Transition fracture toughness testing with notched round bars (NRB)

The notched round bar (NRB) geometry was assessed for use with ASTM E 1921-97 Standard for Test Method for the Determination of Reference Temperature, T 0 , for Ferritic Steels in the Transition Range. Instead of precracking the NRB specimens, apparent fracture toughness using three different notch root radii was extrapolated to a zero radius to infer sharp crack fracture toughness. The reference temperature using A302B NRB specimens was determined to be -89°C, while A3028 C(T) specimens yield To of -87.3°C. In applying ASTM E 1921 to the NRB geometry, a simple scheme to remove notch root radius bias from apparent fracture toughness was developed. In addition, a size correction for converting NRB results to comparable IT-C(T) results was investigated.