Comparison of DIC Methods of Determining Forming Limit Strains

Abstract Digital image correlation (DIC) techniques have been used in forming limit tests to obtain forming limit strains and many different methods have been proposed to determine the onset of localized necking in order to improve the accuracy of forming limit curves in recent ten years. Necking limit strains of four sheet materials, including two high strength steels (MP980 and DP600) and one Al alloys (AA6022-T4), were determined by the existing DIC methods in the literature. Through comparison, it is found that both spatial and temporal aspects of localized necking need to be considered to robustly and accurately catch the subtle moment, the onset of localized necking, namely, to accurately determine forming limit strains associated with the onset of localized necking.