Thermoelastic stress analysis is based on the fact that under adiabatic and reversible conditions, a cyclically loaded structure experiences temperature variations that are proportional to the sum of the principal stresses, triangle open(sigma_1+sigma_2+sigma_3) (1) where t is temperature, rho is density, C_E is the specific heat for constant deformation and alpha is the thermal expansion coefficient. These temperature variations may be measured usgn a sensitive infra-red detector, the most widely used system being the SPATE (Stress Pattern Analysis by Thermal Emission) system. The signal from the detector, S, is related tot he first stress invariant by simplifying equation (1) to give the working expression: triangle open(sigma_1+sigma_2) = AS (2) where A is a calibration constant.
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