Effect of Stacking Sequence on Damage Propagation and Failure Modes in Composite Laminates

The effect of stacking sequence on damage growth and failure modes in composite laminates is discussed. Tests were conducted on AS/3501-6 graphite/epoxy coupons with four different stacking sequences. All laminates had the same percentage of 0, 90, and ±45 degree plies. Constant amplitude fatigue tests were performed at R (minimum to maximum stress ratio) = −1.0 and −∞. The specimens were periodically taken out of the testing machine and subjected to nondestructive inspection using X-ray radiography with diiodobutane.

The results of nondestructive inspection indicate that the direction of damage propagation depends on the stacking sequence in the composite laminate. The damage may propagate predominantly along the loading direction or in a direction at some angle to the loading direction, depending on the stacking sequence. Interlaminar stress analysis of four laminates was performed to correlate the direction of damage propagation with the nature of interlaminar stresses.