PSI - Issue 1

Daniel F. C. Peixoto et al. / Procedia Structural Integrity 1 (2016) 150–157 Author name / Structural Integrity Procedia 00 (2016) 000 – 000

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The used apparatus was based on the mixed-mode testing technique proposed by Richard (1985) that allows to perform mixed-mode loading using a uniaxial testing machine just by changing the loading angle between the longitudinal axis of the specimen and the load direction applied by the testing machine. Three different loading angles were tested 30º, 45º and 60º. Since no numerical solution exists to calculate the K I and K II values a finite element analysis was also done in order to obtain them for the tested conditions. It was observed that the fatigue crack growth direction changed immediately from the initial fatigue mode I pre crack orientation when load direction was changed. The experimental growth direction of the cracks for different load mixities were compared with the predictions based on numerical approaches (ABAQUS and Broek equation) which provide a similar estimation of the crack growth direction and a good agreement with the experimental results. It was observed that for the tested Δ K range the mixed mode fatigue crack growth rates are higher than the mode I fatigue crack growth rates. However, observing the results presented in Figure 14, for lower Δ K values or near the threshold the mixed mode fatigue crack growth rates could be lower than the mode I fatigue crack growths.

Acknowledgements

Daniel Peixoto acknowledges a Calouste Gulbenkian Foundation PhD grant, number 104047-B. The Portuguese Science and Technology Foundation FCT project PTDC/EME- PME/100204/2008 “Railways” is acknowledged . The kind collaboration of Prof. J.A. Martins Ferreira (University of Coimbra) and Prof L. Borrego (ISEC), sharing their knowledge, grips and experience in this type of tests is gratefully acknowledged.

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