Experimental and numerical determination of mode II fracture toughness of woven composites verified through unidirectional composite test data

Due to the increase in prevalence of fibre-reinforced polymer matrix composites (FRPMC) in aircraft structures, the need for adaption of failure prediction tools such as fatigue spectra has become more pertinent. Fracture toughness is an important measure with regard to fatigue, while adequate techniques and an ASTM standard for unidirectional FRPMC exist, there are mixed opinions when investigating woven FRPMC. This study describes a three-dimensional finite element model developed to assist in determining the mode II interlaminar fracture toughness (G_IIc) of fibre-reinforced woven composites, validated by an experimental and numerical comparison of G_IIc determination for unidirectional FRPMC. Experimental testing mirroring the ASTM D7905 resulted in a measure of 1176 J m⁻² for the unidirectional specimen, while comparisons made with the literature achieved an average value of 1459.24 J m⁻² or the woven specimen. Three numerical methods were employed due to their prominence in the literature: displacement field, virtual crack closure techniques and the J integral. Both the J integral and the displacement field three-dimensional models produced satisfactory unidirectional G_IIc estimates of 1284 and 1116.8 J m⁻², respectively. Displacement field had a 5% uncertainty in G_IIc when compared with experimental results, while J integral had an approximately 8.5% uncertainty. Extending the analysis to the woven specimens, values of 1302.8 and 1465.3 J m⁻² were obtained from J integral and displacement field methods, respectively, both within 10% of the experimental values. Hence, numerically determined unidirectional G_IIc values were verified with experimental results, leading to the successful employment and extension to woven composites which displayed similar agreement.