Thick-walled Titanium Alloy tube parts are widely used in aerospace and other fields due to their strong weight ratio, excellent corrosion resistance and fatigue resistance. Plastic forming process to obtain thick-walled titanium alloy pipe fittings with good plasticity, high strength and other characteristics (such as extrusion, spinning, drawing), has become the main method of processing titanium alloy pipe parts titanium tee.
Analysis of the plastic deformation behavior of the pipe is to ensure accurate plastic forming of the pipe premise and foundation, and the firmness of the deformation analysis often depends on the mechanical properties of the material at the time of deformation, in particular, the plastic stress-strain relationship. Because the plastic stress-strain relationship of the material and its stress state, therefore, according to the specific forming process of the material stress state to choose the appropriate test method to confirm the plastic parameters of the material.
For the plastic forming process of thick-walled titanium tubes which mainly involves compression deformation, such as spinning and extrusion, it is necessary to confirm the stress-strain relationship under compression. However, due to the hollow structure of the tubes, the traditional axial compression test method for cylindrical specimens is difficult to be used to confirm the compressive mechanical properties of the tubes. Therefore, how to accurately confirm the stress-strain relationship of thick-walled titanium tubing in compression has become a key issue in accurately analyzing the plastic deformation behavior of thick-walled titanium tees.
Force-strain relationship. Among them, the local cut block compression specimen intercepts the specimen directly on the pipe wall, which is greatly affected by the wall thickness of the pipe and is easy to be destabilized in the compression process. Arc stacking specimen is suitable for thin-walled pipe, and its principle is the same as the cut block specimen. Different from the cut block and stacked compression test, the overall ring specimen axial compression test stability is better, and the pipe plastic forming process is closer to the real stress state, has been widely used.
However, under the influence of friction, the whole annular specimen will be unevenly deformed along the radial direction in the compression process, and the phenomenon of bulging belly will occur. The hollow structure of the pipe makes it difficult to trim the specimen shape to the bulge. As a result, the test method, can only be obtained before the occurrence of bulging small strain range of compressive stress-strain relationship of the material, bulging occurs after the calculation of the stress, strain data and the actual value of the difference is large. The pipe plastic molding generally belongs to the large deformation process, the need for large strain range of stress-strain relationship curve.
In view of the above problems, some scholars have proposed to confirm the stress-strain relationship of the material by combining the test with the analytical formula (or finite element) and optimization algorithm in the inverse method. The essence of the inverse method is that the failure parameters of 5052 aluminum alloy material are inversely calculated through test, using one-way tensile test combined with numerical simulation.
The hardening index of strength coefficient and strain in the strengthening equation of titanium tee tube is confirmed by backcalculation. The method adopts too many assumption conditions in the process of establishing the analytical relationship between the material parameters and the force-displacement curve, and thus the accuracy of its analytical expression has a great influence on the accuracy of the identification of the material parameters.
