Strain accumulation due to packages of cycles with varying amplitude and/or average stress - On the bundling of cycles and the loss of the cyclic preloading memory

In order to predict permanent deformations by means of a high-cycle accumulation (HCA) model, a random cyclic loading, i.e. a loading with frequently changing amplitudes, has to be grouped into packages of cycles each with a constant amplitude. Based on a series of drained triaxial tests on fine sand, in which the same cycles have been applied either in an order with frequently changing amplitudes or in packages of cycles, it is demonstrated that such bundling is conservative. Predictions by the HCA model of Niemunis et al. [19] are confronted with experimental data and with other approaches for the prediction of permanent deformations under packages of cycles, among them the frequently cited procedure of Stewart [26]. An effect not captured in the HCA model or in any other approach yet has been detected in another series of tests with a change of the average stress between bundles of cycles: The monotonic loading associated with this change can partially or fully erase the memory of the sand regarding its cyclic preloading history.