## 5 Numerical Model Verifications for Smooth Specimens  
To further validate the accuracy of the JC flow stress model as well as the JC damage parameters that were calculated in the previous sections, DIC analysis was attempted for specimens subjected to uniaxial tension under different strain rates. To perform the DIC analysis, commercially available software was used called \"GOM Correlate\". It is a DIC evaluation software program that is extensively used for material research and compound testing purposes. GOM Correlate follows a parametric approach that guarantees reliability for measuring required strains through a parametric approach. While using GOM Correlate, users have to define initial parameters regarding strain surface components for the area of interest, and the software creates facets which are square shaped across the whole range of supplied image data. Based on a high-contrast stochastic pattern that the user has to apply on the area of interest where strain is required to be measured, the software identifies these facets based on the quality of the aforementioned stochastic pattern. An additional parameter that requires adjustment from the user is the distance between adjacent facets on a center-to-center basis. This setting directly influences and it is correlated to the point density within the area of interest, and by decreased said distance, higher spatial resolution can be obtained by decreasing the distance of adjacent facets [28; 29; 30]. In this work, a full-frame CMOS camera was used to capture 1920 \(\times\) 1080 pixel-sized image series and videos to be used for the DIC analysis. For DIC, the captured stochastic pattern (Figure 18) was processed using a facet size of 14 and a distance of 9 to evaluate the corresponding strain fields. To compare the experimental results with the numerical modeling, strain was recorded along the axis of the cylindrical specimens and was compared with the resulting strain in central nodes of the FE model. Due to camera limitations regarding video framerate capturing capabilities, as well as applied pattern-related shortcomings, although DIC analysis was attempted for all experimental cases, it was only successful for quasi-static and 0.5 s\({}^{-1}\) experimental cases. Namely, for higher strain-rates, to capture a significant amount of image series, 120 fps video recording was attempted, but only a resolution up to 1280 \(\times\) 720 pixels was available. The lowered resolution coupled with brittleness of the coloring used to create the stochastic speckle pattern severely limited the amount of usable data for the DIC analysis. The resulting strain profile can be seen in Figure 19 for (a) the quasi-static tensile case and for (b) the dynamic case with a strain rate of 0.5 s\({}^{-1}\). In both Figure 19a,b, the horizontal axis data for finite element modeling (FEM) case have been shifted by an amount suitable to each case in order to align the portion of the gauge length in which necking and, correspondingly, fracture occurred. To aid with the visualization of the data, true strain and normalized gauge length data points are being used. For the quasi-static case, due to stochastic pattern degradation, strain data were captured up to approximately 0.2 strain. Figure 18: Stochastic speckle pattern used for DIC analysis during (a) beginning of the tensile test and (b) one frame before rupture. When comparing the FEM analysis results with DIC for 0.001 s\({}^{-1}\) strain rate, around the area where necking occurs, high strain region is concentrated for 22.6% of the normalized length as opposed to the DIC, which is 26.5%, resulting in the tensile specimen forming a longer necking region by 3.9%. For the case of 0.5 s\({}^{-1}\) strain rate, even better accuracy is observed with the FEM results underestimating the length where necking occurs by 1.6%. Overall, in both cases, good accuracy is observed between the DIC and FEM results, further reinforcing the suitability of the proposed JC model and damage parameters for SBPR 930/1080 Type B No.