https://www.sciencedirect.com/science/article/pii/S2214914723001186
" Studies have shown that every material or a combination of materials, with enough thickness, can defeat a projectile [11,12]. However, the use of one material can be either expensive or can lead to a very heavy structure. For that reason, a multi-layered structure is more suitable, consisted of three distinct layers, according to STANAG 4569 [[13], [14], [15]]. Different approaches have been employed to create a composite armour, but the most common practise is the use of a backplate made from materials such as Steel, Al alloys and Ti alloys, an intermediate part of ceramic plates/tiles such as SiC, Al2O3 and B4C, and a front plate made of fibre reinforced polymers such as polyethylene (PE) and aramid fibres, bonding together with the use of epoxy resins, polyethylene resins or/and polyurethane resins [[16], [17], [18]]. The two frontal plates (front plate and intermediate plate) are related to the fragmentation and the mitigation of the projectile’s nose, while the last plate (backplate) is responsible for holding the two front plates, stop the fragments and absorb a significant amount of energy, created from the projectile (∼40%) [[19], [20], [21]]. Due to the relatively high density of materials (metallic character), used in the rear (backplate) of the composite protection system, these materials usually constitute a significant percentage of the total weight of the composite protection system [[22], [23], [24]]."
https://www.sciencedirect.com/science/article/abs/pii/S0272884221013158:
" A novel multi-layered composite armor system is proposed for ballistic protection in the present study. The composite armor is composed of a ductile metal front, followed by a ceramic/UHMWPE laminate composite as the intermediate layer, and a ductile metal back layer. The ballistic performance of the composite armor against flat-nosed projectile was investigated experimentally and numerically. Experimental results show that the proposed composite armor exhibited several failure modes, including ductile hole enlargement of metallic face sheets, fragmentations and cracks of the ceramic layer, delamination, fiber fracture and bulge deformation of UHMWPE laminates. Three-dimensional numerical model was established to analyze the evolution of the whole ballistic response, and to discuss the effect of the ceramic layer placement and the mass allocation between the ceramic layer and UHMWPE laminate layer on the ballistic performance. Simulation results reveal the evident reduction in residual velocity that results from the optimal placement of the ceramic layer. Good balance among the contributions of the target components can be achieved to maximize the total energy absorption of composite armor by optimizing the ceramic placement strategy. The projectile residual velocity and the total energy absorption are insensitive to the mass ratio of ceramic layer to UHMWPE laminate layer within a certain range. Under the condition of a higher mass ratio, the specific energy absorption of UHMWPE layer can be significantly improved due to the full development of its bulging deformation. Consequently, it would benefit the energy absorption capability of the composite armor."
Oh no, metallic backplates with spall mitigation in between!