Composites also have an advantage from the point of view of crack detection. The diagram shows how cracks grow in different materials as a function of fatigue exposure time, the threshold crack size for detection, and the critical crack size for fast fracture. It is seen that composites can have larger cracks before the rapid fracture crack size is reached, and that the crack growth past the inspection detection threshold is slower.

Composites are said to have a 'soft' failure mode with respect to fatigue damage.