PSI - Issue 4

Stefan Kolitsch et al. / Procedia Structural Integrity 4 (2017) 95–105 Stefan Kolitsch/ Structural Integrity Procedia 00 (2017) 000 – 000

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Fig. 3. Comparison for all considered different materials for bending load and surface roughness in the as-rolled condition in the Smith diagram.

3.2. Fracture mechanics approach

If notches are very sharp and hence can be considered as cracks, the stress based design is not valid anymore and a fracture mechanics approach has to be used as a design criterion. The stress intensity factor (SIF) range Δ K of the crack is calculated by

a         , K Y

(12)

where Δ σ denotes the applied stress range, Y the geometry factor depending on the crack shape and position and a represents the crack length. Equivalently to the Smith diagram, an endurance limit can be calculated, yet in the fracture mechanics approach it is based on the crack length and represented in the Kitagawa-Takahashi diagram (Kitagawa 1976), cf. Fig. 4.