The Three-Point Bend Test for Adhesive Joints

Unless a large amount of degradation has occurred in the interfacial region of a metal-to-metal adhesive bond, the T-peel and wedge opening test usually provide only mode I information on the bulk adhesive. The single-lap shear test shows primarily mixed-mode failure. However, the thickness of the adherend must be carefully considered in order not to have a large amount of mode I failure. When these three tests failed consistently to find defects that were incorporated into the interfacial region of test specimens, the three-point bend test geometry was evaluated. This initial study, utilizing the short beam shear test geometry, has shown that several pieces of information may be obtained from the experimental data. The initial portion of the test curve appears quite linear and the slope of the curve seems directly related to the bulk properties of the adhesive. The portion of the curve where a definitive failure occurs appears directly related to interfacial failure of the bonded joint.