Numerical Modeling of Ductile Tearing Effects on Cleavage Fracture Toughness

摘要

Previous work by the authors described a micromechanics fracture model to correct measured Jc-values for the mechanistic effects of large-scale yielding. This new work extends the model to also include the influence of ductile crack extension prior to cleavage. Ductile crack extensions of 10-15 x the crack-tip opening displacement at initiation are considered in plane- strain, finite element computations. The finite element results demonstrate a significant elevation in crack-tip constraint due to macroscopic sharpening of the extending tip relative to the blunt tip at initiation of growth. However, this effect is offset partially by the additional plastic deformation associated with the increased applied J required to grow the crack. The initial a/W ratio, tearing modulus, strain hardening exponent and specimen size interact in a complex manner to define the evolving near-tip conditions for cleavage fracture. The paper explores development of the new model, provides necessary graphs and procedures for its application and demonstrates the effects of the model on fracture data sets for two pressure vessel steels (A533B and A515).