PSI - Issue 19

Rainer Wagener et al. / Procedia Structural Integrity 19 (2019) 380–387 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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Figure 8: Wöhler curves of different built jobs with Z-orientation

Figure 9: Influence of notches on the fatigue strength

Related to the reason, that the fatigue strength depends on the built job, the influence of notches will be discussed for different notched specimens of one built job. The Wöhler test results are represented in Fig. 9. As expected, the notches inlfuence the fatigue strength. With growing notch factor the resulting fatigue strength decreases. As long as fatigue strength dominating parameters of the laser powder bed fusion process are not identified, the transferability of the fatigue parameters to another built job has to be questioned. Therefore an accelarated test is required, which could be used to get an impression of the resulting fatigue strength of the printed component of the individual built job. In case of fatigue approaches using load-based methods the numeriacal effort is low, but different Wöhler curves to consider the influences of mean-stresses and notches on the fatigue life are required. In contrast the strain-based fatigue approach methods require less experimental efforts but the numerical effort increases. In order to get a first impression of the resulting fatigue strength strain-controlled fatigue test can get in the focus of interest as long as the results are equivalent to the stress-controlled fatigue tests. In order to switch from load-controlled to strain-controlled fatigue tests for the production accompanying inspections it must be ensured, that the resulting fatigue lives and strengthes are comparable. Therefore, strain controlled fatigue tests are carried out with constant amplitudes. In order to compare strain- and stress-controlled test results, the stress-controlled fatigue results are transferred to the strain domain by dividing the strain amplitude by the Young’s modulus. The strain domain is favored, because the Fatigue Life Curve, which has been published by Wagener and Melz (2017), is the only continuous Wöhler-curve from the Low Cycle Fatigue up to the Very High Cycle Fatigue regime and can be used in the framework of a local strain-based fatigue approach to describe the strain life relation and can reduce the test effort essential, if it is applicable. Fig. 10 shows the comparison of the stress- and strain-controlled fatigue tests. Due to the advantage of being a contious Wöhler-curve within the whole range of 3.2 Strain-life curve