基于极限应力分析的十字形双向拉伸试件设计

十字形试件双向拉伸实验是实现复杂加载路径的有效方法,是研究板料后继屈服行为和成形极限可行的实验手段,解决十字形试件中心区的大变形、应力均匀性、应力测量计算方法等是其应用的主要问题.通过试件中心区减薄实现了中心区大变形以致颈缩破裂,给出了3种不同形式的中心区减薄形状,从应力均匀性、最大变形出现位置和避免应力集中等方面进行了优化对比分析,并探讨了计算中心区应力的解析方法.结果表明,中心区方形减薄的十字形试件有更好的中心区应力分布均匀性,更容易实现大变形以致破裂发生在中心区,能较好地控制应力集中,是更适用于板料成形极限应力图研究的实验装备. 

FEM design of cruciform biaxial tensile specimen based on limit stress analysis

The cruciform biaxial tensile test is an effective and practical method to realize the process of complex strain paths for the investigation of subsequent yield behavior and forming limit of sheet metal,and the key questions should be solved including the large deformation,homogeneousness of stress distribution and the method to measure the stress in the center region.Using cruciform specimen with thinning center region,the necking even fracture was realized.Three types of cruciform specimen with different geometrical shape of thinning center region were presented,and the homogeneous distribution of stress,the appearance of largest deformation and the avoidence of stress concentration in the center region were analysed.A mathematical method was discussed to calculate the stress in the center region.The result shows that the cruciform specimen with square thinning center region is the superior device for the investigation of forming limit stress diagram(FLSD) to obtain the more homogeneous stress distribution in the center region,to realize the large deformation and the fracture appears in the center region more easily,and to control the stress concentration preferably.