Microstructural Characterization of Fatigue Damage of CFRP in the Very High Cycle Fatigue Regime

Structural components in aircrafts made of carbon fiber reinforced polymers (CFRP) are often subjected to 108 and more loading cycles during their time in service. To obtain a comprehensive knowledge about the fatigue behavior of CFRP in the very high cycle fatigue (VHCF) regime and the corresponding failure mechanisms at loading cycles higher than 108, a new Ultrasonic Testing Facility for cyclic 3-point bending at 20 kHz has been developed. The system enables VHCF experiments up to 109 loading cycles in twelve days without unacceptable heating of the specimens. The investigated material is an aircraft qualified carbon fiber fabric reinforced polyphenylensulfide (CF-PPS). Constant load amplitude tests have been realized to characterize the fatigue behavior. Detailed light optical and SEM investigations have been performed in defined fatigue states and after failure or finally after reaching 109 cycles. Based on these results the failure mechanisms of CF-PPS in the VHCF regime were documented and analyzed.