Measuring the Flexural Strength of Ceramics at Elevated Temperatures - An Uncertainty Analysis

The flexural mechanical strength was measured at room and elevated temperatures on green ceramic samples made from quartz electroporcelain mixture. An apparatus exploited the three-point-bending mechanical arrangement and a magazine for 10 samples that are favorable at the temperature measurements from 20 degrees C to 1000 degrees C. A description of the apparatus from the point of possible sources of uncertainties is also given. The uncertainty analysis taking into account thermal expansion of the sample and span between the supports is performed for 600 degrees C. Friction between the sample and supports as well as friction between mechanical parts of the apparatus is also considered. The value of the mechanical strength at the temperature of 600 degrees C is 13.23 +/- 0.50 MPa, where the second term is an expanded standard uncertainty. Such an uncertainty is mostly caused by inhomogeneities in measured samples. The biggest part of the uncertainty arises from the repeatability of the loading force which reflects a scatter of the sample properties. The influence of the temperature on the uncertainty value is very small.