Robust shape optimization of tubular butt joints for characterizing thin adhesive layers under uniform normal and shear stresses

Thin-walled tubular joints, bonded end to end, are commonly used specimens to measure the mechanical properties of thin adhesive layers subjected to uniform shear stress distributions. Unfortunately, the application of an axial loading to this geometry leads to strong stress concentrations at the edges of the adherend–adhesive interface. This drawback undermines the use of this test for characterizing adhesives under biaxial stress conditions. With the aim of removing these stress concentrations, this paper suggests the introduction of stress relieving grooves on the internal and external surfaces of the tubular adherends.The optimal shape of the groove is identified following the Taguchi robust optimization technique. Via finite element analyses, the stress concentrations at the edges of the adherend–adhesive interface are calculated. Many geometries are examined for different adherend and adhesive properties (noise factors) in order to identify the groove shape that minimizes the stress concentrations for all experimental conditions.The analysis shows that a shallow V-shaped groove close to the adherend–adhesive interface smoothes significantly the stress peaks due to axial loading.With this simple modification, a tubular butt joint becomes a universal specimen for applying any combinations of reasonably uniform shear and normal stresses to thin adhesive layers