Multi-Axial Fatigue and Fracture Behavior in Metals

Dear Colleagues,

The continuous study of material fatigue and the development of new testing devices and methods for its characterization prove its importance, not only in scientific terms but also in its practical application. With the development of new materials and alloys, there is an increasing demand for materials which are reliable, can be obtained in a timely manner, and possess predictable properties. Through detailed characterization, more complex designs with reduced weight improvement and longer lifespans can be created and achieved with increased reliability, confidence, and safety.

Fatigue tests were initially predominantly focused on inducing uniaxial loads. However, since most components and machines are subjected to multiaxial cyclic loads, many researchers have dedicated their studies to multiaxial loading and these technological developments are associated with the materials’ fatigue characteristics and properties.

As fatigue multiaxial inducing technics have increased in reliability and versatility, tailored towards the material and shape under analysis, the same can be said of the testing cyclic frequency. Fatigue failure was once thought to be limited to 10E7 cycles (the fatigue limit) and it was assumed that no failure would occur, i.e., materials would have an infinite lifespan, beyond the fatigue limit. Nevertheless, later research suggested that the problem of fatigue failure could still be overcome. Thereafter, failure occurring beyond the believed fatigue limit was established to be within the very high cycle fatigue (VHCF) regime, between 10E7 and 10E10 cycles.

Conventional fatigue testing machines have operational frequencies that typically range between 20 and 150 Hz. This means that it is not feasible to use these machines to test materials up to the VHCF regime and achieve reliable fatigue characterization for such a considerable number of cycles in a practical amount of time. With the aim of inducing fatigue damage in higher fatigue frequency regimes, new testing methods have been proposed, namely ultrasonic fatigue testing (UFT) either in uniaxial or biaxial loadings, including tension/torsion or in-plane bi-axial loadings.

Prof. Dr. Manuel Freitas
Guest Editor

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• fatigue
• notches
• critical distance
• multiaxial fatigue
• tension/torsion loading
• bi-axial loading
• cruciform specimens
• very high cycle fatigue
• uniaxial and biaxial VHCF
• mixed-mode fracture
• failure analysis