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Fracture toughness — Master Curve (ASTM E1921)

K_JC(T) Master Curve · 1T-equivalent

Plots the median + 5/95 % envelope of K_JC against temperature. The standard tool for setting MDMT (UCS-66), assessing RPV irradiation embrittlement (NRC RG 1.99 R2), and B31.3 §323.2.2 impact-test exemption.

Inputs

°C
Reference temperature where K_JC,med = 100 MPa√m for 1T specimens. Determined by E1921 test or estimated from charpy correlation.
°C
MPa·√m
K_I = Y·σ·√(πa). Use the /console/fracture page to compute it for a given crack + stress.
normalized PV plate

Results

Master Curve fracture toughness · ASTM E1921
median5 % (lower bound)95 %T₀ = -50 °CK_app = 60SF_med = 2.24-150-100-500501001500100200300400Test temperature (°C)K_JC (MPa·√m, 1T-equiv)ASTM E1921 · K_JC,med = 30 + 70·exp(0.019·(T − T₀)) · 1T-equivalent · used for RPV irradiation embrittlement / UCS-66 MDMT
T₀ = -50 °C · K_JC,med(T_svc=-29°C) = 134 · K_JC,5%(T_svc) = 74 · K_app = 60 → SAFE (SF_5% = 1.24)
K_JC,med at T_svc134MPa·√m
K_JC,5% at T_svc74MPa·√m
Safety factor (median)2.24
Safety factor (5 % lower)1.24
VerdictPASS — comfortable margin to lower bound
The Master Curve is unique to ferritic steels in the transition region — it does NOT apply to austenitic stainless or fully ductile fracture. For irradiated RPV steels apply EWO (Eason-Wright-Odette) shift to T₀.
Download all inputs + calculations + outputs as a single PDF.