Biaxial Load Effects on Fatigue Properties

This study aims to aid many issues related to fatigue, namely biaxial loading, the definition of the finite geometry correction factor of the stress intensity factor and the understanding of the energy dissipation per fatigue crack growth. In our work, we are using the geometry correction factor definition that uses the ratio of external work introduced to the material. Using different biaxiality ratios varies the external work done, thus makes it possible for us to observe how the geometry correction factor handles this variation. The trend of strain energy release rate per crack growth is also investigated through biaxiality. Moreover, the common discussion of the effects of biaxiality on fatigue properties is aided with yet another study. For this purpose, cruciform shaped plate specimen from an aluminum alloy are manufactured and biaxially loaded. Crack growth is observed while load-to-displacement data is recorded to evaluate the external work done on the specimen. As a result, it is seen that biaxiality delays the fatigue failure. Crack growth rates decreases as the biaxiality increases for a given effective stress intensity factor. Making use of the work values for the calculation of the finite geometry correction factor handles the effects of biaxiality well. Strain energy release rate increases as the crack propagates, but there is no trend between strain energy release rate and biaxiality of the loading. In the future works, observing also the crack tip plasticity and trying out a wider range of biaxiality ratios with different types of material would result in more generalizable conclusions. Moreover, more repetitions of the fatigue tests would give more accurate values for the amount work introduced to the material with changing biaxiality.