Review of Multiaxial Testing for Very High Cycle Fatigue: From ‘Conventional’ to Ultrasonic Machines

Abstract

Fatigue is one of the main causes for in service failure of mechanical components and structures. With the development of new materials, such as high strength aluminium or titanium alloys with different microstructures from steels, materials no longer have a fatigue limit in the classical sense, where it was accepted that they would have ‘infinite life’ from 10 million (107) cycles. The emergence of new materials used in critical mechanical parts, including parts obtained from metal additive manufacturing (AM), the need for weight reduction and the ambition to travel greater distances in shorter periods of time, have brought many challenges to design engineers, since they demand predictability of material properties and that they are readily available. Most fatigue testing today still uses uniaxial loads. However, it is generally recognised that multiaxial stresses occur in many full-scale structures, being rare the occurrence of pure uniaxial stress states. By combining both Ultrasonic Fatigue Testing with multiaxial testing through Single-Input-Multiple-Output Modal Analysis, the high costs of both equipment and time to conduct experiments have seen a massive improvement. It is presently possible to test materials under multiaxial loading conditions and for a very high number of cycles in a fraction of the time compared to non-ultrasonic fatigue testing methods (days compared to months or years). This work presents the current status of ultrasonic fatigue testing machines working at a frequency of 20 kHz to date, with emphasis on multiaxial fatigue and very high cycle fatigue. Special attention will be put into the performance of multiaxial fatigue tests of classical cylindrical specimens under tension/torsion and flat cruciform specimens under in-plane bi-axial testing using low cost piezoelectric transducers. Together with the description of the testing machines and associated instrumentation, some experimental results of fatigue tests are presented in order to demonstrate how ultrasonic fatigue testing can be used to determine the behaviour of a steel alloy from a railway wheel at very high cycle fatigue regime when subjected to multiaxial tension/torsion loadings.

Experimental and Numerical Vibration Analysis of Octet-Truss-Lattice-Based Gas Turbine Blades

“…Numerical analysis reduces the number of iterations required experimentally and provides a basis for experimental work. Numerical modal analysis also provides mode shapes that help clarify the type of deformation at resonant frequencies [19].…”

A Novel Model of Ultrasonic Fatigue Test in Pure Bending

“…An ultrasonic fatigue test instrument is indeed a resonant system, which is composed of an excitation power supply, a piezoelectric transducer, a horn, and the specimen sequentially assembled in series by fastening connections. The mechanical vibration generated by the piezoelectric actuator is meant to reproduce a pure sine wave with a frequency of 20 ± 0.5 kHz [ 20 , 21 ].…”

Very high cycle fatigue under tension/torsion loading of mold low alloy steel

“…Different examples of multiaxial dynamic loads are present in many industries, including railway, aerospace, industrial manufacturing machines, energy, aerospace, and others. [24][25][26] In the present study, three new axisymmetric specimens were numerically developed, designed, manufactured, and tested in a modified tensioncompression UFT machine with the objective of inducing a biaxial tension/torsion stress combination. The designed ultrasonic testing machine applies, just as every previously referenced ultrasonic machine, resonance principles to reach a 20-kHz cyclic multiaxial stress state in a testing specimen.…”