## 1 Introduction  
The development of personal protection systems with improved ballistic performance and reduced weight has received a great interest in the last decade with the unfortunate ever-increasing threats and conflicts. Nowadays, ballistic protection systems are being increased in their functionality and technological aspects. Many efforts have been taken to improve their ballistic resistance alongside the weight reduction. Armor systems development works concern many sectors of the economy, including defense and security, where the key role is played by personal protective equipment (e.g., bulletproof vests, ballistic inserts, etc.). Their main objective is to provide adequate impact (ballistic) protection for the user who is exposed to the hazards of loss of life or health due to the nature of his or her work. While applying different ballistic and high performance materials, like ceramic tiles composites and Twaron/Kevlar based composites, integrated into one armor (ballistic) system, it is also possible to use the personal ballistic protection system, or enforcement for different valuable goods or properties like vehicles, airplanes or military equipment. Among the systems intended for the implementation of personal protective equipment, such as ballistic vests, body armor plays a leading role. Ballistic body armor is broadly classified into two categories, namely hard body armor and soft body armor. Soft armor should protect the wearer against most common and low to medium energy projectiles which could go up to a velocity of 500 m/s. These types of body armor are mostly made from high performance fibers, such as aramid or Ultra High Molecular Weight Polyethylene (UHMWPE) fibers and are widely used in personnel ballistic protective clothing for military and law enforcement application thanks to typical flexibility and light weight [1; 2; 3; 4]. On the other hand, hard body armor was designed to resist projectile velocity of NIJ Standard level IIIA [5], or more than 500 m/s velocity when worn in conjunction with soft armor. Hard body armor is made mainly of metal, composite, or ceramic plates [6; 7; 8]. Ceramic materials such as aluminum oxide (A12O3), silicon carbide (SiC), or boron carbine (B4C) have been widely applied in armor design due to their high compressive strength, high hardness, and low density. High hardness and high compressive strength of ceramic materials contribute to projectile destruction and/or spreading of the impact load on a larger area of the armor during ballistic impact [9; 10; 11; 12]. The shape and dimensions of the ceramic elements have a significant influence on the ballistic resistance of the hard body armor. According to [PERSON] and [PERSON]'s studies [13], the ballistic simulation tests show differences between regular hexagonal and square shapes of ceramic panels. During the research, it was shown that the hexagon units have better performance in the intersection points of panels while the ballistic performance of square unit and regular hexagonal unit is basically the same in central and eccentric areas of panels. Moreover, the results of the simulation were confirmed to the real ballistic test. The ballistic efficiency of alumina tiles with various sizes, shapes, and target configurations was also measured by [PERSON] et al. [14]. The ballistic efficiency of square tiles roughly 8 mm thick struck by 12.7 mm diameter bullets rapidly increased with tile size up to about 100 mm. Circular shape tiles had lower ballistic efficiencies than those of square shape tiles for the same width and thickness. The authors explained the obtained results by the effect of reflected waves at edges and the propagation of resulting cracks on the projectile penetration process. In turn, [PERSON] and co-workers [15] performed tests with different areal geometries silicon carbide square tiles. The tiles were manufactured via two different processes, and have been bonded to polycarbonate layers to evaluate their ballistic performance.