The brittle fracture constraint effect in two different weld thermal simulated microstructures of a 500 MPa steel is investigated through testing of bending specimens with different a/W ratios. It is found that on average the constraint effect is higher in the CGHAZ microstructure compared to the ICCGHAZ. The procedure for calibration of Weibull parameters proposed by Gao et al. [1] has been applied to the results. It is found that a lower m-value is calibrated for the ICCGHAZ microstructure due to the lower constraint effect observed. Three-parameter representations of the Weibull distribution better represent the distribution of the fracture toughness values compared to two-parameter representations.
