Evolution of surface cracks under rolling contact: 3D crack morphology and influence of material composition
File(s)
Author(s)
Bertuccioli, Chiara
Type
Thesis
Abstract
Rolling contact fatigue (RCF) is the major failure mechanism in highly stressed, rolling-sliding, lubricated contacts, such as those found in bearings. A fundamental understanding of the mechanisms driving the crack propagation is currently lacking. This knowledge is essential to improve the accuracy of predicted fatigue life of rolling element bearings to eventually tailor materials for rolling bearings reducing risks of crack propagation.
This thesis aims to provide new experimental data on the evolution of the morphology of RCF surface cracks during crack growth, on the influence of material composition on crack morphology, and finally on the interaction of this morphology with the material microstructure. In this study, Focused Ion Beam and X-Ray tomography were employed to obtain 3D RCF cracks morphologies in different materials, three steels and an Inconel, at different stages of crack development after rolling contact fatigue tests using a triple disc fatigue rig. The three-dimensional shapes were extracted using a newly developed methodology, which uses a tailored post-processing data procedure to extract simplified cracks geometries. This new methodology enables the comparison of cracks shapes across different materials and at different stages of their lives. The three-dimensional analysis showed that crack shapes are far more complex than the commonly assumed half penny shape and evolve in time.
The outcomes of this thesis can be used to improve the numerical predictions of RCF crack propagation by including a more realistic crack morphology as revealed here, as well as attempting to incorporate the basic material features that were identified as interacting with the crack path. Such predictive tools can lead to improved in-service bearing life prognostics, key to the successful proactive maintenance strategies that can significantly reduce the downtime and improve operational safety of numerous mechanical systems.
This thesis aims to provide new experimental data on the evolution of the morphology of RCF surface cracks during crack growth, on the influence of material composition on crack morphology, and finally on the interaction of this morphology with the material microstructure. In this study, Focused Ion Beam and X-Ray tomography were employed to obtain 3D RCF cracks morphologies in different materials, three steels and an Inconel, at different stages of crack development after rolling contact fatigue tests using a triple disc fatigue rig. The three-dimensional shapes were extracted using a newly developed methodology, which uses a tailored post-processing data procedure to extract simplified cracks geometries. This new methodology enables the comparison of cracks shapes across different materials and at different stages of their lives. The three-dimensional analysis showed that crack shapes are far more complex than the commonly assumed half penny shape and evolve in time.
The outcomes of this thesis can be used to improve the numerical predictions of RCF crack propagation by including a more realistic crack morphology as revealed here, as well as attempting to incorporate the basic material features that were identified as interacting with the crack path. Such predictive tools can lead to improved in-service bearing life prognostics, key to the successful proactive maintenance strategies that can significantly reduce the downtime and improve operational safety of numerous mechanical systems.
Version
Open Access
Date Issued
2023-03-11
Date Awarded
01/12/2023
License URL
Advisor
Kadiric, Amir
Dini, Daniele
Sponsor
SKF (Firm)
Publisher Department
Mechanical Engineering
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)