University of Illinois Urbana-Champaign

On stress dependence of high-temperature static fatigue life of ceramics

Dey, Nishit; Hsia, K. Jimmy; Socie, Darrell F.

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https://hdl.handle.net/2142/112582

Description

Title
On stress dependence of high-temperature static fatigue life of ceramics
Author(s)
  • Dey, Nishit
  • Hsia, K. Jimmy
  • Socie, Darrell F.
Issue Date
1998-02
Keyword(s)
  • High-temperature Static Fatigue
  • Ceramics
  • Stress Dependence
Abstract
The mechanisms controlling the static fatigue life of ceramic materials containing grain boundary glass phase at elevated temperatures are investigated. Experiments are performed on a vitreous bonded aluminum oxide at 1000°, 1100°, and 1175°C in air. The stress dependence of the static fatigue life is measured. The failed specimens are sectioned and examined with scanning electron microscopy (SEM) to reveal the failure mechanisms. The results show that the fatigue life at each temperature obeys a power-law dependence on the applied stress. However, the stress exponents measured from the experimental data are 11.9 and 11.1 at 1000° and 1175°C, respectively, but that at 1100°C is 20.0. SEM examination shows that failure in all specimens is a result of combined dispersed creep damage and slow crack growth. Creep damage seems to be the dominant mechanism at low stress levels (higher temperatures), whereas slow crack growth dominates at high stress levels (lower temperatures). A mechanistic model based on these two mechanisms is developed. The creep damage in the form of cavity growth and microcracking until the emergence of a subcritical macrocrack is modeled using a statistical approach. The slow crack growth is modeled using a fracture mechanics approach. The total fatigue life is assumed to be the cumulative time of these two processes. The model predicts that, at a given temperature, the stress exponent for the fatigue life is a function of applied stress level. At very low stress level, the fatigue stress exponent is equal to one, indicating a failure process dominated by well dispersed creep damage. At very high stress level, the exponent is equal to two with a failure process dominated by slow crack growth. However, in the intermediate stress range, the stress exponent may vary from 1 to above 20 depending on temperature, stress level, and microstructure. The model predictions provide a plausible mechanistic explanation of the experimental results.
Publisher
Department of Theoretical and Applied Mechanics. College of Engineering. University of Illinois at Urbana-Champaign
Series/Report Name or Number
  • TAM R 877
  • 1998-6003
ISSN
0073-5264
Type of Resource
text
Language
eng
Permalink
http://hdl.handle.net/2142/112582
Sponsor(s)/Grant Number(s)
Energy Department DE-FG02-96ER-45439
Copyright and License Information
Copyright 1998 Board of Trustees of the University of Illinois

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TAM technical reports include manuscripts intended for publication, theses judged to have general interest, notes prepared for short courses, symposia compiled from outstanding undergraduate projects, and reports prepared for research-sponsoring agencies.