Design Analysis And Experimental Research Of An In-situ Biaxial Tensile Device For Characterizing Mechanics Of Materials

In general service conditions, materials always inevitably undergo complicated loads. Itwill aggravate failure and fracture of the material.Biaxial tensile testing could provide variousplane stress condition. Therefore, many researchers adopted biaxial tensile testing to study themechanical behavior under plan stress. The research about the cruciform biaxial tensilespecimen received extensive attention of researchers. In recent years, by combiningcommercial imaging device and testing machine, the test that observe the process of fractureof the material in the real time develop into in-situ testing technology. So in-situ biaxial testingbecome one of the focus in the material testing technology.Because the existing biaxial tensile testing device is too large to integrated withmicroscopic imaging device, in-situ biaxial tensile testing technology research carried out isless. Some small commercial in-situ biaxial device come out abroad. But they are singlefunction,high cost and high-end technology embargo. The related research work in China isfall behind. The commerial in-situ biaxial device is less. It’s significance to develop the devicewith our own intellectual property rights for study the microscopic mechanism of failure.Aiming at this requirement, based on the comprehensive analysis and the review of homeand abroad research and development of in-situ biaxial tensile device, this paper develops anovel device for in-situ biaxial tensile testing. The main work is as follow.1.A new design project was carried out. The working principle was analysised. The keyparts of the device was simulated by finite element analysis and modal analysis. According tothe analysis result, the structure was optimized, and the instrument was precisely assemble.2. Integrating the mechanical part and control part of the testing system, the force anddisplacement sensor were calibrated by experiment.Because the strain measured in experimentis higher, elastic modulus calculated is smaller.Firsrly, fitting the deformation of transitionsection and clamping section with an algorithm.Secondly, testing the deformation of the device in the experiment, a linear relationship between deformation of device and loadingforce was found. A correction method was put forward for fitting the deformation of the device.Uniaxial test with the device along the two axial was carried out many times. And for the samekind of material, with the commercialization of tensile testing machine, the same experimentwas carried out. Finally, contrasted the uniaxial tensile test result, the experiment verified thereliability and stability of the instrument.3.Some experiment were carried out to study the mechanical properties of typical metalmaterrial, such as6061aluminum, copper, AZ31B magnesium alloy under biaxial tension. Thebiaxial tensile test was carried out by finite element analysis. The simulation results andbiaxial tensile test results were almost same. It verified the finite element analysis method forgetting the material mechanics performance under biaxial load state was accuracy andfeasibility. In the condition of variable temperature, some experiments were carried out forgetting change rule of the mechanical properties of the copper under biaxial load. The resultsshowed that with the tempreture increased, strenghth and elongation of copper decreased. Thecruciform specimen of6061aluminum under biaxial tensile load deformation performancewas studied, The gage section edge of cruciform specimen put forward a nonlineardeformation of exponential fitting method. By the surface micro indentation method, microdefects on the surface of copper sheet derivative rules were studied under biaxial load state.The result illustrated bi-directional stress state expanded the surface morphology, and thedecrease of the indentation depth the bidirectional stress would be beneficial to keep smoothand flat for the surface of the specimen. By the in-situ observation with Olympus microscope,AZ31B magnesium alloy sheet’s microstructure changes of the phenomenon under biaxialtensile loading was studied. Microstructure changes of the specimen was the same tomacroscopic fracture failure phenomenon, It verified the macroscopic fracture and failure wasderived from microstructure damage and change.