Inelastic Strain and Damage in Surface Instability Tests

Chu Shu Kao, Ali Tarokh, Luigi Biolzi, Joseph F. Labuz

Research output: Contribution to journalArticlepeer-review

12 Scopus citations


Spalling near a free surface in laboratory experiments on two sandstones was characterized using acoustic emission and digital image correlation. A surface instability apparatus was used to reproduce a state of plane strain near a free surface in a modeled semi-infinite medium subjected to far-field compressive stress. Comparison between AE locations and crack trajectory mapped after the test showed good consistency. Digital image correlation was used to find the displacements in directions parallel (axial direction) and perpendicular (lateral direction) to the free surface at various stages of loading. At a load ratio, LR = current load/peak load, of approximately 30 %, elastic deformation was measured. At 70–80 % LR, the free-face effect started to appear in the displacement contours, especially for the lateral displacement measurements. As the axial compressive stress increased close to peak, extensional lateral strain started to show concentrations associated with localized damage. Continuum damage mechanics was used to describe damage evolution in the surface instability test, and it was shown that a critical value of extensional inelastic strain, on the order of −10−3 for the virgin sandstones, may provide an indicator for determining the onset of surface spalling.

Original languageEnglish (US)
Pages (from-to)401-415
Number of pages15
JournalRock Mechanics and Rock Engineering
Issue number2
StatePublished - Feb 1 2016

Bibliographical note

Publisher Copyright:
© 2015, Springer-Verlag Wien.


  • Acoustic emission
  • Continuum damage mechanics
  • Digital image correlation
  • Surface spalling


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