Scaling of the fracture process zone in rock

Ali Tarokh, Roman Y. Makhnenko, Ali Fakhimi, Joseph F. Labuz

Research output: Contribution to journalArticlepeer-review

55 Scopus citations


The zone of microcracks surrounding a notch tip—the process zone—is a phenomenon observed in fracture of quasi-brittle materials, and the characterization of the process zone is the topic of the paper. Specimens of different sizes with a center notch fabricated from a granite of large grain (Rockville granite, average grain size of 10 mm), were tested in three-point bending. Acoustic emissions were recorded and locations of microcracks were determined up to peak load. The results show that both the length and width of the process zone increase with the increase of the specimen size. Furthermore, the suitability of a proposed theoretical relationship between the length and width of the process zone and specimen size was studied experimentally and numerically. The discrete element method with a tension softening contact bond model was used to investigate the development of the process zone with the specimen size. A synthetic rock composed of rigid circular particles that interact through normal and shear springs was tested in the numerical simulations. It was shown that the limiting specimen size, beyond which no further noticeable increase in the length of the process zone is observed, is significantly larger than the limiting specimen size beyond which the width of the process zone shows no size effect.

Original languageEnglish (US)
Pages (from-to)191-204
Number of pages14
JournalInternational Journal of Fracture
Issue number2
StatePublished - Apr 1 2017

Bibliographical note

Publisher Copyright:
© 2016, Springer Science+Business Media Dordrecht.


  • Acoustic emission
  • Brittleness number
  • Discrete element method
  • Fracture process zone
  • Size effect


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