Experimental methodology and analytical solution for cruciform ultrasonic fatigue Testing.

Abstract

As transportation and general machinery demand higher working speeds, reliability, and life spans [1], a higher life span characterisation method was required. In the middle of the 20th century, Mason devised a new fatigue testing method very different from the established ‘conventional’. The designated ultrasonic fatigue machine utilises resonance principles to achieve a considerably higher testing frequency. With Mason’s generally accepted 20 kHz standard reaching a billion cycles was made reliable. To make ultrasonic fatigue machines accessible and accepted, a trusted deterministic experimental methodology is necessary. Claude Bathias, the ultrasonic fatigue pioneer [1], brought ultrasonic fatigue testing (UFT) to the fatigue research world. His book details UTF methodology extensively for all uniaxial loading conditions [2]. Bathias et al. [3] have also shown piezoelectric fatigue testing machines in high and low temperatures, with R≠ -1 stress ratios and fretting. Considerable worldwide research has followed Bathias well described and methodically presented methodologies [4]–[6]. The first ‘conventional’ fatigue machines focused on pure uniaxial cyclical load, meaning one single direction load. Multiaxial stresses were later recognised as the leading dynamic stress state in machines and structures [7]. Thereafter, several different multiaxial testing methods came to fruition over the years, replicating the different cyclic loads. Just as ‘conventional’ fatigue transposed from uniaxial to multiaxial testing mechanisms, UFT developments will follow the same trend. Palin Luc et al. [8] induced a biaxial bending stress state with a carefully shaped disk. P. Costa et al. [9] created an altered ultrasonic setup capable of inducing a specimen in a tension-torsion stress state. In this study, a detailed methodology description with a proposed analytical solution is made to the already proven and working cruciform specimens created by D. Montalvão et al. [10]. Due to the cruciform deformation complexity, finite element analysis (FEA) was used to adjust Bathias analytical concepts.