Available experimental data from uniaxial tests are analyzed to estimate values for parameters of a microcrack dependent model of material response. The experimental data on microcrack density evolution during uniaxial deformation were obtained with small-angle X-ray scattering techniques on polymer specimens. The parameters of the microcrack dependent model are the opening and size of the microcracks, a thermodynamic potential for microcrack kinetics that describes energy conditions for microcrack creation, and coefficients in a nonlinear Onsager type relationship to describe rate kinetics of microcrack creation. The Onsager relationship contains a nonequilibrium thermodynamic measure that is the work done per microcrack created minus the thermodynamic energy per microcrack created. Deformation stability concepts of microcrack dependent material response are discussed in terms of mechanical stability, thermodynamic stability, and global or system stability of the uniaxial test.

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