Component design: The interface between threshold and endurance limit

This paper discusses the Use of methods derived from fracture-mechanics for the assessment of stress concentrations in components. It is known that so me sharp notches can be modelled as cracks, their fatigue;limits correspond ing to the threshold value for a crack of the same length. Using this metho dology for the assessment:of components gives rise to two problems. The fir st problem concerns geometry: real stress concentrations have complex shape and cannot be modelled as notches of simple profile. The second problem co ncerns notch size: can short notches be modelled in the same way as short c racks? An approach has been developed which is an extension of the well-kno wn critical-distance concept. It can be applied to both cracks and notches and takes into account the size effect. This has been:tested using data:fro m specimens containing short cracks and circular notches of various sizes; it has also been successfully applied to the analysis of a component in ser vice.