The change of mechanical stress-strain-hysteresis and different physical parameters during fatigue tests have been measured to demonstrate the fatigue behaviour and damage evolution processes of metallic materials. The electrical resistance e.g. can provide important information regarding the microstructural alteration by indicating the development of dislocation density. The states of such parameters of a fatigue specimen in a load-free sequence can represent the state of a component with a defined cyclic loading history. Therefore, conventional techniques measuring these parameters of common fatigue tests or even of service load tests with additional load-free sequences should have the application potential of remaining service life estimation and must be experimentally validated. In the scope of this paper, characteristic cycle-dependent changes of diverse physical parameters of fatigue specimens made from normalized SAE 1045 steel were determined and correlated with the residual stress state and dislocation density quantified by X-ray diffraction (XRD) and transmission electron microscopy (TEM) respectively.