Thermography applied to the evaluation of non-uniform deformation heat of metals

This article deals with digital filtering techniques to separate heat sources and heal diffusion effects in subsequent infrared images during plastic deformation of metals. Information about the deformation heat as a function of position and time of a sample under plastic deformation potentially indicates the degree of (non-) uniformity of the deformation process itself and of the metal microstructure after rolling and heat treatment. However, the raw, unfiltered infrared images suffer from blurring effects due to heat diffusion and therefore deformation heat effects originating from dissipated energy are hard to distinguish. Thermomechanical coupling sources like the thermo-elastic effect are not taken into account here. To overcome the problem of blurring effects, digital filters based on the heat diffusion equation have been implemented. The filter procedure has been tested on a steel sample during plastic deformation with constant strain rate. The initiation and propagation process of deformation bands were clearly observed and the propagation speed of Luders bands could be quantified experimentally. The ratio between dissipated power and mechanical power deduced from the present experiments is significantly lower than values reported in literature.