| There are no unified theories about the internal mechanism of stress corrosion due to many influential factors and complicated process of stress corrosion.Therefore,the life and reliability of the material under the combined action of corrosive environment and stress can not be evaluated simply and effectively.Traditional slow strain rate test method focuses on material’s test phenomenon of stress-strain curve and fracture surface,and the process of crack initiation and expansion of stress corrosion cracking(SCC)is lacking in-depth study.In-situ test technology can monitor the detailed process of material’s microstructure damage during the test in real time,and it is very important to study the mechanism of stress corrosion.Combines in situ testing techniques,a slow strain Rate stress-corrosion in-situ testing Instrument is designed in this paper.and the experimental study is carried out about the typical materials on the basis of the Instrument.In this paper,a miniaturized horizontal slow strain rate stress-corrosion in-situ testing instrument is designed based on the existing theory of slow strain rate stress corrosion test.Lightweight and compact design makes the test device easy to move,compatible with most optical microscopes.Designed a corrosive media pool adapt to the in-situ test.A new sealing method for the corrosive media pool was Invented,the sealing method can transform one dynamic sealing into two static sealing,which solved the problem of difficult sealing of rectangular cross section specimen.A nonstandard sample was designed to accommodate the in-situ test.The simulation and analysis of the key components are carried out to verify the reliability of the test equipment.A suitable servo control system was designed.The performance of the testing instrument was analyzed.The precision sensor was calibrated to verify the accuracy of the test data.The systematic error caused by the indirect measurement method of deformation of the specimen was analyzed,and the corresponding correction algorithm was proposed to eliminate the error.The stability of the tensile speed of the testing instrument was tested and three factors influencing the tensile speed were analyzed.It is found that the weak of frame stiffness and contact stiffness of the transmission chain decrease tensile speed of the elastic deformation stage,the method of detecting the tensile velocity error is given,and the corresponding correction algorithm is deduced.The influence of electromagnetic interference on the fluctuation of the tensile speed is analyzed.The influence of the fixture reliability on the tensile speed was tested.A repeatability test was conducted to verify the reliability of the test results.Compared with the standard commercial testing machine,the experimental results show that the design of the test device is accurate.The performance of the water bath was verified by the experiment,and the temperature stability was found to be good.On the basis of the test equipment developed in this paper,the stress corrosion test of typical materials is studied.The process of stress corrosion cracking of 7075 aluminum in 3.5%Na Cl solution was observed in-situ.It was found that 7075 aluminum produced pitting in the surface of the early test.Under the combined action of stress and corrosive environment,cracks will be sprouted near the pitting,and the crack propagation in different positions will be connected together,leading to the breakage of the specimen.The effect of strain rate on stress corrosion of 304 stainless steel was studied.It was found that 304 stainless steel had the greatest stress corrosion susceptibility when strain rate was 3×10-6/s.In this paper,the slow strain rate stress corrosion in-situ testing instrument has been developed to provide a new method for stress corrosion research,which is favorable to the study of stress corrosion mechanism.Some of the design and analysis work carried out in this paper have universal reference significance. |
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