Fracture Toughness Testing with Notched Round Bars

A method to simplify fracture toughness testing and reduce testing costs is discussed. An alternative specimen geometry, the notched round bar (NRB), has been combined with a simpler testing methodology. A multispecimen technique using notched round bars with finite notch root radii ρ was applied to 2024-T351 and overaged 2024 aluminum alloy. No fatigue precracking was used. A graph of apparent fracture toughness Kρ versus the square root of notch root radius √ρ was extrapolated to ρ = 0, corresponding to a fatigue precracked configuration. The resulting fracture toughness values were the same as those obtained from ASTM E 399 tests. Apparent fracture toughness Jρ, determined from NRB J-R curves for overaged 2024, was graphed versus notch root radius ρ. The extrapolated value of fracture toughness was the same as that obtained from ASTM E 813 and E 1152 tests.