CONSTITUTIVE-EQUATIONS IN NONLINEAR DAMAGE MECHANICS

The classical method of solving problems concerning the delayed fractu re of structural materials and elements is based on analysis of their stabilized stress-strain state arid the use of parametric relations wh ich include the time or number of cycles to failure. Over the last twe nty years, researchers have developed another approach employing the c oncept of internal variables [1, 2, 22] along with a system of evoluti onary equations and failure criteria. Entropy, internal energy, empiri cal temperature, internal time, strain-hardening, and damage are the q uantities most often chosen as the internal variables. In the present study, we examine methods of constructing adequate evolutionary equati ons for a damage parameter that cannot be measured directly.