Fatigue behavior of impacted carbon fiber reinforced plastics

Impact events are common throughout an aircraft's lifespan, and the use of carbon fiber reinforced polymers (CFRP) in aircraft structures complicates their management. Unlike metals, CFRP dissipates energy through mechanisms such as delamination and fiber fractures, creating complex damage patterns that are difficult to detect and may propagate over time due to fatigue, threatening the structural integrity of the aircraft.

While compression after impact (CAI) fatigue has been widely studied, gaps remain in fully understanding this phenomenon. This study provides a comprehensive analysis of CAI fatigue. Ultrasound and digital image correlation (DIC) techniques revealed delamination growth within the impact cone, which later extended beyond the initial damage area, challenging prior assumptions about plateau phases of no-delamination growth. Further analysis of acoustic emission using a convolutional neural network allowed to classify the damage modes and study their progression under different load conditions. Distinct load levels were found to trigger different damage modes, leading to different phases of propagation.
Additionally, a surrogate impact damage fatigue test and a numerical modeling approach are presented to study some delamination growth patterns observed in CAI fatigue under simplified conditions.