HW 4: Problem 1
The wear rate starts out relatively low as the applied normal load is small. The low pressure caused by
the low force makes for fine particle wear (small volume of material removal). As the equation to
calculate the volume of material suggests,
𝑣
𝐹 ∙𝐿
𝑚=𝐾∙ 𝑁
𝐻
an increase in force will cause an increase in the volume of material removal. This results in course
particle wear. Finally, the very large applied normal load causes a high amount of friction. This increase
in friction can cause the materials to heat up and become brittle and harder. It can be seen from the
equation above that the hardness is indirectly proportional to the volume of wear. Thus an increase in
hardness will result in a decrease in volume of wear if K, L, and F are held constant. In this case, 𝐹𝑁 is
increasing however H is increasing at a higher rate.
HW4: Problem 2
Mild Wear- At low speeds, high temperature is not developed. A thin oxide layer separates the
asperities resulting in the removal of fine particles causing low wear.
Mild Oxidation Wear - The surface becomes heated due to the friction of the contacting asperities thus
leading to a higher rate of oxidation. This results in the development of a thick and brittle layer of oxide.
Increase in load results in penetration through the oxide layer causing metal to metal contact and more
wear. Temperature increase hardens the base material as well as creates a thicker oxidation layer,
protecting it from further metal to metal contact wear.
Severe Oxidation Wear - Sliding speeds high enough to cause severe oxidation wear result in a
continuous film of oxide to form at the surface. Lower wear rates occur.
Seizure - Once the sliding speeds reach a high enough velocity and pressure, seizure can occur where the
system "seizes" up and the sliding motion cannot overcome the velocity. An example of this occurrence
would be an un-oiled engine.