Size effects determined from tensile tests of perforated MEMS scale specimens

A systematic study of small-scale size effects has been conducted on elliptically perforated specimens with minimum radius of curvature of 1 micron. This study aimed at assessing the dependence of failure stress at the tip of a notch on varying: (a) stress concentration for constant radius of curvature, (b) radius of curvature of micro-notches relative to the material grain size and constant stress concentration. The experiments demonstrate a strong influence of notch radius on the failure strength of MEMS scale specimens, while the effect of the stress concentration factor is of rather secondary importance. The local failure strength at the tip of a notch increases when the radius of curvature becomes smaller, which is in accordance with the probabilistic nature of failure. When the notch radius becomes as small as 1 micron (only three times larger than the grain size) then a strong size effect is observed. This effect becomes moderate for larger radii of curvature, up to 8 microns (25 times the grain size), when the failure stress at the notch tip almost reaches the tensile strength recorded for 50 micron wide samples.