PSI - Issue 42

Numan Berat Yondu et al. / Procedia Structural Integrity 42 (2022) 1567–1575 Author name / StructuralIntegrity Procedia 00 (2019) 000 – 000

1570

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conditions. In high temperature calculated NCR values are evidence for stress magnitude dependency of dwell sensitivity for Inconel718.

Figure4. NCR values comparisons for room temperature (RT) and high temperature (HT) Material’s cyclic behavior change can be seen for different test conditions. Change in life results can be caused by different factors. Since the fatigue behavior is also dependent on material overall strength, to understand these results further hardness measurements have been performed. Hardness measurements are performed in three different measurement zones of fractured specimens, named; I, II, III. These regions represent the distances that are stated in Table1 . In Figure5 it can be seen that specimens show softening since the material's initial hardness values are approximately 500-520 Vickers. This softening phenomenon can be seen in all test types. With increasing the temperature softening trend also increases its slope, different stress levels also showed different amounts of decrease in hardness value which means softening is a stress-dependent phenomenon. It is important to note that softening is observed at room temperature too which means this phenomenon is not thermally dominated. The specimen which is subjected to dwell also showed lower hardness values than its counterpart without dwell. Change in hardness provides illuminating perspective to understand the cyclic life change however these results raised new questions on material toughness and overall plastic capability.

Table 1.Distance ranges of Vickers measurements from failure surface. Measurement Zone

Distance Ranges From Failure Surface (mm)

I

0,15-0,23

II

1.0-3.0 2.0-4.0

III

Plastic work capacities are compared with using materials reaction under applied load in nano scale. In Figure6 shows that there are no significant change between non-dwell fatigue tests and dwell fatigue tests. Although decrease