Consideration of the local notch effect

In the notch stress concept (KSK) are used as basis and facing locally tolerable voltages for the fail-critical crack initiation site locally present in the notch root elastic stresses to assess fatigue safety. In contrast to the nominal stress and structural stress concept in this case the stress spikes due to the weld geometry and taken into account by the so-called notch stress on the stress side. The geometry values and the material condition must therefore be completely describable in the vicinity of the critical point fail. An analytical determination of notch stresses is possible only for simple geometric shapes in general. In general, the notch stresses are determined using finite element methods (FEM).

FE model for determining the notch stresses at the seam transitions a butt weld
FE model for determining the notch stresses at the seam transitions a butt weld

Fictitious notch radius and notch local case class

Mesh refinement to the seam transitions with fictitious notch radius
Mesh refinement to the seam transitions with fictitious notch radius

The beginnings of the notch stress concept goes back to Radaj and relate to the fatigue strength, since there occur approximately purely elastic stresses at the notch root. The real radius of the notch is this fictitious rounded depending on the material and strength of the hypothesis that local stress at the notch root for the full amount on the fatigue strength are effective (micro-support). The stresses obtained by this fictitious radius are then compared directly to the fatigue strength of the base material. The generalization in the fatigue strength range was carried out by SEEGER by the characteristics and functions of the nominal stress concept have been transferred to the notch stress concept. The thus calculated notch stresses are compared with notch stress - WOEHLER lines. Existing variations, such as at a weld seam geometry as a result, roughness, weld defects, residual stresses and material strength are in the WOEHLER lines included. As a recommendation is given for this notch stress - WOEHLER - line from IIW a characteristic resistance value of 225 MPa (FAT225).