The measurement of thermal diffusivity on bulk samples has been previously performed using techniques which require a modulated point heating of the surface and a movement of the temperature detector or of the heating source to determine the phase shift of the modulated surface temperature at an increasing distance from the heating source. Such a movement must be realized with great accuracy and can be the cause of many experimental difficulties. The method proposed herewith is based on the fact that the modulated heating of a bulk sample on a surface spot gives a phase shift, between modulated temperature and heating source, which only depends on the ratio between the spot linear dimension and the thermal diffusion length. A frequency sweep produces a variation of the thermal diffusion length and a variation of the measured phase shift between 0° and -45°, thus allowing for a static single sided measurement of the thermal diffusivity of the sample.
The aerospace industry makes large use of aluminum components, which must undergo severe fatigue tests simulating the real loads at which they will be subjected. The problem is that the high thermal diffusivity and the low frequency at which fatigue tests on real components can normally be performed often prevent the achievement of adiabatic conditions, and the attainment of quantitative results. Starting on the study of models involving different kinds of mono-dimensional stress distributions, the temperature attenuation can be evaluated and linked to the phase shift. The result is independent from the load applied and from the material. A computer program has been elaborated to correct non adiabatic TSA results on the base of the relation phase shift - attenuation.