Abstract: Three kinds of metal rods with different ductility were used to study the strain ranges and mechanical properties of metal under different stress states by tension and torsion tests. The Bridgman method was used to measure the hardening curve from the beginning of necking to the final fracture. Comparison and analysis of the two test results show that the uniform strain ranges of the metal rod in the torsion state are larger than those in the tension state because of the difference of mechanical stability. Due to the difference of the fracture mechanism under different stress states, the strain ranges before fracture of metal in torsion test are larger than those in tension test. So the total strain ranges measured in torsion test are larger than those in tension test with Bridgman method. The Bridgman method has limitations, which is only applicable to metals with large ductility and weak hardening ability, while, torsion test is versatile and suitable for metal with different properties. Comparing with the tension or compression state, the metal rod exhibits different degrees of “softening phenomenon” in the torsion state, that is, the metal is more likely to reach plastic yield in the torsion state, and the hardening ability and the ultimate bearing capacity are obviously weakened.

Key words: materials synthesis and processing technology, hardening curve, tension and torsion, strain, necking