The higher-order asymptotic crack-tip fields are considered for a Mode I in power-law plastic and creeping materials under plane strain conditions. Using an asymptotic expansion and separation of variables for the stress function, a series solution is obtained for stress components at a crack tip. In addition, full-field finite element analysis based on a modified layer approach is employed to model the effects of biaxial loading on nonlinear behavior. Loadings were applied related to a range of biaxial stress ratio (−2, +2). The radial and angular stress distributions and higher-order amplitude coefficients for plastic materials are obtained. Crack tip higher-order fields under various conditions of biaxial loading and spanning the range of times from small scale creep to extensive creep are presented. Account is taken of the radial distance accompanying crack tip blunting. The phenomenon of stress redistributions along crack plane on creep time as a function of biaxial stress ratio is stated. The regions of dominance of the HRR-type field under various biaxial stress ratio, crack distance, hardening exponent, and creep time are found. Good agreement analytical findings with finite element results conforms that HRR-solution corresponds only to the equi-biaxial tension which is a particular case of biaxial loading. It is further demonstrated that the higher-order both for plastic and creeping fields are controlled through constraint parameter A2 by biaxial stress ratio. By fitting numerical results for plastic and creeping materials, two empirical formulas were obtained to describe the higher-order terms amplitude coefficients A2 distributions depending on biaxial stress ratio, crack distance, hardening exponent, and creep time.
This study is concerned with assessing the integrity of cracked steam turbine rotor which operates under creep conditions. Damage accumulation and growth for turbine rotor took place on the inner surface of hole in a shaft. In this case the crack front was nearly half-elliptical shape. The model based on the critical distance concept is presented for expressing crack growth rate in terms of creep damage accumulation in a process zone ahead of the crack tip. An engineering approach to the prediction of residual lifetime of a turbine rotor which is sensitive to the loading history at maintenance is proposed. Full-size stress-strain state analysis of turbine rotor is represented for different stages of lifetime under considering loading conditions. As a result accumulated creep strain in critical zones of turbine rotor depending on time of loading is defined. The creep fracture mechanics parameters that are found numerically are used to characterize the local strain rate and stress fields at any instant around the crack tip in a turbine rotor subjected extensive creep conditions. The meaning of the critical creep ductility appropriate to the stress state at the crack tip is defined as the difference between permissible and accumulated creep strains at different times of loading. Approximate estimations of carrying capacity are presented for the different stress-strain state of a steam turbine rotor at the operation. It is found that the individual mean lifetime of a turbine rotor can be predicted with reasonable accuracy from knowledge of the stress-strain distributives and the material uniaxial creep ductility and creep rupture strength.
Is described the method of approximate calculation of the functional characteristics of gas-pumping units and the method of diagnostics of the value of the impairment of the working wheel of the central center of the main gas pipelines is described. It is clear that the deposits are inflated with the impairment of productivity and productivity, and that is efficiency factor of superchargers. The architecture of the program complex is described, as well as the necessary system and technical facilities for carrying out the transfer for fragmentation at the warehouse of the automatic transmission system of the gas transmission system. Experimentally, the accuracy of the value of the radial prominence in the gaps of the working wheel on the buttstock of the "Demag" 655 P2 type was verified. The revision of the growth rates from the results of the straight lines to the open flow part was not shifted 0.15 mm. Descriptions of the method of implementation by a complex of programs, allow to carry out the development of the main indicators of the functional and technical mill of the VCN GPA: vitreous-pressure, forceful, polytropic KKD characteristics. These indicators are used for the purpose of determining the overall performance of the energy efficiency of the robotic skin GPU: the effective effort of the gas turbines, the vitrates of the fired gas from the of the coated gas pump, which is displayed in the real demand. The economics of the robotics of compressor stations, the supply of the pumped gas, the confirmation of the plans for the supply of gas to the residents and the safe functioning of the gas transportation system (GTS) of Ukraine, a significant world of possessing the functional To this, it is of particular importance to build up the development of new methods and to provide diagnostics, to ensure that the actual FCS possesses an assessment. At present, there is evidence of the actual state of possession of a more efficient operation of the plant in the transition from a traditional technical service to a resource-saving one. The obtained results show that the calculation of the actual characteristics of the VCN using the proposed method allows to take into account the influence of seal wear on the actual parameters of the regime over the entire range of workloads of single-stage and multistage superchargers.
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