The effects of stacking sequence and specimen geometry on fracture toughness were investigated for quasi-isotropic graphite/epoxy laminates. Two different stacking sequences were used. One stacking sequence was $(\pm45/0/90)_s$, which produces large interlaminar tensile stresses along straight free edges of a tensile specimen, and the second was $(90/0/\pm45)_s$, which produces compression at the same free edges. Regardless of stacking sequences, same values of characteristic lengths from average stress criterion or point stress criterion could be obtained by modifying experimental data. Specimen geometry included double edge cracks and center cracks in conjunction with both stacking sequences. Applicability of average stress criterion and point stress criterion to double edge cracks were examined experimentally, and experimental data of fracture toughness for double edge cracks were fitted to Weibull distribution. The predictability of COD (crack opening displacement) for double edge cracked quasi-isotropic composite laminates was investigated by utilizing COD equation for isotropic materials.
