Analysis of Failure in Dual Phase Steel Sheets Subject to Electrohydraulic Forming

Abstract

In previous work, the formability of dual phase steel sheets formed under quasistatic and high strain rate conditions was investigated in macroscale (Golovashchenko et al., 2013, “Formability of Dual Phase Steels in Electrohydraulic Forming,â€‌ J. Mater. Process. Technol., 213, pp. 1191–1212) and microscale (Samei et al., 2013, “Quantitative Microstructural Analysis of Formability Enhancement in Dual Phase Steels Subject to Electrohydraulic Forming,â€‌ J. Mater. Eng. Perform., 22(7), pp. 2080–2088). The Nakazima test and electrohydraulic forming (EHF) were used for quasistatic and high strain rate forming, respectively. It was shown that dual phase steel sheets exhibit hyperplastic behavior when subject to EHF into a conical die and the micromechanisms of formability improvement were discussed (Samei et al., 2014, “Metallurgical Investigations on Hyperplasticity in Dual Phase Steel Sheets,â€‌ ASME J. Manuf. Sci. Eng. (in press)). In this paper, mechanisms of failure in dual phase steels formed under quasistatic and EHF conditions are discussed. For this purpose, the nucleation, growth, and volume fraction of voids were studied. Also, fractography was carried out to understand the different types of fractures in the three grades of dual phase steels. The main objective of this work was to determine how failure was suppressed in the EHF specimens formed in the conical die compared to the Nakazima specimens. The impact of the sheet against the die was found to be the major reason for the delay in failure in the EHF specimens.