Bending deformation of tape-springs by a curved indenter

Rigidity of cylindrical shells plays important roles in designing industrial products or even in mechanical functionality of living organisms. Geometrically nonlinear response of shells is observed when we bend an open cylindrical shell or a tape-spring. Upon small deformation, the tape-spring bend uniformly. When the applied moment (or indenting force on three-point bending) reaches the critical value, the bending deformation is localized and then the tape-spring snaps. Despite the number of studies on the mechanical performance of tape-springs, the effects of geometry of indenters have not been clarified so far. Here, we perform three-point bending test for tape-springs, using the indenters of different-shaped caps to uncover their roles. We find that the curvature of indenter plays a central role in critical snap-buckling load. The change of their mechanical performance originates from the subtle interplay of elasticity and geometry. We note that this change in buckling behavior can be found in the sound of nail-clipping. We believe that the tunable buckling behavior in tape-springs could be useful in enlarging the design space of industrial applications such as deployable structures.