Design of Cruciform Test Specimens with different Biaxiality ratios for VHCF Fatigue.

Abstract

The necessity to increase performances in terms of lifetime and security in mechanical components or structures is the motivation for intense research in fatigue. Applications range from aeronautic to medical devices. With the development of new materials, there is no longer a fatigue limit in the classical sense, where it was accepted that the fatigue limit is the stress level such that there is no fracture up to 1E7 cycles. The recent development of ultrasonic testing machines where frequencies can go as high as 20 kHz enabled tests to be extended to ranges larger than 1E9 in just a few days. This area of studies is now known as Very High Cycle Fatigue (VHCF). On the other hand, most of the existing test equipment in the market for both classical and VHCF are uniaxial test machines. However, critical components used in Engineering applications are usually subjected to complex multi-axial loading conditions. In this paper, Finite Element Analysis (FEA) will be used as part of the methodology. It aims at re-designing existing cruciform test specimens that can be used to create an in-plane biaxial state of stress when used in ‘uniaxial’ VHCF ultrasonic testing machines. Furthermore, it will be shown how to get different stress ratios between the two orthogonal directions. The framework on how to design these specimens will be laid out in a clear way so that other researchers in the field can engage in the exciting range of opportunities that are now opened with the outcomes from this research work.