An Interlaminar Fracture Toughness Test in Mode I for Composite Laminates

Abstract

Linear elastic fracture mechanics is applied to estimation of interlaminar fracture toughness of carbon fiber reinforced composite laminates. Energy release rate approach to double cantilever beam (DCB) specimen is investigated analytically and experimentally. Configurations of specimen and loading system are considered and a new DCB specimen is proposed. Deformation and energy release rate of the DCB specimen is analyzed numerically by using finite element method, and polynomial expressions of compliance and energy release rate, as the functions of crack length, are obtained. Compliance method based on the analysis is successfully applied to mode I interlaminar fracture toughness test. Unidirectionally reinforced carbon/epoxy laminates used for the test. Initial interlaminar crack is introduced mechanically and effect of crack width is examined. The applicability of analytical equations of compliance is examined experimentally. Agreement of the analytical and the experimental results are excellent. The critical energy release rate in mode I crack propagation is measured automatically by using the compliance method. The results are compared with those of the conventional method. The accuracy is improved remarkably.