Badanie wpływu odkształcenia plastycznego na zachowanie się metalu przy różnych drogach wtórnego obciążenia

The present study is concerned with the experimental investigation of the yield strength of material undergoing previous plastic deformation and is comparing the results with the theoretical analysis based upon various hardening rules. In general, this study is of a basic character though it has a practical aspect too showing a possibility of finding the range of prestressing programmes which give an optimum material property. The research as a whole is carried out according to the new scientific idea of the surfaces describing the influence of various prestressing programmes on the behaviour of metal under repeated loading following the fixed loading path. To this end an apparatus was designed for plastic deforming of the tubular specimens under the condition of complex state of stresses. It gives the possibility of investigations under biaxial tension-tension and biaxial tension-compression. The tests were carried out on the specimens made of brass. It was found that the changes of yield strength of this material caused by various ways of primary loading do not obey the kinematic or isotropic hardening rules. However, one of the kinematic-isotropic hardening rules adapted here describes the qualitative and quantitative changes of the yield strength independently of the assumed yield criterion (per cent offset) for various values of primary loadings. This hardening rule is simple enough for practical use.