13th International Conference on Fracture June 16–21, 2013, Beijing, China -4- Discussion of the results The results of distribution of the SIF and the T-stress along the crack front for different mixed mode loading conditions are summarized in Fig. 2 and 3. To study the effect of specimen thickness on Tzz-stress, the compressive load was adjusted so that the Txx-stress was remained approximately constant at variation of the specimen thickness (b= 0,2; 0,4; 0,8 and 1,6) at constant l=1/3 (for the corresponding values of mixity parameter Me). The increase of the specimen thickness is 8 times greatly reduces (in absolute value) the Tzz-stress (up to 75% at Me=0,25), whereas the value of Txx is virtually unchanged (Table 2). The predicted results are consistent with the data of numerical calculations [6]. Thus, magnitudes of the Tzz- stress have significant correlation with thickness of the specimen and allows taking into account the level of the out-of-constraint which should be included into assessment of the fracture toughness of full-scale structures. Table 2. The effect of thickness on the SIF and T-stresses for Me=0,25 b KI, MPa·m0,5 KII, MPa·m0,5 Txx, MPa Tzz, MPa 0,2 0,105 0,252 -2,691 -0,309 0,4 0,104 0,255 -2,681 -0,206 0,8 0,099 0,254 -2,647 -0,121 1,6 0,087 0,246 -2,581 -0,079 To reflect mixed mode loading conditions, an effective SIF (Keff) is introduced into consideration as follows 2 2 II I eff K K K = + (6) There are dependence of Keff on Txx and Tzz in the middle plane of the crack front (s=0) for varied parameters Me at different thickness (b=0,2; 0,4; 0,8; 1,6) of the specimen and constant value of l=1/3 ( Fig. 2 and 3).
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