The calculations are based on the relative opening, sliding and tearing displacements derived from an orthogonal set of axes at each crack front node, as shown at one crack position in the image for a symmetry model. These relative displacements are used to calculate the stress intensity factors using equations derived from the Westergaard solution for the stress field around a crack tip. The equations that are used are valid for linear elastic isotropic materials.

The relative opening displacement is also an important quantity in determining a local "open" or "closed" status for a crack front node. This status has implications for crack growth integration.

If the analysis also includes a j-integral evaluation, a conversion of the j-integral to mode I stress intensity factor is also reported. This is strictly only valid if there are no mode II or mode III effects present.

For Abaqus and Ansys interfaces the interaction integral calculations for stress intensity factors may also be requested.

The following may be calculated:

• Ki, Kii and Kiii from nodal displacements using crack tip opening displacements (CTOD) - only valid for linear elastic isotropic materials
• Ki, Kii and Kiii from integration integral calculations (Abaqus and Ansys)
• equivalent energy release rate from displacement-based or interaction integral Ki, Kii and Kiii
• Ki from j-integral energy release rate (mode I conversion)
• relative opening displacements to define a proper "open" or "closed" status at crack front and crack face nodes
• the local crack growth direction from the local maximum energy release rate
• the local crack growth direction from the stress intensity factors.