On the fracture toughness of irradiated F82H: Effects of loss of constraint and strain hardening capacity

Constraint loss adjustments, based on finite element (FE) stress analysis and local critical stress, σ*, critical stressed volume, V*, cleavage criteria were applied to fracture toughness data from small pre-cracked bend bars of the IEA heat of F82H irradiated to 6.6 dpa at 300 °C in the High Flux Isotope Reactor. The 100 MPa√m master curve method reference temperature shifts were evaluated based on both the measured toughness (ΔTm) and after size-adjusting the toughness to small-scale yielding conditions at reference specimen size (ΔTo) with values of ≈142 and 205 °C, respectively. The model based prediction ΔTo = CoΔ〈σfl〉, where Co ≈ 0.68 and Δ〈σfl〉 is the change in the average flow stress over 0–10% strain is in excellent agreement with ΔTo. The FE analyses also demonstrates an upper-bound KJc that can be measured with these small bend bars for irradiated alloys that suffer severe loss of strain hardening.