Estimation of accuracy in measurement by flash method of thermal diffusivity of two-layer composites.

Accuracy in determining by the flash method proposed by the authors of the thermal diffusivity of one layer of two layer composites is estimated theoretically and experimentally. The present method can be applied to the two-layer composites with the thermal contact resistance at the interface of the layers, if the thermal conductivities of two layers and the thermal diffusivity of the other layer are known. Influence of each relative error of thickness of layers, thermal conductivities, the other thermal diffusivity, and thirty and seventy percent time on accuracy of the results obtained by this method of thermal diffusivity and thermal contact resistance is estimated theoretically. The present method is applied to some joining specimens whose thermophysical properties have been all measured in advance by the laser flash half-time method. Influence of the amount of scatter in measured values of thirty and seventy percent time and influence of the combinations of various percent time on the estimated results of thermal diffusivity and thermal contact resistance are investigated. It is confirmed that the most important factor of accuracy in the present method is the measured time in temperature history of the rear surface such as thirty and seventy percent time. Influence of the accuracy of the thermophysical properties used on accuracy of the results is relatively small.