Protective materials and structures found in natural organisms may inspire new armors with improved resistance to penetration, flexibility, light weight, and other interesting properties such as transparency and breathability. All these attributes can be found in teleost fish scales, which are the most common types of scales in modern fish species. In this work, we have studied the structure and mechanics of fish scales from striped bass (Morone saxatilis). This scale is about 200–300 µm thick and consists of a hard outer bony layer supported by a softer cross‐ply of collagen fibrils. Perforation tests with a sharp needle indicated that a single fish scale provides a high resistance to penetration which is superior to polystyrene and polycarbonate, two engineering polymers that are typically used for light transparent packaging or protective equipment. Under puncture, the scale undergoes a sequence of two distinct failure events: First, the outer bony layer cracks following a well defined cross‐like pattern which generates four “flaps” of bony material. The deflection of the flaps by the needle is resisted by the collagen layer, which in biaxial tension acts as a retaining membrane. Remarkably this second stage of the penetration process is highly stable, so that an additional 50% penetration force is required to eventually puncture the collagen layer. The combination of a hard layer that can fail in a controlled fashion with a soft and extensible backing layer is the key to the resistance to penetration of individual scales.

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a b s t r a c tBiological and manmade structures often share the same specifications and design constraints: structural support, lightweight or protection against specific threats. In this context, the structure of fishscales, consisting of small rigid plates growing out of the skin of a majority of fish species, are characterized by a large variety of shape, size and properties in order to achieve particular functions. The present study introduces a basic two-dimensional micromechanical model that permits to establish a correlation between the flexural response of a scaled skin and the nature of its underlying structure, including both geometric and material aspects. The model is used to predict trends in the structure's response and illustrates the fact that the scale design, arrangement and properties can be tailored to achieve a wide spectrum of response. In particular, fishscale structure possesses an inherent strain-stiffening response that can be suppressed or magnified by certain structural features. This particularity, shared by most biological materials, ensures that the structure provides both a structural and protective support for the animal.

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