Uncertainty in Ductile Fracture Initiation Toughness (J_Ic) Resulting From Compliance Measurement Available to Purchase

ASTM E1820-13 for determining ductile fracture initiation toughness (J_Ic) includes a single-specimen technique where crack length is determined using the compliance measurement from partial unloads. Noise and nonlinearity in the compliance data, together with the method used to select data to perform linear regression, lead to statistical uncertainty in the resulting crack lengths and J_Ic. Statistical analysis of linear regression was used to quantify variability in compliance for different selection methods. A Monte Carlo simulation was conducted to propagate that variability to the determination of J_Ic and to quantify the resulting uncertainty. Recommendations are made regarding how to select data for linear regression to minimize uncertainty. The simulation shows that a standard error on compliance of less than 0.25 % of the compliance results in a standard deviation in J_Ic of less than 4 % of the mean J_Ic.