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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3.2. Influence of the load-time history on the stress-strain behaviour and the damage accumulation

The influence of the load-sequence on the stress-strain relation is mainly based on the stability of dislocation structures towards cyclic deformation. Therefore, in case of a wavy slip character, the cyclically stabilized stress strain behaviour will depend strongly on the load-time function applied, as the comparison of cyclically stabilized stress-strain curves for a quenched and tempered 42CrMo4+QT heat treatable steel in Fig. 10 shows.

Fig. 10. Comparison of the stress-strain behaviour for load-time functions

In addition to the stress-strain relation, also the local stress-strain response to an external load depends on the load time history, if elasto-plastic loading is admissible, see Fig. 11. Especially during single elasto-plastic overloads, the mean stress for consecutive elastic loading may be shifted significantly. In order to be able to account for the related load sequence effects, the external load time function has to be transferred to the local system first by evaluating the local strain response to the external load.

Fig. 11. Comparison between global load-time function and local response