Experimental evaluation of the similarity in the interface fracture energy between PMMA/epoxy/PMMA and PMMA/epoxy joints

Abstract

In this investigation, a comparison of the interface fracture energy in the adhesive joints PMMA/PMMA bonded by epoxy and PMMA/epoxy is presented. The work focuses on the question of how similar is the fracture energy in these joints, including its dependence on the fracture mode mixity. Series of tests for Brazilian disk specimens subjected to compressive loading were carried out in order to obtain the fracture energy as a function of the fracture mode mixity. A careful observation with a high-speed camera of the steps of crack growth allowed to determine the validity of each sample and explore the different forms of failure. The present results show a high level of similarity in the fracture energy prediction for the two configurations, having the largest differences for the largest fracture mode-mixity angles. The similarity between the results for the two configurations is useful to simplify some analyzes in practical applications. Nonlinear finite element models, including plastic effects, show that different process zones in the two configurations could be the source of the small discrepancy found between the two configurations in the experimental results. These results pinpoint the relevance of the constraining effect of the thin adhesive layer on the process zone.