Test Method And Experimental Study On Torsional Mechanical Properties Of Micro-scale Fiber Materials

With the development of micro-electromechanical systems,the study of mechanical properties of micro-scale materials has become one of the hot areas.In order to characterize the torsional behavior of micron-scale specimens,a direct technique based on the principle of torsion balance and an improved torsion pendulum technique based on image processing are establishedIn order to obtain the static torsional mechanical properties of micro-scale materials,a new micro-torsion experiment device based on the principle of torsion balance is designed.The sensitivity of the torque sensor of the device is adjustable and can reach nNm level.It can automatically test single fibers/wires diameter from 50 to 5 microns and obtains the torque-rotation curve.Several sets of tests show the good repeatability of the experiments.In addition,a new specimen assembly method is proposed to improve the coaxiality of the specimen with the torsion wire in the torsion experiments.The experimental device can also accurately measure the shear modulus of fibers / wires.The mechanical properties of copper wires,silver wires and carbon fibers were measured successfully.In order to study the mechanical properties of spider silks,Nephila pilipes spiders was collected twice in Xishuangbanna Tropical Wild Botanical Garden,and their drag line silks was successfully extracted as the experimental materials.From the torque-rotation curve of the drag line silks,it is found that the torsional mechanical properties of the spider silks are obviously different from those of the metal filament.In order to obtain the torsional vibration performance of micro-scale materials,a torsional pendulum device based on image processing is designed.The torsion device consists of a camera,cantilever bracket and three-dimensional translation table and so on.The oscillator hanged by the specimens do the torsional oscillation.The camera records the oscillating position image of the oscillator.The self-made image analysis software is used to read the angle data of the oscillator in the video.Finally,the twist angle-time curve of the specimens are obtained.The angle measurement range of the device is not limited,and its resolution is determined by the number of camera frames and the image resolution.The copper wires,silver wires,carbon fibers,tungsten filament and spider silks were tested by this device.Experiments show that the damping coefficient of the wires will increase with the increase of the initial excitation angle.The longitudinal shear modulus of the tungsten wires do not change significantly with the increase of the diameter.Unlike the torsional pendulum vibration behavior of the wires,the spider silks have a large amplitude attenuation during the first vibration cycle,and then do a damped free vibration at a new equilibrium position that deviates from the original equilibrium position.