Optimizing Pure Shear Experiment to Properly Characterize the Shear Properties of Thin-Walled Aluminum Alloy Tubes

Background

For an anisotropic thin-walled tube without changing its circular geometry, only the experimental data of initial yield and subsequent plastic deformation along the axial and circumferential directions can be obtained till now. These experimental data are not sufficient to construct an anisotropic constitutive relation for simulations of tube deformation processes.

Objective

A novel shear test of tubular materials is proposed to achieve the state of shearing plastic deformation along the axial direction of thin-walled tubes.

Methods

Two semi-circle mandrels and one specially designed tubular specimen are used in the shear experiment. Optimizations of the specimen shape and mandrel structure were carried out by using FE simulation. The influence of the specimen shape, such as the length of the shear zone and the length of the axial slot, on the stress state of the shear zone was discussed. A thin-walled 5052 aluminum tube was used in the shear experiment using the optimized specimen shape. To understand the corresponding relationship between the tensile properties and the shear properties of an anisotropic tube, the uniaxial tension stress-strain relationship was equivalently transformed to the shear stress-stain relationship using the Mises, Tresca, Hill48, and Barlat-lian constitutive functions.

Results

After optimizing the specimen shape, the shearing condition of the tested tube is closer to the pure shear stress state. Based on the tests, the pure shear stress state can be maintained to a large deformation extent. The experimental shear stress-strain relationship was compared with the converted stress-strain relationship based on the uniaxial tension tests using the Mises, Tresca, Hill48, and Barlat-lian constitutive functions. The results show a large difference between the transformed stress-strain relationship and the shear stress-strain relationship.

Conclusions

This testing method can provide necessary empirical data with the principal stress directions along the direction at an angle of 45° to the tube axis. The shear plastic deformation properties of some anisotropic materials cannot be equivalently described by the experimental data of the tensile test. The shearing characteristics obtained by this novel experimental method can be applied to the characterizations of anisotropic constitutive relations for simulations of tube deformation processes.