A Strain-Based Methodology for High Temperature Lifetime Prediction

Published

September 1, 1998

Author(s)

Sheldon M. Wiederhorn, William E. Luecke, Ralph Krause

Abstract

In structural materials, lifetime is often strain-determined. Once a part exceeds its allowable strain, its functional integrity is lost. Although most ceramics are designed to a brittle failure criterion, silicon nitride at the temperatures expected in gas turbines is an exception to this generality. In the temperature range and at the stresses expected in gas turbines, silicon nitride can easily exhibit strains to failure that exceed 1 percent. Because an allowable strain of only 0.5 percent is used for gas turbine design, the necessity of a strain-determined design methodology must be considered. In this paper the consequences of creep on design are considered for an allowable strain of 0.5 percent and a reliability of one failure in 10,000. For a given stress and failure time, we show that reductions in operating temperature by as much as 40 C are needed when strain rather than creep rupture is considered as the failure criterion. An additional 25 C reduction is needed to assure the reliability level to one part in 10,000.

Citation

Ceramic Science and Engineering Transactions

Volume

19

Issue

No. 4

Pub Type

Journals

Keywords

creep, design, high temperaure, silicon nitride

Citation

Wiederhorn, S. , Luecke, W. and Krause, R. (1998), A Strain-Based Methodology for High Temperature Lifetime Prediction, Ceramic Science and Engineering Transactions (Accessed April 24, 2024)