Some studies on the incremental step (fatigue) test

Cylindrical specimens of AISI 304LN austenitic strainless stael and Nimonic 90 were deformed under strain cycling at room temperature by repeated application of strain blocks consisting of waveforms in which the amplitude gradually increased and then decreased. The dependence of the cyclic stress-strain (CSS) curve on the number of waveforms in the applied strain block was found to be considerably less for Nimonic 90 than for the stainless steel. The CSS curves generated using blocks having lower maximum strain amplitudes were below the CSS curves obtained using blocks having higher maximum strain amplitudes. The difference between the CSS curves generated using blocks of different maximum strain amplitudes was greater in stainless steel than in Nimonic 90 due to strain-induced martensite formation in the former. © 1994.