# Fracture Prediction in Weldox 700E Steel Subjected to High Velocity Impact Using LS-DYNA
## 1 Introduction
[PERSON] and [PERSON] [13] found that fracture in ductile materials is primarily caused by the accumulation of plastic strain. [PERSON] and [PERSON] [14] concluded that the third stress invariant sometimes plays a significant role in crack growth, beyond the influence of mean stress and equivalent stress. In some metals, fracture occurs due to the development of micro-voids [15] and the ductile fracture is also predicted by modified anisotropic yield criteria [16]. [PERSON] et al. [17] performed the investigation on ductile fracture of high-strength steel at low triaxiality. [PERSON] and [PERSON] [18] performed a metallurgical investigation and found that the strength and toughness increased due to the presence of martensite and ferrite-pearlite in a steel component. The finite element (FE) technique employed to examine the ballistic behaviour of bi-layer Armor 500T steel in different configurations, concludes a better ballistic resistance at 30\({}^{\circ}\) angle [19]. [PERSON] et al. [20] revealed that the impact strength improved with the addition of several UD layers to nonwoven mats. [PERSON] et al. [21] studied the fracture characteristics of laminated composites during low-velocity impact and found that higher impact energy results in greater contact force and a larger fracture area. The performance of an additively manufactured honeycomb structure made of SS 316 plates showed that increased thickness enhances energy absorption and ballistic resistance [22]. Further, the study analyzing in-plane preloaded CFRP plates concluded that the ballistic limit is lower for preloaded specimens [23]. The value of the critical fracture parameter is a crucial factor in predicting the ballistic limit, perforation resistance, and deformation of target plates. Few studies have explored its significance. For instance, [PERSON] et al. [24] used a value of 0.5 for the fracture parameter with the AISI 1045 steel Taylor rod. Similarly, [PERSON] et al. [25] employed fracture values ranging from 0.90 to 0.99 to model structures under high-velocity impacts, effectively capturing crack growth in the material. Additionally, a few studies have incorporated a fracture value of unity [2; 6; 26]. Based on the literature, various fracture models and values of critical fracture parameters have been used to study the fracture behaviour, ballistic resistance, and perforation resistance of metallic plates, composite material plates, and CRPF plates. However, comparative studies on fracture strain models and different values of critical fracture parameters in fracture models have been limited in the literature. This highlights the need for a detailed investigation into fracture behaviour due to the variation in critical fracture parameters and fracture strain criteria. The insight into the fracture behaviour of flat target plates with varying thicknesses, when impacted by projectiles at different initial velocities and masses, requires further investigation with critical emphasis on the fracture parameters. This study aims to address these gaps by examining the fracture behaviour of Weldox 700E steel plates, considering varying values of critical fracture parameter and fracture strain criteria across different thicknesses. The plates are subjected to blunt-nosed projectiles of varying velocities and masses.