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Description
There are two common definitions of the Crack Tip Opening Displacement (CTOD):
1. The opening displacement of the original crack tip.
2. The displacement at the intersection of a 90° vertex with the crack flanks.
The crack tip opening displacement (CTOD) of a crack at the edge of a three-point bending specimen is shown below:
where CTODm is the measured crack tip opening displacement, usually near the edge of the specimen for ease of access, CTOD is the real crack tip opening displacement, a is the length of the crack, and b is the width of the rest of the specimen.
Please note that the figure is for illustration purpose only and not to scale. From simple geometry of two similar triangles:
where ?p is a dimensionless rotational factor used to locate the center of the hinge.
For simplicity, let's assume that the center of the hinge locates at the center of b, i.e. p?1/2. The CTOD then becomes
The above hinge model may not be accurate when the displacement is mostly elastic. A more accurate approach is to separate the CTOD into an elastic part and a plastic part:
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