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.