Determination of New Plasticity Characteristic of Alloys at Mechanical Compression and Tensile Tests and the Influence of Structural Factors on Plasticity

In physics and mechanics, plasticity is defined as the ability of a material to undergo irreversible (plastic) deformation. Conventionally, the plastic strain at fracture in tensile tests, δ, has been used as a quantitative measure of plasticity. However, δ does not follow the scientific definition of plasticity. The influence of structural factors, temperature and strain rate on the value of δ were not elaborated over many decades. This lack of well-founded quantitative characteristic hindered efforts to control and to increase plasticity of materials. The plasticity characteristic that corresponds to the scientific definition of this quantity, δ* = plastic strain ε р / total strain ε t , has been successfully used by many scientists to determine plasticity δ* by indentation. In the present work, the technique for the determination of the plasticity characteristic δ* during mechanical compression and tensile tests of metallic alloys has been introduced for the first time. In this case, δ* is determined more precisely than by indentation, and the second deformation curve δ*=f* ( ε t ) is constructed. A theory of the influence of structural factors (grain size, dislocation density, disperse particles of the second phase) on the plasticity characteristic δ* has now been developed, making it possible to estimate the influence of the indicated factors on δ* and to design alloys with an optimal combination of strength and plasticity. The discovered correlation of the values of δ* and δ for steels and for aluminum alloys allows us to use the developed theory to calculate the influence of the structural factors on d for these materials as well.