Hierarchical structure and mechanical properties of fish scales from Lutjanidae with different habitat depths.

In recent days, many researchers are focusing on emerging a new class of bio-inspired architectured materials. The primary strategy of these architecture designs is directly dependent on the types of available literature based on higher-ordered species such as nacre and fish scales. In this study, the authors have investigated the microstructural features and mechanical properties of five different ray-finned fish scales from Lutjanidae family collected in Iran. It was found that habitat depth and habits may result in significant changes in scale's surface morphology and mechanical properties. Interestingly, the variations in cross-sectional microstructural features such as fibre orientation and layer thickness ratios in scales did not show noticeable differences. It has also been proved that the mechanical performance of fish scales is influenced by the shape, array pattern and compactness of strips on posterior edges in a scale. Moreover, the radii count at anterior positions is higher in fishes living in wide-ranging depth; it supports in achieving higher scale stiffness and flexibility during movement. Consideration of these factors may help in optimising the performance of newly designed architectured materials subjected to mechanical loadings.

Structural and mechanical properties of fish scales for the bio-inspired design of flexible body armors: A review.

Natural protection offered to living beings is the result of millions of years of biological revolution. The protections provided in fishes, armadillos, and turtles by unique hierarchal designs help them to survive in surrounding environments. Natural armors offer protections with outstanding mechanical properties, such as high penetration resistance and toughness to weight ratio. The mechanical properties are not the only key features that make scales unique; they are also highly flexible and breathable. In this study, we aim to review the structural and mechanical characteristics of the scales from ray-finned or teleost fishes, which can be used for new bio-inspired armor designs. It is also essential to consider the hierarchical structure of extinct and existing natural armors. The basic characteristics, as mentioned above, are the foundation for developing high-performance, well-structured flexible natural armors. Furthermore, the present review justifies the importance of interaction between toughness, hardness, and deformability in well-engineered bio-inspired body armor. At last, some suggestions are proposed for the design and fabrication of new bio-inspired flexible body armors.

A new design and performance optimization of bio-inspired flexible protective equipment.

In this study, a new biomimetic design of protective equipment has been proposed. Basically, teleost fish scales combine a two-layered structure, a tough high mineralized bony layer with a relatively soft collagen and fiber-based sublayer arranged in a periodic overlapping design, which offers excellent flexibility and puncture resistance. For the biomimetic design of fish scales, a hard-ceramic layer with an ultra-high-molecular-weight polyethylene based-sublayer is used for the design of protective equipment. Finite element analysis of the bio-inspired protective design and its ballistic performance is done by a commercially available 3D simulation software LS-DYNA. Various design parameters, including the overlapping angle of adjacent scales, frictional coefficient between scales, number of Kevlar layers in the backing layer, ceramic types in the scale are discussed and analyzed to optimize the flexibility aspects of protective equipment. The ballistic performance of newly designed protective equipment with a failure pattern is examined as per the National Institute of Justice (NIJ) standards level III. Results based on experimental outcome and optimized parameters defined the critical performance limit of the protective equipment. Therefore, the results of this research provide valuable information related to ballistic safety equipment for improving the existing designs and/or fabricating innovative protective equipment.

Uniaxial Tensile Behavior of Carbon Textile Reinforced Mortar.

This paper investigates the effects of the reinforcement ratio, volume fraction of steel fibers, and prestressing on the uniaxial tensile behavior of carbon textile reinforced mortar (CTRM) through uniaxial tensile tests. The results show that the tensile strength of CTRM specimens increases with the reinforcement ratio, however the textile⁻matrix bond strength becomes weaker and debonding can occur. Short steel fibers are able to improve the mechanical properties of the entire CTRM composite and provide additional "shear resistant ability" to enhance the textile⁻ matrix bond strength, resulting in finer cracks with smaller spacing and width. Investigations into the fracture surfaces using an optical microscope clarify these inferences. Increases in first-crack stress and tensile strength are also observed in prestressed TRM specimens. In this study, the combination of 1% steel fibers and prestressing at 15% of the ultimate tensile strength of two-layer textiles is found to be the optimum configuration, producing the highest first-crack stress and tensile strength and the most reasonable multi-cracking pattern.

Flexural Behaviour of Carbon Textile-Reinforced Concrete with Prestress and Steel Fibres.

Four-point bending tests were adopted to investigate the influences of the number of textile layers, volume content of steel fibres, and prestress on the flexural behaviour of carbon textile-reinforced concrete (TRC). The failure mode of the specimen changed from debonding failure to shear failure, accompanied by the matrix-textile interfacial debonding with an increasing number of textile layers. The interfacial bonding performance between the textile and matrix improved with the addition of steel fibres in the TRC specimens. The presence of prestress or steel fibres improved first-crack and ultimate stresses of the TRC specimen. In comparison with the first-crack stress, a more pronounced enhancement in the ultimate stress was achieved by the addition of steel fibres. However, the effect of prestress on the first-crack stress was found to be more significant than on the ultimate stress. The prestress combined with steel fibres further improved the flexural behaviour of the TRC specimens. The prestressed TRC specimens with 1% volume content of steel fibres effectively avoided debonding. Thus, the utilization of the textiles could be improved.

The nonlinear flexural response of a whole teleost fish: Contribution of scales and skin.

The scaled skin of fish is an intricate system that provides mechanical protection against hard and sharp puncture, while maintaining the high flexural compliance required for unhindered locomotion. This unusual combination of local hardness and global compliance makes fish skin an interesting model for bioinspired protective systems. In this work we investigate the flexural response of whole teleost fish, and how scales may affect global flexural stiffness. A bending moment is imposed on the entire body of a striped bass (Morone saxatilis). Imaging is used to measure local curvature, to generate moment-curvature curves as function of position along the entire axis of the fish. We find that the flexural stiffness is the highest in the thick middle portion of the fish, and lowest in the caudal and rostral ends. The flexural response is nonlinear, with an initial soft response followed by significant stiffening at larger flexural deformations. Low flexural stiffness at low curvatures promotes efficient swimming, while higher stiffness at high curvatures enables a possible tendon effect, where the mechanical energy at the end of a stroke is stored in the form of strain energy in the fish skin. To assess the contribution of the scales to stiffening we performed flexural tests with and without scales, following a careful protocol to take in account tissue degradation and the effects of temperature. Our findings suggest that scales do not substantially increase the whole body flexural stiffness of teleost fish over ranges of deformations which are typical of swimming and maneuvering. Teleost scales are thin and relatively flexible, so they can accommodate large flexural deformations. This finding is in contrast to the bulkier ganoid scales which were shown in previous reports to have a profound impact of global flexural deformations and swimming in fish like gar or Polypterus.

Mechanical Characterization of the Tensile Properties of Glass Fiber and Its Reinforced Polymer (GFRP) Composite under Varying Strain Rates and Temperatures.

Unidirectional glass fiber reinforced polymer (GFRP) is tested at four initial strain rates (25, 50, 100 and 200 s-1) and six temperatures (-25, 0, 25, 50, 75 and 100 °C) on a servo-hydraulic high-rate testing system to investigate any possible effects on their mechanical properties and failure patterns. Meanwhile, for the sake of illuminating strain rate and temperature effect mechanisms, glass yarn samples were complementally tested at four different strain rates (40, 80, 120 and 160 s-1) and varying temperatures (25, 50, 75 and 100 °C) utilizing an Instron drop-weight impact system. In addition, quasi-static properties of GFRP and glass yarn are supplemented as references. The stress⁻strain responses at varying strain rates and elevated temperatures are discussed. A Weibull statistics model is used to quantify the degree of variability in tensile strength and to obtain Weibull parameters for engineering applications.

Puncture resistance of the scaled skin from striped bass: collective mechanisms and inspiration for new flexible armor designs.

The structure and mechanics of fish scales display unusual and attractive features which could inspire new protective materials and systems. This natural material is therefore attracting attention over the past few years, and recent work demonstrated the remarkable performance of individual fish scales. A puncture event as would occur from a predator's attack however involves more than one scale, and in this article we therefore investigate collective mechanisms occurring within the scaled skin of a fish in the event of a predator's attack. We first demonstrate that in striped bass (Morone saxatilis), the scales increase by four to five times the force required to puncture the skin. We show that individual scales from striped bass provide a remarkable barrier against sharp puncture, regardless of the stiffness of the substrate. The scalation pattern in striped bass is such that three scales overlap at any point on the surface of the fish, which we show effectively multiplies the puncture force by three. We determined that the friction between scales is negligible and therefore it does not contribute to increasing puncture force. Likewise, we found that the local arrangement of the scales had little effect on the puncture performance. Interestingly, because the scales are several orders of magnitude stiffer than the substrate, indenting a few isolated scales results in "sinking" of the scales into the substrate. The high local deflections and strain within the soft tissue may then result in blunt injury before the sharp indenter penetrates the scales. Stereo-imaging and image correlation performed around a puncture site in fish reveal that the surrounding scales collectively contribute to redistributing the puncture force over large volume, limiting local deflections and strains in the soft tissues. The structure and mechanisms of natural fish scales therefore offer an effective protection against several types of threat, and may inspire novel versatile protective systems with attractive flexural properties.