2-D Analytical Model of Heat and Moisture Diffusion in Bonded Single Lap Joints

Abstract

Abstract A two-dimensional elastic analytical model for bonded single lap joints subjected to heat and moisture diffusion is presented. The distributions of peel and shear stress in the bond area are calculated. Local moisture concentration and bondline temperature determine the properties of the adhesive layer, which vary in the space and time coordinates. Adhesive diffusivity coefficient and absolute saturated concentration are affected by the material temperature, and scenarios of individual and combined heat and moisture diffusion are analyzed. The governing partial differential equations are solved numerically, and a simplified shear stress formulation is introduced for low-modulus adhesives. Two-dimensional gradients in the adhesive properties affect the peel and shear stress in the bondline. Diffusive patterns in the direction of the loading axis of the joint can contribute to a positive stress redistribution along the overlap, while the results of this study show that softening patterns in the transverse direction may severely impact the joint performance. In the initial stages of environmental exposure, significant increases in peak shear stress are observed in the innermost portions of the bond area. Less significant gradients are observed for the peel stress distribution, under the same conditions. A 3-D Finite Elements Analysis is used to compute adhesive peel and shear stresses, and the results are in reasonable agreement with the proposed analytical model.