Class I vs Class II stability: a demonstration of size effect

J. F. Labuz, L. Biolzi

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The objectives of this work are to offer an analytical explanation and to present experimental evidence of the Class I "ductile" vs the Class II "brittle" response observed on the global level for rock and rock-like materials. The general basis of the theory is that the potential energy of the system, stored per unit of volume, is converted to fracture energy within the rock, dissipated per unit of area. Consequently, a natural size dependence appears in the load-displacement response. Tensile fracture in beam elements and shear fracture in compression elements are analyzed using a cohesive-zone representation of fracture. It is shown that the Class I-Class II stability behaviour of of an elastic, softening rock tested under the same loading conditions is due to geometry and size. Once the deformation of the specimen becomes localized, the stiffness of the testing machine is not the sole factor in determining a stable or an unstable response.

Original languageEnglish (US)
Pages (from-to)199-205
Number of pages7
JournalInternational Journal of Rock Mechanics and Mining Sciences and
Issue number2-3
StatePublished - May 1991

Bibliographical note

Funding Information:
Acknowledgements--Partial support from the National Science Foundation (MSS-8906185) and the Institute of Technology of the University of Minnesota is acknowledged.


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