Fracture properties evaluation of structural adhesives using the dual actuator test frame and digital image correlation technique

This paper implements a dual actuator testing protocol to evaluate the fracture behavior of a toughened epoxy adhesive under mode I and mixed mode I+II loading conditions. Digital image correlation is used to monitor crack propagation and assess adherend and adhesive deformations. A good repeatability between the test results is observed for both failure modes (I and I+II). The constitutive law is obtained by evaluating the J-integral while measuring the crack tip opening displacement. Different mixed mode test strategies are developed in this work. First, an actuator load control protocol is implemented so as to propagate the crack under constant mixed mode I+II ratio and evaluate the fracture envelope of the studied adhesive, which turns out to be adequately described by the Gong-Benzeggagh failure criterion. A second strategy is proposed with a variable mixed mode ratio during the experiment for faster investigation. Using this technique, stable fracture energy values are recorded along the crack propagation path, thus leading to very fast and accurate results