MECHANICAL AND MICROSTRUCTURAL INVESTIGATIONS OF AN AUSTENITIC STAINLESS STEEL UNDER NON-PROPORTIONAL LOADINGS IN TENSION-TORSION-INTERNAL AND EXTERNAL PRESSURE

摘要

This paper is concerned with the experimental behaviour of a 316 austenitic stainless steel at room temperature and under nonproportional cyclic strainings in tension-torsion-internal and external pressures. The main investigations deal with the overstrengthening due to the multiaxiality of the loadings. A classification of the different kinds of cyclic tests can be established with respect to the increasing maximum overstrengthening. Concerning the ratchetting effect, from tests performed under in or out-of-phase cyclic tension-torsion plus a static stress due to internal pressure, it is shown that the rate of the diametrical ratchetting is an increasing function of the phase lag between the cyclic components. Dislocation substructures resulting from the cyclic and the ratchetting tests are investigated and various kinds of substructures were reported. From these observations it has been possible to evaluate the intragranular back stress and the effective stress as a function of the strengthening.