극박 순 타이타늄 판재의 성형한계선도 평가를 위한 실험적 연구

Abstract

In this work, the forming limit diagram (FLD) of a 0.1 mm commercially pure (CP) titanium sheet, developed for fuel cell bipolar plate applications, was experimentally determined. Currently, no standard method exists for determining the FLD of such thin sheets. For instance, the standard method, ISO 12004-2, which is used to determine the FLD of metallic sheets, applies only to thicknesses ranging from 0.3 to 4 mm. Despite this limitation, the Nakajima and Marciniak test methods, as outlined in ISO 12004-2, were employed. Due to the strong anisotropy of the CP titanium sheet, achieving strain path from plane strain tension to biaxial tension proved challenging with the standard specimen designs. To address this, a new specimen shape was designed and tested. Using the newly designed samples, the FLDs of the investigated material were successfully measured with both test methods. However, differences in the strain paths were observed between the two methods, particularly when using the circular sample designed for the equi-biaxial strain path. By comparing the results from both methods, this study suggests a more suitable approach for determining the FLD of ultra-thin CP titanium sheets.