Phenomenological Criterion of the Limit State of Structural Materials with Account of their Damageability

Abstract

The paper analyzes the main criteria for the limit state of structural materials at the stage of macrocrack nucleation, which are based on the basic provisions of thermodynamics of irreversible processes in continuum mechanics of damageability. The limits of their application for the case of complex stressed state are established. A model of scattered damage accumulation depending on the level of irreversible strain is presented and the dependences of kinetics parameters of damage accumulation and damage limit value on the elastic-plastic characteristics of the material under pure tension conditions are established. The kinetics of damage accumulation according to the presented model is compared to the experimental values for several of structural materials. The methodology of the basic experiment with cylindrical solid specimens is described, taking into account the non-uniformity of the strain distribution along the specimen radius. The results of damage accumulation by shear failure mechanism obtained via the developed technique are compared with the experimental results of thin-walled specimens. It is shown that the value of damageability parameter essentially depends on the type of stressed state. On the basis of Davidenkov–Fridman approach, which takes into account two (tear and shear) failure mechanisms, a generalized phenomenological criterion of limiting state is proposed and substantiated using the Nadai–Lode stress state type parameter.