The effects of aspect ratio and bi-axial loading on the initiation of plastic deformation in three-dimensional semi-elliptical effects

The aim of this paper is to investigate the effect of biaxial loading ratio and defect geometry on the elastic-plastic stress and strain fields of 3D surface braking semi-ellipsoids. Defect sizes studied spans those typically observed in different applications such as wind offshore monopiles and O&G pipelines and for this preliminary study were considered to be ellipsoidal. Elastic-plastic finite elements of 32 different models was performed for 4 biaxial loading conditions resulting in 128 unique cases. Results showed relatively evenly distributed elevated stresses at the defect surroundings and highly localised plastic deformation either at the defect bottom or mouth. It was observed in general that the maximum elastic stress occurs at the base of the defects but after the onset of plastic deformation, stresses are redistributed, and the maximum stress occurred slightly away from the pit base. However, the accumulation of plastic strain is more apparent at the pit mouth rather than the base due to a reduced constraint condition at the mouth. Applications of results are useful for understanding crack initiation from notches with relevance to pitting corrosion crack initiation.