Measurement of differential hardening of pure titanium sheet based on multiaxial tube expansion testing and hole expansion forming simulation

Abstract

In order to elucidate the plastic deformation behavior, biaxial tensile stress tests using tubular specimens for multiaxial tube expansion method are carried out under seven liner stress paths. Contours of plastic work (CPW) at different levels of plastic work are measured. The range of the reference plastic strain, ε₀^p , applied to the material is ε₀^p d 0.17 . It is observed that the shape of CPW significantly change; this material shows strong DH. From the biaxial stress tests data, the applicability of anisotropic yield functions to the accurate prediction of the plastic deformation behavior is discussed. Furthermore, DH model which is based on Yld2000-2d yield function with exponent and material parameters changing as functions of ε₀^p is determined. Using these yield function, finite element analysis of the hole expansion forming process are conducted. It is found that the yield function which represent the material anisotropy and DH predict the direction of minimum thickness. But the magnitude of plastic strain is not correctly predicted. This would be attributed to the material modeling method in which the variation of the r-values with ε₀^p is note taken into account.