Characterization of the shear behaviour of a thin-walled tubular material

This study aims at determining the shear behaviour of a tubular material. Simple shear tests are useful for this purpose, since they yield homogeneous strain fields up to 100% shear strain (γ=2ε=100%γ=2ε=100%); whereas torsion tests yield heterogeneous strain fields at low strain (γ<50%γ<50%) because of the instability of the structure resulting from the buckling of the test-piece. Simple shear tests were performed on samples prepared by machining the tube into strips, which made it possible to obtain a larger number of samples than for torsion tests from a tube of the same length. The apparatus used to perform simple shear tests can be easily adapted to the conventional torsion-compression test-bench, whereas torsion tests require a special machine. The tubes studied here, which were used to manufacture airbag gas generators, were produced using cold mechanical drawing processes. They had a small diameter (<35mm) and were made of thin (<2.5mm thick) mild steel with a low carbon content. Comparisons between the stress–strain curves obtained during torsion tests and simple shear tests performed on these tubes show that shear test set-up is valid mean of characterizing the elasto-visco-plastic behaviour of thin-walled tubes. The data obtained in this way on the material under investigation were completed by performing longitudinal tensile tests.