An energy-based microstructure model to account for fatigue scatter in polycrystals

Michael D. Sangid, Hans J. Maier, Huseyin Sehitoglu

Research output: Contribution to journalArticle

Abstract

Scatter observed in the fatigue response of a nickel-based superalloy, U720, is linked to the variability in the microstructure. Our approach is to model the energy of a persistent slip band (PSB) structure and use its stability with respect to dislocation motion as our failure criterion for fatigue crack initiation. The components that contribute to the energy of the PSB are identified, namely, the stress field resulting from the applied external forces, dislocation pile-ups, and work-hardening of the material is calculated at the continuum scale. Further, energies for dislocations creating slip in the matrix/precipitates, interacting with the GBs, and nucleating/agglomerating within the PSB are computed via molecular dynamics simulations. Through this methodology, fatigue life is predicted based on the energy of the PSB, which inherently accounts for the microstructure of the material. The present approach circumvents the introduction of uncertainty principles in material properties. It builds a framework based on mechanics of microstructure, and from this framework, we construct simulated microstructures based on the measured distributions of grain size, orientation, neighbor information, and grain boundary character, which allows us to calculate fatigue scatter using a deterministic approach. The uniqueness of the approach is that it avoids the large number of parameters prevalent in previous fatigue models. The predicted lives are in excellent agreement with the experimental data validating the model capabilities.

Original languageEnglish (US)
Pages (from-to)595-609
Number of pages15
JournalJournal of the Mechanics and Physics of Solids
Volume59
Issue number3
DOIs
StatePublished - Mar 1 2011

Keywords

  • Energy methods
  • Fatigue crack initiationlife prediction
  • Grain boundaries
  • Microstructures
  • Polycrystalline material
  • Scatter

ASJC Scopus subject areas

  • Condensed Matter Physics
  • Mechanics of Materials
  • Mechanical Engineering

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