In-depth growth of micro-cracks in a ferritic-martensitic steel

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The extension of fatigue cracks in materials containing soft and hard phases is strongly dependent on the spatial distribution of the phases. Martensite region act as a barrier against micro-crack extension in a ferritic-martensitic steel. Once this barrier has been overcome the crack extends along rather tortuous crack paths. This implies that a detailed fracture mechanics analysis of these fatigue cracks is very difficult. This proposal aims at developing loading parameters for fatigue cracks ina ferritic-martensitic steel, and , in addition, at understanding the role of the martensitic phase once the first barrier har been breached. In this context, it is improtant to take the three-dimensional shape of the crack into accout, as a crack which has been stopped by a martensite region on the surface may continue to extend in depth direction.