When setting up a C*-integral calculation, consider the following hints and recommendations:
The recommended element type for 3-D fracture models along the crack tip is the 3-D 20-node structural solid (brick) element SOLID186.
A finer sweep mesh (larger value specified for Crack Front Division in Semi-Elliptical Crack) along the crack front yields more accurate results.
When contour results begin with the first ring of elements around crack tip nodes (Contour 1 in Figure 44.15: C* - Integral along the Crack Front - Rectangular Block and Figure 44.19: C* Integral Values Along the Crack Front - X-Joint Pipe), the first contour result is discarded. In such cases, experience has shown that the first contour it is less accurate than the other contours due to highly concentrated local deformation.
The C*-integral could be path-independent only when steady-state creep deformation dominates the integration domain around the crack tip.