A fatigue damage parameter for life assessment of off-axis unidirectional GRP composites

The present study develops a fatigue damage parameter to assess the fatigue damage of unidirectional glass fiber reinforced plastic (GRP) composites. The proposed parameter is based on the physics and the mechanism of fatigue cracking within three damage regions of matrix (I), fiber-matrix interface (II), and fiber (III) in these materials as the number of cycles progresses. In region I, damage was initiated in the form of microcracks within the matrix. For region II, damage progress took place along the matrix-fiber interface leading to fiber fracture in region III. The proposed fatigue damage model successfully correlated fatigue lives of unidirectional GRP composites at various off-axis angles theta and stress ratios R as compared with other earlier developed fatigue parameters.