Measurement of the thermal diffusivity of thin slab specimens by the lock-in heating-cooling method

The present work describes a new test method for the in-situ non-destructive measurement of the thermal diffusivity of solid materials.A periodic thermal disturbance is supplied to the inspected material by a thermoelectric source based on the Peltier effect. This procedure alternates heating and cooling stages and provides, if properly controlled, a harmonic perturbation with null net heat flux. Thus, a steady-periodic temperature field can be induced within the specimen. The diffusivity of the material is estimated by monitoring the propagation of the temperature cycles along the optically-accessible surface of the specimen, adjacent to the thermal input surface area. A digital camera for infrared thermography is used to obtain non-intrusive surface temperature measurements.At the current stage of development, the focus is on an accurate reproduction of the theoretical model on which the method is based. Ease of operation and portability of the test equipment are also pursued. This notwithstanding, early tests on thin specimens of known materials have given results in encouraging agreement with the nominal values.