Investigating apparent plateau phases in fatigue after impact damage growth in CFRP with ultrasound scan and acoustic emissions

In previous literature, a plateau phase in fatigue growth of impact delamination projected area in CFRP was found. Explaining this plateau phase still represents a knowledge gap. In the present work, echo-pulse and through thickness transmission ultrasonic scan inspections were combined with acoustic emission monitoring to explain this plateau phase. Before the onset of growth outside of projected area, growth of delamination in the central impact cone and growth of smaller delamination was observed. Low-frequency acoustic emissions localized in the impact damage were recorded even before any type of growth was measured. The provided evidence suggests that an actual plateau phase may not exist if all the damage mechanisms are properly considered.