Sphere contact fatigue of a coarse-grained Al2O3 ceramic
Fett, T; Ernst, E; Rizzi, G; Munz, D; Badenheim, D; Oberacker, R
FATIGUE & FRACTURE OF ENGINEERING MATERIALS & STRUCTURES, 2006, Band 29, Heft 11, S. 876-886
The opposite sphere test is an appropriate tool to determine crack-growth exponents for fatigue under repeated contact loading. Lifetime measurements for a coarse-grained Al2O3 are reported. To explain the fatigue exponents that strongly deviated from those obtained in cyclic bending tests, a fracture mechanics analysis was carried out. It was aimed at determining the correct stress intensity factor solution for the tests, including limited dimensions of test specimens deviating from the case of a cone crack in a half space. Cone crack development was observed microscopically and the related stress intensity factors were computed for the observed crack shape. For modelling the fatigue behaviour, it is assumed that the fatigue effect is influenced by a reduction of the shielding term of crack growth resistance due to periodical friction between the grain-interlock bridges in coarse-grained alumina. This results in a loss of traction at the junctions, crack tip shielding is reduced, and the effective load at the crack tip is increased.