Ultrasonic Monitoring of the Fracture Process Zone in Fracture Toughness Tests of Granite

Toshiyuki Hashida, Tsuyoshi Ueda, Kazuhiro Date, Hideaki Takahashi, Hiroyuki Abé

Research output: Contribution to journalArticlepeer-review

1 Citation (Scopus)


A microcracking fracture process zone is known to accompany tensile macrocrack propagation in rocks. The fracture process zone with nonnegligible length is suggested to be largely responsible for the dependence of fracture mechanics data on the specimen size and geometry. In this paper, an ultrasonic timing method is employed to detect the extent of the fracture process zone (FPZ) during fracture toughness tests of granite, where the travel time of longitudinal waves propagating through fractures is monitored using 500-kHz transducers with commercially available equipment. It is demonstrated that the travel time technique can locate the tip of the FPZ continuously during fracture experiments. The growth behavior of the FPZ observed by the ultrasonic method is shown to agree with the previously published results of numerical analysis that is based on the tension- softening model. Finally, a method is developed for determining the critical J-integral value, Jc on the basis of the length of the FPZ, and the measured Jc values are compared with those obtained by Li’s proposed multiple-specimen technique. It is shown that the present method permits a valid fracture- toughness value to be evaluated by use of a single fracture specimen.

Original languageEnglish
Pages (from-to)1177-1182
Number of pages6
JournalNihon Kikai Gakkai Ronbunshu, A Hen/Transactions of the Japan Society of Mechanical Engineers, Part A
Issue number525
Publication statusPublished - 1990


  • Fracture
  • Fracture Process Zone
  • Fracture Toughness
  • J-integral
  • Rock
  • Tension-Softening Model
  • Ultrasonics


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