# Fracture Prediction in Weldox 700E Steel Subjected to High Velocity Impact Using LS-DYNA
## 3 Results and Discussion
### Investigation of Fracture Behaviour
#### 3.3.3 Fracture Behaviour with Varying Target Plate Thickness  
This FE model is applied to analyze the fracture behaviour with varying target plate thickness of Weldox 700E steel ranging from 2 mm to 6 mm. The projectile velocity of 400 m/s with a mass of 6.4 g is used, while the other process parameters remain the same. The material and fracture constants are given in Section 2.3.  
1. Plug formation  
Figure 21 shows the plug formation in the target plate with varying plate thickness. It is observed that the greater thickness experienced greater deformation than the lower thickness.  
2. Effect on fracture parameters  
The \"top\" element experiences higher values of fracture parameter, representing earlier fracture for a 6 mm plate followed by 4 mm and 2 mm plate thickness, respectively, as shown in Figure 22. Figure 23 indicates that the increase in equivalent plastic strain is greater for larger plate thickness. A similar trend is also observed for triaxiality (Figure 24). Therefore, at initial impact, the element in the plate with the lowest thickness experienced greater elongation compared to the plate with the highest thickness. The load-carrying capacity of the larger plate thickness decreases more than that of the lower plate thickness, as shown in Figure 25. However, no significant effect of temperature was observed on the top elements (Figure 26). Therefore, one can deduce that the top elements are primarily deleted due to the prominent effect of equivalent plastic strain.  
Figure 21: Plug formation with varying plate thickness.  
Figure 23: Trend for equivalent plastic strain with varying target plate thickness.  
Figure 24: Trend for triaxiality with varying target plate thickness.  
Figure 22: Trend for fracture parameter with varying target plate thickness.  
The \"mid\" element was deleted earlier for a 2 mm thick plate compared to the 4 mm and 6 mm thick plates (Figure 22). The triaxiality value remains near zero or approaches negative up to 0.9 us for the 2 mm thick plate, 6.5 us for the 4 mm plate, and up to 23 us for the 6 mm plate, as shown in Figure 24. During this time, the von Mises stress remains almost constant (Figure 25), and fracture occurs due to a nominal increase in triaxiality value. Therefore, one can say that the element is deleted due to the shearing effect. Figure 26 shows that the temperature for the 2 mm plate is approximately 311 K, which is close to the reference temperature (298 K), whereas the temperature reaches very high values for 4 mm and 6 mm plates. Hence, for the \"mid\" element, the prominent factors for fracture are plastic strain rate and temperature in the case of the 4 mm and 6 mm plates, while for the 2 mm plate, it is primarily plastic strain rate.  
Figures 23 and 24 show that, for the \"bottom\" element, the equivalent plastic strain and triaxiality remain almost constant up to 23 us for the 6 mm plate, whereas it is up to 2.2 us for 2 mm plate thickness, and for the 4 mm plate, it is up to 6.7 us. During this period, the von Mises stress also remains almost constant, as shown in Figure 25. Further, there is no significant effect of temperature for lower-thickness plates, but it becomes a prominent factor as the plate thickness increases.  
Overall, it can be observed that fracture occurs earliest in the 2 mm plate, followed by the 4 mm and 6 mm plate, respectively. Further, it is found that plastic strain rate and temperature are the prominent factors for thick plates, whereas for thin plates, only the plastic strain rate is the primary factor influencing element deletion.  
Figure 26: Trend for temperature with varying target plate thickness.  
Figure 25: Trend for von Mises stress with varying target plate thickness.