Calculating a damage parameter and bridging stress from GIC delamination tests on fibre composites

In this paper, a number of experimental round-robin data sets obtained using the mode I double cantilever beam (DCB) specimen to evaluate GIC for fibre composite laminates have been reanalysed with a view to determining additional parameters to describe microcracking and damage in the composite arm, and the bridging stresses at the crack tip. The additional parameters are derived using the length correction term deduced from corrected beam theory. However, the reanalysis of the round-robin data revealed significant variations in this length correction term. It is argued here that these variations originate from errors in the measurement of crack length which can be either random or systematic. An alternative analysis scheme is proposed from which the crack lengths are calculated using the measured compliance and a pre-determined flexural modulus value. Such an approach yields considerable insight into the accuracy of the test method.