Fatigue of materials used in microscopic components

This paper discusses the fatigue behaviour of materials used in microscopic components, which are defined as components in which the section size is between one and ten grain diameters. Experimental data were obtained on microscopic and conventional (macroscopic) notched specimens of 316L stainless steel, which is used in many biomedical components including the cardiovascular stent. Microscopic specimens showed unusual behaviour: low threshold values and very flat stress‐life(S‐N) curves. The low threshold values were attributed to the extremely small thickness, which may be preventing closure; a secondary contribution may be coming from a change in the length of non‐propagating cracks. Good predictions could be achieved using the Smith–Miller approach and the theory of critical distances (TCD) if this reduced threshold was taken into account or if, alternatively, the critical distance was made equal to the grain size.