## 4 Discussion
peak stress and the DEFORM-3D simulation peak stress. A similar observation was noted in previous studies [24; 25; 26]. The maximum permissible discrepancy between experimental and simulation results for hot deformation studies has not been clearly defined. However, from previous studies [24; 25; 26; 27; 28], discrepancies of 15.7%, 16%, 22%, and up to 25% have been reported. Despite the noted difference in the peak stress value at 10/s, the peak flow stress obtained at higher strain rates (20, 50, and 1000/s) fit perfectly on a linear plot with a high correlation value of at least 0.98 (Figure 3). This clearly indicates that the constitutive parameters could be used to generate flow stress data beyond the experimental strain rate. To validate the peak stress obtained at high strain rates, selected uniaxial compression testing was performed on the commercial-grade Ti-6 Al-4V alloy at high strain rates using the Gleeble 3500 thermomechanical simulator. The Ti-6 Al-4V alloy was intentionally selected because it is the most studied and well-understood titanium alloy. The results (Figure 5) were compared with the flow stress data generated from the DEFORM-3D uniaxial compression testing simulation (Figure 4). A continuous flow softening trend was observed in both experimental and DEFORM simulation flow curves. However, flow oscillations accompanied flow softening for the experimental condition. This then raises the question of whether the flow oscillation is a metallurgical phenomenon or caused by the load cells of the machine. One major limitation of high strain rate testing using servo-hydraulic systems is the vibration of the load cells, which affects the flow stress values. The corresponding optical microstructure for the two validation experiments showed refined grains with globular or near-equiaxed morphology, which are features that support the oscillations and continuous flow softening seen on the experimental flow curves. Despite the observed metallurgical features, the authors were unable to quantify how much of the flow oscillation was due to a metallurgical phenomenon and how much could be attributed to the vibration of the servo-hydraulic system. This makes testing at high strain rates using this system challenging from a research point of view. It is worth mentioning that the two experimental results presented in this study to validate the DEFORM-3D simulation were repeated at least three times before the targeted strain rate was achieved. This was because different parametric adjustments had to be made based on trial and error before achieving the desired strain rate. For studies involving the development of new and expensive alloys, such efforts are not beneficial for research and development. Therefore, it is important that a new approach, such as the one presented in this study, be considered, especially where only screw-driven or servo-hydraulic facilities are available. Based on this study, we found that the peak flow stress values obtained from simulation and experiment at 20 and 50/s strain rates are close (Table 3). The difference in the flow stress values was less than the 20% reported in previous studies [24; 25; 26; 32; 33]. This confirmed that for uniaxial compression testing involving high strain rates, DEFORM-3D simulation could be used in as much as constitutive parameters can be established from experimental data at lower strain rates. The major advantage of this approach is that wear and tear of machine parts, wasting research time and resources, and difficulty reproducing results during high strain rate experimental testing could be avoided. The limitation of using this approach is that post-deformation characterization of experimental samples will be impossible if only DEFORM-3D is used. Therefore, correlating