Instability-Related Delamination Growth in Thermoset and Thermoplastic Composites

Mixed-mode crack propagation in compressively loaded thermoset and thermoplastic composite columns with an imbedded through-width delamination (ITWD) is investigated. Beam theory is used to analyze the geometrically nonlinear load-deformation relationship of the delaminated subregion. The beam-theory model incorporated the effects of elastic restraint at the ends of the delaminated subregion. The elastic restraint model (ERM), combined with existing finite-element modeling of the crack-tip region yields expressions for the Mode I and Mode II components of the strain energy release rate G_I and G_II to predict the critical load at the onset of delamination growth. Experimental data were generated for geometries yielding a wide range of G_I/G_II ratios at the onset of crack growth. A linear mixed-mode crack growth criterion (G_I/G_Ic + G_II/G_IIc = 1) in conjunction with the ERM provides good agreement between predicted and measured critical loads for both materials studied.