13th International Conference on Fracture June 16–21, 2013, Beijing, China -3- Free of hydrogen specimens before the test were considered and, consequently, the initial condition of null hydrogen concentration at the initial time (C( x,t)|t=0 = 0) was applied in simulations. The material considered in this study is a hot rolled bar of eutectoid pearlitic steel (C 0.75%, Mn 0.67%, Si 0.200%, P 0.009%, S 0.009%, Cr 0.187%, V 0.053%), whose mechanical properties are: Young´s modulus 195 GPa, Yield Strength 720 MPa and ultimate tensile strength (UTS) 1270 MPa. Finally the values of relevant parameters of metal-hydrogen interaction were obtained from previous works [18,19] as D = 6.6 10-11 m2/s y VH = 2 10 –6 m3/mol. The geometry of a round notched specimen can be defined by two parameters (Table 1): the notch tip radius ρ and notch depth a. To have results independent of sample dimensions these parameters were normalized with the specimen diameter d (where d = 12 mm for all the notched geometries analyzed in this study). Table 1. Notch parameters of the analyzed notched specimens Parameter A B C D ρ/d 0.03 0.05 0.40 0.40 a/d 0.10 0.30 0.10 0.30 Fig. 1 shows a scheme of the four analyzed notched specimens, including the corresponding notation used to identify each one. To analyze the effect on hydrogen diffusion of the extension rate during the CERT tests, two different values were considered: fast extension rate, 0.1 mm/min, and slow extension rate, 0.001 mm/min. Two numerical approaches of hydrogen diffusion model, based in previous research [13,20], are used in present work: the one-dimensional approach (1D) and the quite more realistic (although time-consuming) two-dimensional approach (2D). Transient stress state generated in the specimen by remote loading during CERT test is included as input data in the FEM code developed ad hoc for both simulations of diffusion process. The specimen stress state is obtained from a previous mechanical simulation of the CERT test with a commercial FEM code considering small-strain. The same stress field was considered in the two approaches (1D and 2D) used in this paper. Fig. 1. Scheme of the notched specimens and parameters used for describing the notch
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