Failure Mechanisms

Abrasive wear (two-body)

Hard particles (silica, metal carbides) embedded in a soft surface cut grooves in the opposing surface. Silica at Mohs 7 abrades steel surfaces at Mohs 5–6.5. Produces angular, ribbon-like wear particles in oil analysis. Primary cause: air intake breach introducing silica into lube system.

Abrasive wear (three-body)

Hard particles free in the lubricant gap between two surfaces act as rolling abrasive media, creating micro-pitting on both surfaces. The 5–15 µm particle range is most damaging — sizes matching bearing clearances where particles are trapped and roll under load.

Adhesive wear

Occurs when lubricant film fails between two metallic surfaces under load — metal-to-metal contact creates adhesion (welding at asperities). Produces smooth, featureless wear particles. Primary causes: insufficient lubricant viscosity, thermal degradation of oil film, bearing overload.

Surface fatigue wear

Repeated stress cycling in bearing raceways creates subsurface fatigue cracks that propagate to the surface, releasing flat, smooth, uniformly sized platelets. Accelerated by fine particle contamination (1–5 µm) that increases contact stress in EHD lubrication films.

Filtration failure root causes

Five failure modes: (1) seal failure allowing ingress above filtration capacity; (2) element bypass from over-service interval; (3) bypass valve stuck open; (4) incorrect filter specification (wrong Beta, wrong particle size); (5) commissioning contamination never flushed from system.

Silica hardness

Mohs 7 (steel = 5–6.5)

Critical abrasive particle range

5–15 µm (bearing clearance range)

Large particle diagnostic threshold

>100 µm = acute wear event

Fine particle chronic wear indicator

<25 µm sustained increase