A new piezoelectric fatigue testing machine in pure torsion for ultrasonic gigacycle fatigue tests: application to forged and extruded titanium alloys

Abstract

This article briefly discusses the history of the development of ultrasonic fatigue testing methods, with respect to industrial needs. The development of ultrasonic techniques and the progress made in the computer industry have led to improvements in ultrasonic testing techniques. It has been shown, that existing ultrasonic testing systems have limitations that lead to the need for a new ultrasonic fatigue testing machine operating in pure torsion. This paper introduces the development of a new piezoelectric machine working in the continuous regime (i.e. without pulse-pause). This machine has been used to investigate the Very High Cycle Fatigue (VHCF) properties of the VT3-1 alpha beta aeronautical titanium alloy (which is similar to Ti–6Al–4V) produced by two manufacturing processes: forging and extrusion. The extruded titanium alloy has a higher VHCF strength in torsion compared to the forged one. Despite the maximum shear stress occurring at the specimen surface under torsion loading, internal fatigue crack initiation can be observed in both the forged and extruded alloys.