Enhanced crack stability in micro scale fracture testing via optimized bridge notches

In micro cantilever fracture, a bridge notch geometry with material ligaments at the notch ends helps to reduce focused ion beam artefacts near the notch root by arresting initial cracks and promoting fracture from sharp, natural cracks. Thus, it significantly reduces the statistical scatter in fracture toughness, a common but undesirable feature in micro fracture testing. Although this concept has been validated in simulations and experiments, systematic investigations into the optimal geometry remain lacking. In this study, we experimentally examine the influence of bridge width and notch depth on the fracture toughness of micro cantilevers, using single crystalline silicon as a model material. We found that samples with thinner material bridges and deeper notches exhibit crack arrest before failure, while those with thicker bridges do not show crack arrest instead exhibit apparent toughening. Cantilevers with an optimized bridge notch geometry for crack arrest exhibit a K_IC of 1.09 ± 0.02 MPa m^0.5, which agrees with previously reported fracture toughness for the Si (111) surface. Additionally, discrepancies between the bridge geometry in the experiment and the ideal structure resulted in a mismatch between the predicted and observed notch requirements for crack arrest. Our findings offer practical guidelines for designing bridge notch geometries to promote bridge failure, thus improving statistical analysis in micro fracture.