The effect of different number of layer and different joining techniques on ballistic performance in armor design

In this study, the failure modes and ballistic performances of monolithic, triple-layered and nine-layered structures made of hardened AISI 4340 steel were investigated experimentally and by the finite element method. The effect of dry contact and adhesive bonding of the layers on ballistic success was also evaluated. It was not possible to reach more layers at constant thickness with 4340 steel. More layered structures were fabricated with Ck75 spring steel and three-, 20-, and 40-layered cases were experimentally investigated. Experiments were carried out with 7.62 mm x 51 (M61) armor-piercing projectile. Perpendicular shots were made to the target surfaces with the experimental set-up used. According to the data obtained as a result of the research, it has been seen that the ballistic resistance of monolithic structures made of 4340 steel is superior to that of triple- and nine-layered structures. The reason for this is the decrease in bending resistance with the increase in the number of layers. While there is failure by ductile hole formation in monolithic structures, dishing failure has occurred as a result of bending in layered structures. It has been observed that joining the layers with adhesive increases the bending resistance of the structure and reduces the amount of deformation. With the finite element analysis, the ballistic success of the structures was correctly predicted. As a result of the analysis, the failure mechanisms and deformation patterns in the structures were also compatible with the experimental data. When the plates made of CK75 spring steel were examined, it was understood that the ballistic strength decreases with the increase in the number of layers, similar to 4340 steel. Depending on the strength of the adhesive used, delamination has occurred in the layered structures.