Study on the Effects of Face-Sheet Thickness on the Impact Response and Residual Compressive Strength of Composite Foam Sandwich Panels

To investigate the effects of face sheet thickness on the impact resistance and residual compressive strength of composite foam sandwich panels, carbon fiber/PET foam specimens with face sheet thicknesses of 0.9 mm, 1.8 mm, and 2.7 mm were prepared. Drop-weight impact tests and subsequent compression after impact (CAI) tests were conducted at four impact energy levels: 5, 15, 25, and 35 J. The results indicated that face sheet thickness significantly influenced the impact response and damage modes, with thicker face sheets exhibiting superior impact resistance. Impact-induced damage reduced the residual compressive strength, and the magnitude of this reduction increased with higher impact energy. Specifically, as the impact energy increased from 5 J to 35 J, the compressive strength of the 2.7 mm specimens decreased from 28.25 MPa to 21.19 MPa. Furthermore, a model mapping the normalized residual compressive strength to impact energy was established. The critical damage threshold energies (E_th) for the three thicknesses were identified as 0.160 J, 1.433 J, and 2.465 J, respectively, indicating that increased face sheet thickness enhances structural damage tolerance. Finally, by introducing a thickness correction term K(t), a prediction model for normalized residual compressive strength incorporating thickness effects was proposed, yielding a good fit with the experimental data. This study provides a theoretical basis for the design optimization and safety assessment of composite foam sandwich structures under impact loading conditions.