Mechanical APDL Structural Analysis Guide

11.3.2.1. Using VCCT for Energy-Release Rat e Calculation

VCCT is based on the assumption that the energy needed to separat e a surface is the same as the energy
needed to close the same surface. The implementation described here uses the modified crack-closure
method (a VCCT-based method) and assumes further that stress states around the crack tip do not
change significantly when the crack grows by a small amount (∆a).

11.3.2.1.1. 2-D Crack Geometry

For 2-D crack geometry with a low-order element mesh, the energy-release rat e is defined as:

I= − ∆ Y∆

= − ∆ X∆

where:

GI and GII = mode I and II energy-release rate, respectively

∆u and ∆v = relative displacement between the top and bottom nodes of the crack face in

local coordinates x and y, respectively

Rx and Ry = reaction forces at the crack-tip node

∆a = crack extension, as shown in the following figure:

Figure 11.9: 2-D Crack Geometry Schematic

11.3.2.1.2. 3-D Crack Geometry

For 3-D crack geometry with a low-order element mesh, the energy-release rat e is defined as:

= − ∆ ∆

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Numerical Evaluation of Fracture Mechanics Parameters