observations[3] and theoretical analysis[4~8] .However,&nbsp; the knowledge obtained so far of the ductile fracture is far to be sufficient and the related investigations in the fine－blanking process are much less.There is still much to do in this field as the ductile fracture plays an important role in the fine-blanking process. Fine-blanking process can be broadly divided into three phases[9] .During the first phase the punch moves downward and elastic and plastic deformations take place.&nbsp; In the period of the second phase,&nbsp; the cutting edge of the punch penetrates the material and the deformation accumulates until the limit shear strength of the material is reached and the material is sheared along the cutting edge.&nbsp; The third phase consists of crack growth and propagation and the operation ends when the material is completely separated.&nbsp; From a numerical point of view.the main difficulty to simulate the fine-blanking process is to describe the material behavior continuously from the beginning of the operation up to the complete ruptune. A good description of the above stages of fine-blanking process requires the development of reliable algorithms.&nbsp; Finite element method has recently been applied extensively in the numerical analysis and is proved to be a powerful means. There have been several investigations into the understanding of the mechanics of fine-blanking process[10~12].but these investigations did not consider the fracture and the studied problem was of two dimensions.&nbsp; Therefore, these investigations are not sufficient to clarify the mechanics of the process and haven' t well simulated the bulk deformation.&nbsp; Based on the above situations the purpose of this paper is to propose a 3- D finite element method that is capable of numerically analyzing all the phases of the fine-blanking&nbsp; process without computational divergence.</p><p>2&nbsp; METHOD OF ANALYSIS<br/>2. 1&nbsp; Modeling of ductile fracture<br/>&nbsp;&nbsp;&nbsp; Accurate knowledge of the fracture process helps to select a suitable damage model.&nbsp; Numerous authors have studied different physical mechanisms leading to the final ruptured[13~19] .It is well known that ductile fracture occurs on the micro-scale mainly by voids nucleation growth and coalescence. In this study ,the yield function proposed by Gurson[20], developed by&nbsp; T vergarrd and Needleman[21~23] by introducing meterial constants q1.q2, and q3 into the yield equation on considering the voids coalescence is written as:<br/></p><p>…………<br/></p><br/>

[此贴子已经被作者于2006-5-11 9:31:08编辑过]

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