The lock-in heating-cooling method for the measurement of the thermal diffusivity of solid materials

A new test method is presented for the on-field nondestructive 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 can alternate heating and cooling stages and provide, it properly controlled, a harmonic disturbance with null net heat flux. A steady-periodic temperature field can thus be induced within the specimen. The diffusivity of the material is then 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 camera tor infrared thermography is used for nonintrusive surface temperature measurement. At the current stage of development, the focus is on the accurate reproduction of the theoretical model on which the method is based. Ease of operation and portability of the test equipment are also par,sited. However, tests on thin specimens of materials with known properties give measurements in encouraging agreement with the nominal values.