7,803 research outputs found
Frictional Effects in Biomimetic Scales Engagement
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 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 stiffness of the structure. This dual nature of friction
which influences both 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 frictional limits.Comment: 4 pages, 4 figure
Indentation of ellipsoidal and cylindrical elastic shells
Thin shells are found in nature at scales ranging from viruses to hens’ eggs; the stiffness of such shells is essential for their function. We present the results of numerical simulations and theoretical analyses for the indentation of ellipsoidal and cylindrical elastic shells, considering both pressurized and unpressurized shells. We provide a theoretical foundation for the experimental findings of Lazarus et al. [Phys. Rev. Lett. (submitted)] and for previous work inferring the turgor pressure of bacteria from measurements of their indentation stiffness; we also identify a new regime at large indentation. We show that the indentation stiffness of convex shells is dominated by either the mean or Gaussian curvature of the shell depending on the pressurization and indentation depth. Our results reveal how geometry rules the rigidity of shells
The indentation of pressurized elastic shells: From polymeric capsules to yeast cells
Pressurized elastic capsules arise at scales ranging from the 10 m diameter pressure vessels used to store propane at oil refineries to the microscopic polymeric capsules that may be used in drug delivery. Nature also makes extensive use of pressurized elastic capsules: plant cells, bacteria and fungi have stiff walls, which are subject to an internal turgor pressure. Here we present theoretical, numerical and experimental investigations of the indentation of a linearly elastic shell subject to a constant internal pressure. We show that, unlike unpressurized shells, the relationship between force and displacement demonstrates two linear regimes. We determine analytical expressions for the effective stiffness in each of these regimes in terms of the material properties of the shell and the pressure difference. As a consequence, a single indentation experiment over a range of displacements may be used as a simple assay to determine both the internal pressure and elastic properties of capsules. Our results are relevant for determining the internal pressure in bacterial, fungal or plant cells. As an illustration of this, we apply our results to recent measurements of the stiffness of baker’s yeast and infer from these experiments that the internal osmotic pressure of yeast cells may be regulated in response to changes in the osmotic pressure of the external medium
Wrinkling reveals a new isometry of pressurized elastic shells
We consider the point indentation of a pressurized, spherical elastic shell.
Previously it was shown that such shells wrinkle once the indentation reaches a
threshold value. Here, we study the behaviour of this system beyond the onset
of instability. We show that rather than simply approaching the classical
`mirror-buckled' shape, the wrinkled shell approaches a new, universal shape
that reflects a nontrivial type of isometry. For a given indentation depth,
this ``asymptotic isometry", which is only made possible by wrinkling, is
reached in the doubly asymptotic limit of weak pressure and vanishing shell
thickness.Comment: 6 pages main text plus 14 pages of supplementary informatio
Wrinkling of pressurized elastic shells
We study the formation of localized structures formed by the point loading of an internally pressurized elastic shell. While unpressurized shells (such as a ping pong ball) buckle into polygonal structures, we show that pressurized shells are subject to a wrinkling instability. We present scaling laws for the critical indentation at which wrinkling occurs and the number of wrinkles formed in terms of the internal pressurization and material properties of the shell. These results are validated by numerical simulations. We show that the evolution of the wrinkle length with increasing indentation can be understood for highly pressurized shells from membrane theory. These results suggest that the position and number of wrinkles may be used in combination to give simple methods for the estimation of the mechanical properties of highly pressurized shells
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