Low-velocity impact damage and compression after impact behavior of CF/PEEK thermoplastic composite laminates

Impact resistance and damage tolerance are of great significance in the design of composite structures. This study researched the damage and failure mechanism of carbon fiber reinforced poly-ether-ether-ketone (CF/PEEK) composite laminates under the low-velocity impact (LVI) and compression after impact (CAI) loading conditions. The test included four impact energy levels (15, 30, 45, and 60 J) and compared the effect of two different stacking sequences ([0°/90°]_8S and [0°/45°/90°/−45°]_4S) on performance. The results shown that the peak impact force of the two different stacking sequences increased from 7.8 kN/8.3 kN–11.4 kN/13.7 kN, and the CAI strength decreased from 370.5 MPa/419.3 MPa to 212.8 MPa/232.5 MPa, respectively. Nondestructive testing of low-velocity impact specimens by ultrasonic C-Scan was employed to investigate structural damage. Digital image correlation (DIC) was employed to perform full-field displacement measurements for the CAI experiment. The cross-section of typical specimen was observed using a scanning electron microscope (SEM) to determine the failure mode of the specimen. In addition, a 3D damage model based on continuum damage mechanics was established, with the consideration of the interlaminar delamination damage and intralaminar damage. Compared with the experimental results, the errors of the numerical simulation of the peak impact force, impact energy absorption, and CAI strength are 3.8%–14.8%, 3.7%–6.9%, and 2.2%–6.7%, respectively, which verifies the validity and rationality of the model. Furthermore, the numerical model and interpolation function were used to predict the ultimate residual strength.