Diffusion in a Butt Joint

Due to the fact that non-Fickean diffusion is influenced by a change in the free volume of the adhesive, the viscoelastic bulk and shear compliances in the form of two separate Prony series are used. Poisson s ratio is allowed to vary with time for the adhesive. A shift factor definition based on the free-volume concept is used in the analysis. The adhesive is assumed to be initially moisture-free. A moisture concentration value of unity is specified on the adhesive boundary. 

FIGURE 14. Geometry, loading, and finite-element mesh and boundary conditions for a lap joint. 

FIGURE 15. Variation of shear stress along the upper bondline for a composite lap joint. 

FIGURE 17. Geometry and boundary conditions for diffusion in a butt joint with viscoelastic adhesive. 

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This problem involves moisture diffusion in a butt joint with a viscoelastic adhesive layer. The geometry and loading are shown in Figure 17. Due to the symmetry of the problem, only a quarter of the Joint is modeled. The material properties and the diffusion parameters for the adhesive are given in Table 7. Since the adhesive has very high compliance, the adherend is assumed to behave as a perfectly rigid body relative to the adhesive. Hence, the adherend is replaced by a specified uniform displacement of 0.004 mm (2% strain in the adhesive) in the axial direction. 

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