Experimental Investigation of Face-Core Debonding Crack Growth in Ships Sandwich Structures for Damage Identification

The sandwich material utilizes two different material properties for the faceplate and core layers, resulting in damage vulnerability. Face-core debonding is the fatal damage mode in sandwich structures. This damage mechanism can reduce the structure's integrity. In complex structures, debonding damage may not be visible by visual inspection, so it becomes propagated and causes structural failure. Debonding at the interface between the faceplates and polyurethane core may be caused by static or cyclic loading during structural operation. This experimental study investigated the mechanism of face-core debonding due to mode-II loading (sliding). Several End-Notch Flexure (ENF) beam specimens are fabricated for damage experiments under mode-II loading. The strain energy release rate is obtained to investigate the resistance against debonding crack growth at the interface of the faceplate and core. The resistance curve (R-curve) is plotted to depict the interface crack growth characteristic. The type of R-curve based on the results of this experiment is a rising R-curve, where the GII will continue to increase as the crack length increases indicating the energy required to extend cracks becomes greater. However, it shows a softening trend at the end of the loading phase, indicating that the material's resistance to crack growth has reached a plateau. This flattening occurs because the toughening mechanisms are exhausted; any further increase in the crack length results in a minimal or no increase in resistance. At this point, the crack growth may transition from stable to unstable.