J and CTOD Estimation Procedures for Welded Fracture Specimens Including Effects of Weld Strength Overmatch

Analytical efforts to support the development of laboratory measurements for fracture toughness values have focused primarily on estimating J and CTOD from plastic work. The approach employs a plastic eta-factor to relate the crack driving force (J and CTOD) to the area under the load versus displacement (LLD or CMOD) for cracked configurations. Because of its relative ease with which the load-displacement records can be measured in conventional test specimens, the method is most suited for standardized procedures of fracture toughness testing for structural steels such as ASTM E1820. However, while used effectively in testing protocols utilizing high constraint fracture specimens, application of the  methodology in toughness evaluation procedures for welded fracture specimens may provide unwarranted estimates of J and CTOD values.

This work focuses on the evaluation procedure to determine the elastic-plastic J-integral and CTOD fracture toughness based upon the eta-method for common fracture specimens made of welded steels. The primary objective of this investigation is to enlarge on previous developments of J and CTOD estimation procedures for C(T), SE(B) and SE(T) configurations based upon plastic eta-factors used to estimate elastic-plastic fracture parameters from plastic work. The present analyses enable the introduction of a larger set of plastic eta-factors  for a wide range of crack sizes (as measured by the  a∕W-ratio) and material properties, including different levels of weld strength mismatch, applicable to structural, pipeline and pressure vessel steels. Very detailed non-linear finite element analyses for plane-strain and full 3-D models of standard fracture specimens provide the evolution of load with increased crack mouth opening displacement required for the estimation procedure. Overall, the present study, when taken together with previous investigations, provides a fairly extensive body of results to determine parameters J and CTOD for different materials using fracture specimens with varying overmatch conditions.