Calculation Model for r-value of Commercially Pure Titanium Sheet

Abstract

A calculation model for predicting the plastic strain ratio (r-value) of commercially pure titanium sheet with hcp structure is developed. It is assumed that the sheet deforms only by basal, prism and pyramidal slips and not by twinning at the early stage of tension test. From consideration of the relative values of the critical resolved shear stresses (CRSS) for the three slip planes which are also affected by the interstitial impurity, in this model the CRSS is expressed by the critical Schmid factor of each slip plane. According to this model, the effects of slip planes and interstitial elements on the r-values can be evaluated.
The r-values of three kinds of titanium sheets, which had different amounts of oxygen, were measured and compared with the calculated r-values from this model. The observed and calculated values showed a good agreement.