G.R Ahmadzadeh - PhD student
A Shirazi - PhD student
A Varvani-Farahani - Professor, Department of Mechanical Engineering, Ryerson University,۵۰ Victoria Street, Toronto Ontario M۵BK۳, Canada

This paper presents a stiffness-based model to characterize the progressive fatigue damage in quasi-isotropic carbon fiber reinforced polymer (CFRP) composite laminate with [90/±45/0]s stacking sequences. The proposed damage model was constructed based on (i) cracking mechanism and damage progress in matrix (Region I), matrix-fiber interface (Region II) and fiber (Region III) and (ii) corresponding stiffness reduction of unidirectional 90°, 0° and ±45° angle-ply laminates as the number of cycles progresses. The proposed method has been further extended in present study to predict the damage of the [90/±45/0]s laminate using the weighting factors distinguishing the damage accumulation at the constituents plies. The weighting factor η90, η0 and η45 are obtained based on the damage mechanisms within the plies of 90°, 0° and ±45° respectively of the laminate. Damage model has been verified using CFRP [90/±45/0]s laminates test coupons made of graphite/epoxy 3501-6/AS4 laminate. It has been observed that experimental fatigue damage data of [90/±45/0]s composite laminates fall between the predicted damage curves of 0° ply, ±45° ply, 90° and 0/±45° ply over fatigue cycles under different stress levels. Predicted damage results for CFRP [90/±45/0]s laminates showed good agreement with experimental data.

Fatigue damage, stiffness degradation, CFRP [90/±45/0]s composite layup, matrix cracking