13th International Conference on Fracture June 16–21, 2013, Beijing, China -1- Effect of corrosion pits on fatigue life and crack initiation Xin-Yan Zhang 1, Shu-Xin Li 1,*, Rui Liang 1, R. Akid 2 1 School of PetroChemical Engineering Lanzhou University of Technology, Lanzhou 730050, China 2 Corrosion & Protection Centre, School of Materials, University of Manchester, Manchester M13 9PL * Corresponding author: li_shuxin@163.com Abstract Corrosion fatigue is identified as one of the main failure mechanism for structures working in corrosive environment. The existing study on pit corrosion showed that cracks do not necessarily initiate from the bottom of the pit. Where the crack initiate from pit depends on the pit shape (aspect ratio), loading and the corrosive environment. In this study, firstly, the corrosion pit development in size and shape and its effect on fatigue life were reviewed. Fatigue tests were conducted on pre-pitted and smooth samples to further investigate the pit effect. Then various aspect ratios of pits were modeled to calculate the SCF in a round bar under tension and bending loadings.In addition, the SCF of a wide range of aspect ratios of pits were calculated, by which it is expected to offer the engineering practice and researchers convenience to find SCF value. Keywords Corrosion pits 1; Aspect ratio 2; Stress concentration factor 3; Fatigue life 4 1. Introduction Pitting corrosion is considered to be one of the principal degradation mechanisms for many metallic materials subjected to corrosive environment. The fatigue life was shortened due to formation of corrosion pits on surface of the material causing the initial damage and then cracks initiated from these pits. Pit development and its effect on corrosion fatigue crack growth have been extensively studied, but there is little consensus with regard to the exact relationship between the pit size and the time due to the interaction of environment and loading and the dependence on microstructural state and stress level. The main purpose of the present paper is to provide a review of the pit formation and its effect on fatigue lives, attempting to develop a generalized understanding of how the pits develop. Then fatigue tests were conducted on pre-pitted and smooth samples to further investigate the pit effect. Finally, various aspect ratios of pits were modeled to calculate the SCF in a round bar under tension and bending loadings. 2. Corrosion pit development 2.1 Pit size development Corrosion pit size varies as exposure time in solution increases and depends on electrochemical and mechanical conditions. Many researchers have conducted extensive studies on pit development and various relationships between and pit size and time were proposed. Sriraman et al [1] developed a model that considers the coexistence of corrosive environment and fatigue loading conditions and took into account the influence of cyclic stresses in the pitting corrosion process. Boag et al [2] observed stable pit formation on AA2024-T3 in a NaCl environment, and indicated that local clustering played an important role in pit initiation. Ryuichiro Ebara [3] emphasizes initiation and growth of corrosion pits in the corrosion fatigue crack initiation process. The pit size distribution
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