Prediction of Forming Limit Diagrams under combined Bending-Stretching loadings

A number of parts and components involved in the automotive industry are made of thin bent sheets. Unfortunately, the classical predictions based on traditional Forming Limit Diagrams are not relevant when the strain distribution is heterogonous over the thickness, as is the case for bent sheet metals. The aim of the present contribution is to propose an extension of the well-known Marciniak‒Kuczynski approach to account for the effect of bending on formability prediction. The new developed tool allows predicting the limit strains for the whole range of strain paths. The mechanical behavior of the studied sheets follows the rigid–plastic flow theory. Through numerical results, it is shown that bending tends to decrease the formability limit of the sheet metal