V. B. Poroshin

THE GENERALIZED SIMILARITY PRINCIPLE AND A KINETIC DAMAGE MODEL AS TOOLS FOR ESTIMATING DURABILITY UNDER LOW-CYCLE LOADING INVOLVING CREEP

The paper demonstrates the application of known progressive adequate models of deformation and strength properties of steels and alloys in engineering practice. The models are designed to analyze the kinetics of the stress-strain state and fatigue damage accumulation under fairly general loading programs. They cover conditions of cyclic inelastic loading at elevated temperatures with stages of fast and slow load variation, subsequent additional loading, and holding under various static and kinematic conditions.

The stress-strain kinetics is analyzed with the application of the so-called generalized similarity principle (GSP) formulated in the form of the state equation in macroscopic parameters together with memory rules about the deformation and temperature history. The GSP is a direct consequence of the Gokhfeld – Sadakov structural model of an elastic-viscoplastic medium, which is based on the concept of the microheterogeneity of real materials.

The process of fatigue damage accumulation is described by a kinetic damage model developed by the author. The rate of fatigue damage accumulated by a material volume element is a linear homogeneous function of inelastic strain rate. It is assumed that fatigue damage is related only to the alternating component of inelastic strain. There are different damage processes, namely the one at the stage of fast (plastic) deformation and that at creep, which have their own damage components. One of the components can be only increasing, and the other is partially reversible.

The paper presents the main provisions and constitutive relations of the mentioned mathematical models of deformation and strength properties. It gives an example of constructing the trajectory of a material state point in the stress–strain space under a specified program of cyclic loading, including periods of holding, fast and slow deformation. On this basis, the kinetic model of damage accumulation is used to analyze fatigue damage variation in a cycle and to evaluate the number of cycles to failure by the macrocracking criterion.

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