Thermal shock and thermal fatigue study of alumina

Preliminary results on the thermal shock and thermal fatigue behaviour of alumina studied in a newly designed novel and simple test equipment are reported. The top surface of a test sample was heated by an oxy-hydrogen flame while the opposite surface was cooled to generate temperature and thermal stress gradients. The maximum stressed zone and the effect of the thickness of the sample on critical temperature difference (ΔTC) were studied by conducting actual experiments on plain and indented alumina specimens and also by modelling temperature and thermal stress distribution in the sample using a finite element (FE) software. It was observed that the maximum stress was experienced near the periphery of the top surface and ΔTC was more for thicker samples. Thermal fatigue study was conducted by varying temperature difference of the fatigue cycles and also by inducing different crack lengths in the sample. It was observed that the fatigue life sharply decreased with increase in initial crack length or by increasing the temperature difference of the fatigue cycles. The acoustic emission (AE) signals corresponding to formation and growth of large number of micro-cracks were observed.