Experimental study on anti-penetration mechanism of bolted composite protective structure with limited span under impact of low-velocity projectile

In order to study the influence of the bolt joint mode on low-velocity projectiles penetrating the composite protective structure, two bolt joint models which connect the composite target to the fixed frame were designed, the ballistic test of the bolted composite protective structure with limited span was carried out, and the bearing and failure characteristics of the bolted region, as well as the energy dissipation of each part of the structure, were analyzed. The results show that in the condition of low-velocity impact, there are three failure modes for the bolted composite protective structure subjected to projectile penetration, including failure of the impact point of the composite target, failure of protective structure connecting components and failure of the holes in the bolted region of the composite target; the failure mode of bolt holes in the bolted region has a great influence on the protection performance, and the allowable value of the bearing capacity of the bolted region depends on the sum of the minimum failure load in the failure modes and the friction force; shear-out failure occurring in the bolt holes in the bolted region exerts the greatest effect on ballistic performance, which should be avoided; When simultaneous failure occurs in the bolted region and the free deformation region of the composite protective structure, the energy absorption per unit surface density of the composite protective structure reaches the maximum, which can give full play to its anti-penetration efficiency.