PSI - Issue 18

Matthias Hell et al. / Procedia Structural Integrity 18 (2019) 823–836 Author name / Structural Integrity Procedia 00 (2019) 000–000

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4. Interfaces for transfer approaches

The fatigue life assessment with the local elasto-plastic notch base approach has different possible interfaces for the different influencing factors. The Influences act as transfer functions, which allow to mirror peculiarities of the component related material behaviour into a digital twin, i.e. a numerical model of the fatigue problem. Fig. 12 shows possible transfer functions, which may be employed depending on the fatigue assessment problem.

Fig. 12. Interfaces for the implementation of different transfer functions

Microstructure related effects [13] have to be assessed with respect to their scale dependency by fatigue testing with different specimen sizes. It is necessary, that the microstructural configuration of the specimens is equivalent to the state of the component material. The microstructure related effects are implemented using appropriate stress-strain relations, which are assigned, for example, on basis of forging or heat treatment simulations. For the evaluation of the statistical size effect, the Weakest Link Approach according to Weibull, modified by Böhm et al. [14] is used. The impact of the notch support effect, which is caused by local plasticity, is already implemented, if a sufficient material modelling in the course of the finite element modelling has been done. The load sequence effects with respect to the relation between external load and internal stress or strain ratio has also to be assessed by appropriate finite element modelling. A simplified approach, which avoids the numerical modelling of every single load step is discussed later.