With the stress field calculated along the characteristic curve and the FWC factor applied to the stress field, the Yamada-Sun failure criterion is applied. The failure criterion is shown in Eq. 35, where f is the failure index, X is the normal strength of the laminate, and S is the shear strength of the laminate [48].
The failure criterion is evaluated along the characteristic curve where the location of the maximum failure index θf determines the predicted mode of failure in the three regions. This can be seen in the image below, where the three angular regions are defined in Eqs 36-38 [44,47].
Currently, mixed mode failure is not considered in the analysis. If the maximum failure index falls outside of the defined failure mode regions, the region closest to the location of maximum failure index is used as the failure mode.