Abstract
Recent research has established that polymer–metal laminates are able to provide enhanced impact perforation resistance compared to monolithic metallic plates of the same mass. A number of mechanisms have been proposed to explain this benefit, including the dissipation of energy within the polymer itself, and the polymer deformation enhancing dissipation within the metallic layer. This understanding of the layer interactions and synergies informs the optimisation of the laminate. However, the effect of the nose shape geometry of the projectile on perforation resistance of a particular laminate configuration has not been established. An optimal laminate configuration for one projectile may be sub-optimal for another. This investigation aims to clarify this nose shape sensitivity for both the quasi-static and impact perforation resistance of light-weight polymer–metal laminates. Bi-layer plates are investigated, with a polyethylene layer positioned on either the impacted or distal face of a thin aluminium alloy substrate. Three contrasting nose shapes are considered: blunt, hemi-spherical and conical. These have been shown to induce distinctly different deformation and fracture modes when impacting monolithic metallic targets. For all projectile nose shapes, placing a polyethylene layer on the impacted (rather than distal) face of the bi-layer plate results in an increase in perforation resistance compared to the bare substrate, by promoting plastic deformation in the metal backing. However, the effectiveness of the polymer in enhancing perforation resistance is sensitive to both the thickness of the polymer layer and the nose shape of the projectile. For a thin polyethylene layer placed on the impacted face, the perforation resistance is greatest for the blunt projectile, followed by the hemi-spherical and conical nose geometries. As the thickness of the polymer facing layer approaches the projectile radius, there is a convergence in both failure mode and perforation energy for all three nose shapes. Bi-layer targets can outperform monolithic metallic targets on an equal mass basis, though this is sensitive to the type of polyethylene used, the polymer layer thickness and the projectile nose shape. The greatest benefit of bi-layer construction (on an equal mass basis) is seen for blunt projectiles, using a polyethylene that maintains a high degree of strain hardening at high strain rates (i.e. UHMWPE), and a polymer thickness just sufficient to switch the failure mode in the metal layer from discing (failure at the projectile perimeter) to tensile failure at the plate centre.
Highlights
There is currently a growing interest in using polymer coatings to enhance the impact and blast resistance of structural panels (Mock et al, 2005; Roland et al, 2010; Barsoum and Dudt, 2010; Amini et al, 2010a, 2010b)
The aim of this investigation is to determine how the impact perforation mechanisms and synergies between layers reported by Mohagheghian et al, in press for light-weight bi-layer plates are influenced by the nose shape of the projectile
Mohagheghian et al (2015) showed that the key mechanical characteristics influencing the impact perforation resistance of ductile polymers is sensitive to the projectile nose shape
Summary
There is currently a growing interest in using polymer coatings to enhance the impact and blast resistance of structural panels (Mock et al, 2005; Roland et al, 2010; Barsoum and Dudt, 2010; Amini et al, 2010a, 2010b). The only previous investigation identified by the authors that has systematically compared the impact performance of a polymer–metal bi-layer plate for different projectile nose shapes was conducted by Xue et al (2010) Their numerical results suggest that placing a polyurea backing on the distal face of a steel plate is more effective against impacts by a conical projectile, and rather less effective for a blunt projectile (42% and 13% improvement relative to the bare substrate, respectively). They argued that for a conical projectile, the energy absorption in the metal layer is increased with the addition of a polymer coating due to a delay in the onset of fracture of the steel plate.
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