Fatigue Wear
Fatigue wear is the weakening and detachment of surface material caused by cyclic loading, where micro-cracks initiate and grow on the surface or subsurface until wear particles detach via cyclic crack growth. It is the predominant failure mode in rolling contacts like bearings and gears, traditionally modeled using the Lundberg-Palmgren theory for bearing life.
In shop floor maintenance, fatigue wear is tracked in CMMS as a probabilistic 'wear-out' failure requiring scheduled replacement based on revolutions or load cycles rather than fixed time. Detection methods include vibration analysis for high-cycle fatigue and ultrasonic inspection for subsurface cracks. Preventive actions involve maintaining a high lambda ratio for lubrication quality and reducing Hertzian contact pressure. This applies to bearings, gear teeth, and rolling elements where cyclic stress causes pitting or spalling.
How does fatigue wear differ from high-cycle vs. low-cycle fatigue?
High-cycle fatigue involves high-frequency, low-amplitude loading causing crack propagation over 10^4 to 10^5 cycles; low-cycle fatigue involves low-frequency, high-amplitude loading failing in less than 10^4 cycles.
Why is fatigue wear probabilistic?
Failure cycles vary between homogeneous samples due to microscopic crack initiation sites and material irregularities; life is modeled via Weibull analysis.
What is the critical design parameter to avoid pitting?
Maintain low Hertzian pressure and high lambda ratio; use low-friction lubricants with additives tailored to the component's stress profile.
Can fatigue wear be detected before failure?
Early cracks are often undetectable by X-ray; advanced non-destructive testing like acoustic emission, ultrasonic, and vibration monitoring are required for early detection.
Is fatigue wear coupled with adhesive wear?
Yes; modern models treat wear and fatigue as coupled, mutually reinforcing phenomena, where surface wear alters geometry and redistributes contact loads, driving fatigue initiation.