Mode I Interlaminar Fracture Toughness of Composites Using Slender Double Cantilevered Beam Specimens

Abstract

The use of slender double cantilever beam specimens for measuring the mode I in terlaminar fracture toughness was critically evaluated. Experiments were performed with unidirectional composites to judge the validity of using data from multiple crack jumps on a single specimen. Three approaches for calculating the strain energy release rate were compared. These included an energy rate determination of the JI-integral, a compliance calibration procedure and an analytical equation based on linear beam bending. The fracture toughness was overestimated by the latter two approaches. Per manent deflection was seen to accumulate in the arms of the double cantilever beam specimens as the cracked surface area increased. This component of deflection must be accounted for in all forms of analysis with DCB specimens.