Computer modeling of the deformation of elements of operating power equipment with damages
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COMPUTER MODELING OF THE DEFORMATION OF ELEMENTS OF OPERATING POWER EQUIPMENT WITH DAMAGES B. D. Drobenko We consider the results of computer modeling of the deformation process of a collector with damages under in-service conditions with regard for the elastoplastic character of deformation and the real geometry of the collector and crack-like defects. We also establish the probable causes of damage initiation. Keywords: computer modeling, crack-like defects, thermoelastoplasticity, fracture of materials.
Among the most important problems of domestic power engineering, one should mention the prolongation of operation life of the assemblies and articles of power equipment [1, 2]. As a result of the long-term action of mechanical loads, elevated temperature, and corrosive environment, various defects and damages, including the most dangerous, crack-like ones, are formed in such elements. These damages are often removed by withdrawing a part of the metal together with the defect zone, which, however, leads to the loss of initial shape of the element and, hence, to stress perturbation in the neighborhood of such zones. Reliable software, developed on the basis of adequate present-day mathematical models and methods, enables one to analyze, for short terms, the behavior of this or that structural element with damages or repair withdrawal of the material under conditions modeling the in-service ones and to obtain an expert evaluation of its safety margin. These data are used in deciding on the possibility of temporary prolongation of the operation life or renewal of the assemblies and elements of power equipment with damages as well as in developing recommendations on the corresponding repair measures (choice of the rational, as to stresses, geometrical parameters of withdrawals). In the present work, we consider the main results obtained by computer modeling of the deformation of collectors of the primary steam superheaters of thermal power plants under in-service conditions, carried out by the finite element method [3]. In the course of operation, crack-like defects are formed in collectors between the holes for coils (Fig. 1). To establish the cause of their appearance, we carried out a series of computational experiments on determining the stressed state of a collector without damages under in-service conditions. We took a three-dimensional hollow cylinder with holes (Fig. 2) as the computational model. The cylinder, occupying a domain , with internal R1 and external R2 radii is loaded with internal pressure p at temperature T and closed with bottoms on both sides. A series of holes (three in each) of radius r is placed at distances 2L y from one another in the direction of the longitudinal axis of the cylinder. Similar distances between the hole centers in the circumferential direction (they are measured over the external surface of the cylinder) are equal to L . The pressure on the hole surfaces is also equal to p . Pidstryhach Institute for Applied Problems of Mechanics and Mathematics, Ukrainian National Acade
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