Bearing Failure Analysis: Damage Modes and Root Causes (ISO 15243)
Over 90% of bearing damage stems not from the bearing itself but from external causes. Following the ISO 15243 classification, learn to read the marks of fatigue, wear, corrosion, electrical erosion, plastic deformation, and cracking — and their root causes.
Failure Is a Symptom, Not a Cause
When a bearing stops, concluding "the bearing was bad" is not analysis. The damaged surface is evidence that records what went wrong. The international standard ISO 15243 classifies rolling-bearing damage into six primary modes. Reading the damage pattern lets you trace back to the root cause.
1. Rolling Contact Fatigue
The most "natural" failure mode. Repeated loading grows micro-cracks at or just below the surface until material breaks away — spalling.
- Surface-initiated fatigue — begins at dents from contaminant particles or under poor lubrication (low λ)
- Subsurface-initiated fatigue — begins at the depth of maximum shear stress; the natural life of a clean, properly loaded bearing
Spalling spread evenly through the load zone suggests natural end of life; localized spalling points to misalignment or overload.
2. Wear
- Abrasive wear — hard contaminant particles grind the surface; raceways turn dull and lose their sheen. A sealing/cleanliness problem.
- Adhesive wear (smearing) — sliding occurs without an intact film and metal transfers. Caused by rapid acceleration/deceleration or operation below the minimum load, where rolling elements skid.
3. Corrosion
- Moisture corrosion — water or condensation produces reddish-brown oxidation; the resulting pits become fatigue initiation sites.
- Fretting corrosion — fitted surfaces rub under micro-vibration, generating reddish-brown oxide powder. Caused by loose fits or vibration at standstill (including transport damage).
- False brinelling — vibration of a non-rotating bearing wears depressions at each rolling-element position.
4. Electrical Erosion
When current passes through a bearing, discharge at the contact melts tiny craters.
- Excessive-voltage discharge — single-event damage
- Current leakage — repeated discharge forms regular ridges on the raceway, a fluting (washboard) pattern. Common on inverter-driven motors; addressed with insulated bearings or grounding brushes.
5. Plastic Deformation
- Overload brinelling — a static overload (installation impact, a drop) leaves permanent indentations at each rolling-element position.
- Debris denting — hard particles in the lubricant are pressed in, raising micro-ridges whose edges become fatigue initiators.
6. Fracture and Cracking
- Forced fracture — excessive hammering during mounting, or forced press-fit
- Fatigue cracking — excessive fit-induced stress
- Thermal cracking — local overheating from sliding
The Path to Root Cause
Once the damage mode is identified, check:
- Lubrication — type, quantity, interval, contamination, temperature
- Load & alignment — overload, misalignment, operation below minimum load
- Fits — shaft/housing tolerances, looseness or over-interference
- Sealing & environment — moisture, dust, chemicals, electrical current
- Handling & mounting — impact, wrong tools, transport vibration
If you cannot answer why it failed before replacing a bearing, the new one will live the same life and stop in the same place. Reading the damaged surface is not a cost — it is an investment.