The geometry and mechanics of the Chinese finger trap

Abstract

We investigate the kinematics and mechanical mechanisms of cylindrically woven straps with a plain twill pattern, which form a tubular structure known as the Chinese Finger Trap. Our findings, derived from a combination of analytical, experimental, and numerical methods, demonstrate that when subjected to axial tension, the straps within the structure undergo reconfiguration, resulting in radial contraction. The geometry of the straps influences this contraction. As the structure compacts, the linear axial force transforms into an exponential force, resulting in a catenary-like profile in woven tubes due to the axially symmetric distribution of straps. Our study of this tension-induced contraction strategy proposes a straightforward approach to manufacturing morphable structures capable of efficiently converting axial elongation into radial contraction. This technique holds potential for medical, architecture, and soft robotics applications, offering accessible and controlled engagement and disengagement capabilities.