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Adhesive wear frequently occurs because of
shearing at points of contact or asperities that undergo
adhesion or cold welding. Shearing occurs through the
weakest section, which is not necessarily at the adhesion
plane. In many cases, shearing occurs in the softer
material, but such a comparison is based on shear tests of
relatively large pure samples. The adhesion junctions, on
the other hand, are very small spots of weakness or impurity
that would be insignificant in a large specimen but in
practice may be sufficient to permit shearing through the
harder material. In some instances the wearing surfaces of
materials with different hardness can contain traces of
material from the other face. Theoretically, this type of
wear does not remove material but merely transfers it
between wearing surfaces. However, the transferred material
is often loosely deposited and eventually flakes away in
microscopic particles; these, in turn, cause wear.
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