High-speed observation of bending fracture process of carbon fiber reinforced plastic composite/Nomex™ honeycomb sandwich panel

Failure mechanism of sandwich panels is very complicated. The objective of this study is to demonstrate the usefulness of high-speed observation to elucidate the failure mechanism of sandwich panels. Failure processes of carbon fiber reinforced plastic composite/Nomex™ honeycomb sandwich panels were observed using two synchronized high-speed cameras with an 8 µs frame rate. The sandwich panel was subjected to a four-point bending load in accordance with ASTM-D7249. Digital image correlation was also adopted for measuring the surface strain. Results show fracture initiation: (1) local (intra-cell or wrinkling) buckling of the face sheet at the edge (Type I and III), or (2) local buckling (intra-cell or wrinkling) of the face sheet at the middle of the specimen (Type II). Following local buckling of the face sheet, debonding between the face sheet and the honeycomb core occurred within 10–20 µs. Subsequently, crack propagation of the face sheet occurred, leading to final failure of the sandwich panel. It was about 150–200 µs from the local buckling of face sheet to the final failure of sandwich panel. Results demonstrated that high-speed observations are effective to elucidate failure mechanisms of the sandwich panel subjected to a bending load.