Polished notch modification of SENB-S fracture toughness testing

Abstract In fracture toughness testing it is common for reasons of simplicity and reproducibility to use notches to approximate sharp cracks. However, a dependence of measured fracture toughness ( K Ic ) on notch-root radius is observed. This can be explained as a consequence of the interaction of a distorted stress field with material flaws in front of a notch. A relationship to quantify this effect is presented and examined. It is shown that to measure true fracture toughness sharp notches of the size of microstructural features are required. A simple method to make very sharp notches is presented. Fracture toughness values determined with sharp-notched samples are compared with the results of experiments with conventional sawn-in notches. It is shown that sharp notches deliver considerably lower, more accurate and reproducible values of K Ic for materials with fine microstructures. These values are thought to lie at the beginning of any R -curve.