Study On The Key Technologies Of Instrumentation Of Impact Stress-strain Inspection

With the increasing demand for dynamic testing in many military and civilian fields,such as metal processing,explosion,aerospace,high-speed impact,etc.,the research on dynamic mechanical properties of materials under dynamic loading has been paid more attention by researchers.Split Hopkinson pressure bar(SHPB)is tested under the high strain rate dynamic mechanical properties of the most effective techniques,its application has been gradually extended to the soft material from the metal material,brittle material,concrete material,film,fiber sensor and MEMS.However,the SHPB experimental technology is difficult to be instrumented,and the existing SHPB experimental device is not only bulky,it needs professionals to build,but also requires the operation of dynamic professionals.For the study of the non professional researchers and designers,just need the dynamic mechanical parameters of materials.On the other hand,due to the influence of human factors,the repeatability of the different SHPB experimental devices is poor,and the results are often not universal,resulting in waste of time,funds and resources.In this paper,the SHPB experimental device is improved and three key technical problems are solved.The prototype of the impact stress strain instrument is designed and manufactured,and the instrumentation of the SHPB device is realized.1.In the aspect of launching system,the seven stage reluctance coil type electromagnetic launcher is used instead of the traditional air gun to realize the miniaturization of the SHPB device.Analysis of the acceleration mechanism of multistage electromagnetic emission model,through the finite element method in-depth study of the impact of power loss and winding loss and consumption consumption of the loop resistance on the electromagnetic emission of the speed of the bullet,the related design parameters.Secondly,two models based on voltage emission and switching timing are established,which can control the launch speed accurately and meet the requirements of different speed for different samples.Through the improvement and optimization,the launch speed can reach 43.2m/s,the control accuracy is 2%,better than the air gun firing accuracy,so that it can meet most of the dynamic testing requirements of impact speed.2.In order to ensure the reliability and consistency of strain gauge sticking in SHPB experiment,a kind of automatic sticking device for strain gauge is proposed.The device can pinpoint the position of strain gauge,paste and automate the strain gauge,can effectively improve the bonding quality of the strain gauge,ensuring consistency of paste effect,save paste time,the operator can use the experience without manual paste,greatly reduce the adverse impact of human factors on the experiment result,the the consistency of original data acquisition conditions and repeatability.3.In the aspect of emission data processing and automatic control,combined with the hardware developed a computer program that can be set according to the parameters of the precise control of the projectile launch speed;get the experimental data and the impact of computer automatic calculation of the stress-strain curve,from the launch control to calculate the whole process is controlled by computer automatically.Finally,the dynamic mechanical properties of the use of the impact stress strain gauge of 3D printing materials,through the comparison of nylon material in Selective Laser Sintering(SLS)and conventional Computer Numerical Control(CNC)to obtain specimens under impact stress strain characteristics.The final results show that the dynamic stress hardening rate and stress ultimate strength of the specimens processed by SLS technology are significantly higher than those of the CNC processed specimens.