## 2 Methods and Materials
### Data Processing
#### 2.4.1 Tensile Data Processing
As long as the heat dissipation is uniform across the chosen region, the temperature within it can be represented very accurately by that polynomial function. However, if the heat dissipation is not uniform, the regression approach causes a smoothing effect: the higher the smoothing factor, the sharper the transitions in the source function. In the tensile test, the heat dissipation is relatively homogeneous as long as plastic deformation is uniform and no local plastic instabilities, such as necking, Luders bands, or Portevin-Le Chatelier bands show up. In general, the larger the regression radius, the less noise. However, the notice is in place that the regression radius should be small enough to cover the area of the approximately uniform heat dissipation, i.e., the appropriate regression radius depends on the feature size observed in the test. The procedure is illustrated in Figure 5.  
The procedure repeats itself for the entire ROI in each image automatically once the operator confirms the satisfactory results of data regression. The results from local regression obtained from IRT data were transformed to fit the DIC data to track the temperature evolution and its Laplacian transform entering Equation (10). The power density of the heat sources is calculated according to Equation (10), and, since the temperature evolution following changes in the heat source was tracked for a given control volume, the power density was integrated over time to find the total energy dissipated at each point of the surface over time. The integration over the volume yields the total power or energy dissipated in the region of interest. The thermoelastic effect is most significant in the elastic region, and it has only a small effect on the source function in the plastic region. Nevertheless, the source function was corrected for it to give the mechanical power dissipated as heat \(p_{D}\). Once the mechanical work expended for deformation, and the energy dissipated as heat have been simultaneously measured, the first law of thermodynamics can be used to calculate the stored energy [103; 104; 105; 106] (see also a comprehensive review by [PERSON] et al. [107] and references therein). This quantity is of particular interest not only because it relates to the microstructure and deformation mechanisms, but also because it serves as a physically-sound measure of deformation-induced damage. The IRT technique provides a direct estimate of this quantity that is not accessible by in situ measurements otherwise. As a final note to this session, one can notice that the procedures for joint processing of visual and thermal images could be greatly simplified if thermal and visual cameras were be equipped with lens sets having the same viewing angle and magnification. However, the use of infrared and optical measurements can have different objectives. For the sake of versatility, it is important to keep the possibility to perform the test using different optics on both systems, thus referring to not necessarily exactly the same but overlapping ROI. The ultimate goal of AE signal processing is to recover properties of the emitting stress relaxation process (or, possibly, multiple processes operating either simultaneously or in a sequence) from the observed data. This pseudo real-time information helps to gain better understanding of underlying accommodative mechanisms active under load. To reduce subjectivity in the interpretation of AE results, the analysis should be non-supervised and data driven. To this end, the processing of the continuously recorded data was performed based on the procedures described in [49]. The continuously streamed acoustic emission data are sectioned into consecutive equal segments of 1024-4096 readings, depending on the temporal scale of the observed transients. After conversion to the frequency domain by the fast fourier transform (FFT), the power spectral density (PSD) function \(G(f)\) was estimated using the [PERSON]'s method.