PSI - Issue 7

Dalila Dimaggio et al. / Procedia Structural Integrity 7 (2017) 198–205 D. Dimaggio et al. / Structural Integrity Procedia 00 (2017) 000–000

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Figure 2: S-N results at T=120°C under constant amplitude loading

It can be observed that the fatigue strength for axial loading drops for higher stress ratios (R σ >0), as expected. Moreover, test results for bending at R=0 are even higher than at axial load with R=0, which was also to be expected. Specimens that did not fail after N=10 7 load cycles were indicated as run-outs (arrows pointing to the right). All samples showed crack origins at the surface. The slope k in the LCF regime was evaluated by regression analysis using the test results up to the knee point N k . The slope after the knee point N k was estimated to be k*=44.9 with a 5% decrease per decade according to [4]. Thus the S-N curves are described by means of the relationship: ( ) k k k N N 1 / / − = σ σ for N

Figure 3: S-N results at T=120°C under near-service load spectrum, where CA and VA refers to constant and variable amplitude tests