International Journal of Adhesion and Adhesives
One of the main challenges in the joining of multi-material components is the assessment of the nature and magnitude of the residual stresses developing in the adhesive bond during the heat curing manufacturing process. Numerical modeling of these residual stresses can provide insights for making informed decisions related to (i) material substrate properties; (ii) adhesive properties i.e., low, medium, or high stiffness; (iii) bondline geometry i.e., bondline width and bead thickness; (iv) curing cycle characteristics; and (v) fixation design i.e., type, spacing, the number of joints. This work presents a cure history-dependent viscoelastic-plastic material description for the modeling of adhesive bonded joints. The main highlight of the work is the multi-physics modeling package consisting of a curing kinetics model, a cure-dependent viscoelastic model, and a temperature, strain-rate dependent plastic model formulation which can be coded in any finite element solver. The modeling approach can predict the residual stresses in the adhesive bond due to the accumulated viscoelastic as well as plastic strains occurring during the heat curing process. For the purpose of validation, the model is coded into a user-defined material subroutine (UMAT) in LS-DYNA. The modeling approach is verified at a small specimen level by simulating a uniaxial tension specimen at various temperatures and strain rates. The performance of the modeling approach is further evaluated at the component level using specially designed experiments involving heat curing of a sub-sized multi-material automotive roof model. The thermal displacements and distortions in the roof structure captured using 3D digital image correlation are compared to the finite element model predictions. Several design guidelines related to adhesive selection and mechanical fixations are proposed as a result of the study.
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