成形极限曲线的新概念

NEW CONCEPT OF FORMING LIMIT CURVE

失稳理论是成形极限曲线（ＦＬＣ）的理论基础。本文论述了ＦＬＣ理论研究中存在的问题。研究指出：一般出厂板的表面状况不会影响板料的集中失稳；板内损伤平面应变时最严重；双拉时，板内损伤的积累、发展，导致应力状态向平面应变漂移；拉压时，载荷失稳后引起的双拉，也会导致平面应变。因此平面应变状态的出现是板料集中失稳的共同原因。在此基础上，建立了ＦＬＣ左右两半部统一的模型。新模型与试验结果符合良好，优于Ｍ－Ｋ理论。

A very important tool in the description of sheet metal formability is the well known Forming Limit Curve(FLC),prediction of which is generally based on models using instability theories.Our experimental observations indicate that the surface roughness of as-received metal sheets generally does not lead to strain localization.At the same level of effective strain,the internal damage of a metal sheet is the most severe situation in plane strain state.When deformation is at tension-tension state,damage developme nt results in the drifting of the strain state to plane strain state.When deformation is at tension-compression state,the stretch caused by load instability also lead to the development of plane strain state.Based on these results,a united model for the construction of both the left and righ halves of FLC is proposed.FLCs predicted by this new model is consistent ched well with experimental results and the new model is proven to be bet ter than the M-K theory.