Design and Development of an Ultrasonic Fatigue Testing System for Very High Cycle Fatigue 2020-01-0183

There has been growing demand for increased fuel efficiency, reduced emissions and improved power performance while maintaining reliability and durability of mechanical and structural systems in many different industries. The structural engineering components often experience long loading histories, typically ten million cycles or greater, i.e. high cycle fatigue (HCF) and very high cycle fatigue (VHCF) regimes. HCF in the range of 10⁶-10⁸ cycles and VHCF in the range of 10⁸-10¹⁰ cycles are key design criteria for aerospace, automotive, military, transportation and many other industries. However, fatigue characterization of metal alloys in the HCF and VHCF regimes is hindered by limitations of traditional fatigue testing machines due to time and cost constraints. The development of high power piezoceramic actuators enables efficient and reliable fatigue tests in the HCF and VHCF regimes within a very short time frame on the basis of ultrasonic fatigue testing approaches. A fully instrumented ultrasonic fatigue test machine operating at 20 kHz was designed and built to investigate HCF and VHCF behavior of lightweight metallic alloys. The fatigue testing machine went through several stages of design and development. Finite element modeling was employed to design and optimize three versions of an acoustic stack including an acoustical horn, a single half wavelength booster and a test specimen. Two aluminum alloys, namely extruded 2024-T351 and 7075-T6 alloys were used to machine test specimens in order to generate representative fatigue test data. Fatigue tests in the HCF and VHCF regime were successfully conducted and fatigue data was found in very good agreement with published corresponding data in the literature.