Speaker
Description
The practical utilisation of microstructures, including those in MEMS (Microelectromechanical Systems), is currently advancing across diverse industries. The behaviour of materials at the micro-scale differs from that at the macro-scale, necessitating the assessment of fatigue life in micro-size specimens to ensure the reliability of microstructures (1). Typically, mechanical property evaluation of microstructures is primarily performed using the Nanoindentation technique. However, this method provides only indirect property measurements and is challenging for assessing cyclic properties. Furthermore, in high-cycle fatigue testing exceeding 1 million cycles, conducting tests at the macro-scale requires significantly longer testing durations. However, by using micro-scale specimens, it is possible to drastically reduce the testing time at the same testing speed (2). This study aims to develop a fatigue test system capable of conducting high-cycle fatigue testing exceeding 1 million cycles on micro-scale specimens within a high-vacuum chamber. Additionally, the system accommodates a stroke range from 50 nm to 20 µm, enabling the characterization of material properties across a wide range of materials. The fatigue test system utilised in this study incorporates a high-durability shortened piezoelectric actuator, enabling fatigue testing exceeding 1 million cycles to be conducted within one hour at the maximum frequency of 200 Hz. Furthermore, the system incorporates a 5-axis piezo stage, enabling simultaneous testing and SEM measurements within the high-vacuum chamber. The final structure of the fatigue test system is determined by considering the degree of freedom and usability through the fabrication of a mockup with the same dimensions using 3D printing technology. Considering the specimen geometry required for tension, compression, and bending testing modes, a micro-grip design is developed. The testing apparatus utilises two optical microscopes with a magnification of 1000x, set up vertically and horizontally, to precisely align the grip and specimen. The utilisation of the developed micro fatigue test system allows for rapid assessment of the fatigue properties of microstructures in various materials, based on different testing modes (tension, compression, bending).
References
(1) Lavenstein, Steven, and Jaafar A. El-Awady. "Micro-scale fatigue mechanisms in metals: Insights gained from small-scale experiments and discrete dislocation dynamics simulations." Current Opinion in Solid State and Materials Science 23.5 (2019): 100765.
(2) Sweeney, Caoimhe A., et al. "Micro-scale testing and micromechanical modelling for high cycle fatigue of CoCr stent material." Journal of the mechanical behavior of biomedical materials 46 (2015): 244-260.
| Keywords | : Fatigue Test System, Micro-scale, High-cycle Fatigue |
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