BEHAVIOR OF ADHESIVELY BONDED JOINTS UNDER CYCLIC LOADING.

The paper explains the state of the art in determining the fundamental mechanisms of fatigue degradation in structural adhesive joints and in identifying the dominant fatigue mechanisms with the service environmental regimes, including cyclic mechanical load, temperature and humidity. The scope involves an in-depth assessment of fatigue mechanisms and failure modes primarily in adhesively bonded metal/metal joints over the range of loads and environmental conditions experienced by modern high performance aircraft. Interdisciplinary scientific methodologies are applied to establish the physical and mechanical property changes that occur during fatigue cycling. Analytical and experimental stress analysis methods are described to quantitatively define the constitutive relations for the adhesive interlayer material in bonded joints and to describe the changes (and rate of changes) that occur during instrumented fatigue testing. Relevant methods of testing and interpretation of test results are discussed. The joints are analyzed to describe the stress/strain distributions developed within the adhesive interlayer by load/environmental fatigue conditions. Joints fatigued to various stages of joint life, including failure, are examined for degradation mechanisms. The development of methodology for predicting the necessary service life of adhesively bonded joints is outlined.