SURFACE FAILURE OF ALUMINA BALLS DUE TO REPEATED STRESSES APPLIED IN ROLLING CONTACT AT TEMPERATURES TO 2000 ° F

/The five-ball fatigue "tester was used to study the behavior of alumina balls under repeat e"cT stresses applied in rolling contact. Hot-pressed and cold-pressed-and-sintered l/2-inch alumina balls were tested at 80 ° and 700 ° F, maximum Hertz stresses of 250,000 to 650,000 psi, a contact^angle of 20°, and a shaft speed of 950 rpm with a mineral oil lubricant, f j] Failure appearance in alumina was unlike fatigue pits found in bearing steels and a crystallized-glass ceramic. A typical failure was a shallow eroded area approximately 1 mil deep progressing slowly from a very small pit to one spanning the track width. Failure appearance and rate of progression were similar for hot-pressed and cold-pressed-and-sintered alumina. Tests at 80 ° F with mineral oil lubrication over a range of stresses show that life varies inversely with stress raised to a power that ranges from 9.4 to 10.8 for the hot-pressed alumina and from 6.0 to 8.1 for cold-pressed-and-sintered alumina. The load capacity of hot-pressed alumina at 80 ° F was one-fifteenth that of a typical bearing steel, seven times that of cold-pressed