ANALYSIS OF THE PEEL TEST - PREDICTION OF ADHEREND PLASTIC DISSIPATION AND EXTRACTION OF FRACTURE ENERGY IN METAL-TO-METAL ADHESIVE JOINTS

The peel test has been widely used for the mechanical measurement of t he adhesion phenomenon. However the proportion of the energy input dis sipated plastically within the adherend is a major concern in analyzin g peel test data. This paper presents an analytical approach to predic t the adherend plastic dissipation in the peel test for metal-to-metal adhesive joints, thereby allowing the fracture energy to be extracted from the test data using an energy balance approach. Expressions are developed for the deflection of an elastic-plastic beam on an elastic foundation, which is then combined with known solutions for the deform ation of an elastic-plastic strip under large displacement. The model takes into account both the adhesive and adherend compliance effects o n the plastic dissipation. Numerical predictions of the model are pres ented to gain insight into the effects of adherend properties and peel angle on plastic dissipation in the peel test. It is demonstrated tha t experimental results with various adherend properties and peel angle s are consistent with the predictions of the model. An important concl usion is that for typical structural adhesives, the effects of plastic dissipation may be kept small by using a relatively low yield strengt h alloy with a thickness much smaller than the critical thickness at w hich the plastic dissipation effect is a maximum. The extraction of th e fracture energy from the test data is also discussed with regard to the mixed-mode nature of the peel test.