Experimental Study on the Effects of Stacking Sequence on Low Velocity Impact and Quasi-Static Response of Foam Sandwich Composite Structures

In this study, investigation has been made on the impact response of twill weave carbon fabric/epoxy foam sandwich composites by subjecting two types of stacking sequences of a sandwich composite structure, SC1 and SC2 to quasi-static indentation and low velocity impact loading. SC1 and SC2 had a sequence of [0/90, +/- 45, Core, 0/90, +/- 45], [0/90, +/- 45, 0/90, +/- 45, 0/90, Core, 0/90, 0/90, 0/90, 0/90], respectively. This work was done by use of material testing system and an instrumented Drop-Weight Machine (CEAST 9350 drop tower). Foam sandwich composite structures are mainly used in making an Engine Hood. The analysis was done with increase of impact energy on both types of stacking sequences, until complete perforation of the specimens at 25 Joule impact energy occurs. The failure processes of the damaged specimens under the three different impact energies (5 J, 15 J, and 25 J) were evaluated by comparing load-displacement curves. Images of damaged samples were taken from both impacted side and non-impacted side and compared for all impact energies. Cross-sections of damaged specimens were also inspected visually and discussed. The load-displacement curves were obtained to characterize the failure mechanisms in the face sheets and core. Failure modes were also studied by sectioning the samples at the impact location and observed under an optical microscope. The primary damage mode was found due to the fiber fracture, delamination, matrix crack, and foam crack.