Stretchability of Commercially Pure Titanium Thin Sheet

Stretchability of the commercially pure titanium thin sheet which is used for plate type heat exchanger was determined in comparison with the tensile properties. In stretch forming the strain hardenability in the transverse direction, in which the maximum principal strain is oriented to the transverse direction, is greater than that in the longitudinal direction, while in uniaxial tension the strain hardenability is much smaller in the transverse direction than that in the longitudinal direction. Thus, the stretchability is controlled by the poorer ductility resulting from the smaller strain hardenability in stretch forming in the longitudinal direction. In the longitudinal direction the strain hardenability increases with increasing grain size in both uniaxial tension and stretch forming. Therefore, the stretchability is improved since the longitudinal ductility in stretch forming increases with increasing grain size. The behavior of strain hardening is satisfactorily explained by the amount of the twins produced during plastic deformation. Namely, higher density of deformation twin produced in both longitudinal uniaxial tension and stretch forming in the transverse direction results in greater strain hardenability. Moreover, the density of twin produced in both deformation modes increases with increasing grain size in the longitudinal direction.