Abstract
The influence of notch and water environment on the quasi-static and fatigue fracture behaviour was investigated in single crystal silicon microelements. The tests were conducted in smooth and notched microcantilever beam samples. Smooth specimens were prepared by micromachining (photo-etching) of (110) silicon wafers. For some specimens, nanometre-sized notch was machined 100 μm away from the sample root by using a focused ion beam system. A machining condition was optimized, and the V-shaped notch was successfully introduced. The fracture strength decreased with an increase in notch depth, even though the notch depth was on the order of nanometre. This means that nanometre order notch, which is often regarded as surface roughness in ordinary-sized mechanical components, caused a decrease in the fracture strength of Si microelements. Fatigue tests were also conducted in laboratory air and in pure water. In laboratory air, no fatigue damage was observed even though the surface was nanoscopically examined by an AFM. However, when the fatigue tests were conducted in pure water, the fatigue lives in water were decreased.
