STRUCTURAL ASPECTS OF CYCLICAL STRENGTH OF A SUPERHEATER WELDMENT
The relevance of researching power generator weldments is associated with the necessity of increasing the operational reliability of the heat-power equipment frequently damaged and most critical units. One of the working efficiency increasing factors is the consideration of internal structural stre...
| Format: | Article |
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| Language: | Russian |
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Tomsk Polytechnic University
2019-04-01
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| Series: | Известия Томского политехнического университета: Инжиниринг георесурсов |
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| Online Access: | http://izvestiya.tpu.ru/archive/article/view/216 |
| Summary: | The relevance of researching power generator weldments is associated with the necessity of increasing the operational reliability of the heat-power equipment frequently damaged and most critical units. One of the working efficiency increasing factors is the consideration of internal structural stresses, formation mechanism of which is associated with the structural heterogeneity developing in exploitation and resource structural degradation leading to destruction. The aim of the research is to establish interrelationships between the structural damage accumulation, internal stresses and cracking under the mechanical cyclic loads influence. Subject: welded superheater unit made of low-alloy heat-resistant steel 12Cr1MoV. Methods: physical modeling of operating conditions by external mechanical cyclic deformation, microscopic surface morphology research, x-ray diffraction of deformed samples, evaluation of internal structural stresses, mean square atoms displacement during deformation and characteristic temperature. Results. The paper demonstrates the role and the influence of the cyclic load on fracture. It means that wave periodic deformation «hardening–softening» and the cyclic variation of internal structural stresses are the most important. It was established that under variable cyclic load conditions the periodic internal stresses relaxation is typical. This process corresponds to the rupture of interatomic bonds and formation of a microstructural short crack. According to relaxation conditions, based on Griffith ideas, the authors have determined the critical crack opening stress. The values of mean square displacement of atoms and the characteristic temperature during cyclic deformation reflect the structural features of plasticity, porosity and brittle state. Conclusions. The paper introduces a new methodology for estimating critical states of the weld-affected zone based on the use of relations between internal stresses and the structural damage accumulation. It is shown that internal stresses, vibrational amplitude of Ū2 atoms and characteristic temperature can be a sign of structural transformation diagnostic: the brittle fracture sign is a deep (to zero) relaxation of the first kind internal stresses; the structural plasticity sign is an increased amplitude of atomic Ū2 displacements; and the structural porosity feature is an abnormal increase in the vibrational atoms amplitude and characteristic temperature decrease.
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| ISSN: | 2500-1019 2413-1830 |