An improved torsion pendulum based on image processing for single fibers

Abstract

An improved torsion pendulum technique based on image processing is developed, which allows the measurement of the torsional oscillation of individual fibers. The torsion pendulum is composed of a length of fiber specimen and a ring-shaped mass attached to one of its ends. The oscillation motion of the mass is recorded with a video camera overhead. An image processing method is developed to accurately calculate the twist angle of single fibers in the torsion pendulum. All images are firstly converted into matrices and then the edge detection is applied to calculate the twist angle at corresponding time to obtain the angle-time relation. The oscillation frequency is determined by the fast Fourier transform (FFT) method. By applying this technique, we have performed tests on four types of fibers, namely T300 carbon fiber, copper, silver and tungsten wires. The longitudinal shear modulus measured for each type of these fibers is presented.

Direct measurement of torsional properties of single fibers

“…Such a calibration method has been proved to be unsatisfactory because of the friction in the pulley used to redirect the load. Here, we adopt an improved torsion pendulum based on image processing [27] to determine the shear modulus of the torsion wire accurately, as shown in Fig.2(a). Here, we chose tungsten wires ranging in diameter from 15 to 40μm as the torsion wires.…”

“…The oscillation frequency was then determined by the Fast Fourier Transform (FFT). The shear modulus of the tungsten wire can be calculated as [26,27]   . The detailed description of the torsion pendulum is given by Yu et al [27] As shown in Fig.…”

“…The shear modulus of the tungsten wire can be calculated as [26,27]   . The detailed description of the torsion pendulum is given by Yu et al [27] As shown in Fig. 2(a), by providing and releasing a small initial torque, we set the pendulum under a free torsional oscillation.…”

Peculiar torsion dynamical response of spider dragline silk

“…Today the torsion balance or pendulum is still one of the most sensitive tools for measuring the torsional properties of individual fibers 14,15,21,22 . In this study we use an improved torsion pendulum based on image processing 22 (see Fig.1 (a)) to explore the torsional relaxation dynamics of the dragline silks from two orb-weaver species: Nephila edulis (N. edulis) and Nephila pilipes (N. pilipes) spiders, and other types of fibers (e.g. metallic wires, carbon fiber, and human hair).…”

“…1(c), panel III and IV). The bob was taken to initial twist angles corresponding to ～0.61×10 -3 and～1.22×10 -3 in strain, When the initial surface strain is within the elastic region (＜0.6×10 -3 ) 22 , the pendulum oscillates around its original position, see panel III of fibers (e.g. human hair), and metallic wires (e.g.…”