Research Papers: Other (Seals, Manufacturing)

A Statistical Damage Mechanics Model for Subsurface Initiated Spalling in Rolling Contacts

[+] Author and Article Information
Nihar Raje

School of Mechanical Engineering, Purdue University, West Lafayette, IN 47907nraje@purdue.edu

Farshid Sadeghi

School of Mechanical Engineering, Purdue University, West Lafayette, IN 47907sadeghi@ecn.purdue.edu

Richard G. Rateick

Engines, Systems and Services, Honeywell Aerospace, South Bend, IN 46620richard.rateick@honeywell.com

J. Tribol 130(4), 042201 (Aug 06, 2008) (11 pages) doi:10.1115/1.2959109 History: Received January 18, 2008; Revised March 18, 2008; Published August 06, 2008

Fatigue lives of rolling element bearings exhibit a wide scatter due to the statistical nature of the rolling contact fatigue failure process. Empirical life models that account for this dispersion do not provide insights into the physical mechanisms that lead to this scatter. One of the primary reasons for dispersion in lives is the stochastic nature of the bearing material. Here, a damage mechanics based fatigue model is introduced in conjunction with the idea of discrete material representation that takes the effect of material microstructure explicitly into account. Two sources of material randomness are considered: (1) the topological randomness due to geometric variability in the material microstructure and (2) the material property randomness due to nonuniform distribution of properties throughout the material. The effect of these variations on the subsurface stress fields in rolling element line contacts is studied. The damage model, which incorporates cyclic damage accumulation and progressive degradation of material properties with rolling contact cycling, is used to study the mechanisms of subsurface initiated spalling in bearing contacts. Crack initiation as well as propagation stages are modeled using damaged material zones in a unified framework. The spalling phenomenon is found to occur through microcrack initiation below the surface where multiple microcracks coalesce and subsequent cracks propagate to the surface. The computed crack trajectories and spall profiles are found to be consistent with experimental observations. The microcrack initiation phase is found to be only a small fraction of the total spalling life and the scatter in total life is primarily governed by the scatter in the propagation phase of the cracks through the microstructure. Spalling lives are found to follow a three-parameter Weibull distribution more closely compared to the conventionally used two-parameter Weibull distribution. The Weibull slopes obtained are within experimentally observed values for bearing steels. Spalling lives are found to follow an inverse power law relationship with respect to the contact pressure with a stress-life exponent of 9.35.

Copyright © 2008 by American Society of Mechanical Engineers
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Figure 2

(a) Interelement contact in the discrete model; (b) fiber model

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Figure 3

Simulation of a rolling contact cycle

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Figure 1

(a) Discrete representation of the semi-infinite domain forming the bearing line contact; (b) zoomed view

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Figure 15

Weibull life plots with variable elastic properties

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Figure 16

A material domain with five initial flaws

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Figure 4

Stress components on an interelement joint in rolling contact

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Figure 5

Degradation of joint tangential stiffness with damage accumulation

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Figure 6

Piecewise linear approximation for damage evolution

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Figure 7

S-N curve for bearing steel AISI-52100 in completely reversed torsion (26)

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Figure 8

Formation of subsurface initiated spall through microcrack initiation and coalescence; (a) first microcrack initiated (11.84×106cycles), (b) multiple microcracks initiated (14.83×106cycles), and (c) multiple crack coalescence and spall formation (123.25×106cycles)

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Figure 9

Damage evolution in a randomly selected interelement joint

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Figure 10

Subsurface initiated spalls for different material domains

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Figure 11

Relative initiation and propagation lives for different material domains

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Figure 12

Weibull life plots for different material domains with constant elastic properties

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Figure 13

Effect of damage increment ΔD on fatigue life

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Figure 14

The three-parameter Weibull curve fitted to model data

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Figure 17

Weibull life plots with internal flaws: (a) initiation lives and (b) total lives

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Figure 18

Weibull life plots for different contact pressures

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Figure 19

Variation of L10 life with contact pressure (E=200GPa constant)

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Figure 20

Variation of percentage of life spent in crack initiation with contact pressure (E=200GPa constant)



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