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This paper provides a state -of-the -art review of the techniques in the recent development in infrared measurement technology for experimental stress analysis. These techniques are based on the use of radiometric systems to determine by non -contact means the thermoelastic effect in structures and materials subjected to dynamic loading.The recent advent of highly sensitive infrared systems, some of which are capable of measuring dynamic temperature changes as small as 1 mK, has led to versatile instrumentation for the evaluation of stresses in engineering models and actual components. The most important feature of the techniques is that it provides a unique method of direct measurement of stress in a material of a test component by non -contact means. Methods have recently been developed to determine dynamic stresses over a frequency of less than 1 Hz up to many KHz.It is now recognised that the technique has become a new important tool for stress analysis and already considerable experience has been gained in practical application.Following an introduction to the technique and a historical review of the development of measurement methods there is an outline of the theoretical basis of the measurement method.The principles of infrared measurement and the techniques and operating characteristics employed in instrumentation, with particular reference to the SPATE technique, are then reviewed.

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This paper describes a novel method of stress determination in structures under dynamic loading conditions. The principle is based on the thermodynamic property of a material in which, under adiabatic conditions, heat is produced or absorbed in direct proportion to the magnitude of the stresses to which it is being subjected. An instrument is described which uses infra -red radiation to measure, remotely, the resulting minute local temperature changes in the material, with oscillating mirrors to provide a raster type scan of the item under test. Spatial resolution down to 1 mm and a temperature discrimination of about 0.002 °C have been achieved, this latter representing a stress change of less than 300 lb /in2 in steel.