Design And Experiments Of Variable Tensile Rate Stress Corrosion Control Unit

Materials are used in various environments,so they are easy to be destroyed by corrosion.The economic loss caused by corrosion of materials is huge every year.Due to stress corrosion failure plays a very high role in corrosion failure and its process is complex,a lot of stress corrosion tests have been carried out to determine the mechanism of material stress corrosion failure.The constant strain rate test method has been widely applied to explore the mechanism of stress corrosion due to its own characteristics.The constant strain rate loading on specimen is the key to the test method,which means at the different tensile stages in the specimen,the test device works at the corresponding tensile speed.Constant strain rate loading is the key to the test method.In this paper,a variable tension rate loading control unit was designed for stress corrosion testing device,and the related experiments were carried out.The function of the test device was analyzed,and the functions of four modules,such as the mechanical loading unit,the electronic control system,the temperature control heating device and the in-situ observation device,were analyzed in detail.Through the function analysis,the working principle of the test device was clarified,and the mathematical model between the input voltage of the DC servo motor and the tension rate of test device was established.In MATLAB/Simulink,the PID control and fuzzy PID control simulation model of the test device were established,and the control effect of the two control strategies was studied by simulation.The conclusion that the fuzzy PID control strategy has better control effect than the PID control strategy was obtained.The fuzzy PID control was applied to the test device with variable tension rate loading.The simulation results show that the control effect is good.The control software was designed based on Lab VIEW programming language.The control software mainly includes four modules:initialization module,data acquisition,processing,display and storage module,close loop control module of variable tensile rate of test device and auxiliary module.The functions of data acquisition,data processing and display,data storage,variable tensile rate loading of testing device,automatic stop loading of testing device,sensor calibration and image playback and screenshot were realized.The performance test of the variable tensile rate control unit was carried out.Through the control effect test of the fuzzy PID control strategy and three kinds of tensile rate loading modes,it is proved that the variable tensile rate control unit developed in this paper has good control effect.The theory and method of stress corrosion test were analyzed,including the characteristics of stress corrosion cracking,the design principle and evaluation standard of constant strain rate stress corrosion test,and the influence of the tensile rate of the testing device on the strain rate of the specimen.The stress corrosion test of 7075 aluminum alloy in 3.5%NaCl solution at different strain rates was carried out.The conclusion that the maximum stress corrosion sensitivity of 7075 aluminum alloy materials in 3.5%NaCl solution was obtained when the strain rate was 10^-6/s.