Forming-limit Prediction of Perforated Steel Sheets Considering the Effect of Strain Gradient

Abstract

The forming-limit strains of perforated steel sheets with circular holes were theoretically and experimentally estimated for two types of hole arrangements: square and triangular patterns. The theoretical forming-limit curves were obtained by finite-element analyses on a unit module of the perforated sheets using two different approaches. Hill’s quadratic anisotropic yield function was used. To determine the forming limits, the effect of strain gradient on the stretch flange deformation limit was considered, which was investigated by hole expansion tests. The experimental forming-limit strains were also obtained through Nakazima stretching tests. The theoretical predictability of the forming-limit curves was assessed by comparing the theoretical and experimental results.