Thermal Stresses in Adhesively Bonded Joints/Patches and Their Modeling: A Critical Review

Abstract

The adhesive bonding technique is widely used for joining similar or dissimilar materials in various engineering areas. Mismatches in the thermal expansion coefficients of adhesive and adherend materials in the vicinity of bi-material interfaces result in incompatible thermal strains and discontinuous thermal stress distributions along the bi-material interfaces. During the adhesive curing process, thermal residual stresses are induced due to the chemical and physical changes in adhesive material. The expansion of the adhesive with changes in moisture and temperature levels is the reason for hygroscopic residual stresses. Non-uniform temperature or material composition distributions also result in non-uniform thermal strain and stress distributions. Loading with a relatively high frequency cyclic component may result in a temperature rise due to internal heat generation and consideration of viscoelastic time-temperature effects may become necessary in the stress analysis even at moderately low temperatures. The crack nucleation, initiation and propagation around bi-material notches, and the fatigue crack growth in adhesively bonded integrated structures are important design considerations under cycling thermal loads. Therefore, the thermal strain and stress states of the adhesive joints should be analysed in order to predict the joint strength accurately and to improve joint service life. This article reviews from simple to more complicated mathematical models to analyse the thermal stress and deformation states of various adhesive joints under both steady state and transient thermal conditions.