THE STRESS CONDITION PARAMETER ACCORDING MATERIAL PROPERTIES AND ITS INFLUENCE ON PLASTICITY

Abstract

The purpose of the research is grounding of the stress condition parameter, taking into consideration the material properties in the process of approximation of the plasticity diagram by monotonic function, its constant searching and verification for various materials. Design/methodology/approach. The stress condition parameter is offered as a sum of relative main tensions with the coefficients of their influence. Coefficients of influence are mechanical properties of material. The diagram of plasticity is suggested to approximate with an exponential function through this index. Verification for three different materials has shown the sufficient closeness of experimental points to the diagram of plasticity. There are dependences with which it is possible to make the calculation of coefficients of influence on the basis of specimen test in the conditions of shear, axial tension, plain strain and biaxial tension. There are recommendations on the determination of the coefficients for arbitrary types of tests. The minimum number of tests are 4. Findings. The greatest influence on the plasticity of the material has a relative first principal stress (the ratio of the maximum normal stress to the von Mises stress). Relative influence of the second and the third principal stress is much smaller. The third parameter is the relative influence of principal stress for two different aluminum alloys is practically the same. Based on this we can assume that it will be permanent for certain groups of materials. Originality/value. Using the stress condition parameters, taking into consideration the properties of the material it makes possible to approximate the plasticity chart monotone functions with much less deviation from the experimental data than by using the stress triaxiality.