Changes in dynamic mechanical behavior of CFRP laminates under multiple low energy impacts

Composite laminates used in aircraft structures are easily subjected to multiple impacts during their service period. The detailed analysis of impact responses could reflect the stiffness of composite structure. Nevertheless, the impact response of laminates with a large width-thickness ratio is quite different from that of ordinary laminates. The deflection could reach several times the thickness during the impact. The present paper performed an experimental study using drop weight equipment to investigate the changes in dynamic mechanical behavior of carbon fiber reinforced polymer(CFRP) laminates during multiple low energy impacts. Three kinds of impact energy levels of 5, 10 and 15J were applied for the single impact event. The specimens impacted at 5 and 10J were then subjected to subsequent impacts in order to explore the differences between single and multiple strikes with the same total impact energy. The global mechanical responses during each impact procedure were recorded and analyzed by the changes of impact force, contact time, peak energy moment, energy absorption and displacement after every single impact. Although the first strike had introduced damages into the plates, the peak force and maximum displacement increased unexpectedly rather than decreased during the second strike. Meanwhile, the damage was evaluated using ultrasonic C-scan and visual inspection. The results indicated that the multiple impacts did not produce as much damage as the first strike. Short matrix cracks were observed at the edge of the dent except for the single impact with 5J energy.