Procedure proposal for the correction of nonadiabatic thermoelastic stress analysis results

Design of many aeronautic components takes into account fatigue tests intended to study the component behavior under load and eventually to verify their safety before they are put into production. Components under cyclic loads undergo a periodic temperature fluctuation proportional to the local principal stress sum (thermoelastic effect). In case of adiabatic conditions, which, for a material with a given thermal diffusivity, are achieved for frequencies above a certain level, the measured amplitude of the oscillating temperature can be used to determine the local stress in the sample. In many cases, fatigue tests are performed at low frequencies and they are unable to achieve the adiabatic conditions for a given material. For non-adiabatic conditions, the heat flow, that takes place from points with higher stress concentration to points with lower stress concentration, modifies the temperature distribution, preventing the point by point measurement of the correct stress value. The present article describes a procedure which has been elaborated and successfully used to recover the adiabatic surface temperature and measure the stress distribution for metal samples subjected to fatigue test in non-adiabatic conditions.