Fig. The influence of critical plastic strain on the load-displacement curve for double notched specimen
5.7 Compact tension (CT) specimen
Finally, the crack initiation and propagation for a CT specimen have been investigated. The geometry and boundary conditions are shown in Table 3-VI. The specimen contains a horizontal notch at its mid-height, and load is applied by a top pin which is displaced vertically, whereas the lower pin is fixed.
The material parameters are those of Material II in Table 1. The mesh comprises 14722 quadrilateral elements with refinement in the areas where the crack is expected to form. In this test, the \(q\) parameter does not significantly influence the crack path, the experimentally observed crack pattern being well captured for both \(q\ =\ 1\) and\(q\ =\ 0.5\).
The crack pattern results are shown in Fig.13. It can be observed a horizontal crack propagates inward from the notch tip. The phase-field failure simulation based on the proposed model indicates that a length scale of the specimen shows slight differences in the load-displacement curve. As is well known from the curve, the small length scale leads to more fracture-resistant than the large ones.
Fig.12 shows the measured load vs. crack extension behavior for CT specimens evaluated in this study. The general shape of these curves consists of a stable crack growth region characterized by increasing load during crack extension followed by an unstable crack growth region characterized by decreasing load during crack extension. The maximum fracture load for each test defines the transition from stable to unstable crack extension. Finally, the rather smooth drops in loading at the initiation of fracture for the cases that ignore the material weakening.