CYCLIC STRESS-STRAIN, STRESS-TEMPERATURE AND STRESS-ELECTRICAL RESISTANCE RESPONSE OF NICUMO ALLOYED SINTERED STEEL

The influence of sintering temperature on the fatigue behaviour of a N iCuMo alloy was determined. It is common practice to characterize the cyclic deformation behaviour by means of plastic strain amplitudes. Fo r sintered materials the quantity of the plastic strain amplitudes is influenced by microstructural changes as well as crack opening and cra ck growth effects and does not allow any distinction between these mec hanisms. In the present work cyclic stress-strain, cyclic stress-tempe rature and cyclic stress-electrical resistance measurements were studi ed simultaneously to get a more comprehensive description of the fatig ue behaviour of sintered steels. The temperature is essentially sensit ive to the work of plastic deformation during cyclic loading. The elec trical resistance responds to microstructural changes, e.g. dislocatio n rearrangements and void formation as well as to crack initiation and propagation. Beyond that it is shown that continuous stress-increase tests are a suitable short term testing method to determine cyclic str ess-strain curves which are in a very good agreement with those from s ingle step tests.