Mode I Stress Intensity Factors for Symmetrically-Cracked Orthotropic Strips

The effects of material anisotropy on the stress intensity factor are investigated numerically for both double-edge-cracked and center-cracked orthotropic tensile strips. The material properties employed correspond to homogeneous material models of mid-plane symmetric fiber composite laminates of varying ply orientation and ply properties.

The effects of anisotropy are found to be dependent on both specimen geometry and material properties. Complete decoupling of these geometric and material influences does not appear possible. However, the principal geometric parameter seems to be the distance from the crack tip to the free edge of the specimen; the effects of material properties appear to correlate with the in-plane elastic shear modulus. It is suggested that anisotropic effects can be sufficiently controlled, by means of specimen geometry, to justify the use of the known isotropic stress intensity factor as a reasonable (and usually conservative) estimate of the anisotropic value in most materials.