Determination of Plastic Strain Ratio r-value of Metallic Materials

Based on ISO 10113:2006and GB/T 5027-2007,analyzing the plastic strain ratio r-value of non-homogeneous plastic strain materials should use linear regression method,and the regression line fitted must bethrough the origin as the boundary condition.In this paper the r-values of homogeneous plastic strain material andnon-homogeneous plastic strain material were calculated by three different methods including single strain pairsmethod,linear regression method with the regression line through the origin(set intercept being 0)and conventionallinear regression method(dont set any boundary condition),and comparisons of these three methods were done.Atthe same time,the rationality of setting boundary condition for linear regression method was discussed.The resultsshow single strain pairs method,linear regression method with the regression line through the origin andconventional linear regression method all could be used to analyze the r-value accurately for homogeneous plasticstrain materials,but for non-homogeneous plastic strain materials,the r-value could only be analyzed by usingconventional linear regression method,and the single strain pairs method and linear regression method with theregression line through the origin could not be used.