Fabrication, testing and modeling of a new flexible armor inspired from natural fish scales and osteoderms

Abstract

Crocodiles, armadillo, turtles, fish and many other animal species have evolved flexible armored skins in the form of hard scales or osteoderms, which can be described as hard plates of finite size embedded in softer tissues. The individual hard segments provide protection from predators, while the relative motion of these segments provides the flexibility required for efficient locomotion. In this work, we duplicated these broad concepts in a bio-inspired segmented armor. Hexagonal segments of well-defined size and shape were carved within a thin glass plate using laser engraving. The engraved plate was then placed on a soft substrate which simulated soft tissues, and then punctured with a sharp needle mounted on a miniature loading stage. The resistance of our segmented armor was significantly higher when smaller hexagons were used, and our bio-inspired segmented glass displayed an increase in puncture resistance of up to 70% compared to a continuous plate of glass of the same thickness. Detailed structural analyses aided by finite elements revealed that this extraordinary improvement is due to the reduced span of individual segments, which decreases flexural stresses and delays fracture. This effect can however only be achieved if the plates are at least 1000 stiffer than the underlying substrate, which is the case for natural armor systems. Our bio-inspired system also displayed many of the attributes of natural armors: flexible, robust with 'multi-hit' capabilities. This new segmented glass therefore suggests interesting bio-inspired strategies and mechanisms which could be systematically exploited in high-performance flexible armors. This study also provides new insights and a better understanding of the mechanics of natural armors such as scales and osteoderms.

Teleost fish scales amongst the toughest collagenous materials

“…Mechanical characterization typically involved tensile testing (Ikoma et al, 2003;Garrano et al, 2012;Lin et al, 2011;Zhu et al, 2012) or indentation and puncture tests on individual scales (Bruet et al, 2008;Meyers et al, 2012;Zhu et al, 2012) or multiple scales (Zhu et al, 2013). Fish scales have also started to inspire new flexible protective systems (Browning et al, 2013;Chintapalli et al, 2014). Tensile tests on natural teleost fish scales confirmed the scale as a stiff, strong a tough material.…”

Progress and Perspective of Studies on Biomimetic Shark Skin Drag Reduction

“…In the case of shark skin, the hard dermal denticles forming its epidermis bestow it special surface morphology and features. Moreover, the dermis and the subcutaneous tissue beneath the epidermal layer form the main bulk of the skin's structural organization called the elastic matrix, or compliant surface in a literature 30. Naresh et al 31 investigated the mechanical behaviors and the histological characteristics of shark skin in detail.…”

“…Hydrophilic or hydrophobic behavior can suppress instability growth in the boundary layer by changing the interaction behavior of the flow‐wall interface; thus, drag reduction is achieved. Third, physical and mechanical properties of matrixes, including flexibility 30, stiffness 64, and viscoelasticity 49, can induce the riblet‐structured wall to exhibit different responses to fluid flow, thereby resulting in different drag‐reduction effects.…”

Bending of biomimetic scale covered beams under discrete non-periodic engagement

“…This design showed that overlapping of scales provides flexibility, damage tolerance, and more importantly resistance to puncture. Similarly, armadillo scales have also been used as a source of inspiration for designing flexible armor fabricated using hexagonal glass plates placed on an elastomer substrate [25]. This type of synthetic armors also yielded a good resistance to puncture as well as flexibility.…”