Cyclic Fatigue of Intrinsically Brittle Ceramics in Contact with Spheres

Published

December 1, 1999

Author(s)

D K. Kim, Yeon-Gil G. Jung, I M. Peterson, Brian R. Lawn

Abstract

Contact damage modes in cyclic loading with spheres are investigated in three relatively brittle ceramics, soda-lime glass, porcelain and fine-grain silicon nitride, in moist environments. Initial damage at small numbers of cycles and low loads consists of tensile-driven macroscopic cone cracks (brittle mode). Secondary damage at large numbers of cycles and high loads consists of shear-driven distributed microdamage (quasi-plastic mode), with attendant radial cracks and a new form of deeply penetrating subsidiary cone cracks. Strength tests on indented specimens are used to quantify the degree of damage. Both damage modes degrade the strength: the first, immediately after cone crack initiation, relatively slowly; the second, after development of radial cracks, much more rapidly. A fracture mechanics model describing the first mode, based on time-integration of slow growth of cone cracks, is presented. This model provides simple power-law relations for remaining strength in terms of number of cycles and contact load for materials design. Extrapolations of these relations into the quasi-plastic region are shown to be non-conservative, highlighting the need for further understanding of the deleterious quasi-plastic mode in tougher ceramics. Comparison with static contact data indicates a strong mechanical (as opposed to chemical) component in the cyclic fatigue in the quasi-plastic region.

Citation

Acta Materialia

Volume

47

Issue

No. 18

Pub Type

Journals

Keywords

brittle materials, cone cracks, contact damage, cyclic fatigue, radial cracks, strength degradation

Citation

Kim, D. , Jung, Y. , Peterson, I. and Lawn, B. (1999), Cyclic Fatigue of Intrinsically Brittle Ceramics in Contact with Spheres, Acta Materialia (Accessed May 17, 2024)