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Influence of electrical discharges on white etching crack formation and their detection using electrostatic sensing technique

Influence of electrical discharges on white etching crack formation and their detection using electrostatic sensing technique
Influence of electrical discharges on white etching crack formation and their detection using electrostatic sensing technique
The reliability of bearings in wind and automotive applications has been substantially affected by the formation of white etching crack (WEC). WECs are networks of cracks formed in rolling element bearings that extend several millimetres beneath the surface with microstructural change called white etching area (WEA), which can cause a bearing failure within 1-20 % of the bearing’s expected L10 life. While the exact mechanisms of WEC formation are still under debate, electrical discharging at a current level below 200 μA has been suggested as a driver of WECs formation in bearings. To date, limited academic and industrial research has been conducted to assess the influence of electrical discharges on WECs formation and evaluate the feasibility of WECs detection using sensing techniques. Also, currently, no study is performed to detect, characterise and assess the electrical discharges in WEC tests. Electrostatic sensing techniques have shown to be able to monitor the health-state of bearings by measuring charge generation at the bearing interface, thus has been investigated in this study for monitoring the electrical discharges and WEC formation. A series of tests were initially performed on a twin-roller machine and for the first time, it was shown that electrostatic (ES) sensing technique detects the charging and discharging events, and the discharges are identical in pattern to those of conventional voltage measurement technique. For the first time, an algorithm was developed to count each discharge event and evaluate its amplitude, which enabled the quantification, characterisation and tracking of discharges within the tests. It was further shown that electrical and operating parameters influence electrical discharges both in quantity and amplitude. Rolling contact fatigue (RCF) tests were conducted on a twin-roller machine, and for the first time, WECs under the influence of electrical discharges were created in twin-roller machine. It was found that for the creation of WECs in the rollers, in addition to a supply voltage of 10 V, a low lambda of 0.71 to 0.76, a high contact pressure of 2.5 GPa and a high temperature of above 92.2 °C vi are necessary. WEC tests showed a substantially higher electrical resistance of 24.36-24.69 kΩ in comparison to a maximum of 13.08 kΩ for non-WEC tests and demonstrated a voltage across the discs’ contact of 2.95-3 V in comparison to a maximum of 1.82 for non-WEC tests. Also, quantification of electrical discharges showed that there is a substantial difference between the WEC and non-WEC tests, with WEC tests showing electrical discharges approximately 3 times higher in amplitude but 2 or 3 times less frequent. A series of tests were further performed on the University of Erlangen-Nuremberg IPAT bearing test rig, and it was found that a similar electrical behaviour, as observed for twin-roller tests, exists between WECs and non-WEC tests. WEC tests showed an electrical resistance of 152- 341.11 kΩ in comparison to 23.84-36.97 kΩ for non-WEC tests. For the WEC tests, the voltage across the bearings as a share of the supply voltage was also shown to reach as high as 63-82 % in comparison to 21-31 % for non-WEC tests. Also, ES sensing technique was shown to react to a change in operating conditions including a change in flow rate, and detect signatures possibly associated with WECs failure event at approximately the same time as the acoustic emission sensing technique. Finally, WECs were created on a test bench with cylindrical roller bearings of type NU222, under variable loading conditions, and without any supply voltage. Results indicated that electrical charging and discharging are present both in the running-in and running-to-failure periods and only during the high-loading cases. Electrical discharges reached a peak of above 0.3 pC in amplitude (in some instances as high as 0.75 pC in amplitude) before the failure of the bearings. High-frequency peaks associated with material degradation were also detected in the ES sensors and were shown to be unique for each ES sensor. Before the failure of bearings, the corresponding ES sensor detected peaks reaching an amplitude as high as 0.75 pC in positive and -0.75 pC in negative amplitudes. Thus, tracking the electrical discharges and material degradation signatures in the signals from the ES sensors can enable both the detection of WEC critical operating conditions and provide early detection, as well as diagnosis of a degradation event due to WEC formation.
University of Southampton
Esmaeili, Kamran
99ab4049-5a0c-46dd-9478-91fc9c82f711
Esmaeili, Kamran
99ab4049-5a0c-46dd-9478-91fc9c82f711
Wang, Ling
c50767b1-7474-4094-9b06-4fe64e9fe362
White, Neil
c7be4c26-e419-4e5c-9420-09fc02e2ac9c
Harvey, Terence
3b94322b-18da-4de8-b1af-56d202677e04

Esmaeili, Kamran (2021) Influence of electrical discharges on white etching crack formation and their detection using electrostatic sensing technique. Doctoral Thesis, 269pp.

Record type: Thesis (Doctoral)

Abstract

The reliability of bearings in wind and automotive applications has been substantially affected by the formation of white etching crack (WEC). WECs are networks of cracks formed in rolling element bearings that extend several millimetres beneath the surface with microstructural change called white etching area (WEA), which can cause a bearing failure within 1-20 % of the bearing’s expected L10 life. While the exact mechanisms of WEC formation are still under debate, electrical discharging at a current level below 200 μA has been suggested as a driver of WECs formation in bearings. To date, limited academic and industrial research has been conducted to assess the influence of electrical discharges on WECs formation and evaluate the feasibility of WECs detection using sensing techniques. Also, currently, no study is performed to detect, characterise and assess the electrical discharges in WEC tests. Electrostatic sensing techniques have shown to be able to monitor the health-state of bearings by measuring charge generation at the bearing interface, thus has been investigated in this study for monitoring the electrical discharges and WEC formation. A series of tests were initially performed on a twin-roller machine and for the first time, it was shown that electrostatic (ES) sensing technique detects the charging and discharging events, and the discharges are identical in pattern to those of conventional voltage measurement technique. For the first time, an algorithm was developed to count each discharge event and evaluate its amplitude, which enabled the quantification, characterisation and tracking of discharges within the tests. It was further shown that electrical and operating parameters influence electrical discharges both in quantity and amplitude. Rolling contact fatigue (RCF) tests were conducted on a twin-roller machine, and for the first time, WECs under the influence of electrical discharges were created in twin-roller machine. It was found that for the creation of WECs in the rollers, in addition to a supply voltage of 10 V, a low lambda of 0.71 to 0.76, a high contact pressure of 2.5 GPa and a high temperature of above 92.2 °C vi are necessary. WEC tests showed a substantially higher electrical resistance of 24.36-24.69 kΩ in comparison to a maximum of 13.08 kΩ for non-WEC tests and demonstrated a voltage across the discs’ contact of 2.95-3 V in comparison to a maximum of 1.82 for non-WEC tests. Also, quantification of electrical discharges showed that there is a substantial difference between the WEC and non-WEC tests, with WEC tests showing electrical discharges approximately 3 times higher in amplitude but 2 or 3 times less frequent. A series of tests were further performed on the University of Erlangen-Nuremberg IPAT bearing test rig, and it was found that a similar electrical behaviour, as observed for twin-roller tests, exists between WECs and non-WEC tests. WEC tests showed an electrical resistance of 152- 341.11 kΩ in comparison to 23.84-36.97 kΩ for non-WEC tests. For the WEC tests, the voltage across the bearings as a share of the supply voltage was also shown to reach as high as 63-82 % in comparison to 21-31 % for non-WEC tests. Also, ES sensing technique was shown to react to a change in operating conditions including a change in flow rate, and detect signatures possibly associated with WECs failure event at approximately the same time as the acoustic emission sensing technique. Finally, WECs were created on a test bench with cylindrical roller bearings of type NU222, under variable loading conditions, and without any supply voltage. Results indicated that electrical charging and discharging are present both in the running-in and running-to-failure periods and only during the high-loading cases. Electrical discharges reached a peak of above 0.3 pC in amplitude (in some instances as high as 0.75 pC in amplitude) before the failure of the bearings. High-frequency peaks associated with material degradation were also detected in the ES sensors and were shown to be unique for each ES sensor. Before the failure of bearings, the corresponding ES sensor detected peaks reaching an amplitude as high as 0.75 pC in positive and -0.75 pC in negative amplitudes. Thus, tracking the electrical discharges and material degradation signatures in the signals from the ES sensors can enable both the detection of WEC critical operating conditions and provide early detection, as well as diagnosis of a degradation event due to WEC formation.

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Published date: April 2021

Identifiers

Local EPrints ID: 450171
URI: http://eprints.soton.ac.uk/id/eprint/450171
PURE UUID: 45ee64e1-0679-4ffb-b975-66e8b449f5dd
ORCID for Ling Wang: ORCID iD orcid.org/0000-0002-2894-6784
ORCID for Neil White: ORCID iD orcid.org/0000-0003-1532-6452

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Date deposited: 14 Jul 2021 16:48
Last modified: 17 Mar 2024 06:40

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Contributors

Author: Kamran Esmaeili
Thesis advisor: Ling Wang ORCID iD
Thesis advisor: Neil White ORCID iD
Thesis advisor: Terence Harvey

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