FRACTURE TOUGHNESS OF CERAMIC BALLS

摘要

In this work a variation of the surface crack in flexure test, a standardised test for ceramics, is applied to specimens machined from balls. Tensile stresses can be generated in a notched ball by compression perpendicular to the notch. Starting cracks of known size are introduced into the region of the ball where tensile stresses occur during this test by a Knoop indenter. For the determination of fracture toughness from such tests the stresses at the location of the crack and the geometry factor for the test configuration have to be known. These quantities are assessed by analytical methods as well as by numerical simulations.The expected error in K_κc as determined by the new method is evaluated to be in the range of ± 5% to 7%. Based on experience gained during experiments it can be concluded that the method can be employed to advanced ceramic balls with diameters from 5 mm to 20 mm. Experiments on balls and bars made from the same Si_3N_4 material indicate that the new method delivers the same K_κ-values as measurements on bars.