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

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The aim of this research proposal is to use the potential of a non-destructive testing methods, the digitalisation of the measurement techniques as well as signal processing and to combine this with a new one-specimen test strategy in order to achieve a significant gain in information concerning the fatigue behaviour with a simultaneous reduction of experimental effort and costs. The result might be therefore not only a considerable advantage with respect to conventional determined S,N data, but also to established short-term procedures, if it is possible 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.Within the new fatigue life calculation method SteBLife (Stepped Bar Fatigue Life Evaluation) a stepped specimen geometry with several gauge lengths is used in order to detect the local material responses through the application of different NDT techniques. First preliminary investigations for specimens from the steel C45E/SAE1045 have already shown very promising results. Within that investigations, the material response was measured by means of an infrared camera, which is to be intensified by additional thermocouple measurements in the framework of this research proposal and also extended to magnetic measurement methods. Contrary to the conventional approach, the specimens are to be magnetized not with electric or permanent magnets, but by means of an applied constant/alternating current or voltage to generate a specific microstructure related magnetic field. The measuring signals will be analysed in terms of specific features; in particular, the simulation of the measurement signals using commercial simulation software solutions like COMSOL might give a significant contribution to the understanding and interpretation of the results. The experimental investigations, simulations and signal analysis will be made on/for unalloyed and low alloyed carbon steels C20E, C45E and 42CrMo4 in normalized and one commercially available quenched and tempered condition each.