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Use of simple load‐independent constraint parameter for prediction of brittle fracture
Author(s) -
NOVÁK J.,
LAUEROVÁ D.
Publication year - 2006
Publication title -
fatigue and fracture of engineering materials and structures
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.887
H-Index - 84
eISSN - 1460-2695
pISSN - 8756-758X
DOI - 10.1111/j.1460-2695.2006.01063.x
Subject(s) - charpy impact test , constraint (computer aided design) , fracture toughness , brittleness , materials science , stress intensity factor , fracture (geology) , stress (linguistics) , structural engineering , yield (engineering) , toughness , fracture mechanics , mechanics , composite material , mathematics , geometry , engineering , physics , linguistics , philosophy
ABSTRACT In this paper, a load‐independent constraint parameter based on T‐ stress is suggested for prediction of brittle fracture in the ductile‐to‐brittle transition region under different constraint conditions. This parameter is applied to the results of EU project VOCALIST and in particular to fracture toughness data for pre‐cracked Charpy specimens with deep and shallow cracks (steel A533B specially heat treated to achieve an elevated yield stress). These were obtained from the VOCALIST project in NRI Řež. In contrast to the usual procedure using a non‐dimensional ratio of T ‐stress and yield stress, T /σ y , for constraint evaluation, a slightly different parameter is proposed. This is based on the load‐independent ratio of T ‐stress and the stress intensity factor K I , T/K I , for prediction of constraint‐dependent brittle fracture. A simple ‘universal’ dependence of constraint correction factor f = K c mat / K mat on constraint parameter T/K I seems to accurately describe the behaviour of ferritic steels, provided that ductile crack growth preceding brittle fracture is non‐existent or negligibly small. In the paper, both calibration of the dependence and its verification through independent data for two other ferritic steels are performed. In addition, a modification of the factor f = 1 +α(− T /σ y ) m used in the R6 procedure is proposed and leads to a ‘universal’ dependence of fracture toughness ratio K c mat / K mat on constraint. Finally, results of the application of the constraint corrected toughness concept within the Failure Assessment Diagram of the R6 procedure when applied to VOCALIST data are presented.