Effects of Fixture Configurations and Weld Strength Mismatch on J-Integral Calculation Procedure for SE(B) Specimens

This work presents the development of a J-integral estimation procedure for deep and shallow cracked bend specimens based upon plastic η(pl) factors for a butt weld made in an S690 QL high strength low alloyed steel. Experimental procedures include the characterization of average material properties by tensile testing and evaluation of base and weld metal resistance to stable tearing by fracture testing of square SE(B) specimens containing a weld centerline notch. J-integral has been estimated from plastic work using a single specimen approach and the normalization data reduction technique. A comprehensive parametric finite element study has been conducted to calibrate plastic factor η(pl) and geometry factor λ for various fixture and weld configurations, while a corresponding plastic factor γ(pl) was computed on the basis of the former two. The modified η(pl) and γ(pl) factors were then incorporated in the J computation procedure given by the ASTM E1820 standard, for evaluation of the plastic component of J and its corresponding correction due to crack growth, respectively. Two kinds of J-R curves were computed on the basis of modified and standard η(pl) and γ(pl) factors, where the latter are given by ASTM E1820. A comparison of produced J-R curves for the base material revealed that variations in specimen fixtures can lead to ≈10% overestimation of computed fracture toughness J(Ic). Furthermore, a comparison of J-R curves for overmatched single-material idealized welds revealed that the application of standard η(pl) and γ(pl) factors can lead to the overestimation of computed fracture toughness J(Ic) by more than 10%. Similar observations are made for undermatched single material idealized welds, where fracture toughness J(Ic) is overestimated by ≈5%.