Monitoring of the fatigue state of single-lip deep-drilled specimens made of the quenched and tempered steel AISI 4140 using micromagnetic methods

Fatigue is one of the main causes for the failure of technical components. Therefore, the monitoring of fatigue-related material degradation is a target-oriented way to extend the lifetime of safety-relevant components. In terms of sustainability and resource conservation, the implementation of reliable fatigue monitoring is of crucial importance. Fatigue damage is manifested by a variety of microstructural and micromechanical property changes such as grain refinement, relaxation of residual stresses, increase of dislocation density and hardness change. An application of micromagnetic techniques is very promising, since it is known that Barkhausen noise analysis and eddy current testing are sensitive to these parameters. This work deals with the separation of the micromagnetic parameters with respect to fatigue-induced changes. This separation is necessary to identify, quantify and evaluate the relevant fatigue damage mechanisms and thereby assess the remaining lifetime of the monitored components. In this work, multiple amplitude fatigue tests were performed on specimens drilled under different conditions and as a consequence partly feature a white etching layer. Under these aspects the capability of Barkhausen noise analysis and eddy current testing was compared and assessed.