Fatigue damage assessment of unidirectional GRP and CFRP composites

The present thesis has developed an energy-based critical plane fatigue damage parameter to assess the fatigue damage of unidirectional GRP and CFRP composites. The proposed model is based on the physics and the mechanism of fatigue cracking within three damage regions of the matrix (I), the fiber-matrix interface (II), and the fiber (III) in unidirectional GRP and CFRP composites as the number of cycles progresses. The model involved the shear and normal energies calculated from stress and strain components acting on (i) a relatively ductile matrix, (ii) the matrix-fiber interface, and (iii) the unidrectional brittle fibers. For the regions III, and I the cracking is dominantly based on the maximum shear stress and the maximum normal principal stress, respectively and the fatigure damage was assessed based on the Varvani-Farahani damage approach. For region II, the damage process along the matrix-fiber interface was evaluated based on the Plumtree-Cheng approach.

The proposed fatigue damage analysis has addressed the cracking and damage progress within three regions over the life of unidirectional GRP and CFRP composites and showed a good capability in unifying the experimentally obtained fatigue lives with various off-axis angles and stress ratios as compared with other well-known damage criteria available in the literature.