1 Copyright ©2011 by ASME IMPROVED J AND CTOD ESTIMATION FORMULAS FOR C(T) FRACTURE SPECIMENS INCLUDING OVERMATCHED WELDMENTS Rafael G. Savioli Department of Naval Architecture and Ocean Engineering,University of São Paulo São Paulo, SP 05508−900, Brazil Email: savioli@usp.br Proceedings of the ASME 2011 Pressure Vessels & Piping Division Conference PVP2011 July 17−21, 2011, Baltimore, Maryland, USA PVP2011-57030 Claudio Ruggieri Department of Naval Architecture and Ocean Engineering,University of São Paulo, São Paulo, SP 05508−900, Brazil Email: claudio.ruggieri@usp.br ABSTRACT This work focuses on the evaluation procedure to determine the elastic-plastic J-integral and CTOD fracture toughness based upon the η -method for C(T) fracture specimens made of homo- geneous and welded steels. The primary objective of this inves- tigation 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 η -factors. The present analyses enable the introduction of a larg- er set of factor η for a wide range of crack sizes (as measured by the a∕W-ratio) and material properties, including different lev- els of weld strength mismatch, applicable to structural, pipeline and pressure vessel steels. Very detailed non-linear finite ele- ment analyses for plane-strain models of square groove, center cracked C(T) 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 differ- ent materials using C(T) specimens with varying overmatch con- ditions. INTRODUCTION Fracture mechanics based approaches, also referred to as Engi- neering Critical Assessment (ECA) procedures, applicable to structural components rely upon the notion that a single parame- ter defining the crack driving force characterizes the fracture re- sistance of the material [1-3]. These approaches provide a means for introducing acceptance criteria for cracked structural compo- nents by relating the operating conditions to a critical applied load or critical crack size. In particular, assessments of cleavage fracture for ferritic steels in the ductile-to-brittle transition (DBT) region are based on the one-parameter elastic-plastic characterization of macroscopic loading, most commonly the J- integral or the Crack Tip Opening Displacement (CTOD, δ ), and their corresponding macroscopic measures of cleavage frac- ture toughness ( J c or δ c ). Conventional testing programs to measure cleavage frac- ture toughness of ferritic steels, including pipeline steels and their weldments, routinely employ three-point bend specimens containing deep, through cracks ( a∕W ≥ 0.5 ). In particular, fracture testing of pipeline steel weldments make extensive use of single edge notch bend (SE(B)) specimens with through-