Boundary layer analysis of the ridge singularity in a thin plate

Abstract

Large deformations of thin elastic plates and shells present a formidable problem in continuum mechanics that is generally intractable except by numerical methods. Conventional approaches break down in the limit of small plate thickness due to the appearance of discontinuities in the solution that require a boundary layer treatment. We examine a simple case of a plate bent by forces exerted along its boundary so as to create a sharp crease in the limit of infinitely small thickness. We find a separable boundary layer solution of the von K\'arm\'an plate equations that is valid along the ridge line. We confirm a scaling argument [T. A. Witten and Hao Li, Europhys. Lett. 23, 51 (1993)] that the ridge possesses a characteristic radius of curvature R given by the thickness of the sheet h and the length of the ridge X, viz., R\ensuremath{\sim}${\mathit{h}}^{1/3}$${\mathit{X}}^{2/3}$. The elastic energy of the ridge scales as E\ensuremath{\sim}\ensuremath{\kappa}(X/h${)}^{1/3}$, where \ensuremath{\kappa} is the bending modulus of the sheet. We determine the dependence of these quantities on the dihedral angle of the ridge \ensuremath{\pi}-2\ensuremath{\alpha}. For all angles R\ensuremath{\sim}${\mathrm{\ensuremath{\alpha}}}^{\mathrm{\ensuremath{-}}4/3}$ and E\ensuremath{\sim}${\mathrm{\ensuremath{\alpha}}}^{7/3}$. The framework developed in this paper is suitable for the determination of other properties of ridges such as their interaction or behavior under various types of loading. We expect these results to have broad importance in describing forced crumpling of thin sheets. \textcopyright{} 1996 The American Physical Society.