Detection of spiral bevel gear damage modes using oil debris particle distributions

Damage progression tests were performed in the NASA Glenn Spiral Bevel Gear Fatigue Rig. During testing, debris generated were measured with an inductance type oil debris sensor, while different classes, modes and degrees of damage occurred on the gear teeth. Debris particle counts, their approximate size and mass were measured by the oil debris sensor. Tooth damage was documented with photographs at the start of the test, when damage occurred on one gear or pinion tooth and when damage transferred to two or more teeth. American Gear Manufacturers Association (AGMA) and American Society for Testing (ASTM) standards were used to describe gear tooth damage. Discrete thresholds based on counts and mass were defined for three gear set states: Healthy, Inspect and Damage. Histograms of particle size distributions were plotted for eight tests at the three gear states. Methods to predict particle size based on gear design and operating conditions were also presented. Results found monitoring oil debris mass provided a good indication of damage progression for slow progressing fatigue failures, while monitoring counts alone did not provide a good indication. The oil debris sensor could not be used to detect scuffing failure modes. Scuffing transfers material between the meshing gears and is less likely to generate debris. If historical data is unavailable, gear geometry and operational conditions could be used to estimate a threshold on mass and average particle size for indicating a contact fatigue damage state.