Energy Absorption and Ballistic Performance of Epoxy Composite Reinforced with Arapaima Scales

Abstract

Arapaima scales possess a hierarchical structure capable of absorbing a considerable amount of energy before fracture. These natural dermal armors present significant potential in the sustainable development of cost-effective composites. This work aimed, for the first time, to analyze the impact resistance and ballistic performance of arapaima scale-reinforced epoxy composites and their potential application in multilayered armor systems (MAS). Composite plates were prepared with 20%, 30%, and 40 vol% of arapaima scales. Composite specimens were subjected to notched Izod impact and residual velocity stand-alone tests and their MAS through backface signature (BFS) tests, with their fracture surfaces studied using SEM. The Izod tests confirmed the effect of scales' volume fraction on the energy absorbed by the composites, showing an increase with volume fraction. Residual velocity tests showed that composites with 30 vol% of scales resulted in the most significant improvement in absorbed energy. All MAS formulations presented BFS depths lower than the trauma limit specified by the NIJ standard. Fractographic analysis showed that the scales' toughening mechanisms improved the composites' energy absorption capacity. The experimental results substantiate the potential use of arapaima scales as a reinforcement agent in polymeric composites, with 30 vol% being the optimal volume fraction for energy-absorbing applications.

Keywords: DGEBA/TETA epoxy; arapaima fish scales; ballistic behavior; energy absorption; green composites.

Figure 1

The Arapaima gigas, its scale, and a schematic representation of the hierarchical structure of the scales.

Figure 2

Fabricated plate of arapaima scales-reinforced epoxy composites (a); assembled multilayered armor system (MAS) using the arapaima scales-reinforced composite plates as the second layer (b).

Figure 3

Schematic diagram of the CAEX shooting line showing, in accordance with the NIJ standard procedure [36]: (a) the gun barrel and the 7.62 caliber ammunition used; (b) the arapaima scales-epoxy intermediate layer MAS mounted on the clay witness; and (c) the measurement procedure using a laser sensor.

Figure 4

Average absorbed energy values of the composites reinforced with 20, 30, and 40 vol% of arapaima scales against 0.22 ammunition compared to those reported for sedge [40] and tucum [41] fiber-reinforced composites.

Figure 5

Average absorbed energy values of the composites reinforced with 20, 30, and 40 vol% of arapaima scales against 7.62 mm ammunition compared to those reported for Kevlar™.

Figure 6

BFS measured for the multilayered armor systems with different volumetric fractions of arapaima scales: 20, 30, and 40 vol%, the maximum value allowed by NIJ standard and the values reported for Dyneema [34].

Figure 7

Fractured specimens after Izod impact test.

Figure 8

SEM image of the fracture surface of the composite with 20 vol% of arapaima scales after the Izod test with magnifications of: 50× (a) and 1000× (b).

Figure 9

SEM image of the fracture surface of the 40 vol% of arapaima scales reinforced composite after the Izod test with 50× (a) and 200× magnification (b).

Figure 10

Stand-alone test samples after ballistic impact: (a) tested with 0.22 caliber and (b) 7.62 mm caliber ammunitions, in which the perforation damage after the multiple shots is highlighted by the red circles.

Figure 11

Macroscopic aspect of the MAS using arapaima scales-epoxy composites as the intermediate layer: (a) ceramic fragments arrested by the composite plate, and fracture of plate into different pieces; (b) energy absorption mechanisms in the arapaima scales-epoxy composites.

Figure 12

SEM images showing the different energy absorption mechanisms from the arapaima scales: (a,b) delamination, stretching and fracture of fibers from external layers; (c,d) rotation of fibers and fiber pullout.

Figure 13

SEM images presenting different mechanisms of energy absorption shown by the composites: (a) “river marks” and the arapaima scales mechanisms, such as inner layers fracture; and (b) interfacial separation.