Effects of the environment and curing on the strength of adhesive joints

Abstract

_—The influences of four parameters - pretreatment of the adherend, curing cycle, time before testing, and humidity _— on the strength of adhesively-bonded single lap joints were investigated for aluminium 2024-T3 adherend and modified epoxy FM73M adhesive. The importance of conditioning the aluminium surface prior to bonding was confirmed. Furthermore, the pretreatment should be attuned to the environmental conditions under which the joint will be used. We found that roughening the aluminium surface gave a poorer joint strength. Cooling joints in normal environmental conditions after the curing procedure gave satisfactory strengths if a relaxation period of 30 days was allowed before loading. The fitting of the experiments to a statistical distribution was examined to allow use of the experimental results for finite element techniques with probabilistic models. The same statistical behaviour as that for joints submitted to cyclic loading was found for joints submitted to humidity.

Keywords:

• Adhesively bonded joints
• surface pretreatment
• statistical treatment
• humidity
• aluminium adherend