A nonlinear evaluation of a tubular adhesive scarf joint loaded in tension and in torsion

In this thesis, a simple analytical model is developed and utilized to determine the adhesive shear strain and stress distributions in tubular adhesive scarf joints. Both tensile and torsional loading conditions are investigated because they are often seen as primary loads in structures consisting of tubular components. In addition, a mathematical representation consisting of linear and exponential functions is employed to model the elastic/plastic-like behavior observed at many structural adhesives. Two governing equations derived for the tension and the torsion cases are found to be in the form of nonlinear second-degree ordinary differential equations with variable coefficients. Numerical methods required for solving these equations are also introduced. Both linear and nonlinear numerical analyses based on the developed theory are validated with Finite Element Analysis, utilizing the commercially available software, ANSYS 5.6, a general-purpose software system. An approach for failure prediction is also proposed, in conjunction with the analytical model, and the approach is evaluated by representative experiments. The experiments are conducted both in tension and in torsion with aluminum tubular adherends bonded by Hysol EA9394, a two-part paste adhesive manufactured by Dexter Aerospace. A complete joint failure is assumed to occur when the maximum shear strain in the adhesive attains the value of the ultimate shear strain near the joint terminations.; It is shown that both the linear and nonlinear approximate solutions are closely comparable to the FEA results for small scarf angles and elastic isotropic adherends. A scarf joint experiences lower peak strains and relatively more uniform distributions compared to those of a conventional lap joint, while a lap joint exhibits a deep elastic trough considered as a good inhibitor to creep. Both tension and torsion experiments show evidence of good correlation with failure predictions estimated by the theory. Guidelines applied to adhesive joint design and to manufacturing are also introduced.