An investigation into the mechanisms of cone bore growth in railroad bearings
Neu, Richard William
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Permalink
https://hdl.handle.net/2142/19594
Description
Title
An investigation into the mechanisms of cone bore growth in railroad bearings
Author(s)
Neu, Richard William
Issue Date
1991
Doctoral Committee Chair(s)
Sehitoglu, Huseyin
Department of Study
Mechanical Science and Engineering
Discipline
Mechanical Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Mechanical
Engineering, Metallurgy
Engineering, Materials Science
Language
eng
Abstract
The mechanisms of cone bore growth in railroad bearings have been investigated. Systematic studies of (1) stress-induced transformation of retained austenite to martensite, (2) thermal-induced transformation of retained austenite to bainite, and (3) low temperature creep have been conducted. Both carburized and uncarburized 4320 steels were tested. The retained austenite contents (A$\sb{\rm ret}$) of the two carburized steels were 35% and 14%.
Stress-induces transformation was studied by conducting monotonic and cyclic tests at temperatures ranging from 22$\sp\circ$C to 150$\sp\circ$C. Stress-induced transformation was only observed in the A$\sb{\rm ret}$ = 35% steel at temperatures below 60$\sp\circ$C when a tensile stress was applied. Under a uniaxial tensile stress, the transformation strain was anisotropic; the axial transformation strain exceeded the diametral.
Thermal-induced transformation occurred primarily between 80$\sp\circ$C and 200$\sp\circ$C only in the A$\sb{\rm ret}$ = 35% steel. The transformation rate increased with temperature and with positive stress. Unlike stress-induced transformation, thermal-induced transformation also occurred under a compressive stress. The anisotropy of the transformation strain was dependent on stress direction and magnitude.
Creep strains of at least 0.05% at stresses near the 0.001% offset yield strength were measured at 70$\sp\circ$C and above in all treatments of the steel. The creep rates obeyed a logarithmic creep law and increased with temperature and stress magnitude.
The fatigue life of the A$\sb{\rm ret}$ = 35% steel was a factor of 10 greater than the other steels. A compressive mean stress developed from the volume increase associated with stress-induced transformation within the first four cycles.
The Three Ring Model was developed to simulate a cone as an assemblage of the outer case, core, and inner case. The model simulated the dimensional changes at the bore during both service and recondition treatment after service. Results indicated that both creep and thermal-induced transformation can cause bore growth during service. However, only creep can explain the recovery of the residual stresses during the recondition treatment.
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