Ballistic Behavior of Bioinspired Nacre-like Composites

Abstract

In this paper, the ballistic performance of a multilayered composite inspired by the structural characteristics of nacre is numerically investigated using finite element (FE) simulations. Nacre is a natural composite material found in the shells of some marine mollusks, which has remarkable toughness due to its hierarchical layered structure. The bioinspired nacre-like composites investigated here were made of five wavy aluminum alloy 7075-T651 (AA7075) layers composed of ~1.1-mm thick square tablets bonded together with toughened epoxy resin. Two composite configurations with continuous layers (either wavy or flat) were also studied. The ballistic performance of the composite plates was compared to that of a bulk monolithic AA7075 plate. The ballistic impact was simulated in the 300-600 m/s range using two types of spherical projectiles, i.e., rigid and elastoplastic. The results showed that the nacre plate exhibited improved ballistic performance compared to the bulk plate and the plates with continuous layers. The structural design of the nacre plate improved the ballistic performance by producing a more ductile failure and enabling localized energy absorption via the plastic deformation of the tablets and the globalized energy dissipation due to interface debonding and friction. All the plate configurations exhibited a better ballistic performance when impacted by an elastoplastic projectile compared to a rigid one, which is explained by the projectile plastic deformation absorbing some of the impact energy and the enlarged contact area between the projectile and the plates producing more energy absorption by the plates.

Keywords: aluminum alloy; ballistic performance; bioinspired composite; cohesive interface; elastoplastic projectile; finite element simulation; impact behavior; layered structure; multilayer plate; nacre-like composite.

Figure 1

(a) FE mesh of the nacre-like composite plate; (b) close-up view of the cohesive element layers; and (c) close-up view of the brick element layers (the middle brick element layer is not displayed to show the interior).

Figure 2

Cross section of the FE mesh of the various plate configurations: (a) nacre plate; (b) wavy plate; (c) flat plate; and (d) bulk plate.

Figure 3

Residual velocities for various plate configurations using rigid and elastoplastic projectiles and impact velocities of (a) $V_i$ = 400 m/s; and (b) $V_i$ = 600 m/s.

Figure 4

Projectile velocity–time curves for various plate configurations using (a) rigid and (b) elastoplastic projectiles with $V_i$= 400 m/s.

Figure 5

Contour plots of the equivalent plastic strain (PEEQ) at t = 0.02 ms and t = 0.04 ms of various plate configurations impacted by a rigid projectile with an initial velocity of 400 m/s: (a) nacre plate; (b) bulk plate; (c) wavy plate; and (d) flat plate. Areas with high plastic strain levels larger than 0.2 are indicated in gray.

Figure 6

Contour plots of the equivalent plastic strain (PEEQ) at t = 0.02 ms and t = 0.04 ms of various plate configurations impacted by an elastoplastic projectile with an initial velocity of 400 m/s: (a) nacre plate; (b) bulk plate; (c) wavy plate; and (d) flat plate. Areas with high plastic strain levels larger than 0.2 are indicated in gray.

Figure 7

Contour plots of the equivalent plastic strain (PEEQ) at t = 0.015 of the (a) nacre plate; (b) flat plate; and (c) bulk plate impacted by an elastoplastic projectile with an initial velocity of 400 m/s. Areas with high plastic strain levels larger than 0.2 are indicated in gray.

Figure 8

Contour plots of the equivalent plastic strain (PEEQ) at t = 0.03 ms of the nacre and bulk plates impacted by projectiles with an initial velocity of 400 m/s: (a) rigid projectile; and (b) elastoplastic projectile. Areas with high plastic strain levels larger than 0.5 are indicated in gray.

Figure 9

Projectiles impacting the composite plates with an initial velocity of 400 m/s at t = 0.06 ms: (a) rigid projectile; (b) elastoplastic projectile impacting the nacre plate; and (c) elastoplastic projectile impacting the bulk plate. Areas with high plastic strain levels larger than 0.5 are indicated in gray.

Figure 10

Predicted projectile residual velocity versus impact velocity for the nacre and bulk plates impacted by: (a) rigid projectile; and (b) elastoplastic projectile. The solid lines represent fits to the predicted data of the Recht–Ipson model.

Figure 11

Normalized kinetic energy loss $∆K_p$ of the rigid and elastoplastic projectiles after impacting various plate configurations with (a) $V_i$ = 400 m/s; and (b) $V_i$ = 600 m/s.