Crack Geometry Effect on Stress-Strain Fields for Crack Under Biaxial Loading

With increasing demand of high-strength and high-pressure pipelines in gas transmission industries, the fracture control design of pipelines has been a driving factor to ensure the integrity of the pipeline. This paper addresses the stress and strain fields for a crack in a wide plate component under biaxial loading, which simulates a large-diameter pipe subjected to inner pressure coupled with axial loading. Attention is focused on the initiation of brittle fracture (stress controlled type) as well as ductile fracture (strain controlled type). Three-dimensional finite element-analyses are conducted. It was found that biaxial loading has a significant effect on the stress fields of through-thickness crack; the near-crack-tip stress is elevated to a large extent by biaxial loading. By contrast, the stress field for a surface crack is not sensitive to biaxial loading, while the near-crack-tip stress at the crack corner is increased locally by biaxial loading. The Weibull stress criterion was applied to discuss the biaxial loading effect on the brittle fracture strength of the wide plate. Ductile crack initiation properties are also discussed with two-parameter (plastic strain and stress triaxiality) diagram. The ductile damage is increased by biaxial loading for a through-thickness crack, whereas a surface crack has little effect of biaxial loading on the ductile damage.