Investigation of Bearing Fatigue Damage Life Prediction Using Oil Debris Monitoring

Research was performed to determine if a diagnostic tool for detecting fatigue damage of helicopter tapered roller bearings can be used to determine remaining useful life (RUL). The taper roller bearings under study were installed on the tail gearbox (TGB) output shaft of UH- 60M helicopters, removed from the helicopters and subsequently installed in a bearing spall propagation test rig. The diagnostic tool was developed and evaluated experimentally by collecting oil debris data during spall progression tests on four bearings. During each test, data from an on-line, in-line, inductance type oil debris sensor was monitored and recorded for the occurrence of pitting damage. Results from the four bearings tested indicate that measuring the debris generated when a bearing outer race begins to spall can be used to indicate bearing damage progression and remaining bearing life

Piston ring lubrication and friction reduction through surface modification

Frictional at the piston ring/cylinder liner (PRCL) interface is the single most significant contributor to the mechanical loss in an internal combustion engine. The purpose of this study is to: (a) advance the understanding of the frictional loss phenomenon at the PRCL contact in internal combustion engines through correlation of the numerical models developed herein and previously obtained experimental results; (b) Examine methods of reducing the parasitic losses at the PRCL contact through the use of modified surfaces. Three mixed lubrication models of progressively increasing complexity are developed and used to investigate the tribological behavior of the PRCL contact. The first model utilizes a typical stochastic asperity contact model coupled with a cavitation enabled Reynolds equation. Lubrication regime transitions are investigated and compared to experimental results with good agreement. The second model utilizes a new, semi-deterministic approach to modeling the asperity contact pressure. It is shown that this method allows for more accurate prediction of friction in the case of non-Gaussian surfaces. The third model handles mixed lubrication using a fully deterministic approach, which allows the inclusion of surface modifications. Modified surfaces are shown to provide a significant (50-60%) decrease in the average frictional loss over the cycle. Two approaches for the numerical synthesis of honed cylinder liner surfaces are then described and compared to measured surfaces with good agreement. Experiments conducted with a small engine dynamometer show reduced friction in the presence of laser modified surfaces

Comparison of Test Stand and Helicopter Oil Cooler Bearing Condition Indicators

The focus of this paper was to compare the performance of HUMS condition indicators (CI) when detecting a bearing fault in a test stand or on a helicopter. This study compared data from two sources: first, CI data collected from accelerometers installed on two UH-60 Black Hawk helicopters when oil cooler bearing faults occurred, along with data from helicopters with no bearing faults; and second, CI data that was collected from ten cooler bearings, healthy and faulted, that were removed from fielded helicopters and installed in a test stand. A method using Receiver Operating Characteristic (ROC) curves to compare CI performance was demonstrated. Results indicated the bearing energy CI responded differently for the helicopter and the test stand. Future research is required if test stand data is to be used validate condition indicator performance on a helicopter

Correlate Life Predictions and Condition Indicators in Helicopter Tail Gearbox Bearings

Research to correlate bearing remaining useful life (RUL) predictions with Helicopter Health Usage Monitoring Systems (HUMS) condition indicators (CI) to indicate the damage state of a transmission component has been developed. Condition indicators were monitored and recorded on UH-60M (Black Hawk) tail gearbox output shaft thrust bearings, which had been removed from helicopters and installed in a bearing spall propagation test rig. Condition indicators monitoring the tail gearbox output shaft thrust bearings in UH-60M helicopters were also recorded from an on-board HUMS. The spal-lpropagation data collected in the test rig was used to generate condition indicators for bearing fault detection. A damage progression model was also developed from this data. Determining the RUL of this component in a helicopter requires the CI response to be mapped to the damage state. The data from helicopters and a test rig were analyzed to determine if bearing remaining useful life predictions could be correlated with HUMS condition indicators (CI). Results indicate data fusion analysis techniques can be used to map the CI response to the damage levels