PSI - Issue 30

L.V. Moskvitina et al. / Procedia Structural Integrity 30 (2020) 100–104 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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accelerated development of the crack conglomerates of the deformed grains occur in the plastic zone (Fig. 3a). The conglomerate consists of a core of slightly deformed grains (white) and firmly deformed grains (grey) on the edges. The crack passed on the boundary of conglomerate by tearing away and slipping on the slickensides. On the electronic-microscopic image of metal microstructure of this area, the spread of subgrains relative to each other with microcracks on their boundaries is observed (Fig. 3b). The initial subgrains are divided into great number of shallow fragments, which are also disoriented to each other. On some initial subgrains the strip structures of deformation are visible. There are microcracks on the boundary of initial subgrains and strip structures. On the microfractograms there is a fracture of the area of accelerated development of the crack consisting of shallow relief facets, proportionate with sizes of initial subgrains, intragranular facets and flat quazifacets of splitting on the strip structures (Fig. 3c, d). For the first time on operating destruction the forms of the fragmentation are demonstrated on different structural levels, beginning from nano dimensional blocks and initial subgrains, separate grains to the conglomerates of grains. All of them were engaged in the rotary process of deformation that resulted in the accelerated development of the mainstream crack, turning into pre-cascade destruction and complete destruction. It is generally accepted (Elsukova et al.1990; Panin 2009) that the rotary processes on all structural levels are characteristic to high temperature deformation. In this case the non-crystallographic turns occurred at temperature -40 0 С . The metal destruction on all structural levels, possibly, is characteristic for low temperature rotary process at high alternating tensions. 4. Conclusion Well-defined dents and small cavities in elements-concentrators of tensions as the valve openings in the wheel rim of cars occur under the influence of corrosion and alternating tensions and specify on the end of the incubation period of the fatigue deformation. Intensive alternating loadings in combination with dynamic shots at low temperatures caused a sudden change of structural levels of deformation in steel of the rim of wheel, such as moving boundaries of grains, cellular and fragmented subgranular structures. The ageing area of TAZ welding is considered as the preferable area of distribution of fatigue cracks. The heterogeneity of micromechanical properties of metal of the ageing area under the cyclic loadings in a low environment temperature contributed to the propagation of cracks by a low-cycle mechanism. Non-crystallographic turns on all structural levels, including the macroscopic turn of conglomerates of grains are characteristic to the low temperature destruction of metal of rim in the stage of accelerated development of crack. In the manufacture of wheel rims of tippers the valve opening must be placed out of area of TAZ welding. References Elsukova, T.F., Zhukova, K.P., Veselov O. V, etc. 1990. Structural levels of deformation and destruction of polycrystals at different kinds of loading Journal News HIGH SCHOOL Physics 2, 69-88. Grabin V F, 1982. Metallurgical science of fusion welded structures. (Ed). Naukova Dumka, Kiev, Ukraina, pp 399. Gordeeva, T A, Zhegina I P, 1978. Analysis of fractures at estimation of reliability of materials. (Ed). Machine building, Moscow, Russia, pp 199. Gulyaev A P, Zelenova B D, Knorozova T V, Ustilovskiy S J, 1973. Electronic-microscopic research of fatigue breaks. Journal Problems of durability 5, 24-27. Ivanova V S, Terentyev V F, 1975. Nature of metal fatigue. (Ed). Metallurgy Мoscow, Russia pp 454. Koneva N A, Kozlov E V, 1990. Physical nature of phasing plastic deformation. Journal News HIGH SCHOOL Physics 2, 89-104. Krasovsky A J, 1980. Fragility of metals at low temperatures. (Ed). Naukova dumka, Kiev, Ukraina, pp 336. Panin V E, 1990. Structural levels of plastic deformation and destruction. (Ed). Science Novosibirsk, Russia, pp 251. Panin V E, Elsukova T F, Egorushkin V E, Vaulina O J, Pochivalov J I 2009. Mechanisms of deformation and mass transfer in strongly disbalanced polycrystals at alternating bend Journal Deformation and destruction of materials 6 , 2-12. Troshchenko V T, Prokopenko A V, Pokrovsky B B, 1978. Research of characteristic of viscosity of metal destruction at cyclic loading. Journal Problems of durability 3, 3-8.