Damage initiation in polymer matrix composites under high-cycle fatigue loading – A question of definition or a material property?

• Evidence that fatigue damage initiation in composites is a material property.
• Normalization of fatigue data with static strength provides master curve.
• Master curve is independent of fiber type, specimen geometry and test setup.

Damage initiation in composites under high-cycle fatigue loading is often defined by the presence of a crack of detectable size. This article is intended to assess if damage initiation under cyclic loading can also be described in a more physical way. In order to achieve this, SN-curves for fatigue damage initiation are normalized by dividing the maximum stress per load cycle by the static strength. By presenting normalized fatigue damage initiation data, the influence of specimen geometry, test setup and fiber type can be eliminated. The normalized presentation of the experimental data suggests that fatigue damage initiation in composites subjected to high-cycle fatigue loading may indeed be a material property of the resin which can be described by a normalized SN-curve.