Fatigue of 1 μm-scale gold by vibration with reduced resonant frequency

In order to investigate the fatigue strength of micro-metal (1 μm-scale), a testing method using resonant vibration is developed. Although the loading by vibration can solve the difficulties associated with the fatigue experiment of micro-specimen (e.g., specimen gripping and high-cycle loading under tension-compression), it inherently has an excessively high resonance frequency (more than several GHz at least) in a 1 μm-scale metal specimen. For control of the fatigue cycle, the resonance frequency must be reduced to several hundreds of kHz by tuning the specimen shape. We design a cantilever specimen of 1 μm scale gold with a weight at the tip, which reduces the resonant frequency to about 330 kHz. The unique specimen with the test section of 1.26 μm×0.94 μm×1.52 μm is successfully fabricated by a novel technique using a focused ion beam and the tension-compression fatigue cycle is applied to it by means of a piezoelectric actuator. The test section breaks at about 1.6×106 cycles under Δσ/2=230 MPa, which is within the targeted range of this project. It is easy to extend this method to high-cycle fatigue for actual use (including the failure cycles of over 108 cycles). The slip bands observed on the surface, which have concavity and convexity similar to the intrusions/extrusions of PSBs, indicate that the failure is induced by the fatigue.