Creasing of an everted elastomer tube.

A cylindrical elastomer tube can stay in an everted state without any external forces. If the thickness of the tube is small, the everted tube, except for the regions close to the free ends of the tube, maintains a cylindrical shape, and if the thickness is larger than a critical value, the cross-section of the everted tube becomes noncircular, which is caused by mechanical instability. Although eversion-induced instability in an elastomer tube has been reported several decades ago, a satisfying explanation of the phenomenon is still unavailable. In all previous studies, linear analyses have been adopted to predict the critical thickness of the tube for eversion-induced instability. The discrepancy between prediction and experiment is significant. In this communication, based on experiments and theoretical analyses, we show that crease formation on the inner surface of an everted tube is the mechanical instability mode, which cannot be captured by linear stability analyses. Instead, a combination of energetic analyses and numerical simulations of finite deformation in an everted tube enables us to correctly predict both the critical tube thickness for the onset of creases and the profile of the noncircular cross-section of an everted tube.