https://www.sciencedirect.com/science/article/pii/S2214914723001186
’ Moreover, each sequence of the distinct materials, properties and mechanical impedance are significantly important for the performance of the whole structure. Consequently, each of the different laminate has an important role towards preventing projectile piercing of the armour. The two frontal laminates (face sheet and strike face) fragmentate and mitigate the projectile’s nose. The two rear laminates (intermediate and back plate) hold the frontal plates, stop their fragments and absorbs ∼40% of the projectile kinetic energy. Hence, the strike-face should have high hardness and compression strength to break the tip of the projectile and the face-sheet should contribute to the spall protection, from spalls created by the strike-face fragmentation, on the front of the armour and to hold the strike face in position after the impact of a projectile. The subsequent laminates (intermediate and backplate) should have high toughness and energy absorption, to absorb a significant amount of energy during the impact of the projectile, while the third laminate has a great tensile strength to hold the strike-face’s fragments and protect the contact between the strike-face and the backplate. The back plate of common composite protection system is usually made up of a high-density material, especially metals, thus contributing the most to the total mass of the armour system. This research focuses on the reduction of the mass of the backplate and overall composite armour system, through the utilisation of ultra-light weight materials as backplate. The proposed materials is a Metal Matrix Composite (MMC) reinforced by nanomaterials which is designed and manufactured with enhanced mechanical and ballistic properties.’
’ 2.2.2.1. First laminate: face-sheet
The first laminate (face-sheet) is used for the spall protection, after the projectile impact preventing the micro damage to the following strike-face, protection from possible damage associated with system vibrations, protection from various environmental factors (i.e., thermal stress, ultraviolet radiation) and low Radar Cross Section (RCS) signatures. The basic functional requirements for the face-sheet layer are high dynamic stiffness, high-speed inelastic resistance to deformation, high compressive strength, and desirable hardness. These requirements contribute towards the main function of the strike face which is the mitigation of the projectile’s nose and/or the fragmentation and high shear strength due to the shearing behaviour of the material.’
’ 2.2.2.4. Fourth laminate: backplate
The backplate (last laminate layer) is used to absorb the projectile’s remaining kinetic energy through the plastic deformation mechanism, provide structure support to all of the protection laminate, and act as a load bearing element during the post impact period after the damage have taken place in the strike-face, support the strike-face body post-impact fracturing, and deform during the impact and recovery stages producing a high bending recovery and reaction. The backplate basic functional requirements are high toughness (rupture), high flexural strength, high bending stiffness, high fracture strength, suitable thickness (thin plates fail in tension due to the lack of structural rigidity), in-plane and through-the-thickness ductility (since this layer should be in deformation correspondence with the intermediate plate) and support the intermediate layer to avoid surpassing its bending strength under the projectile impacting. The backplate is a very important laminate of the composite armour since it absorbs up to the 40% of the kinetic energy.
Ductile materials, such as metal and polymer fibre composites, are ideal for use in the backplates. Metals are the most common material used for backplate due to low brittleness compared to polymer fibre composites.’
This has already been covered. Spall liners can mitigate spall even between layers, and yes, even metal can act as a spall liner.
https://www.sciencedirect.com/science/article/abs/pii/S0272884221013158
'Results showed that the UHMWPE laminate was beneficial for attenuating the damage state of back face and placing the UHMWPE laminate at the bottom core layer could significantly improve the performance of panels under the combined loads. Chocron et al. [15] developed a simple one-dimensional analytical model to consider the deformation and the erosion of the projectile, and studied the ballistic impact response of ceramic/composite armors. As the support plate of the front ceramic layer, the composite plate could restrain the fragmentation failure of the ceramic plate induced by the brittle failure and absorb the remaining kinetic energy of the projectile [16]. The investigations into the effect of the reinforcement type of back laminates on the ballistic resistance of ceramic/composite armors were carried out experimentally and numerically [[17], [18], [19], [20], [21]]. Nayak et al. [22] conducted experimental studies on the ballistic performance of ceramic-faced aramid laminated composites. For the same target thickness, the composite armors with the twaron-polypropylene back laminates exhibited a higher ballistic limit. The numerical work conducted by Tepeduzu and Karakuzu [19] revealed that the ceramic/composite structures with the aramid/epoxy backing plate showed better ballistic performance than the ones with S2 glass/epoxy or carbon-aramid/epoxy backing plate on the premise of the same area density. Moreover, related researches show the improvement of ballistic performance is available through the combination of different materials as the back plate of composite armors [[23], [24], [25]]. Liu et al. [26] examined the effect of different backplates on the ballistic behavior of the ceramic/composite armors. The results suggested that the composite armor with the backplate of Ti6Al4V/UHMWPE/Ti6Al4V absorbed a large amount of impact energy and showed better ballistic performance during the impact process. The ballistic performance of composite structures depends on not only the intrinsic properties of the materials but also on their spatial arrangement [24]. Changing the ceramic arrangement [27] or employing the ceramic layer [28] as the back plate of the composite material are demonstrated to be effective ways to further improve the ballistic performance of composite armor. Besides, the effect of mass allocation on the ballistic performance of two-component armors was investigated numerically [29] and analytically [30,31]. The results showed that the ceramic layer had a significant effect on slowing down the projectile in cases of targets with a constant areal density. Moreover, an effective methodology was developed for the optimum design of two-component armors.
In the present study, a new multi-layered composite armor with two metallic face sheets and a hybrid SiC/UHMWPE core was proposed. The ballistic behavior of the proposed composite armor against the flat-nosed projectile impact was investigated experimentally and numerically. At first, a series of experiments were conducted to evaluate the ballistic limit and to identify the typical failure modes of the composite armor. Then, a three-dimensional numerical model was established to analyze the effects of the ceramic layer placement and the mass allocation between the ceramic layer and UHMWPE layer on the projectile velocity response and energy absorption characteristics.’