Dissertation Title: Three-Dimensional Finite Element Modeling of Rolling Contact Fatigue
M.S., Purdue University, West Lafayette, 2008
Thesis Title: The Influence of Cage Flexibility on Bearing Dynamics â€“ A Discrete Element Approach
Advisor: Prof. Farshid Sadeghi
B.S., Purdue University, West Lafayette, 2004
585 Purdue Mall
ME Room# G005
West Lafayette, IN 47907
Office Phone: 765-494-0308
Rolling contact fatigue (RCF) is a material failure mode that is encountered in tribological machine components, i.e. rolling element bearings, gears, wheel-on-rail, etc. Repeated contact cycles generate fatigue cracks near the surface that eventually liberate a substantial volume of material, thus ending the componentâ€™s useful service life. This process is significantly influenced by microscale heterogeneous features in the materials from which the parts are manufactured.
This project is part of METLâ€™s ongoing efforts to develop a new class of numerical RCF models. The common goal of these models is to investigate the stochastic nature of subsurface initiated rolling RCF by considering microscale discontinuities and heterogeneity that exist in bearing grade materials. These models incorporate randomly generated Voronoi tessellations as representations of the subsurface material topology, i.e. the grain boundary network. This work extends our capacity for studying RCF to include 3D finite element frameworks, enabling investigations with infinitely wide, elliptical, and circular contact regions. It also provides a means to consider 3D subsurface geometric features and/or variation in the local properties of the material.
By utilizing damage mechanics theory and a novel mesh partitioning algorithm, the model is able to simulate the progression of RCF from the initiation of the first crack to the formation of a mature spall. The modeling laws which govern the evolution of the material from a pristine state to the occurrence of a spall are calibrated by experiments. Rather than drawing upon bearing fatigue test data, which is expensive and time consuming to generate, the model leverages relatively inexpensive torsion fatigue data, citing the shear-driven similarity of the two processes.
Significant computational expense is associated with these investigations for two reasons: (1) the number of contact cycles that must be simulated to accurately capture the phenomenon of RCF is large, and (2) several representative microstructure models must be studied with identical parameters to statistically characterize the effect of each variable. To offset the computational cost, we have developed and/or implemented several strategies to accelerate the solution. As a result, the model can produce load-vs-life data in days/weeks that full-scale testing would require months or years to achieve. Moreover, the scatter predicted and the spalling shapes generated have good agreement with empirical findings.
Collaborations and Related Work
Through collaborative efforts with METL personnel, several of the software components and algorithms developed for the virtual RCF investigations have been enhanced (3D Voronoi volumetric discretization methods, custom meshing and sliver removal algorithms, novel mesh partitioning strategies, strain energy based accelerated integration algorithm). These have been successfully utilized in other numerical simulations of mechanical components experiencing fatigue including:
- Thin sheets structures used in automotive, aerospace, and micro systems
- MEMS components
- Torsion bar specimens for material testing
Limited torsion fatigue data for bearing grade materials is available in the body of published literature. A torsion fatigue test rig with custom mechanical gripping interfaces has been purchased/developed at METL to generate additional fatigue data, thereby expanding the RCF modelâ€™s range of applicability.
- Weinzapfel, N., and Sadeghi, F., â€œA Discrete Element Approach for Modeling Cage Flexibility in Ball Bearing Dynamics Simulations,â€ ASME, Journal of Tribology, Vol. 131(2), 021102, 2009
- Weinzapfel, N., Sadeghi, F., and Bakolas, V., â€œAn Approach for Modeling Material Grain Structure in Investigations of Hertzian Subsurface Stresses and Rolling Contact Fatigue,â€ ASME, Journal of Tribology, Vol. 132(4), 041404, 2010
- Weinzapfel, N., Sadeghi, F., Bakolas, V., and Liebel, A., â€œA 3D Finite Element Study of Fatigue Life Dispersion in Rolling Line Contacts,â€ ASME J. of Tribology. Vol. 133(4), 042202, 2011
- Weinzapfel, N., Sadeghi, F., â€œNumerical Modeling of Sub-Surface Initiated Spalling in Rolling Contacts,â€ Tribology International. TRIBINT-D-11-00303 submitted Aug. 5, 2011 (under review)
- Bomidi, J., Weinzapfel, N., Sadeghi, F., â€œ3D modeling of Intergranular Fatigue Failure of MEMS Devices,â€ Submitted to Fatigue and Fracture of Engineering Materials and Structures, 2011 (under review)
- Bomidi, J., Weinzapfel, N., Wang, C., Sadeghi, F., â€œExperimental and Numerical Investigation of Fatigue of Thin Tensile Specimen,â€ Submitted to International Journal of Fatigue, 2011 (under review)
Popular Engineering Literature
- Weinzapfel, N., Sadeghi, F., and Bakolas, V., â€œMicroscale Influences on Rolling Contact Fatigue Life Dispersion,â€ STLE Tribology and Lubrication Technology, March, pp. 17-19, 2011
- Weinzapfel, N., Sadeghi, F., and Bakolas, V., â€œA 3D Finite Element Model for Investigating Effects of Material Microstructure on Rolling Contact Fatigue,â€ STLE Tribology and Lubrication Technology, January, pp. 17-19, 2011