Life Prediction Methodology for Adhesively Bonded Joints

Abstract

A comprehensive integrated-methodology for adhesive bonded joint life predictions is outlined. The guiding assumption is that the useful life of bonded joints is determined by failure in the adhesive interlayer, and this is the basis for a systematic analysis of information and the techniques required to provide valid predictions. Emphasis is placed on time-dependent fracture mechanics, procedures, including detailed through the-adhesive thickness viscoelastic finite element calculations of the stress-strain distributions, and on analytical methods involving the constitutive relations of the adhesive interlayer. Use is made of instrumented bonded joint data obtained from structural overtest methods under a number of U.S. Air force-sponsored programs. A logical program rationale is outlined which has sufficient generality to apply to any adhesive bonded joint structure including metal and composite adherends, various loading/environmental conditions, which apply to high-performance aircraft. The five main modules of the integrated methodology are: (Definition of) Loads/Environments; (Adhesive) Material Properties; Stress Analysis; Fatigue Mechanisms and Failure Criteria; and Structural Failure Analysis (Life Predictions).