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We expect the formation of wrinkles or creases to be arranged orthogonally to the direction of greatest contraction, and thus aligned with a principal direction of deformation. However, as we show in this paper, the mathematical equations modelling the development of such surface instabilities do not necessarily predict that they should be such principal wrinkles (figure 2a). In fact, we find that for the simplest boundary value problem there is, i.e. that of a deformed semi-infinite solid, the theory predicts that oblique wrinkles (figure 2b) should appear on the free surface prior to the principal wrinkles.
FROM:
Carfagna M, Destrade M, Gower AL, Grillo A. 2017 “Oblique wrinkles”. Phil. Trans. R. Soc. A 375: 20160158. http://dx.doi.org/10.1098/rsta.2016.0158
ABSTRACT: We prove theoretically that when a soft solid is subjected to an extreme deformation, wrinkles can form on its surface at an angle that is oblique to a principal direction of stretch. These oblique wrinkles occur for a strain that is smaller than the one required to obtain wrinkles normal to the direction of greatest compression. We go on to explain why they will probably never be observed in real-world experiments. This article is part of the themed issue ‘Patterning through instabilities in complex media: theory and applications’.
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