# Fracture Prediction in Weldox 700E Steel Subjected to High Velocity Impact Using LS-DYNA
## 3 Results and Discussion
### Investigation of Fracture Behaviour
#### 3.3.4. Fracture Behaviour with Varying Projectile Velocity  
This FE model is applied to analyze the fracture behaviour with varying projectile velocity. The target plate thickness is 4 mm, and the projectile mass is kept at 6.4 g. The investigation is performed with varying projectile velocity viz. 275.7 m/s, 300 m/s, and 400 m/s, while the other process parameters remain the same. The material and fracture constants are given in Section 2.3.  
(a) Plug formation Figure 27 shows the plug formation in a 4 mm thick plate with varying projectile velocities. It is observed that with lower projectile velocity, the plug formation is smoother with higher deformation, whereas with higher velocity, the plug becomes less smooth with reduced deformation in the target plate. This may be due to the fact that higher velocities result in greater kinetic energy, which alters the fracture behaviour.  
(b) Effect on fracture parameters The \"top\" element experiences early fracture at higher projectile velocities (Figure 28) due to higher values of equivalent plastic strain (Figure 29). Figure 30 shows that the von Mises stress increases during the initial impact but decreases rapidly at higher velocities due to a rapid increase in equivalent plastic strain and triaxiality. The triaxiality also follows a similar trend to the equivalent plastic strain (Figure 31). Figure 32 demonstrates that the temperature increase is more significant at lower projectile velocities, reaching 300 K at 400 m/s, 353 K at 300 m/s, and 370 K at 275.7 m/s. This indicates that temperature has no significant effect on the top element at higher projectile velocities but has a more pronounced impact at lower velocities. The load-carrying capacity decreases at higher velocities, leading to earlier element deletion (Figure 28).  
Figure 28. Trend for fracture parameter with varying projectile velocity.  
Figure 27. Plug formation with varying projectile velocity.  
Figure 31: Trend for triaxiality with varying projectile velocity.  
Figure 30: Trend for von Mises stress with varying projectile velocity.  
Figure 29: Trend for equivalent plastic strain with varying projectile velocity.  
For the \"mid\" element, the trend of element deletion is similar to that discussed for the top element, as shown in Figure 28, with the only difference being the time taken for deletion. Figure 29 shows that the equivalent plastic strain remains nearly constant, resulting in elongation of elements. The near-zero value of triaxiality shows that the elements experience fracture due to shear failure. The effect of temperature becomes a more prominent factor for the mid element as projectile velocities decrease, as shown in Figure 32. The increase in temperature is recorded in the range of 650-710 K, with lower temperature values at higher projectile velocity (Figure 32).  
The trend for fracture along the \"bottom\" element is similar to that of the top and mid elements, as shown in Figure 28. Figure 27 shows that the equivalent plastic strain remains constant for approximately 11 us at 275.7 m/s, 9 us at 300 m/s, and 6 us at 400 m/s, with a similar trend observed for triaxiality (Figure 29). During this period, fracture remains constant (Figure 26), and the von Mises stress maintains a constant profile, as shown in Figure 28. Figure 30 demonstrates similar temperature trends to those discussed for the top and mid elements. The increase in temperature is recorded in the range of 370-450 K.  
Overall, the order of plug formation is top-bottom-mid at 275.7 m/s and top-mid-bottom at 300 m/s and 400 m/s. The plug formation occurs from higher to lower velocities, specifically first at 400 m/s, then at 300 m/s, and lastly at 275.7 m/s. The effect of temperature is much more noticeable for the mid element than for the bottom and top elements.