Origin of Unusually High Rigidity in Selected Helical Coil Structures
Origin of Unusually High Rigidity in Selected Helical Coil Structures David Tom´anek1, ∗ and Arthur G. Every2 1Physics and Astronomy Department, Michigan State University, East Lansing, Michigan 48824, USA 2School of Physics, University of the Witwatersrand, Private Bag 3, 2050 Johannesburg, South Africa (Dated: February 18, 2018) Using continuum elasticity theory, we describe the elastic behavior of helical coils with an asym- metric double-helix structure and identify conditions, under which they become very rigid. Theo- retical insight gained for macro-structures including a stretched telephone cord and an unsupported helical staircase is universal and of interest for the elastic behavior of helical structures on the micro- and nanometer scale. PACS numbers: 63.22.-m, 62.20.de, 62.25.Jk I. INTRODUCTION (a) (b) (c) Helical coil structures, ranging from a stretched tele- phone cord in Fig. 1(a) and an unsupported spiral stair- case in Fig. 1(b) on the macro-scale to DNA and proteins L = on the micro-scale abound in Nature. Since their elastic inner [H2+(4πR)2]½ behavior is governed by the same laws of Physics inde- stringer pendent of scale, insight obtained on the macro-scale will H axis H benefit the understanding of helical micro- and nanos- R tructures. An intriguing example of unusual high rigidity i on the macro-scale, which has remained unexplained to outer date, is the unsupported all-wooden spiral staircase in the stringer Loretto Chapel1 in Santa Fe, New Mexico, constructed Ro around 1878 and shown in Fig. 1(b). In the following we explore the elastic behavior of this structure using con- tinuum elasticity theory in order to identify the reason φ for its rigidity2{4.
[Show full text]