The Development And Experimental Study Of An In-Situ Eccentric Tensile Mechanical Testing Device At Elevated Temperature

Material testing is the important measuring method of material science and engineering application.In general service conditions,materials always inevitably undergo complicated loads and high temperature.It will aggravate failure and fracture of the material.According to most of the engineering structure in complex loading stress conditions,the design idea of eccentric tensile mechanical testing device was proposed and a testing device under the eccentric tensile and bending loading condition was developed for in-situ mechanical test.Based on the theoretical analysis of eccentric tensile case,the mechanical part and control part were integrated into testing system to realize the in situ mechanical property testing under the circumstance of eccentric tensile case combined with the software and hardware control system.The testing device can meet the standard of the mechanical performance measuring techniques and provide technical means for temperature response of mater ial mechanical properties.Firstly,the design idea of eccentric tensile mechanical testing device was proposed.The bending deflection curve equation and the rotation angle equation of the specimen was deduced under eccentric tensile load.And on this basis,the correction algorithm was infered for the testing formula of the deformation of arc transition section and clamping section of the specimen.What’s more,the formula was deduced for determining the neutral layer position and fracture position of eccentric tensile specimen.This provided the theoretical support for the test of eccentric tensile and bending load.The dynamic and static characteristics of the key parts in the testing instrument has been analyzed by using the method of the finite element analysis software.Based on program control part,the integration and debugging of electronic control unit and instrument structure were completed.The calibration experiments of displacement sensors and force sensors were carried out and three calibration methods were gived.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 were less than 5%,which verified the reliability and stability of the instrument.Finally,the mechanical behavior of the T2 copper was investigated under eccentric tensile and bending load.In eccentric tensile loading,the out of plane displacement changes from its maximum value at the specimen center to its minimum value near the fixture.As the load is gradually increased,the out of plane displacement at the center increases till it reaches the eccentricity value.Therefore,the failure of the test specimen is due to the combined bending and tensile stresses that occur at the end of the gage length.In the condition of variable temperature,some experiments were carried out for getting change rule of the mechanical properties of the TA2 under eccentric tensile load.The results showed that the variation of temperature at 10°C~300°C has little influence on the elasticity modulus of TA2.What’s more,yield strength and tensile strength strenghth and elongation of TA2 decreased with the tempreture increased.The thesis also observed and recorded the process of the changing of microstructure of the brass specimen with the Super depth of field microscope.Microstructure changes of the specimen was the same to macroscopic fracture failure phenomenon,which analyzed the macroscopic fracture and failure forms of materials.