AN APPARATUS FOR THE THERMAL DIFFUSIVITY MEASUREMENT USING THE LASER FLASH METHOD WITH REPEATED PULSES

The paper deals with the measurement of the thermal diffusivity using the laser flash method with repeated pulses. The flash method with repeated pulses was proposed as an extension of the classical 'one pulse' laser flash method aimed to overcome particular experimental difficulties associated with the measurement of some types of insulators, temperature sensitive materials and large-grain heterogeneous materials. Unlike the other approaches, based on reducing the energy intensity and simultaneously increasing the exposure time (the flash method with extended pulse), or substituting step (continuous) heating for pulse irradiation (the step heating method), respectively, in the flash method with repeated pulses the pulse energy consists of several consecutive pulses periodically applied to the sample front face. The thermal diffusivity is calculated from the resulting temperature rise of the rear face, in a similar way to the standard laser flash method. The paper presents the mathematical basis of the flash method with repeated instantaneous pulses. The simple adiabatic mathematical model as well as the more realistic non-ideal theory that considers heat loss from the sample is reviewed here. The built experimental apparatus that is regularly used for serial measurement of the thermal diffusivity in the Austrian Research Centers (ARC) is described here in details. Results of the thermal diffusivity measurements of CrNi austenitic steel are presented and compared.