Prediction of strains in steel members using infrared thermography

Steel is subjected to temperature variation during straining. The thermal distribution on a steel member can be recorded during loading by infrared cameras and post-processed by appropriate software. In this paper a procedure is presented that allows the determination of true strains in the material from temperature variations and consequently the transformation of thermographic pictures in strain fields. The procedure is based on combined experimental numerical investigations. Experimental tests on tension specimens were performed in which the surface temperature variation of the steel material was recorded by an infrared camera. The same tests were numerically investigated by application of a calibrated FE model. With appropriate post-processing and comparison between the thermographic pictures and the calculated strain fields a relationship between temperature variations and developed strains could be established. Experimental tests were performed at various loading speeds in order to extend this relationship to different strain rates. Using this contact free method dissipative regions, areas where failure is most possible and generally strain fields at larger surfaces may be established during loading.