## 3 Results and Discussion
### Tensile Testing  
The tensile strength shows the ability of the workpiece to resist elastic and plastic deformation and fracture under loads. To assess the mechanical properties of the welded joints, the tensile tests were performed by a universal testing machine (UTM) (INSTRON, Norwood, MA, USA). For tensile tests, the required samples were cut from the welded workpieces according to American National Standard (AWS B4.0:2007) specifications. The specimen specifications for tensile test are presented in Figure 11.  
Figure 10: Shows weld micrographs, i.e., weld face and root face at different EN ratio settings (**a**) 250 A, 0% EN; (**b**) 250 A, 30% EN; and (**c**) 250 A, 50% EN. The tensile tests for 15 samples were carried out and the resultant mechanical properties of welded joints such as ultimate tensile strength (UTS), yield strength (YS) and percentage elongation (\(\updelta\)) are listed in Table 3. For the calculation of UTS and YS, the area was calculated by multiplying thickness of plate, i.e., 5 mm with the width of the specimen at the weld bead i.e., 38 mm. In terms of welding current, the highest value of UTS was obtained at 250 A, whereas the lowest UTS was observed at 150 A. It is due to the fact that increasing current resulted in more heat input to the BM. As a result, penetration depth increased and proper fusion occurred. Figure 12 shows the stress vs. displacement curve at Ia of 150 A and three distinct EN ratios. It was found that at a current of 150 A, an increase in EN ratio resulted in an increase in UTS and \(\updelta\). It was noticed that UTS and \(\updelta\) were increased 3.9% and 11.4%, respectively, when EN ratio was increased from 0% to 50%. The fracture locations of the joints have been shown in an inset of Figure 12. It is interesting to note that, irrespective of EN ratio, the fracture for all samples occurred near the FB and away from the weld centerline. It happened because of the incomplete fusion across the joint sides as sufficient heat for melting the joint sides was required. Similarly, for Ia of 175 A as shown in Figure 13, the quite similar behavior was observed. When EN ratio was increased from 0% to 50%, UTS and \(\updelta\) were increased to 1.5% and 8.2%, respectively. Failure of the butt-welded joint took place away from the weld centerline and close to the FB. For Ia of 200 A as shown in Figure 14, UTS was increased 7.4% as EN ratio was increased from 0% to 50%. However, it was found that \(\updelta\) first increased 27.9% when the EN ratio was increased from 0% to 30% and later it decreased 6.0% when the EN ratio was increased from 30% to 50%. The fracture of the welded joints did not occur in the middle of the weld. Instead, all samples were fractured on the weld joint sides, which was confirmed to be the weakest point in welded joints. It shows that, during the welding, an exorbitant amount of heat was required to properly melt the joint sides to get a strong weld. However, a change in behavior of welded joints under tensile load at Ia of 225 A and 250 A was noticed. According to Figure 15, the highest value of UTS, i.e., 474.10 MPa was obtained at a 30% EN ratio, whereas the highest \(\updelta\), i.e., 13.40, was obtained at a 50% EN ratio. It was interesting to note that, irrespective of the EN ratio, failure of the joints took place away from the FB and weld centerline. The fracture macrographs of welded specimens, as shown in the inset of Figure 15, revealed that fractures occurred 20 mm, 21 mm and 20 mm away from the weld centerline for 0%, 30% and 50% EN ratio, respectively. It shows that proper fusion occurred across the weld joints as sufficient heat was supplied to the BM. Similarly, from Figure 16 for Ia of 250 A, the highest value of UTS, i.e., 477.77 MPa, was obtained at a 0% EN ratio, whereas the highest \(\updelta\), i.e., 12.78, was obtained at a 50% EN ratio. The fracture for all of the samples occurred away from the FB and weld centerline.