Influences of fatigue frequency and hydrogen content on crack propagation in hydrogen embrittlement environment
Yamaguchi Yuichiro; Nakakura Masahiro; Nonaka Hidemasa
Abstract:In this paper, the influences of fatigue frequency and hydrogen content in material were investigated for the crack propagation at 0.5 stress ratio using a low alloy steel by cyclic stress in an overprotective environment. The six frequencies between 10 Hz and 0.05 Hz, and three hydrogen contents were used as the experimental conditions. Three stages divided by crack propagation behavior existed in the relationship between the stress intensity factor and the crack propagation rate. The lower the frequency was, the higher the crack propagation was at the higher stress intensity factor. The crack propagation rate was constant at Stage II. The relationship between crack propagation rate at the Stage II and frequency was expressed as (da/dN)II =1.4x10-7xf-0.763. It was supposed that the cause of the Stage II was due to the lack of hydrogen to crack tip through diffusion. The hydrogen diffusion rate was of the order of 10-7 m/s. The hydrogen content enhanced the crack propagation rate at 1 Hz. The Paris Law in hydrogen embrittlement environment at 1 Hz was expressed as a function of hydrogen content, which was da/dN =C( DK)m where C =1.72x10-10x(10-5.6CH), m =3.05+4.74CH, CH: Hydrogen content in material. Key Words:crack propagation, hydrogen embrittlement, fatigue frequency, low alloy steel, stress intensity factir, Paris law