New Developments In The Use Of Thermal Measurement Techniques For Structural Design Engineering

SummaryThis paper describes a novel method of stress determination in structures under dynamicloading conditions. The principle is based on the thermodynamic property of a material inwhich, under adiabatic conditions, heat is produced or absorbed in direct proportion to themagnitude of the stresses to which it is being subjected. An instrument is described whichuses infra -red radiation to measure, remotely, the resulting minute local temperaturechanges in the material, with oscillating mirrors to provide a raster type scan of the itemunder test. Spatial resolution down to 1 mm and a temperature discrimination of about0.002 °C have been achieved, this latter representing a stress change of less than300 lb /in2 in steel.Measurements made on an aluminium test structure under cyclic loading are described.These demonstrate the way in which the stress distribution over selected areas of astructure can be obtained in order to assist design. Results of comparison of the techniquewith strain gauge measurements are given which show the high resolution capability of theinstrument. An indication is given of the potential value in the field of non -destructivetesting: for example, in the location of fatigue cracks.References