高強度熱延鋼板の打ち抜き端面における塑性歪勾配下でのき裂進展挙動の予測

抄録

In order to clarify the dominant factors controlling stretch flange ability of hot-rolled high-strength steel sheets, a model to predict crack growth under plastic strain gradient beneath pierced edge was constructed based on fracture mechanics. The model predicts crack growth by equating crack growth driving force J_app which is numerically calculated, and crack growth resistance J_mat which is obtained by estimating strain distribution under pierced edge introduced by piercing and has taken into consideration the influence of pre-strain on crack growth resistance. The model could predict actual crack growth on pierced edge at acceptable accuracy. The calculation using the model suggests that stretch flange ability of high-strength steel sheets can be improved by raising crack growth resistance of the material, or reducing strain due to piercing.