Fracture Toughness of Adhesive Joints

Abstract

To define the influence of the processing variables on the resistance of epoxy joints to brittle crack extension during short loading times, the fracture toughness, ℊ_ic, of the joints was measured as a function of the following variables: 1. Hardener type (TEPA vs. HHPA) 2. Ratio of hardener to resin content 3. Post-cure temperature and 4. Joint geometry (thickness and width) It was found that the toughness of the TEPA hardened system varied by a factor of four-to-one as the ratio of hardener to resin content and post-cure temperature varied within what might be considered reasonable limits for manufacturing. The toughness of the HHPA hardened system varied only over the middle half of this same range. For both systems, toughness increased with joint thickness over the range of 2 to 50 mils.