The effect of fiber orientation and stress ratio on the crack growth behavior of fiber metal laminates (FMLs)

The crack growth behavior of fiber metal laminates (FMLs) with fiber orientations of 90°/0° and 45°/45° to load direction was investigated with varying stress ratios of the cyclic constant load. The study shows that crack growth behavior depends on the conditions of the cyclic load and the orientation of the fiberglass orientation. A higher stress ratio of the cyclic constant load causes fatigue life to decrease, and is associated with stress concentration just in front of the crack tip. The stress concentration in the FMLs with 45°/45° fiberglass orientation is higher than that of 90°/0°, which means the fatigue life in the former is shorter. The bridging of the fiber-epoxy composite takes place when the stress ratio of the constant cyclic load is lower than 0.4, which also enhances fatigue life.