How do you apply advanced fracture mechanics for complex aircraft structural configurations?

Advanced fracture mechanics for complex structures involves: 3D stress intensity factor solutions using weight function methods or FEM (VCCT, J-integral, interaction integral); Mixed-mode (I, II, III) fracture assessment using equivalent K or energy release rate; Elastic-plastic fracture (J-integral, CTOD) for ductile materials; Residual strength using R-curve analysis for stable crack growth; Multiple crack interaction effects; Part-through crack solutions; and Constraint effects (T-stress, Q-parameter) affecting transferability. Implementation requires: FEM with crack meshes, fatigue spectrum application using superposition principles, and correlation with fracture testing. Critical for complex fittings, lugs, and thick-section structures.