STEADY-STATE MECHANICS OF DELAMINATION CRACKING IN LAMINATED CERAMIC-MATRIX COMPOSITES

A fracture mechanics delamination cracking model has been developed for brittle-matrix composite laminates. The near-tip mechanics is discussed in the context of material orthotropy and composite material inhomogeneities. A fracture mechanics framework based on the near-tip energy release rate G and the associated phase angle psi has been adopted. In the case of steady-state delamination cracking in a prenotched cross-ply symmetric laminated beam, analytical expressions for the steady-state energy release rate, G(ss), have been obtained for the combined applied loading of an axial force and a bending moment. Parameter studies assessing the effects on G(ss) of load coupling, crack location, and lamination morphology which includes the total number of layers, layer thickness, and material properties are presented. Thus, composite homogenization criteria with respect to the total number of layers placed along the beam height can be obtained for a wide range of material selection. The associated phase angle psi at the delamination crack tip is discussed in the context of existing solutions. The analysis has been developed based on a theory for structural laminates. The delamination model can be used in conjunction with experimental data obtained from model geometries to extract the mixed-mode transverse composite fracture toughness. Thus, conditions for stable delamination crack growth can be established and design criteria based on toughness for composite laminates and composite fasteners can be obtained.