Generalised Neuber Concept of Fictitious Notch Rounding

Abstract

Sharp or pointed notches reduce the fatigue strength or life of structural components drastically, but not to the extent of the elastic notch stress increase. Microstructural support is observed for crack initiation at the notch root. The support effect may be described by averaging the maximum notch stresses in a small material volume (length \( \rho^{\ast} \)) at the notch root (radius \( {\rho} \)), which can be expressed by the maximum stress of a corresponding notch of a slightly enlarged, fictitious radius, ρ f = ρ + \(s\rho^{\ast} \) (Neuber 1937, 1968). The support factor s is derived for elementary notches and V-notches in the three loading modes: in-plane tensile and shear loading as well as out-of-plane shear loading (modes 1, 2 and 3). Out-of-bisector crack initiation and propagation is basic for mode 2 loading. The dependency of s on the notch opening angle 2α is recognised, besides its correlation with multiaxiality conditions and failure criteria. The Neuber concept of fictitious notch rounding is thus generalised. Application-relevant issues such as reference notches, design S–N curves, non-singular stress components, seam-welded cruciform joints and spot-welded lap joints are also dealt with.