Journal
MATERIALS
Volume 14, Issue 6, Pages -Publisher
MDPI
DOI: 10.3390/ma14061562
Keywords
synchrotron tomography; short fatigue crack growth; residual stress; crystal plasticity; very high cycle fatigue
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Funding
- Deutsche Forschungsgemeinschaft (German Science Foundation) [SPP 1466]
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Diffraction and phase contrast tomography techniques were successfully used to investigate the microstructure of a metallic material and the influence of residual stresses on fatigue crack nucleation and propagation. The study demonstrated that residual stresses accumulated in ferritic grains due to cyclic deformation promote crack formation, while microstructural barriers play a crucial role in short fatigue crack growth on the surface and within the material.
Diffraction and phase contrast tomography techniques were successfully applied to an austenitic-ferritic duplex stainless steel representing exemplarily a metallic material containing two phases with different crystal structures. The reconstructed volumes of both phases were discretized by finite elements. A crystal plasticity finite-element analysis was executed in order to simulate the development of the experimentally determined first and second order residual stresses, which built up due to the manufacturing process of the material. Cyclic deformation simulations showed the single-grain-resolved evolution of initial residual stresses in both phases and were found to be in good agreement with the experimental results. Solely in ferritic grains, residual stresses built up due to cyclic deformation, which promoted crack nucleation in this phase. Furthermore, phase contrast tomography was applied in order to analyze the mechanisms of fatigue crack nucleation and short fatigue crack propagation three-dimensionally and nondestructively. The results clearly showed the significance of microstructural barriers for short fatigue crack growth at the surface, as well as into the material. The investigation presented aims for a better understanding of the three-dimensional mechanisms governing short fatigue crack propagation and, in particular, the effect of residual stresses on these mechanisms. The final goal was to generate tailored microstructures for improved fatigue resistance and enhanced fatigue life.
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