A Micromechanics Approach for Assessing the Applicability of Precracked Charpy Specimens to Determine the T₀ Reference Temperature

This work describes an application of a micromechanics model for cleavage fracture to determine the reference temperature for pressure vessel steels from precracked Charpy (PCVN) specimens. A central objective is evaluate the effectiveness of the Weibull stress (σ_w) model to correct effects of constraint loss in PCVN specimens which serve to determine the indexing temperature T₀ based on the Master Curve methodology. Fracture toughness testing conducted on an A285 Grade C pressure vessel steel provides the cleavage fracture resistance data needed to estimate T₀. Very detailed non-linear finite element analyses for 3-D models of plane-sided SE(B) and PCVN specimens provide the evolution of near-tip stress field with increased macroscopic load (in terms of the J-integral) to define the relationship between σ_w and J from which the variation of fracture toughness across different crack configurations is predicted. For the tested material, the Weibull stress methodology yields estimates for the reference temperature, T₀, from small fracture specimens which are in good agreement with the corresponding estimates derived from testing of much larger crack configurations.