CYCLIC STRESS‐STRAIN RESPONSE AND MICROSTRUCTURE UNDER VARIABLE AMPLITUDE LOADING

Abstract

Abstract— In order to study the cyclic stress‐strain behaviour under variable amplitude loading in terms of dislocation glide character and microstructure, various metals and alloys were cyclically loaded in single‐step tests and in an incremental step test (IST). The cyclic stress‐strain curves (CSS curves) which correspond to the different loading conditions were compared and the shapes of the hysteresis loops were analysed with respect to Masing or non‐Masing behaviour. As expected, cyclic loading with constant amplitude leads to the formation of a characteristic dislocation arrangement that depends on the amplitude applied. The amplitude‐related microstructure corresponds to the observation that Masing behaviour was not found in single‐step tests. However, in the IST a state of saturation, or at least approximate saturation, is attained after some or many loading blocks. In the case of single‐phase polycrystalline materials, wavy slip behaviour was found to be a prerequisite for the fulfilment of Masing behaviour. Then, the CSS curve, obtained by means of IST, intersects that of the single‐step tests at an intermediate amplitude. Planar‐slip materials show very similar CSS curves in spite of considerable differences in the dislocation arrangements for different testing modes. The behaviour of particle‐hardened alloys depends very strongly on the relative effectiveness of the precipitates as obstacles for dislocation motion and can be understood analogously to single‐phase materials on the basis of the resulting dislocation glide character.