A new multi-step approach considering bending effects and its application in the stretch bending of rectangular tubes
Received:July 27, 2009  Revised:June 13, 2010
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KeyWord:multi-step approach  bending effects  BST element  the penalty method  stretch bending of rectangular tube
傅立军 上海交通大学塑性成形工程系, 上海
董湘怀 上海交通大学塑性成形工程系, 上海
王鹏 上海交通大学塑性成形工程系, 上海
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      Multi-step approach can take the deformation history into account, adapts to multi-stage forming and has a good application prospect in the simulation of sheet metal forming. But traditional multi-step approaches are mostly based on the membrane element without considering bending effects exactly, not suited to the bending-dominated process, such as the stretch bending of profiles etc. Therefore the rotation-free BST element is introduced here to describe deformation, in which the curvatures are computed by a patch of four adjacent elements. Then using the principle of extremum work and the BST element, a new multi-step formulation is presented, in which the penalty method is adopted to treat the contact between the workpiece and bending tools. Based on the formulation, a program has been developed and utilized to simulate the process for stretch bending of rectangular tubes within six large steps, including pre-stretch and bending, with special attentions paid on the cross sectional distortions and springback problems. The numerical results basically agree with those of incremental analysis and experiments.