Crack shapes and crack driving force distributions for naturally growing fatigue cracks

Extensive literature supports that fatigue cracks tend to a stable stage driven by an iso crack driving force (CDF) distribution that produces a quasi-constant crack shape. Here fatigue crack growth is studied by two means: (1) a finite element simulation based on crack-tip opening displacements and remeshing and mapping strategies and (2) a theoretical analysis based on the multiple-degree-of-freedom scheme and power-law crack growth relationships. Contrary to the literature, naturally growing fatigue cracks are found to converge towards a quasi-constant crack-shape regime promoted by a non-iso CDF distribution that depends on material properties and the stable crack shape.