Abstract: Based on the experimental data,it was clarified that the plastic strain ratio R-value is not equal to Hill's r-value for Ti sheet.From the non-quadratic orthotropic yield function pro- posed recently by the author,an optimal expression between yield stress and r-value for Ti sheet was developed on overall investigation.The suitable value of exponent in the function seems to be 6—8.Thus,an equation was suggested to estimate strength for the pressure vessel made of Ti sheet.

Key words: Ti sheet, yield stress, r-value, anisotropy