Cruciform specimen’s analysis and experiments in ultrasonic fatigue testing.

Abstract

The reliability of any given structure or machine subjected to dynamic loads is mainly dependent on the detailed fatigue study of the applied materials. As the demand for higher life cycles with more complex stress applications increases, so does the necessity for new and more complex fatigue testing methods. Since it was proven before that a fatigue limit should no longer be considered, ultrasonic fatigue tests were developed for the study of the life beyond that point. This is now known as the Very High Cycle Fatigue (VHCF) regime. In these tests, specimens are subjected to stress cycles in frequencies as high as 20 kHz. Most ultrasonic fatigue tests apply uniaxial stresses, but it is important to be able to apply complex multiaxial loading since most components are subjected to a complex stress state when under cyclic loading. In this work, cruciform specimens are used in an ultrasonic fatigue machine. Two different geometries, capable of inducing in-plane biaxial stress combinations (in-phase and out-of-phase) in the VHCF range, are studied. The geometries are subjected to both numerical analysis and experimental testing to understand if they are working as intended. For those who do so, a test until failure was carried through to observe and evaluate the fracture surface.