Abstract
The primary mechanism of fatigue crack growth is crack-tip dislocation emission followed by the glide of the emitted dislocations. Both of these two processes are controlled by the crack-tip resolved shear stress field, which is characterized by the resolved shear stress intensity factor, K Rτ
A dislocation barrier model for fatigue crack growth threshold is constructed. The model assumes that a fatigue crack stops growing when crack-tip slip bands are incapable of penetrating the primary dislocation barrier. The derived and deduced threshold behaviors agree with the observed constant threshold K max,th in the low R region and constant threshold △K th in the high R region. K max,th is the K max at the threshold. The constant K max,th is related to the resistance of the primary dislocation barrier, which in most of cases is grain boundary; and the constant △K th is related to the resistance of secondary barriers. Furthermore, the analysis shows that K max,th is proportional to √d, where d is the grain size. The relation has been observed in steels. The model also helps to explain the characteristics of, and the transition from, microstructure-sensitive to microstructure-insensitive growth.
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Liu, H.W. (1998). A dislocation barrier model for fatigue crack growth threshold. In: Knauss, W.G., Schapery, R.A. (eds) Recent Advances in Fracture Mechanics. Springer, Dordrecht. https://doi.org/10.1007/978-94-017-2854-6_14
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DOI: https://doi.org/10.1007/978-94-017-2854-6_14
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