EFFECT OF TEMPERATURE AND SUPERIMPOSED DYNAMIC AND STATIC STRESSES ON MECHANICAL-PROPERTIES OF EPOXY-BONDED JOINTS

Adhesive joints are subjected during their service life to different combinations of dynamic and static stresses. While the behaviour of the adhesives in relatively simple states of stress is well characterized, their response to superimposed stresses of different types acting in different directions has scarcely been investigated. In the study presented in this paper, single lap joints made with different formulations of epoxy adhesives were subjected to combined shear creep stresses and torsional oscillations applied simultaneously and along perpendicular axes of the specimen. The main conclusion based on the results of this investigation is that such a simple combination of stresses affects considerably the mechanical behaviour of the joint. A significant increase of the shear strength of the joint was recorded for specimens subjected to superimposed stresses at temperatures lower than the T(g) of the adhesive. Application of similar combinations of stresses at temperatures close to or higher than the T(g) led to a decrease of the shear strength of the joint. The fracture morphology of the joints made with the investigated epoxy resins was qualitatively correlated with changes induced by the superimposed loading in the T(g) of the adhesive. The fatigue fracture surface of adhesives is characterized by striations and furrows, similar to bulk specimens that failed in the same fashion.