PSI - Issue 18

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

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In order to modify the damage accumulation, the local strain response was estimated. Therefore, the load-time function of the external loads was divided into purely elastic and elasto-plastic load steps, storing the position in the original load-time function of the external loads. For the elasto-plastic load steps, finite element analyses were carried out in order to estimate the elasto-plastic stress- and strain amplitudes and the mean stresses. Afterwards, the data from the elasto-plastic half-cycles was added to the original load-time function, thus causing a shift in mean stresses. Fig. 18 shows the original external load time function and the modified local load-time function.

Fig. 18. Difference between the external load-time history and the time history of the local stress-strain response

After a rainflow counting and a amplitude transformation, the fatigue life was estimated again, using the local load-time history. As Fig.19 shows, the results of the numerical fatigue assessment with the consequently applied local approach, using also a local load-time function for the damage accumulation, are in good accordance with the experimental results.

Fig. 19. Difference between the external load-time history and the time history of the local stress-strain response

6. Conclusions and Outlook

The consideration of different influencing factors, such as the location and time dependent material behaviour, the statistical size effects and load sequence effect, show potential for the improvement of the fatigue life assessment with local elasto-plastic fatigue design approaches. Most of the influencing factors can be implemented by using simplified approaches without the necessity of difficult mathematical or numerical formulations. An experimental validation with local optical strain measurements is prepared at the moment.