Research on the Plastic Forming Process of Thick-Walled Titanium Three-way Connector

The arc-shaped stacked test sample is suitable for thin-walled pipes, and its principle is the same as that of the cut block sample. Different from the cut block and stacked compression tests, the overall annular test sample axial compression test has better stability and is closer to the real stress state during the plastic forming process of the pipe, and has been widely applied.

However, due to the influence of friction, the overall annular specimen will undergo uneven deformation along the radial direction during the compression process, resulting in a bulging phenomenon. The hollow structure of the pipe makes it difficult to perform bulge removal on the specimen's shape. Therefore, when using this test method, only the stress-strain relationship of the material within the small strain range before bulging can be obtained. After bulging occurs, the calculated stress and strain data differ significantly from the actual values. However, the plastic forming of pipes generally belongs to a large deformation process, which requires a stress-strain relationship curve over a large strain range. In response to the above issues, some scholars have proposed an inverse method that combines experiments with analytical formulas (or finite elements) and optimization algorithms to determine the stress-strain relationship of materials. The essence of the inverse method is to use uniaxial tensile tests combined with numerical simulation to inversely calculate the failure parameters of 5052 aluminum alloy materials through experiments.

The strength coefficient and the strain hardening index in the titanium three-way pipe strengthening equation were confirmed through back-calculation. This method overly relies on assumptions in establishing the analytical relationship between material parameters and force-displacement curves, thus the accuracy of its analytical expression has a significant impact on the identification precision of material parameters.