A simple apparatus for tensile testing of rock

A. Fakhimi, J. F. Labuz

Research output: Contribution to journalArticlepeer-review


Measuring tensile strength of a quasi-brittle material such as rock is a challenging task. Indirect tensile testing methods such as the Brazilian and flexural tests rely on the assumption of linear elastic behavior, which is not valid close to the peak stress. The direct tensile testing method is independent of the constitutive response of the material and should provide more realistic data. Nevertheless, the test set up in direct tensile testing is time consuming and the results can depend on the applied boundary conditions. In this work, a new apparatus is introduced that can measure tensile strength of quasi-brittle materials and provide information regarding the crack opening behavior. The apparatus, which is an aluminum or steel beam with a cut-out and central notch, acts as both the loading fixture and load cell. The specimen is attached to the central part of the apparatus using an epoxy adhesive. Strain gages mounted on the two sides of the apparatus provide the necessary information about the tensile behavior of the specimen. The device is also capable of detecting and quantifying the intensity of asymmetric failure (crack growth) in the specimen, as identified by digital image correlation. The apparatus, its calibration, and some tests results are presented and discussed.

Original languageEnglish (US)
Article number105208
JournalInternational Journal of Rock Mechanics and Mining Sciences
StatePublished - Oct 2022

Bibliographical note

Funding Information:
A provisional patent application has been filed for the tensile test apparatus. The first author received support from the J.S. Braun/Braun Intertec Professorship during his visit to the University of Minnesota. The first author is grateful to New Mexico Institute of Mining and Technology, where he partially developed the CA2 computer program. Jacob Sharpe, Pouyan Asem, and Ali Tarokh assisted with installing strain gages and performing experiments.

Publisher Copyright:
© 2022 Elsevier Ltd


  • Critical crack opening
  • Post-peak behavior
  • Stress-crack opening relation
  • Tensile strength
  • Tensile testing apparatus


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