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Scales engagement can contribute significantly to nonlinear bending behavior of elastic substrates with rigid biomimetic scales. In this letter, we investigate the role of friction in modulating the nonlinearity that arises due to self-contact of scales through an analytical investigation. We model the friction as dry Coulomb's type friction between rigid links and the substrate is taken to be linear elastic. Our results reveal that frictional effects give rise to two possible locking mechanisms, namely static friction lock and kinetic friction lock. These locks arise due to a combination of interfacial behavior and geometry. In addition to these extremes, the frictional behavior is found to increase the stiffness of the structure. This dual nature of friction which influences both the system operation and its terminal limit results in the maximum relative frictional work to lie at intermediate friction coefficients and not at the extremes of the frictional limits. [ABSTRACT FROM AUTHOR]

Hierarchical structures are observed in nature, and can be shown to offer superior efficiency. However, the potential advantages of structural hierarchy are not well understood. We extensively explored a bending-dominated model material (i.e. transversely loaded hexagonal honeycomb) which is susceptible to improvement by simple iterative refinement that replaces each three-edge structural node with a smaller hexagon. Using a blend of analytical and numerical techniques, both elastic and plastic properties were explored over a range of loadings and iteration parameters. A wide variety of specific stiffness and specific strengths (up to fourfold increase) were achieved. The results offer insights into the potential value of iterative structural refinement for creating low-density materials with desired properties and function. [ABSTRACT FROM AUTHOR]

We show that focused ion beam irradiation results in the creation of peculiar one- and two-dimensional nanoscale features on the surface of polyimide--a common polymer in electronics, large scale structures, and the automobile industry, as well as in biomedical applications. The role of ion beam incident angle, acceleration voltage, and fluence on the morphology of the structural features is systematically investigated, and insights into the mechanisms of formation of these nanoscale features are provided. Moreover, by using the maskless patterning method of the focused ion beam system, we have developed a robust technique for controlled modification of the polymeric surface. The technique, which is analogous to using a gray glass with varying darkness to control the radiation from the sun, but at a much smaller scale, enables the ion intensity and angle to be controlled at each surface point of the polymer, giving rise to structural surface features with desired shape and morphology. [ABSTRACT FROM AUTHOR]