## 3 Results and Discussion  
Figure 3 represents the stress/displacement distribution throughout the FOV area. There were three virtual extensometers (gauge length--10 mm) placed in different areas of the FOV--close to the notch tip, central of the FOV and at the left edge of the FOV (along with the calibration target) (Figure 3) An additional virtual extensometer (gauge length--10 mm) was placed 1 mm into the notch area (beyond the FOV). The analysis was done using DIC software. Figure 3: Analysis of stress/displacement distribution throughout the FOV area (image from GOM Correlate). The virtual extensometers used in the stress analysis were set to monitor distance changes relative to the reference stage (first image captured during the test). The graph reveals that the zones further from the notch tip are more prone to displacement than those that are placed closer and previously believed to bear higher strains. This subject is to be studied in more detail in further research. In this experiment, the area of the CT specimen's notch tip was captured on a DSLR camera to compare the displacement data from the DIC with those registered by surface-attached dial gauges. Five virtual extensometers (gauge length--2 mm) were created in GOM software for the DIC analysis. The extensometers were placed within the notched zone of the specimen (0.5 mm into the notch towards the open end), positioned perpendicular to the notch (Figure 4). Such a location of the extensometers was chosen to enable displacement analysis (by DIC software) that can be verified with mathematical calculations (manually). Data represented by GOM software were exported to MS Excel for further analysis. In further analysis, all displacement data obtained from the DIC were compared with displacement data from surface-attached strain gauges. Figure 5 shows the test specimen with the measuring device and the data obtained. Displacement data from surface attached digital dial gauge (NMOD) show similarities to data from the DIC analysis (NTOD) (Figure 6). Both curves are similar in their overall nature and tend to break simultaneously when showing reactions of the material (e.g., day 15 and day 24). For further analysis of data compatibility, the mechanically measured displacements in the NMOD zone were used to mathematically calculate the corresponding NTOD values by similar triangles principle. The obtained results are shown in Figure 7.  
Figure 4: NTOD analysis with the DIC software (image from GOM Correlate). DIC analysis in GOM Correlate software shows a larger NTOD displacement compared to those calculated from the dial gauge data. The trend of both curves is similar. Additionally, calculation principles by [PERSON] (1978) [46] were used to calculate the displacements along the loading axis (Figure 8). Figure 5: Creep monitoring with surface-attached strain gauge: (**a**) Test setup—loaded CT specimen with attached digital dial gauge; (**b**) displacement data obtained from a surface-attached strain gauge. Figure 6: Displacement data from surface attached digital dial gauge (NMOD) compared with data from DIC analysis (NTOD). The following Equations (1)-(4) were used to calculate the displacements along the loading axis (\(\delta_{2}\)) [46]. Opening at the crack edge:  
\[\delta_{1}=\frac{P}{E^{\prime}}V_{1}(\
icefrac{{a}}{{b}}) \tag{1}\]  
Opening at load line:  
\[\delta_{2}=\frac{P}{E^{\prime}}V_{2}(\
icefrac{{a}}{{b}}) \tag{2}\]  
Configuration functions for displacement:  
\[