Effect of Altitude Related Parameters on Wear Rates in Common Aerospace Materials December 15, 2009

Wear rate is affected by relative humidity. A maximum wear rate at low humidity is consistently seen in materials of engineering importance, including steel, aluminum, nickel, and plastics.

Relative Humidity is the observed water vapor partial pressure divided by the saturation vapor pressure. Vapor pressure decreases with increasing altitude.

Since the relationship between wear and relative humidity is known, and the relationship between partial pressure of water vapor and altitude is known, the relationship between wear and altitude can be plotted.

If the effect of pressurizing the air is considered, such as in an aircraft bleed system, it can be seen that the altitude at which wear occurs is is dependent upon local operating pressure.