B runo Levieil

ENSTA Bretagne, Brest, France



The fatigue performance of welded joint is strongly dependent on welding residual stresses as well as the local geometry of the weld toes. To ensure the structural integrity over time of such components, fine predictive models must be proposed together with efficient experimental methods for their assessment.

This study proposes a model based on linear elastic fracture mechanics to forecast fatigue life in service of high strength steel welded joints. This model considers the effect of the local stress ratio (dependent on stabilized residual stresses) on the crack growth rate through the definition of an effective stress range.

The use of Thermoelastic Stress Analysis (TSA) is used to perform in-situ monitoring of fatigue cracks on welded joints to experimentally determine crack growth rates at different load ratios Indeed, under adiabatic conditions, the temperature’s first harmonic at the surface of a structure submitted to cyclic loading is proportional to the stress tensor’s first invariant’s amplitude. As a result, the presence of a surface crack can be witnessed based on the post-processing of infrared films. Moreover, it is shown that new infrared data post-processing methods allow for a fine detection of crack propagation phenomena (such as crack closure) and their assessment.

Firstly, the experimental technique and infrared post-processing is detailed and demonstrated in the case of a controlled specimen. Secondly, the identification of the model parameters is presented. Finally, the model is applied and validated on a real application case.


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