Out-of-Phase Experimental Evidence

The first assessment of fatigue theories to predict the OP behavior of materials will be done checking the von Mises criterion, already analyzed in Sect. 9.3 for the IP situations. In particular, Eq. (9.20) will be used combined with the Basquin-Manson-Cofhn Eq. (6.10) to yield the equivalent strain versus life N 

OP loadings at the same equivalent strain amplitudes suggest that the von Mises criterion underestimates the fatigue damage under non-proportional loadings. 

As said, the criterion is based on the assumption that damage initiation is due to surface slips. This is important to remember because if the initiation process were different the criterion may not be appropriate. This is the case of nodular cast iron in 

Strength of shafting subjected to both twisting and bending. Trans ASME 8, 121-196 (1886) 

The thermodynamic theory of mechanical fatigue and hysteresis in metals. Rep. pp. 358-368. British Association for the Advancement of Science, Liverpool (1923) 

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