Within framework of the continual fracture mechanics, we describe the engineering approach to the assessment of scattered microdamage accumulation kinetics in metallic materials under elastoplastic loading conditions in case of plane stressed state. Automatized experimental stand and the respective investigation technique are discussed. The stand has been developed based on modification of the UMÉ-10T electromechanic test machine. State-of-the-art computer technologies and microprocessing hardware are incorporated in the stand automation. We present the technique of experimental assessment of damage accumulation kinetics in metallic structural materials under complex elastoplastic loading conditions with account of two different fracture (cleavage and shear) processes, which technique is based on measuring the specific electric resistance of the specimen.Keywords: accumulation of defects, complex elastoplastic loading, resistivity of the specimen, testing installation.Introduction. Under conditions of intense elastoplastic deformation and in the processes of creep and low-cycle fatigue of structural elements, microdefects (micropores and microcracks) appear and accumulate in the material in the zones of elevated loading [1][2][3][4][5][6]. The improvement of the accuracy of prediction of the service life of structural elements of this sort in the stage of engineering design and the accuracy of evaluation of the residual service life in the stage of operation mainly depend on the reliability of the system of determining equations which must include the parameters of damageability [4,5]. The damageability of the material characterizes the dependence of the density of microdefects in a certain plane section of an element of the material on the action of external thermal and force factors. At present, there is no common point of view on the physical meaning of the parameter of damageability [7][8][9][10][11][12][13][14].Continual fracture mechanics (CFM) successfully develops for the last 40 years as a promising scientific trend in the mechanics of deformable bodies. The formation of this trend was initiated by Kachanov [4] and Rabotnov [5] who used the concept of internal variables [3, 9, 12] with a system of the corresponding kinetic equations and fracture criteria in the stage of initiation of a microcrack.For the purposes of engineering calculations, the kinetics of accumulation of microdefects is especially conveniently analyzed in terms of macrocharacteristics of the mechanical properties of structural materials in the form of force, deformation, and energy approaches [12,[15][16][17]. In this case, the application of CFM is, as a rule, based on the hypothesis on averaging of microdefects over the volume of the material and the phenomenological parameter of damageability is represented either as a scalar quantity [16], or as a vector [17], or in the tensor form [18]. The analysis of the data available from the literature demonstrates [17,19,20] that, under conditions of complex stressed state, both the general...

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On the basis of the concepts of the continuum mechanics of damage, we propose an engineering method for the analysis of the kinetics of accumulation of scattered defects in metallic structural materials under conditions of elastoplastic deformation and low-cycle fatigue. It is shown that, in the general case of complex loading for the complex stress state, it is reasonable to use the specific energy of additional stresses (with regard for the arc of plastic strains in a loading cycle) as a parameter of damage for two types of fracture (rupture and shear).Keywords: low-cycle fatigue, Bauschinger effect, phenomenological models of accumulation of defects, specific energy of additional stresses.The process of elastoplastic deformation of structural materials is accompanied by the initiation, growth, and accumulation of defects [1][2][3][4][5][6][7][8][9]. It is generally agreed that microdamage should be regarded as a collection of continuous complex and poorly studied processes of changes running in materials under thermomechanical loads on the submicro-, micro-, and macrolevels and leading to the degradation of the mechanical properties of materials accompanied by the decrease in the load-carrying ability of the entire structure [1][2][3][4][5][6][7][8][9][10][11][12].For low-cycle fatigue, the stage of accumulation of scattered defects (SD) in the heavy-duty zones of the load-carrying elements of the structures constitutes up to 90% of total service life (with regard for survivability). The knowledge and analysis of the kinetics of accumulation of SD in structural materials depending on the complex technological and operating thermal and force loading processes enable one to give more reliable predictions (by the numerical and experimental methods) of the service life of structural elements in the stage of design and their residual service life in the process of operation.The most promising approach to the solution of the posed problem is a phenomenological approach, according to which force, strain, or energy quantities are used as quantitative parameters [13][14][15]. This approach is based on the principal concepts of the continuum mechanics of damage (CMD). The principal concepts of the CMD (or the continuum fracture mechanics in the stage of crack initiation) were formulated by Kachanov and Rabotnov as applied to the processes of creep [3,4]. At present, there are no generally accepted reliable procedures for the determination of regularities of the processes of initiation and accumulation of SD [16][17][18]. In the first approximation, as a parameter of damage, it is customary to use a scalar quantity and the regularities of its variation depending on thermal and force loading conditions. In the general case, the model of damage is included in the system of determining equations whose reliability specifies the accuracy of evaluation of the service life of structural elements under conditions of low-cycle fatigue.The results of investigation of cyclic strength for a large class of metallic materials and stru...

The paper presents a procedure whereby the damage accumulation kinetics in structural materials, such as steel 45, stainless steel 12Kh18N10T, aluminum alloy D16T, and titanium alloy VT22, under elastoplastic deformation is studied based on variation parameters of elastic modulus and resistivity. For complex stress conditions, a continuum model for damage accumulation is proposed which relates the damage parameter to the intensity of accumulated plastic strains. The data calculated by the proposed continuum model are compared to the experimental findings of the investigation of the damage accumulation kinetics for some structural metals.

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