Experimental Study On The Damage Of CFRP Laminates Due To Low-velocity Impact

Carbon Fiber Reinforced Plastics(CFRP)have been widely used in a large range of domains especially in aeronautic and aerospace due to their excellent performances.However,due to their poor impact resistance,especially in the low-speed impact,the load-carrying capacity of CFRP laminates will be seriously weakened.Resulting in a certain degree of damage,such as matrix cracking,delamination and fiber fracture,the interaction between different forms of damage will further aggravate the damage of materials.The internal damage cannot be detected and repaired in time,which greatly affects the safety of the structure.In this paper,the experimental tested were performed to study the effects of impact energy on the damage of CFRP laminates,based on the optical full-field measurement method.The main works consist in:(1)A highly sensitive experimental platform for measuring the bending deformation of thin plates was set up.By using this platform,the slope,curvature and out-of-plane displacement fields of the CFRP laminates under a very low load in static were obtained.The reliability of this technique were validated by the comparison with that by numerical simulation.The elastic constants in flexion of CFRP laminates were simultaneously identified by using the virtual fields method.(2)The CFRP laminates of three different sequence orders subjected to different energy impact were tested using a free-falling drop tower testing device.Combining the primary damage modes,the damage pit depth of the laminates and the cracking length of the backside crack were inspected and analyzed.Based on the high-speed photographic technique,and the energy absorption efficiency of CFRP laminates under multiple impacts was analyzed.(3)The damage detection of CFPR laminates plates was carried out by using the optical full-field measurement technique and the infrared thermal imaging detection technique.Combined with the results of the two detection methods,the main damage modes and characteristics of different laminated laminates were obtained.It is considered that the main damage forms are the interlayer delamination,accompanied by matrix cracks and fiber breakage.The low energy impact damage of composites is mainly in the vicinity of the impact point,and the damage on the back surface of impact is often more grave than the front surface.Therefore,the damage inspection on structures should be focused on the impact point and the back surface.