Spicer Drive Axles Failure Analysis Service Manual - Manual (Page 9)

Glossary and Nomenclature
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Radial Runout - Refers to the total amount of movement of the
outside diameter of the ring gear during one revolution.
Rear Axle - The drive axle located in front of the rear, rear drive
axle. This axle will have a power divider unit and is described
as D-Head in Spicer Literature.
Rear Rear Axle - The drive axle located the furthest to the rear
of a tandem set of axles. This axle is described as the R-Head
in Spicer Literature.
Scoring - Damage caused by embedded particles of metal.
Scoring may show up as either deep, wide grooving or narrow,
shallow grooves.
Scuffing - Adhesive wear from progressive removal of material
from a rubbing surface caused by a localized welding and tear-
ing.
Shock Load - A rapidly applied load or force that is severe
enough to exceed the strength of the component and cause it
to crack or fail instantly.
Sustained Overload - A consistent application of force that is
greater than the part can withstand
Spalling - See Surface Fatigue Progression
Stress - Force per unit of area, often defined as force acting
through an area within a plane.
Stress Risers - Changes in contour or discontinuities in struc-
ture that cause local increases in stress.
Surface Fatigue Progression - There are four stages of fatigue
for the surface of a metal part under operating stress:
• Frosting - Superficial material displacement on gear
teeth that present a non-destructive burnished ap-
pearance.
• Pitting - This surface fatigue condition occurs when
the endurance limits of the material are exceeded.
• Initial - This is the mildest stage of pitting. It consists
of definite pits from a pin hole size to .030" in diame-
ter. Initial pitting continues until the tooth is able to
carry the load without further distress.
• Moderate- In this stage, the pits are approximately
double in size of the initial pitting. The gear teeth have
not been weakened and there is no danger of break-
age.
• Destructive - At this stage the pits are considerably
larger and deeper than those with moderate pitting.
Gears found in this stage should be replaced.
• Flaking - An advanced type of pitting resulting from
contact fatigue. Material falls away from the surface
in the form of shallow flakes or scale-like particles.
• Spalling - Deterioration of a highly stressed surface
by surface fatigue producing irregularly shaped,
sharp-edged, deep cavities. Spalling is a severe form
of flaking.
Torsion - A twisting action resulting in shear stresses and
strains.