Slow crack growth analysis of advanced structural ceramics under combined loading conditions: Damage assessment in life prediction testing

Slow crack growth analysis was performed with three different loading histo ries including constant stress-rate/constant stress-rate testing (Case I lo ading), constant stress/constant stress-rate testing (Case II loading), and cyclic stress/constant stress-rate testing (Case III loading). Strength de gradation due to slow crack growth and/or damage accumulation was determine d numerically as a function of percentage of interruption time between the two loading sequences for a given loading history. The numerical solutions were examined with the experimental data determined at elevated temperature s using Sour different advanced ceramic materials, two silicon nitrides, on e silicon carbide and one alumina for the Case I loading history, and alumi na for the Case II loading history. The numerical solutions were in reasona ble agreement with the experimental data, indicating that notwithstanding s ome degree of deep deformation presented for some test materials slow crack growth was a governing mechanism associated with failure Sor all the test materials.