Non-homogeneity of deformation and fracture in sheet metal forming under biaxial stretching

The course of strain localization and fracture in sheet metal depending on the state of strain has been studied and modelled. The presented model expl ains the mechanisms and the relationships between the mechanisms, forms and modes of the above phenomena. It has been established that the localizatio n of strains in shear bands lies at the base of the two phenomena. As a res ult, a common criterion for different newly defined forms of strain localiz ation could be introduced. Moreover, a new method of experimental determina tion of limit strain curves (LSC) has been proposed. This method differs fr om the previous ones in the fact that it takes into account post-homogenous strains which are a sum of the strains that accompany the development of s train localization and the subsequent fracture. This method takes into acco unt both the distinct character of the development of post-homogenous strai ns and changes in their value depending on the state of strain. As a result , the proposed method of constructing LSCs is free from errors which so far have made it difficult to interpret correctly the relationships between ex perimental and theoretical limit strain curves. Thus it has become possible to overcome the above difficulties associated with the plotting of limit s train curves for processes of forming sheets by biaxial stretching.