J and CTOD estimation formulas for C(T) fracture specimens including effects of weld strength overmatch

This work focuses on an evaluation procedure to determine the elastic-plastic J-integral and Crack Tip Opening Displacement (CTOD) fracture toughness based upon the eta-method for C(T) fracture specimens made of homogeneous and welded steels. The primary objective of this investigation is to enlarge on previous developments of J and CTOD estimation procedures for this crack configuration while, at the same time, addressing effects of strength mismatch on the plastic eta-factors. The present analyses enable the introduction of a larger set of factors eta 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 pipeline and pressure vessel steels. Very detailed non-linear finite element analyses for plane-strain and 3-D models of C(T) fracture specimens with centerline-cracked welds provide the evolution of load with increased load-line and 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 C(T) specimens with varying overmatch conditions.