The base of this paper is exact measurement of deformation and fracture material characteristics in laboratory, evaluation of these parameters and their application in models of finite element analysis modelling the fracture behaviour of components with defects. The base of the work is dealing with ductile fracture of forget steel 42CrMo4. R-curve is modelled by 3D FEM using WARP3D and Abaqus. Crack extension is simulated in sense of element extinction algorithms. Determination of micro-mechanical parameters is based on combination of tensile tests and microscopic observation. Input parameters for the next computation and simulation were received on the base of image analysis, namely fN and fo. The possibility of transferring these parameters to another specimen is discussed.
An innovative principle of low-cycle fatigue (LCF) life assessment suggested for WWER nuclear power plants is presented. In the design stage the fatigue life assessment is based on fatigue design curves, which are introduced in graphical form for air environment. Alternatively and especially for operational stage the fatigue curves are constructed on the basis of mathematical formulas. Mathematical descriptions were validated by strain-controlled LCF laboratory tests. Due to such validated mathematical formulas the complex LCF damage analyses of nuclear power plant components and piping are enabled. In the frame of complex LCF assessment the influence of operating temperatures, stress asymmetry ratio, corrosion environment, neutron fluency and multiaxial loading can be taken into account not only for the base steel materials, but also for their welds. The aim of this paper is to summarise the whole methodology of complex LCF assessment and damage prediction including operational limits of fatigue damage defined in the Czech nuclear standard. The innovation process of original Russian LCF formulas has been running since 2010 based on three national R&D projects focused mainly on environmental aspects and multiaxial loading.
In the Czech Republic the NTD A.M.E. (Normatively Technical Documentation of Association of Mechanical Engineers) standard [1] is recommended by the State Office for Nuclear Safety for assessment of components and piping in the nuclear power plants of WWER type. So far the fatigue life assessment is based on fatigue design curves or mathematical formulas which are based on experimental tests in air environment conditions only. The present paper is dealing with the new proposal of Czech approach in the area of corrosion fatigue interaction. Based on original Russian works the environmental aspects were taken into account for the case of fatigue life evaluation. The aim of this work is to clarify the main idea of the new proposal of appropriate part of NTD A.M.E. residual life section. In the frame of primary water corrosion fatigue interaction not only theoretical background, but also low-cycle fatigue tests in primary water are presented.
This paper presents two ways of the constraint determination and description of the body with a various crack length. An extensive set of non-linear 3D FEM analyses of SE(B) specimens has been investigated and characterised in terms of J-Q trajectories. The attention is paid on the influence of hardening exponent of deformation to the history of the idealised true stress-strain material curve described by the Ramberg-Osgood relation. Results of numerical simulations provide "effective" thickness, which can be used further in statistical approaches. Above mentioned tests are used for the correct Weibull stress determination, which is as a measure of the failure probability of cracked body. The Weibull stress model for cleavage fracture of cast steel requires calibration of two micromechanics parameters (m, s u ). Weibull stress seems to be a parameter for prediction of cleavage failure of cracked bodies and the study is focused on the assessment of the effects of constraint loss on cleavage fracture toughness (J c ). To quantify the effects of constraint variation on the cleavage fracture toughness the form of the toughness-scaling model based on the Weibull stress s w is investigated.
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