## 4 Result and Discussion  
### Depth of Penetration and Microstructural Investigation  
Figure 5 shows the results of mesh convergence study of base metal plate FEA model. The results are plotted between depth of penetration vs. number of elements. Further, the results revealed that with the minimum number of elements, the size of element is increased, and after the deletion of elements, it shows a greater depth of penetration. The elements with 3249, 3743, and 4265 numbers show a greater depth of penetration. Further the depth of penetration becomes constant at 4768 and 5220 number of elements. The FEA results for all three investigating materials (base metal, weldment-1 and weldment-2) have been drawn with the highest number of elements, which is 5220. The bullet elements with fewer than 2812 elements causes the access deformation at the nose section which results in the termination of explicit analysis. The FEA simulation results of the investigated materials have been drawn with the 2812 bullet elements. Figure 5: Depth of penetration vs. Number of elements. Figure 6 shows the validation of FEA model depth of penetration results with the experimental results in the form of bar chart. The results are plots for the base metal, weldment-1 and weldment-2 against 7.62 AP bullet. Further, the experiments confirm the depth of penetration for base metal, weldment-1, and weldment-2 as 10.93, 13.65, and 15.20 mm, respectively, against 7.62 AP bullet. The developed FEA model predicts the depth of penetration for base metal, weldment-1 and weldment-2 is 10.11, 12.87, and 14.6. The percentage difference between experimental and FEA results for base metal, weldment-1 and weldment-2 is 8.11%, 5.71%, and 3.94% respectively. The percentage error less than 10% shows the good prediction capability of developed FEA model. Figure 7 shows the bullet penetration experiment cut section for the base metal, weldment-1, and weldment-2. Figure 6: Experimental vs. FEA. Figure 7: 7.62 AP bullet penetration cut section of (**a**) base metal, (**b**) weldment-1, (**c**) weldment-2. Optical micrographs of fracture surface for base metal, weldment-1, and weldment-2 are shown in Figure 8a-c, respectively. In the present research, the thickness of the base metal plate and weldments is 25 mm and 7.62 AP bullet is not able to penetrate throughout. A clear denting is observed in the attack zone area in Figure 8a-c, which represents the inability of projectile in penetration of target plate. The more denting area is shown in Figure 8b (weldment-1) than Figure 8c (weldment-2). Further, the fragmentation failure has been identified in all three investigation materials. The all three investigation material micrographs exhibited the poor penetration ability. Further, the white-etched portion in Figure 8a-c represents the adiabatic shear bands. Figure 9 Shows the finite element analysis (FEA) result of ballistic impact (7.62 AP bullet penetration) against base metal, weldment-1 and weldment-2 in terms of depth of penetration (DOP) at different step time. Three different selected time is 0, 25, and 500 \(\upmu\)s. Further, the given time is the total step time for explicit simulation. Figure 8: Fracture surface optical micrograph (**a**) base metal, (**b**) weldment-1, (**c**) weldment-2. Figure 9 Shows the visualization of FEA results. Figure 10 shows the graph between DOP vs. Time for all three under investigation materials. The ballistic resistance of base metal against 7.62 AP bullet is highest than remaining materials. Base metal, weldment-1 and weldment-2 has DOP of 10.11, 12.87, and 14.60 mm respectively. Weldment-1 has good ballistic resistance than weldment-2 which more DOP at same impact velocity of 820 m/s. The obtained results are in good agreement with the experimental studies of [PERSON] et al. [12] and [PERSON] et al. [23]. [PERSON] et al.