Checking the fatigue limit from thermographic techniques by means of a probabilistic model of the epsilon–N field

The determination of the ε–N field for a certain material, similar to the S–N case, implies a relatively high number of costly and time consuming fatigue tests at different strain amplitudes. For specific applications, the mere estimation of the fatigue limit seems to be sufficient for guaranteeing lifetime safety in fatigue design allowing practical methods to be advantageously applied as a result of the notable reduction of the experimental program implied. In this work, the reliability of the fatigue limit provided by the Risitano thermographic method is investigated in order to check its validity for practical applications. With this aim, an experimental program on a C55E steel under strain control is performed, from which the probabilistic ε–N field is assessed using the Weibull regression model of Castillo et al., which provides a global solution in both low- and long-cycle fatigue regions. The fatigue limit is derived, primarily as stress range and then compared with that resulting from the Risitano methodology. With the purpose of improving the estimation of the fatigue limit, a novel assessment procedure of the thermographic results is presented that allows an improved correspondence between the fatigue limits arising from both models, thus confirming the suitability of the thermographic technique in practical applications.