13th International Conference on Fracture June 16–21, 2013, Beijing, China -9- r E eq r ∂ ∂ =− ε , (1) Thus, the maximum gradient is determined by: 0= ∂ ∂ θ rE and 0 2 2 ≤ ∂ ∂ θ rE , (2) According to this theory, the crack initiated and propagated process on the void material can be described correctly. 5. Discussion By means of the proposed theory, we can explain the new feature of the crack initiated and propagated in the fatigue test. Analyzing the equivalent strain decreasing from the outer edge point and the inner edge point in one hole (such as the left hole in the Fig.14 and 15) and along the path on the radial direction, it is obvious that the gradient of the equivalent strain decrease in the outer point is larger than that in the inner point, although the absolutely equivalent strain value in this two point is almost the same. It can be found that the inner part material between two holes has a larger elastic or plastic deformation than the other part of material. Here, the larger plastic deformation releases large part of the peak stress near the inner point, and postpones the crack initiated in this point. As the first initiated crack startes from the outer point and propagates to some length, the gradient of the equivalent strain decreased, while the deformation around the inner edge point increased to induce the gradient of the equivalent strain decreased in this point increased till larger than that in the outer propagated crack tip. Thus the outer propagated crack stops, and the inner edge crack initiates and propagates. Thereby, the two inner cracks links and the sample separates. 1 A CB D E A A B A B A B A C B A C A B A C B D A C B C E D A A B D C A B E F C D A B GE F C G A D AB E C F MN MX A=.100194 B=.297808 C=.495422 D=.693036 E=.89065 F=1.088 G=1.286 H=1.483 I=1.681 NODAL SOLUTION STEP=1 SUB =16 TIME=1 EPTOEQV (AVG) DMX =11.719 SMN =.001387 SMX =1.78 Fig.15, the equivalent strain distribution around the hole for α=15.
RkJQdWJsaXNoZXIy MjM0NDE=