Tremendous efforts have been devoted to the studies of ceramic materials under transient thermal conditions over the past four decades Such studies are becoming increasingly more important as advanced ceramic materials are demanded for applications at higher temperatures and more severe transient thermal conditions In this paper, the theoretical and experimental studies on the thermal shock behaviour of monolithic ceramics and ceramic composites are reviewed; a survey of the experimental techniques that have been developed for characterising thermal shock damage is also included It is shown that such studies for the monolithic ceramics have been extensive The theoretical analyses are based primarily on the behaviour of monolithic ceramics and have been successfully applied to explain experimental phenomena and predict the thermal shock behaviour of monolithic ceramics However, similar studies of the thermal shock resistance of ceramic composites, especially continuous fibre reinforced composi

Thermal shock behaviour of ceramics and ceramic composites

The theory of structural stability of ceramics in severe thermal environments was explored via the use of precracking. It was shown that structural stability should be possible when an array of precracks is used, but that the precracks required for this purpose are relatively large. The approach is thus limited to systems which are not required to sustain a significant mechanical stress. Preliminary quenching experiments on short cylinders confirmed that stabilization can be achieved by precracking.

Structural Integrity in Severe Thermal Environments

Acoustic spectrometry as used for the evaluation of tribological systems

The thermal fatigue behaviour of circular rods of soda-lime-silica glass subjected to a water quench was predicted from data for the rate of slow crack growth as a function of stress intensity factor, the pertinent physical properties, the initial crack depth as well as the heat transfer environment. A numerical integration technique was developed in order to calculate the total extent of slow crack growth for each cycle over the total duration of the transient thermal stress and temperature, as well as the total number of cycles required for catastrophic failure to occur. Good agreement between the predicted and experimental data was found.

Failure prediction of the thermal fatigue resistance of a glass

The vickers indentation technique used to evaluate thermal shock resistance of brittle materials

An acoustic emission technique for measuring the failure time in thermal shock experiments is described. The technique offers a unique opportunity to measure the heat-transfer coefficient of the test system and hence, to obtain a fully quantitative measure of the peak surface stress generated during the test. Measurements on soda-lime glass have demonstrated that rapid thermal fracture in the material occurs when the surface stress attains a critical value equal to the propagation stress for the most deleterious surface flaw. The effects of slow crack growth on the failure time are also investigated and correlated with recently developed theory.

M. Linzer

Papers

Thermal fracture studies in ceramic systems using an acoustic emission technique