13th International Conference on Fracture June 16–21, 2013, Beijing, China -6- Longitudinal axis -14 -12 -10 -8 -6 -4 -2 0 10 12 14 16 18 20 22 z (mm) y (mm) Simulation MTS MSS Point B Point A notch not follow the route estimated by either MTS criterion or MSS criterion. A path between the prediction of MTS and MSS criteria seems more reasonable compared with the experiment results. From point B, the simulated crack path seems to be controlled by MSS criterion, a negligible deviation can be found in Figure 5(a). In the contrary, large divergence is shown for the crack path estimated by MTS criterion. Based on the LEFM analysis, MTS criterion is valid in tension mode fracture and MSS criterion is used in shear mode problem, both of these two criteria are supported by a large quantity of corresponding experiments. The simulated crack path from point A to point B which keeps the same trend with the experimental result between tensile mode and shear mode is defined as the so called transition mode fracture [10]. Comparing to common investigated tension mode and shear mode, the transition mode is an occasional situation, appearing under very complex and dynamic loading, for instance for the present cyclic non-proportional mixed mode loading. Longitudinal axis 0 2 4 6 8 10 12 -22 -20 -18 -16 -14 -12 -10 z (mm) y (mm) Simulation MTS MSS Point A Point B notch Figure 5. Crack growth path of (a) specimen A7, (b) specimen A8 4.2. Crack propagation behavior of specimen A8 Figure 5(b) shows the propagation crack path ③ for specimen A8. The symbols for different crack growth paths are defined as the same for specimen A7. The crack path starting from the notch root to point A complied perfectly with the prediction of MTS criterion. Beginning with point A, the crack path estimated by MTS criterion propagated almost along with the total previous crack path angle with no obvious transforming for the direction of crack extension. When the MSS criterion predicted crack growth path is contrasted with the MTS one from point A, the difference is very apparent as shown with the triangle diagram in Figure 5(b). The MSS path displayed a sharp deflection with the previous crack path direction and extended nearly in an opposite orientation, which is upward compared to the previous crack path. Obviously, these two crack growth paths do not conform to the experiment result. A path between the prediction of MTS criterion and MSS criterion gradually routed the crack to grow perpendicularly to the longitudinal axial. A transition fracture mode occurred in this specimen. As well as specimen A7, the transition fracture mode is followed by a shear fracture dominant crack path from point B. The MSS criterion predicted crack path could be considered to be perpendicular to the longitudinal axial of specimen. As can be seen from Figure 3(b), in the experiment once the crack changed propagating direction normal to the longitudinal axial, the coplanar shear crack growth is persistent until to the final fracture. (a) (b)
RkJQdWJsaXNoZXIy MjM0NDE=