Viscoelastic model to evaluate the shear and peel stresses in the two-adhesive bonded lap joints

Abstract

This study addresses how to build a viscoelastic model for the two-adhesive single lap joint (SLJ). The two-adhesive bondline contains stiff and flexible adhesives in the overlap with three discrete regions. Stiff adhesive is located in the middle and flexible adhesive is symmetrically at the ends of the overlap. Although the elastic behavior of the two-adhesive SLJs is investigated in the literature, there is no study in the open literature investigating the viscoelastic evaluation of the two-adhesive SLJs when the bending effect is considered. Adhesives are viscoelastic materials, and it is necessary to know the time-dependent behavior of stresses and strains. Here, a term referred to as the hybrid ratio was developed to define the length ratio of the stiff and flexible adhesives used in the overlap, and four different hybrid ratios were identified. Time-dependent shear and peel stress/strain expressions were derived semi-analytically. Adhesive viscoelastic behavior was represented by the three-parameter standard-linear-solid (SLS) material model. The results of the semi-analytical model were compared with those of the finite element (FE) performed by ABAQUS. It was concluded that the shear stresses are considerably affected by the viscoelastic behaviors of the adhesives, and the two-adhesive order is an attractive model causing the reduction in the stresses at the overlap ends. Despite the semi-analytical results showing the time-dependent behavior of peel stresses in a limited range, the FE results precisely estimate the peel stress relaxation at the overlap ends.