On the Choice of Stress Invariants in Solving Problems of Mechanics

It is proposed to formulate strength criteria as a relationship between the stress intensity and dimensionless invariant , which is equal to the ratio of the first stress-tensor invariant to the stress intensity. The use of the invariant in the case of plane stress is proved to be correct. A comparison of calculated and experimental data demonstrates advantages of the proposed formulation of the ultimate state conditions over the classical approach. Possible ways of how to extend the presented approach to a triaxial stress state are indicated.