Prediction of Forming Limit Curve for CP-Ti Sheet Using Equivalent Plastic Work–dependent Evolving Parameters

Commercial Pure-Titanium (CP-Ti) sheet is an attractive material in various industries, particularly automotive industry for hydrogen fuel cell bipolar plates, due to its light weight, high strength, and excellent formability. However, it is difficult to manufacture products due to strong anisotropy arising from hexagonal close-packed (HCP) crystal structure. Therefore, various plasticity theories and constitutive models have been developed to describe them and evaluate the formabilities before mass production. Recently, the prediction accuracy for the strong anisotropic behavior of CP-Ti sheet has been improved by incorporating equivalent plastic work-based evolutionary parameters into the yield function. However, research that theoretically analyzes the prediction of the forming limit curve (FLC) for materials using these advanced constitutive models is limited. In this study, the FLC was predicted using Hora’s modified maximum force criterion and compared with experimental results measured from hemispherical punch stretching test. For the FLC prediction, Swift, Voce, and LSV were applied as the hardening models, and the equivalent plastic work-dependent Hill48 yield function. As a result, the LSV hardening model most accurately predicted the $$\:{\varvec{F}\varvec{L}\varvec{C}}_{0}$$ . Furthermore, it was confirmed that the proposed equivalent plastic work-based evolutionary parameters affected the FLC prediction results by rotating the yield locus.