Influence of small wheel defects on the risk of subsurface-initiated rolling contact fatigue of railway wheels
Publicerad
Författare
Typ
Examensarbete för masterexamen
Master's Thesis
Master's Thesis
Modellbyggare
Tidskriftstitel
ISSN
Volymtitel
Utgivare
Sammanfattning
Due to improved quality control in wheel manufacturing and maintenance actions
in railway operations, subsurface-initiated rolling contact fatigue rarely occurs these
days. However, in some cases, fatigue poses a risk to trigger accidents such as derailments.
Therefore, it requires careful monitoring in wheel maintenance.
The thesis employed Finite Element simulation (FE-simulation) and impact loads
from wheel impact load detectors to study subsurface-initiated rolling contact fatigue.
First, the influence of finite boundary effects on the subsurface stress field
was studied by comparing stress evaluations from elastic Finite Element simulations
with the analytical solutions for semi-infinite bodies. The study included an investigation
of the lateral contact load position. It demonstrated that the finite boundary
effects from the finite wheel body and laterally shifted contacts were insignificant.
Second, the fatigue initiating defect sizes along depths were estimated using the
Dang Van multiaxial criterion and Murakami’s theory. The estimation derived the
Dang Van equivalent stress along depths with two cases, (1) extreme load and (2)
wheel impact loads corresponding to wheel impact load detector measurements. It
was found that a wheel defect at the depth from 1 to 10 mm below the wheel tread
would more likely initiate subsurface rolling contact fatigue. The minimum fatigue
initiating defect size (the critical defect size) occurred at depths 3 ∼ 4 mm beneath
the wheel tread in both cases. The critical defect size was around 1.2 mm and 2.9
mm in each load case with non-detrimental defect size, do = 40 μm.
Finally, the thesis estimated the fatigue life of a wheel containing a defect at a
depth of 6 mm from the peak and mean impact loads measurements. The estimation
derived a reduced equivalent Dang Van Wöhler curve (often called SN curve)
due to material defects. The reasonable fatigue life estimates were around 191×103
and 330×103 km for a defect size 1 mm and non-detrimental defect size, do = 40 μm.
The thesis confirmed the influence of a small defect (defect size of less than 1 mm) on
subsurface-initiated rolling contact fatigue with given realistic impact loads. However,
the analysis results were highly dependent on non-detrimental defect size, do,
equivalent fatigue limit, σeDV, and fatigue limit cycle, Ne. Therefore, it needs reliable
sources for the selection of fatigue properties and durable assumptions to obtain
more accurate results.
Beskrivning
Ämne/nyckelord
Railway wheels, subsurface-initiated rolling contact fatigue, wheel defect, Dang Van criterion, Murakami’s condition