一种建立板料成形极限应力图的新方法

基于塑性理论建立了比例加载条件下双向拉伸应力应变关系,结合Swift分散性失稳准则,提出了一种建立板料成形极限应力图的方法。分别应用Hill 48和Hosford屈服准则以及单向拉伸性能参数,建立了铝合金板(r<1)和薄钢板(r>1)两种材料的成形极限应力图(FLSD),分析表明,不同的屈服准则的选取对于成形极限应力曲线有不同的影响,对于不同类型的材料屈服准则的影响程度也不同。与由通常的成形极限图(FLD)转换所得到的成形极限应力图(FLSD)进行了对比分析,结果表明,所提出的方法计算过程更为简便,并能较为准确地建立成形极限应力图,可以作为复杂加载路径下的成形极限破裂判据。

A new method for establishing forming limit stress diagram of sheet metals

On the basis of constitutive model for sheet metal,the method for establishment of forming limit stress diagram under biaxial tensile stress state is put forward based on the diffuse instability criterion(Swift's criterion) and plastic relation between stress and strain under biaxial tensile stress state evolved with Hill'48 and Hosford yield criteria adopted with the material properties obtained by the standard uniaxial tensile test.And the forming limit stress diagrams of two kinds of sheet metals including aluminum(r<1) and thin steel sheet(r>1) are built and compared with the forming limit stress curves which are calculated based on the general method of the transformation between the forming limit diagram and forming limit stress diagram.The results shows that forming limit stress diagram can be established precisely and more easily by the method which is put forward,and can be used as the criteria of forming limit under complex strain paths.And the different yield criteria which are adopted have different influence to the forming limit stress curves,and level of yield criteria's influence is also different to different materials.