According to Eqs. (4) and (5), , , therefore, the value of and is the slope of the line in the and plot, respectively. The plots of relationships between and and and are shown in Fig. 4(a) and (b), respectively. Then the mean value of all slope rates in Fig. 4(a) is 1/ , thus the value is 5.712. The mean value of all slope rates in Fig. 4(b) is 1/ , and value is 0.061. Finally the stress multiplier could be calculated as =0.011.