ABSTRACT--Thermoelastic stress analysis is a full-field stress measurement technique complementary to local techniques like strain gages. Generally, the heat transfer inside the material is neglected with respect to the frequency of the cyclical loading. An adiabaticity criterion is established to assert this simplification as a function of the thermal diffusion length and the spatial stress gradients. Under nonadiabatic conditions, heat diffusion attenuates the spatial temperature gradients, which leads to an underestimation of stress concentrations. Analytical and numerical considerations allow for the quantification of the spatial resolution. Finally, several inverse techniques can restore the thermally attenuated contrasts.KEY WORDS--Fatigue, mechanical stress, thermoelastic effect, infrared thermography

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A statistical method of signal processing allows for the quantification of small periodic temperature changes, using a standard IR camera and short image sequences without the necessity of any synchronization device. The attenuation of the signal in a high emissivity coating such as a black paint has been quantified by means of a ID thermal model. This same model is used to analyze the heat conduction effects on thermoelastic stress measurements. By analogy with the resolution power of optical systems, a "thermal spatial resolution power" is calculated. The spatial resolution appears to be limited by the heat conduction at low frequencies and by the performance of the radiometer at high frequencies.

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