GEOMETRY OF WEAR IN THE SLIDING 4-BALL WEAR TEST

The geometry of the four-ball test configuration was examined to develop a method to calculate the wear volume of noncircular scars. It was found that the length of the scar normal to the direction of sliding is related to the relative displacement between the upper and lower balls. The width of the scar parallel to the direction of sliding is dependent upon the curvature of the scar normal to the sliding direction. This curvature is a function of upper ball wear, and it is the upper ball wear that causes noncircularity of the lower ball scars. A model was developed to calculate wear volumes for the upper and lower balls using the length and width of the scars on the lower balls to generate a dimensionless profile parameter, alpha. For an inhibited polyphenyl ether-based lubricant, the wear volume of the upper ball is consistently greater than the total wear volume of the three lower balls. In addition to wear volume calculations, this model can also be used to predict the scar shape for given lengths and widths of the lower ball wear scar.