Virtual Lab Fatigue Test
Fatigue Testing
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The practical difficulties with fatigue testing are twofold. First, any specimen must be subjected to a large number of loadings, and due to the statistical scatter in the data, a large number of samples must be tested. Low frequency loading may take considerable time to reach the desired cycles of interest (usually > 106 cycles). For example, at 1 Hz, achieving one million cycles of loading will take about 11.5 days!
One test method that provides high frequency loading is the rotating-bending fatigue test. A schematic of one type of rotating bending machine is shown in Figure 7.4.3:
Figure 7.4.3. Cantilever beam type of rotating-bending fatigue testing machine (from Collins, J.A. (1993), Failure of Materials in Mechanical Design, Wiley).
Much of the available fatigue data is based on the rotating-bending test, which provides a completely reversed loading. A disadvantage of the rotating-bending test is the difficulty with applying a non-zero mean load. In that case, a push-pull fatigue test can be employed (Figure 7.4.4):
Figure 7.4.4. Axial push-pull fatigue testing machine (from Collins, J.A. (1993), Failure of Materials in Mechanical Design, Wiley).