Size and geometry effects in notched compact tension specimens

Abstract

This paper uses Weibull stress analysis to investigate whether the effective notch toughness Kmatρ for cleavage fracture measured using Compact Tension (CT) specimens containing a U-notch is dependent on the size and geometry of the CT specimen. Notched CT specimens are typically used to measure a material's effective notch toughness Kmatρ and to assess failure of a structure containing a non-sharp defect using the Notch Failure Assessment Diagram (NFAD). The paper concludes that Kmatρ is dependent on specimen thickness B over and above the microstructural weakest link effect arising from differences in the volume of the plastic zone; Kmatρ is a function of not only the in-plane effect of the notch radius but also an out-of-plane constraint loss which itself is enhanced by the presence of the notch radius. This out-of-plane constraint loss can be more significant than the in-plane effect of the notch radius. The use of experimentally measured Kmatρ values in an NFAD assessment of a notched structure may therefore be non-conservative if the out-of-plane constraint loss in the CT specimen is more significant than in the structure. For the material considered in this paper, doubling the thickness B of the CT specimen resulted in plane strain conditions being sufficiently dominant to eliminate out-of-plane constraint loss in the CT specimen.