13th International Conference on Fracture June 16–21, 2013, Beijing, China -4- area is observed prior to commencement of fracture. In the figure, we observe the maximum initial stress appeared in the notch tip zone, and this will affect the fracture behavior during the DWTT process. Fig. 3 Equivalent stress distribution and detail around the notch (MPa) Fig.4 shows the equivalent stress distribution sequence during crack propagation (step 2). The equivalent stress is a three-dimensional stress calculated by Eq.(2). A maximum stress of 813 MPa is found at the notch tip and at the loading point, due to high stress concentration at these places. The stress value in the central area between the notch tip and the loading point is relatively small. A ‘butterfly-wing’ stress distribution is observed at the crack tip and at the loading point. The stress distribution is almost symmetrical about the loading line. As the crack propagates, the maximum stress distribution extends along the loading line till the specimen fractures. (2) Where Sij are the components of the stress deviator tensor. Fig.4 Equivalent stress distribution in DWTT sample (MPa)
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