Life Prediction and Reliability Analysis of Ceramic Structures Under Combined Static and Cyclic Fatigue

This paper presents a computational methodology for life prediction and time-dependent reliability analysis of ceramic structures under combined effects of static and cyclic fatigue. It involves (1) a crack-growth equation representing damage contributions from both static and cyclic fatigue, (2) a multivariate nonlinear regression model for performing parameter estimation from fatigue data generated by small specimens, and (3) the Batdorf model for structural reliability analysis. A linear superposition of crack-growth rates obtained from the Power-law and Walker-law equations was used. The model assumes that the time-dependent and cycle-dependent crack growth formulation exponents are identical, and that loading frequency and amplitude do not vary over time. For the parameter estimation, the regression was performed using nonlinear least squares and a modified Levenberg-Marquardt algorithm. This methodology was implemented into the integrated design code named CARES/Life (Ceramics Analysis and Reliability Evaluation of Structures/Life). A numerical example is presented to illustrate the parameter estimation component of this methodology. The results suggest that the predicted stress-life curves based on the proposed model can correlate better with experimental data when compared with either Power-law or the Walker-law models individually.Copyright © 1998 by ASME