High-Temperature Failure

3 Creep and Stress Rupture 4.3.1 High-Temperature Failure 

Schematic of creep curve under constant load. 

2 Larson-Miller Parameter (Prediction of Long-Term Creep Properties) 

Engineering design often requires engineers to predict material properties at high temperatures where no experimental data are available. The creep deformation rate can be so slow that it might require 10 years test time to reach 1% deformation. Reliable predictions based on accelerated test data obtained over a shorter period of time are essential. Several theoretical parameters were proposed to predict long-term metal creep or stress rupture life based on short-term test data. One of the most utilized parameters is the Larson-Miller parameter, as defined by Equation 4.20  

The Larson-Miller parameter is also often converted to and expressed as Equation 4.21  

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Lowrie, F.L. and Rawlings, R.D., Room and high temperature failure mechanisms in solid oxide fuel cell electrolytes, Journal of European Ceramic Society 20, 2000, 751. 

Chu, C.Y., Singh, J.P. and Routbort, J.L. High-temperature failure mechanisms of hot-pressed Si3N4 and Si3N4/Si3N4-whisker-reinforced composites , J. Am. Ceram. Soc., 76[5] (1993) 1349-1353. 

A. G. Evans and A. Rana, High Temperature Failure Mechanisms in Ceramics, Acta Metall., 28, 129-141 (1980). 

J. E. Marion, A. G. Evans, M. D. Drory, and D. R. Clarke, High Temperature Failure Initiation in Liquid Phase Sintered Materials, Acta Metall., 31, 1445-1457 (1983). 

L. X. Han and S. Suresh, High Temperature Failure of an Alumina-Silicon Carbide Composite under Cyclic Loads Mechanisms of Fatigue Crack-Tip Damage, J. Am. Ceram. Soc., 72[7], 1233-1238 (1989). 

High-temperature failure of ceramics typically occurs by either subcritical crack growth or creep. In an attempt to summarize the data available so... 

It is not always disastrous if a material fails to withstand high temperatures. Failure of a material is taken here to mean that it does not behave as intended so a resin that is actually intended to decompose sacrificially, for example in heat shields, is fully expected to be destroyed by heat the first time it is used. Changes in physical properties, induced by temperature changes, are essential elements in the design of certain devices. 

Tschoegl s result is especially interesting in the light of a recent proposal by Shuttleworth (1968, 1969) that equilibrium polymer-filler debonding is responsible for decreased tensile strength at elevated temperatures. This is contrary to the viscoelastic mechanism of high-temperature failure of Halpin and Bueche (1964), which was developed in an earlier section. A possible resolution of the relative importance of the two proposed mechanisms could lie in the application of Tschoegl s experiment to carbon black- or silica-reinforced materials. 

The failure of ceramic polycrystals may generally be related to preexisting flaws (or in cases of high-temperature failure, to flaws generated during service). 

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