On the Influence of Loading Order in Nanostructural Fatigue Crack Propagation in BCC Iron—A Molecular Dynamics Study

Abstract

Most investigations dealing with fatigue crack propagation on the nanoscale, limit their studies on a loading scenario of constant stress or strain amplitudes. Since such a load scenario is rather rare, this paper aims to examine the influence of the load sequence on the crack growth using bcc iron. For this purpose, a specimen containing a central crack was loaded repeatedly by varying the load amplitude. All computations were carried out using molecular dynamics methods (MD), and the material behaviour was represented by utilising an embedded atom method (EAM) potential. Significant deviation in the crack growth behaviour was observed when loading the specimens with variable amplitudes rather than with constant amplitudes. Cracks did not only extend during the loading phase but also in the initial phase of the unloading process where cracks expanded from voids that had been formed in the last phase of loading. These voids coalesced with the main crack as the specimen was subjected to further loading.