Implementation of Damage Tolerance Concepts into Stress-Based Fatigue Dimensioning Guidelines

In the traditional design approach, unflawed components made of a homogeneous material are assumed; they are dimensioned against fatigue with respect to an allowable local maximum stress amplitude. However, real-life engineering materials usually exhibit intrinsic flaws such as precipitates or voids; and real-life engineering components very often are subject to some damage during manufacturing (such as forging defects or quenching cracks) or in operation (foreign object damage). Traditionally, such influences have been accounted for by means of empirical correction factors. However, from a physical point of view, they are best assessed by means of fracture mechanics. In this contribution, a connection is made between concepts from fracture mechanics and classical approaches such as Haigh diagrams (accounting for the mean stress influence) and fatigue notch factors (accounting for gradient and size effects) in order to apply the latter methods to the dimensioning of components containing flaws.