Measurement of local strain path and identification of ductile damage limit based on simple tensile test

摘要

To estimate the strength of automotive bodies under impact loading and to predict the crack occurrence of high strength steel sheets, the local fracture strain and the ductile damage limit must be measured by experiments to provide data for metal forming simulation by using FEM. In the present study, the local strains at the cracking position and its nonlinear strain path during a simple uniaxial tensile test were measured using a digital image grid method developed by authors. Then, a new identification method for the ductile damage limit of steel sheets was proposed with the aid of the measured nonlinear local strain historical path and local fracture strain. By changing the grid pitch length of the digital image grid method, the effect of grid pitch length on the measured local fracture strain and ductile damage limit were investigated. This experimental investigation is very useful to predict the fracture occurrence conditions if various sizes of finite element mesh were employed in the simulation. The ductile damage limit identified by the newly proposed method using a simple uniaxial tensile test agreed very well compared with the conventional press test.