Stress concentration factor and minimum hub length predictions for hollow tubes with internal and external flanges subjected to axial loading

Abstract

This paper presents equations for estimating the elastic stress concentration factor Kt and minimum hub length δ in hollow tubes with internal and external flanges subjected to symmetrical axial pressure over the flat section of the flanges. Results from an extensive finite element study are supported by a limited number of experimental tests. The experimental Kt values are compared with data obtained numerically by the present authors and very good agreement was found between the two methods. Minimum hub lengths, which are an important parameter for fabrication, have been derived on the basis of Saint Venant's principle. It is seen that Kt and δ follow similar trends, being functions of several geometric parameters. Kt and δ values for the internal and external flange-tube intersections contained in this paper cover the most common practical range of geometries. The effect of tube wall radial pre-load (which can result from the compressive radial interface pressure established in the shrink-fitting process, compressive radial residual stress due to the autofrettage process or any other reinforcing process) on Kt and δ has also been studied. Furthermore, the effect of eccentric loading has been studied, using an experimental approach with one geometry. The extensive range of Kt and δ values obtained from the analyses is used to obtain useful prediction equations, using a statistical multiple non-linear regression model and a high level of accuracy is demonstrated. Finally, a direct relationship between elastic stress concentration factor, which is readily available, and minimum hub length, which usually requires a complex numerical analysis, is provided.