Fatigue crack growth "overload effect": Mechanistic insights from in-situ synchrotron measurements

Mark Croft, Najeh Jisrawi, Alexander Ignatov, Ronald L. Holtz, Zhong Zhong

Research output: Contribution to journalArticlepeer-review

6 Scopus citations

Abstract

Synchrotron-based, high-energy X-ray diffraction measurements are used to study the local strain fields underlying the transient fatigue crack growth rate retardation produced by a single overload cycle known as the overload effect. Specifically, 4140 steel compact tension specimens fatigued for varying levels of crack growth after an overload cycle have been studied with in-situ diffraction under varying external loads. The load responses of the strain at the overloadposition, versus at the crack tip, are focused upon in detail. The large compressive residual strain at the overload-point is observed to remain essentially unchanged even after the overload-point is left in the wake of the propagating crack tip. The differential strain-load response at the crack-tip/overload position before and immediately after the overload is seen to be unchanged. Once the overload point is behind the crack tip, a highly nonlinear behavior is observed in which the load response of the strain field transfers from the overload -point to the crack tip when the load exceeds a critical value. The results are discussed in terms of plasticity-induced crack face contact at the overload point as an important local mechanism contributing to the "overload effect" in this specific system.

Original languageEnglish (US)
Pages (from-to)83-94
Number of pages12
JournalJournal of Strain Analysis for Engineering Design
Volume47
Issue number2
DOIs
StatePublished - Feb 2012

All Science Journal Classification (ASJC) codes

  • Mechanics of Materials
  • Mechanical Engineering
  • Applied Mathematics
  • Modeling and Simulation

Keywords

  • Fatigue
  • Overload
  • Strain
  • Synchrotron
  • X-ray

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