A Study of Crack Growth in Sandwich Composite Beams

Abstract

The paper proposes models to track the face-core interfacial delamination growth and crack kinking into the sandwich core, respectively. The models consist in interposing a cohesive layer along a pre-existing delamination or an identified plane of crack propagation. The former, designated as CLD (cohesive layer delamination model) is investigated first in detail using an example of a restrained beam specimen. The Influence of the key parameters of the model, viz. the thickness of the cohesive layer and the strength and stiffness of the cohesive layer material, have been studied. It is found that the model is fairly robust and is not sensitive to changes in parameters other than the critical strain energy release rate. The second model is a highly simplified one, but it is nevertheless a comprehensive model which can track the crack path by identifying crack planes in various elements using a maximum tensile stress criterion. This is designated as CLDK model as it deal with delamination and crack kinking — whichever is the preferred mode of fracture. The models are constructed ensuring that the crack opening is controlled by the critical value of strain energy release rate in mode I fracture. Experimental results of two sandwich specimens, viz. bottom restrained beams with 0° and −10° tilt angle respectively were used for comparison. The results indicate that the both the models are able to capture the initiation and track the growth of the interfacial delamination. The CLDK model tracks the crack kinking into the core, and its subsequent return to the facesheet-core interface.