Stress–Strain Kinetics in Calculations of High-Temperature Strength and Longevity of Reactor Structures

Abstract

The plastic properties of materials must be used more fully as working temperatures and temperature gradients increase. The results of tests performed on refractory chromium-nickel alloys with combined low-cycle strain with prescribed total amplitudes and strain increments per cycle are presented. The results are compared with those obtained with rigid, cyclic, sign-alternating, and monotonic strain. A method of constructing mathematical models of a material that take account of short-and long-time characteristics of a metal in combination with the possibility of their direct use in readily available packages implementing the fi nite-elements method is described.The serviceability, strength, safe life, stability, and safety of the high-temperature reactors now being designed can be secured only by making full use of the plastic and strength properties of the structural materials. Thus far, plastic deformation under the conditions of normal operation has been permitted only in local strictly size-bounded zones of stress concentrations [1,2]. The urgency of going outside these frames is dictated by the prospects for advancing nuclear power by building power-generating units with thermal and fast reactors with coolant temperatures above 500-600°C as well as new-generation reactor facilities, including high-temperature gas and space facilities with temperature 900-1500°C. In addition, it is proposed that conventional heat-resistant and austenitic corrosion-resistant steel as well as new refractory and fi re-and radiation-resistant alloys with the problems of deformation and fracture mechanics formulated in a new way be used [3][4][5][6][7].Low-cycle inelastic deformation includes three types of processes, differing by the consequences, the material properties, and the effect of operational factors: sign-alternating deformation, which is characteristic for local zones of concentration, and progressing shape change -the accumulation of residual displacements and their combinations [8]. The properties of a material in the presence of sign-alternating fl ow are determined during tests in a rigid loading cycle set by the deformation of the working part of the sample. In the presence of progressing shape change, they are close to the diagram of monotonic single deformation with elastic relief of loading. There are many works devoted to the investigation of processes of the fi rst two types [9][10][11][12][13], but the general case of combined deformation, which is characteristic for the widest range of the parameters of the external actions, has not been adequately studied. The tests of materials for such conditions are limited [14][15][16][17]; there are no standards for performing them. Mathematical models of the kinetics of the deformation properties of materials for combined long-time loading processes, which are necessary for calculating the strength and longevity of structures, are also weakly developed.

Probability Modeling Taking into Account Nonlinear Processes of a Deformation and Fracture for the Equipment of Nuclear Power Plants

“…To the traditional solution of a problem of service safety [2,[6][7][8][9][10][20][21][22][23][24][25], three groups of approaches had a direct ratio:…”

“…On the basis of such definition are the functionals that resulted above in Eqs. (4)- (10), which include calculation dependences (state equations, curve of deformations and fractures, and strain and force criteria). In improved calculation zones of welded joints, a plastic deformation in the most loaded zones, variety of operating conditions and impacts, and dispersion of characteristics of mechanical properties [2, 10, 20-29, 31, 34-36] are considered.…”

“…In the proximal (till 2020), midrange (till 2030), and kept away (till 2050) prospects, the evolution of nuclear energetics will be carried out on the basis of operating, built, and designed nuclear power plants. Basis of the fundamental and application analysis of strength, life time, reliability, and safety of operation of NPP elements with reactors of VVER, RBMK, and BN types (Figure 1) in regular both emergency situations are the equations and criteria linear and nonlinear mechanics of deformation and fracture [1][2][3][4][5][6][7][8][9][10][11]. They contain in home and foreign strength standards and are used as at design, so at manufacture and operation of working in extremely conditions, a high-loaded power-generating plants with use physical and mathematical modeling [1,[12][13][14][15][16][17].…”

Determination of the material elasticity modulus in bending

“…Модуль Юнга Е материала балки подсчитывали по формуле (1). Расчетный прогиб образца ∆ 3 определя-ли как разность перемещения точек образца под нагру-жающим валком Δ 1 и усредненным перемещением точек над опорами Δ 2 .…”

Chelyabinsk scientific school of strength engineers: results and prospects

“…Одним из высших научных достижений в России за последние несколько десятилетий стала 51-томная энциклопедия «Безопасность России». Ее научные руководители сочли возможным включить в авторский коллектив ряда томов [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27] сотрудников Челябинской научной школы, основанной в ЧПИ и продолжающей работу в ЮУрГУ при научном руководстве ИМАШ РАН и постоянном сотрудничестве с Уральским отделением РАН.…”