Development And Application Of Micro-newton Tensile Testing System

The testing technology of mechanical properties of micro-/nano-scale materials is one of the important research directions of micro-/nano-scale materials.At present,the sensitivity and testing accuracy of force sensors are increasingly demanding,and continuous breakthroughs are needed to meet the measurement requirements.In order to meet the testing needs of natural spider silk and other polymer material monofilaments,the development and experiment of micro-newton real-time tensile testing and analysis system have been carried out in this paper.The main research work and achievements include:(1)Based on the principle of static torsion balance,a force sensor with ?N-resolution and a real-time tensile test and analysis system are developed.Two methods of dynamic and static calibration are proposed,both of which meet the accuracy requirements of the experiment.In the dynamic calibration method,the programmed frequency analysis program can quickly realize the accurate calibration of the force sensor.In addition,the selfdeveloped test and analysis software has the functions of data acquisition,processing,storage and real-time display of load-deformation curves,which realizes the full automation of the test process.(2)The characteristics of the force sensor with ?N-resolution are analyzed,and the main factors affecting the measurement accuracy of the system are discussed.The results show that the force sensor has the characteristics of wide measuring range,high precision,good linearity and repeatability.Different types of micro-force sensors were assembled with torsion wire with diameters of 100 ?m,150 ?m,200 ?m,and 300 ?m.The analysis shows that their measuring ranges were 300 ?N,1400 ?N,5000 ?N and 26000 ?N,and the minimum resolution was 0.14 ?N,0.74 ?N,2.84 ?N and 15.21 ?N,the accuracy level reaches 1.5,which can meet the requirements of different micro-/nano-scale material tensile experiments.(3)In terms of application,the mechanical properties of spider silk and silkworm silk under different ambient humidity were tested,and important mechanical parameters were obtained.The experimental results show that there is a secondary strengthening phenomenon in the stress-strain curve of spider silk.With the increase of relative humidity,the elastic modulus of spider silk and silkworm silk will decrease significantly,and the elongation at break will increase,but the toughness of silkworm silk basically remains the same.In the continuously changing ambient humidity,both spider silk and silkworm silk have the phenomenon of cyclic shrinkage.With the increase of relative humidity,the stress of silk decreases,while with the decrease of relative humidity,the stress of silk increases.