Critical review on the assessment of fatigue and fracture in composite materials and structures

• Fatigue phenomena in composite structures as structural and damage phenomena.
• Similitude conditions for predicting fatigue in composites with respect to geometry and loading conditions.
• Selection of similitude parameters as damage driving forces.
• Definition of two parameter models based on fractographic observations.

This paper provides a critical review of common approaches to assess fatigue and fracture in composite materials and structures. It explains how fatigue in composite materials and structures should be understood based on the observed fatigue phenomena and mechanisms. In relation to these phenomena, the selection of proper similitude conditions for predictions is discussed and it is explained how mechanistic models can be developed that describe fatigue damage growth in its sequence from first initiation to final failure. An explanation is given for the fact that these mechanistic damage growth approaches have not yet led to suitable prediction models. In addition, this paper illustrates that in-depth understanding of individual damage mechanics may pave the road towards further material optimization with respect to fatigue and durability.