【摘要】 第Ⅰ部分提出"任意复杂变形路径均可简化为线性复合变形路径"、"板材的冲压成形能力亦即板材允许的极限厚度应变",以及"板材在线性复合变形路径下的冲压成形能力取决于其最终变形路径的应变比值"等三个简化假设,依据这些假设在线性复合变形路径以及应变主轴发生转动的条件下,推导出计算板材冲压成形极限应变的公式。根据这些假设和公式,首先计算出板材在初始变形分别为单向拉伸、平面应变和等双拉应变的二重线性复合变形路径作用下且应变主轴发生转动时的成形极限图(Forming limit diagram,FLD),然后通过一定的试验来验证和讨论这些计算结果。试验和讨论表明,根据这些假设和公式计算获取的FLD,与本文试验结果和某些文献报道的试验结果具有吻合性。此外,以往的研究大多从塑性力学或塑性物理方面解释了变形路径改变对FLD的影响,而这里则根据■等值曲线图,从塑性几何方面对变形路径改变FLD图形状态的现象做出了描述。更多还原

【Abstract】 In part (Ⅰ) of this paper published,three assumptions for sheet metal forming are proposed,i.e.any complex swain path can be simplified to the broken-line strain paths combined with a number of linear strain paths;the limit thickness strain is also the sheet metal formability;the formability of sheet metal under the broken-line strain path depends on the final strain ratio in forming process, and on the basis of these assumptions,the theoretical formulas for calculating limit strains in sheet metal forming are deduced under the broken-line strain path with strain principle axes turning during alternating from the prior linear strain path to the subsequent one. The forming limit diagrams (FLDs) are firstly calculated by means of these assumptions and formulas in sheet metal forming under three two-step linear strain paths with strain principle axes turning,whose initial deformation are uniaxial tensile,plane strain and equibiaxial tensile strain respectively.Then these FLDs are discussed and verified through forming limit test.The obtained FLDs tally with the test results mentioned in this paper and those reported by some literature.Moreover,most past researches explained the influence of broken-line strain paths on FLDs from the viewpoint of plastic mechanics or plastic physics,here we on the basis of the ■equivalent curves describe the phenomenon of FLD state changed by broken-line strain paths from the viewpoint of plastic geometry.更多还原