Introducing heterogeneity into brittle fracture modeling of a 22NiMoCr37 ferritic steel ring forging

Xinglong Zhao, David Lidbury, João Quinta Da Fonseca, Andrew Sherry

    Research output: Contribution to journalArticlepeer-review


    Microstructural oservations of the 22NIMoCr37 "EURO" reactor pressure vessel (RPV) steel ring forging reveal that there is a banded structure along the radial direction, composed of alternate layers rich In bainlte and ferrite of wavelength ∼1.5 ±0.75 mm. Heterogeneity at this meso (millimetre)-scale as well as at the micro (micrometre)-scale is currently not considered by conventional fracture mechanics. This paper describes the development of two numerical approaches aimed at incorporating such heterogeneity Into the Beremin local approach model of cleavage failure, a model that has been used extensively for predicting the brittle fracture of ferritlc RPV steels. The approaches developed combine the crystal plasticity finite element method (CPFEM) with continuum finite element analysis (FEA). CPFEM is applied to predict stress distributions at the microscale and to obtain phase-specific yield and flow properties for continuum FEA that derives stresses at the mesoscale. The results confirm that deformation heterogeneity on the micro- and mesoscales influences the local development of stress. At the microscale, the stress distribution within a representative volume of material located within the crack-tip plastic zone is shown to follow a normal distribution with a ratio of mean stress to standard deviation tending towards 0.1. These results Indicate local stress levels that are within approximately ±20 % of those derived using continuum FEA. At the mesoscale, a periodic variation of stress Is predicted within the larger representative volume. This variation is less dramatic than that observed at the microscale, though it still gives a spatial variation in maximum principal stress of approximately ±7 % between bainite- and ferrite-rich microstructural regions. These results suggest a significant Influence of deformation heterogeneity on local stress levels, particularly at the microscale. However, the conventional Beremin cleavage fracture model, modified to account for microscale stress distribution, predicts only a modest influence of deformation heterogeneity on cleavage fracture probability, Increasing Pf by just 5 %. This highlights the need to account for both the spatial variation In cleavage Initiation sites as well as the distribution in stress throughout the microstructure. The paper describes one approach for this development. Copyright © 2008 by ASTM International.
    Original languageEnglish
    JournalJournal of ASTM International
    Issue number4
    Publication statusPublished - Apr 2008


    • Beremin model
    • Brittle fracture
    • Crystal plasticity
    • Microstructural heterogeneity
    • Rpv steel


    Dive into the research topics of 'Introducing heterogeneity into brittle fracture modeling of a 22NiMoCr37 ferritic steel ring forging'. Together they form a unique fingerprint.

    Cite this