| With the continuous development of the industrialization and independent research and innovation, the demand for high-tech materials is growing and the importance of the tensile test is self-evident. Rely solely on the mechanical behavior of uniaxial tensile test of materials cannot be applied in the practice, because in engineering applications, the vast majority of materials will be under complex stress state, for example:the space shuttle housing will being pulled and pressurized in sailing, high strength steel subjected to composite stress in roll forming process, etc., in order to accurately explore these materials, particularly the mechanical properties of anisotropic materials such as high-strength steel, composite materials, it is necessary to provide theoretical support by biaxial tensile testing. The actual deformation characteristics of sheet metal can be seen in the forming of both directions tensile along different loading paths. Therefore, accurately describing the mechanical behavior of materials under different loading paths is very important, and providing a theoretical basis for yield criteria applicability, the sheet metal forming process and fracture prediction.This project has designed and developed the hardware of biaxial tensile test machine, including the design of mechanical transmission parts, selection and structure of hardware about Siemens SIMOTION control system based on multi-axis coordinated motion, as well as the electrical hardware designing and building of the contactor control. Based on the accuracy of the analysis and experimental verification, the device is capable of biaxial tensile test under different loading path, and finished uniaxial tensile test and biaxial tensile test in different loading proportion for Trip590high-strength steel plate due to obtain mechanical performance parameters on different rolling direction and experimental stress-strain curves of biaxial tensile test.Based on VS2003, combined with the principle of plastic work equivalent per unit volume and some other theories about materials molding, the data processing program was finished that can calculate the uniaxial tensile,biaxial tensile stress-strain curves and biaxial tensile test experiments yield locus of different equivalent plastic strain under different proportional loading paths.Made use of data processing program, and seek experimental yield locus of different equivalent plastic strain, and compared with the theoretical yield locus based on Mises yield criterion,Hill48yield criterion(the parameters calculated with yield stress)and Hill48yield criterion(the parameters calculated with r-values)and error analysis. Based on the elastic-plastic mechanics and Drucker postulate, the theoretical stress-strain equations were derived respectively on rolling and transverse direction in specimens based on above yield criterion, and compared with experimental true stress-true strain curves.Made use of Abaqus commercial finite element software, simulated the biaxial tensile test of specimens under different proportional loading paths. The design of cruciform specimen is reasonable verified from the stress cloud; The load of specimen-end-displacement of extensometer point curves were compared with the experimental load-displacement curves. According to the results, got the accuracy of the simulated numerical curves based on Hill48yield criterion (the parameters calculated with yield stress) is better than other simulated numerical curves, and verify the relevant conclusions of Trip590high-strength steel about yield locus and stress-strain curves.From the perspective of the development of modern industrial equipment, experimental methods, developing equipment and experimental research based on biaxial tensile test machine,which is explored in this project, have made the basic work in the field of biaxial tensile test in domestic, provide a theoretical basis for the molding and simulation of Trip590high-strength steel. |
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