Characterisation of rate-dependent mode-II adhesive debonding based on a novel load–displacement curve parametrisation

Abstract

In this study, the mode-II rate dependence of an epoxy adhesive is investigated using end-notched flexure (ENF) tests conducted over loading speeds ranging from 0.1 to 5000 mm/min. To address the pronounced scatter typically observed in mode-II debonding tests, as well as the lack of a procedure for evaluation of the average load–displacement curve, a novel curve-parametrisation and statistical averaging framework is proposed. The load–displacement curves are represented using a set of parameters, enabling the construction of representative average curves for each loading speed and the quantification of parameter variability. The method allows the rate-dependent behaviour to be assessed over the entire load–displacement domain, rather than being restricted to the region typically used for the evaluation of the fracture resistance. The representative values of the critical energy release rate evaluated for each loading speed using the proposed method are in good agreement with the mean values obtained by a conventional specimen-by-specimen analysis. The results show a monotonic increase in mode-II fracture resistance with increasing loading speed, followed by a plateau at higher speeds. However, the proposed method reveals a continued monotonic evolution of the global response with loading speed, indicating that rate-dependent effects extend beyond the critical energy release rate alone. These findings demonstrate that the proposed parametrisation framework enables statistically robust characterisation of rate-dependent mode-II adhesive debonding and improved constitutive modelling.