Criteria of deformity taking into account the properties of the material in the parameter of the stress state

Abstract

Hrushko O., Kyrytsia I. Criteria of deformity taking into account the properties of the material in the parameter of the stress state

The non-monotonic behavior of the plasticity of materials in the area of positive hydrostatic pressure depending on the classical indicator of the stress state leads to the need to find better parameters as an argument of the plasticity diagram. In this article, parameter of the stress state is proposed, which depends on the physical and mechanical properties of the material. Influence coefficients are mechanical properties of the material. The plasticity diagram in the metal map, with the help of the entered stress state parameter, is proposed to be approximated by a monotonically decreasing exponential function. It was established that the influence of the principal normal stresses is unequal in relation to the accumulation of damage in the plastically deformed material. Moreover, this influence depends on the type of material, which makes it possible to form a plasticity model, in particular for materials with different rheology. It was established that the influence factor of the third relative principal stress for low-carbon steels, aluminum and titanium alloys is 0,76...0,85.

It is recommended to use the parameter of the stress state proposed by us as an argument of the plasticity diagram in known models of deformability, since this parameter does not change the physical content of damage accumulation. The scope of application of this or that criterion remains in accordance with the recommendations for its use, depending on the type of process and load history. А comparative calculation of the used plasticity resource was performed according to known criteria and criteria that take into account the properties of the material through the stress state parameter. The use of a plasticity diagram constructed using the proposed stress state parameter for cold plastic deformation processes that occur in the region of positive hydrostatic pressure, depending on the type of deformation path and the features of metal rheology, clarifies the value of the used metal plasticity resource up to 2 times, which allows to reduce the number of defective products up to 50% for processes whose regimes are calculated by limit deformations.