Lifetime and crack initiation of fcc materials in small scale under multiaxial cyclic loading in the high and very high cycle fatigue regimes

摘要

Small-scale fatigue takes place in many applications such as micro-electro-mechanical-systems,surface acoustic wave devices and microelectronics,in which cyclic loading leads to failure.Multiaxialfatigue experiments with micro samples at kHz frequencies require novel experimental setups.Therefore,resonant micro fatigue systems for uniaxial and multiaxial cyclic loading have been developed.Finite Element simulations have shown that dimensions of the samples can be chosen in away that the resonant frequencies of bending and torsional modes are very close,which is a requirementfor multiaxial cyclic loading.For the initial tests,samples made from copper,aluminium,ornickel with a rectangular cross section of 500μm by 200μm have been used.Hence,scaling andsize effects are expected to dominate reliability of such components.Recent FIB analyses haveshown a correlation with sub-surface damage formation in the HCF and VHCF regimes after aresonant frequency decrease of 0.2%.