Design And Experimental Research On High-temperature Testing Instrument Combined With Tension And Fatigue

Usually, the service conditions of materials are complex with several kinds of loads. In terms of the current situation, the study of deformation damage and failure mechanism of materials are not sufficient enough, and the service performance evaluation and life prediction of materials are not accuracy. Besides, some special physical fields, such as high temperature, electric and magnetic field also have effects on the properties of materials. Especially under the environment of high-temperature, the material mechanics behavior of traditional metal change significantly. Therefore, it’s necessary to carry out the material mechanics performance test in actual service condition.In this paper, the research status on tensile, fatigue, high temperature test technology are introduced and reviewed, the principle and method of high temperature tensile-fatigue test were put forward. What’s more, a high-temperature testing instrument combined with tension and fatigue was developed. By this instrument, the tensile test and tensile-fatigue test under normal temperature and high temperature of 500oC to 1600oC can be carried out, which provide the method for analyzing and investigating the mechanical behavior and damage mechanism of materials under complex loading conditions. The research work can be summarized as follows:In this paper, the principle and method of high temperature tensile-fatigue test were put forward, and a high-temperature testing instrument combined with tension and fatigue was designed. The dynamic and static characteristics finite element simulation analysis of key components and the instrument structure were completed, and the feasibility of device was analysed. The design and manufacture work of electronic control unit for testing instrument and the manufacture and assembly of mechanical structure were finished. Based on program control part, the integration and debugging of electronic control unit and instrument structure was completed. Besides, the repetitive property of mechanical structure, the stability of high temperature unit and the reliability of fatigue unit were tested.According to the characteristics of the specimen deformation, the calibration algorithm for gage section of the specimen based on measured value by LVDT was put forward. The rigidity of the instrument was measured and the calculation method of elastic modulus was modified, too. In order to verify the reliability of test instrument, the test results obtained by this instrument and commercial machine was compared with each other. The results showed that the deviation value of elasticity modulus, yield strength and tensile strength tested by the test instrument were less than 5%. Namely, the accuracy and reliability of the high-temperature testing instrument combined with tension and fatigue developed by this article is well.In this paper, the tensile tests of Q235 were carried out under the condition of normal temperature, the test results verified the repeatability and stability of the test instrument. As the tensile speed increased, the tensile strength measured by the instrument had the tendency of increasing. Besides, the tensile-fatigue tests of Q235 were carried out at different stage of material. The tests results showed that the fatigue loading accelerated the fracture process obviously, which lead to the decrease of the break elongation. Another kind of high temperature alloy GH1131 was tested in this paper at different temperature. It was found that as the temperature increased, the yield strength, tensile strength decreased gradually, and the break elongation increased. Before the sudden rupture of the specimen, the tensile load increased gradually as the specimen was stretched at normal temperature. But at high temperature of over 700oC, the tensile load decayed gradually as the specimen was stretched.