Use of non-destructive testing methods in a new one-specimen test strategy for the estimation of fatigue data

The comprehensive characterisation of the change in the metallic materials' microstructure due to an applied load is of prime importance for the understanding of basic fatigue mechanisms or more general damage evolution processes. If they are fully understood, advanced fatigue life calculation methods, which are far away from linear damage accumulation models, can be realised providing even more than only classic fatigue data. Within the scope of this paper, it is shown how the potential of non-destructive testing methods, the digitalisation of the measurement techniques as well as signal processing can be combined with a new one-specimen test strategy in order to achieve a gain in information concerning the fatigue behaviour with a simultaneous reduction of experimental effort and costs. The result is therefore not only a considerable advantage with respect to conventional determined Woehler- or S-N-data, but also to established short-term procedures, due to the possibility to separate several material effects by means of data analysis and to use this for fatigue life calculations based on the results of one single specimen. The SteBLife (step-bar fatigue life) approach is a new short-time calculation method developed at the Chair of Non-Destructive Testing and Quality Assurance at Saarland University, which allows to provide S-N-data on the basis of a small number of fatigue tests. For the first investigations in accordance to the new SteBLife approach, temperature measurements by means of an infrared camera were used. The change in temperature is directly related to deformation-induced changes of the microstructure in the bulk material and is considered to represent the actual fatigue state. Within the framework of this paper, the SteBLife procedure was validated on specimens from normalised SAE1045 steel.