Fatigue testing was performed on a four-ripple convolution. The ID, OD and thickness for the convolution are the default values in the Bellow Data Entry Form. Convolutions were tested in extension with vacuum internal. The results of the testing for Alloy 242 are shown below.
While the results are plotted in the format of a traditional S-N curve, it is important to note that y-axis is stress intensity and not stress. The results suggest an asymptotic behavior near 18,000 psi(in)^0.5. This is believed to be near the fatigue threshold stress intensity for Alloy 242 in the condition used in these tests. The above plot can be used to provide design guidance for Alloy 242 bellow design.