Determination of Nonassociated Constitutive Equation for Rock Salt from Experiments
Starting from precise true triaxial failure tests on cubic rock salt samples a triaxial elastic/viscoplastic constitutive equation has been formulated which comprises: creep (including work hardening and unloading), volume dilatancy and compressibility during deformation, instantaneous failure, or damage with subsequent creep-failure. The main steps to formulate such a constitutive equation are: determination of the instantaneous response of rock salt, the yield function and the viscoplastic potential. All constitutive parameters and functions are determined from the experimental data in three dimensions without any a priori assumption concerning their form; a preliminary uniaxial form of the constitutive equation is not needed. Finally it is discussed under which conditions this constitutive equation can be simplified and when an associated law is possible.
KeywordsConstitutive Equation Rock Salt Failure Surface Steady State Creep Transient Creep
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