| More and more new metal materials continue to appear,among which there are many new metal materials with excellent performance at room temperature,but in extreme environment,there is a dilemma that they dare not to use,will not use.Exploring the mechanical properties of new metal materials in extreme environment has a positive promoting effect on the application of new metal materials.This paper mainly studies the stress-strain characteristics of metal materials in extreme environment.A set of stress and strain testing system for metal materials in vacuum deep cryogenic environment was developed by means of a small tensile testing machine built in the vacuum refrigeration chamber.DIC strain measuring equipment based on digital image correlation method and machine vision is used in the test system to measure the strain of the measured material.This topic mainly carries out experimental research from the following aspects:1.Focus on the research status of material stress and strain measurement at low temperature and the application development of tensile testing machine at low temperature.Various stress and strain measurement methods are compared and analyzed.Combined with the experimental environment and equipment,a method of stress and strain measurement of metal materials under vacuum deep cryogenic environment was proposed and the related test system was built.2.According to the technical principle and thermodynamic principle of the traditional tensile testing machine,the working principle of the small tensile testing machine and the refrigeration mode of the sample in the vacuum deep cryogenic environment are determined.The selection of function parts is carried out according to the technical index.According to the working environment of the small tensile testing machine,the specific structure design is carried out.According to the overall design scheme,the model of small tensile testing machine was established by using Solidworks 3D modeling software and the strength analysis of key components was carried out by using the static structure analysis module of ANSYS finite element simulation software.3.According to the three heat transfer modes in heat transfer,the thermal analysis module of ANSYS finite element simulation software is used to carry out thermal analysis on the small tensile testing machine placed in the vacuum refrigeration chamber.The simulation results show that the cooling guide structure and mode of the designed sample can achieve deep cryogenic and the insulation mode of the functional components also meet the requirements.The thermal stress of the sample under the influence of deep cryogenic was simulated by the thermo-stress coupling analysis module and the installation method was optimized according to the results.Finally,the heat leakage calculation of the test system is carried out.The calculation results show that the heat load of the system is less than the cooling capacity provided by the refrigerator,which meets the requirements of sample refrigeration.4.The 6061-T6 aluminum alloy used in aerospace field was used as the experimental material.Firstly,the sample temperature verification test is carried out,and the results show that the sample temperature can drop to deep low temperature and reach stability after a period of time.The stress-strain curves at room temperature,250 K and 150 K were obtained,and the elastic modulus of the measured material was obtained by curve fitting.By comparing the experimental elastic modulus at room temperature with the standard one,the deviation between the two values is only 1.40%,which verifies the practicability of the test system.Finally,the error source analysis of the test system is carried out,which is convenient to improve the measurement accuracy of the test system. |
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