Effect of reinforcement geometry on stress intensity factor calibrations in composites

Stress intensity factors, for loaded cracked composites of epoxy resin reinforced with E-glass fibres, were determined by employing an experimental compliance procedure. The results indicate that the stress intensity factors are significantly affected by the reinforcement geometry. To extend the applicability of the stress intensity factor to inhomogeneous composite materials, it is proposed that the effect of reinforcement be taken into account in the form: K = f (σ, c, g) where σ is the far field stress, c is the crack depth, and g is a function of the reinforcement geometry. Consequently, the Srawley-Brown K calibration derived for homogeneous materials cannot be used for composites. Instead, procedures, such as the experimental compliance calibration presented in this paper, that account for the effect of reinforcement geometry, should be utilized.