BEHAVIOR AND MODELIZATION OF A 17-12 SPH STAINLESS-STEEL UNDER CYCLIC, UNIDIRECTIONAL AND BIDIRECTIONAL ANISOTHERMAL LOADINGS

It is shown in this article that a knowledge of the mechanical behavio r of the 17-12 SPH stainless steel for different isotherms (20 degrees C less than or equal to T less than or equal to 650 degrees C) is ins ufficient to describe its behaviour correctly under anisothermal therm omechanical loadings. Indeed, this alloy possesses a temperature histo ry memorization effect at intermediate temperatures. This phenomenon i s studied in detail with experiments performed under uniaxial and biax ial mechanical loadings (in-phase or out-of-phase tensile-torsion test s) for different isotherms belonging to judiciously chosen temperature history sequences. The results of cyclic torsion tests under anisothe rmal thermomechanical conditions are presented where strain and temper ature loading evolve simultaneously in phase, in phase opposition, in quarter- and three-quarters-phase. The analysis of the totality of res ults shows that the material memorizes the maximal value of the cyclic stress peak reached in the zone where the derivative of the maximal c yclic stress with respect to the temperature is positive. This observa tion can also be applied to both uniaxial and biaxial cyclic tests. Fr om a physical point of view, this behavior is closely related to the i nteraction phenomena between dislocations and point defects in inserti on solid solutions. In order to describe this history effect, a simple mathematical formulation is proposed in the second part of this artic le which, after being integrated into a unified viscoplastic model dev eloped elswhere and taking into account a few modifications, leads to an acceptable phenomenological representation of the different experim ents presented earlier.