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J. Toribio et alii, Frattura ed Integrità Strutturale, 25 (2013) 124-129 ; DOI: 10.3221/IGF-ESIS.25.18 128 controlled microfracture at hydrogen induced failure in experiments. For the precracking regimes compared in Fig. 6, this distance is fairly the same x  + (K QEAC ) = 8  m, so that it may be supposed to be a characteristic microstructural scale for HAC. Therefore, the heaviest fatigue pre-cracking regimes delay the hydrogen accumulation, and thus the progress of hydrogen degradation in the course of a rising load EAC test. Figure 6 : Mechanical factors of the crack growth by HAC: (a) comparison of the TTS extension and the plastic zones associated with HAC tests: at lower K max -levels, the terminal active plastic zone (open square points) at the end of the HAC test (x APZ at K QEAC ) surpasses the cyclic and the monotonic plastic zones created during fatigue precracking (triangles),  x Y (K max ) and x Y (K max ) respectively; (b) evolutions of the average value of the hydrostatic stress gradient during HAC tests after fatigue pre-cracking at K max /K IC = 0.45 (dashed line) and 0.80 (solid line). C ONCLUSIONS nvironmentally assisted cracking (EAC) of high-strength steel is clearly influenced by fatigue pre-cracking, since cyclic loading affects plastic strains and creates compressive residual stresses in the vicinity of the crack tip. Cyclic accumulation of plastic strain and compressive residual stresses improve the EAC behavior through increase of the failure load in aggressive environment either by: (i) Chemical blunting of the crack tip enhanced by accumulated plastic strain in the near-tip area in the case of EAC in the anodic regime of localized anodic dissolution (LAD) (ii) Delay of hydrogen supply to the fracture process zone near the crack tip by stress-assisted diffusion in the case of EAC in the cathodic regime of hydrogen assisted cracking (HAC). A CKNOWLEDGEMENTS he authors wish to acknowledge the financial support provided by the following Spanish Institutions: Ministry for Science and Technology (MCYT; Grant MAT2002-01831), Ministry for Education and Science (MEC; Grant BIA2005-08965), Ministry for Science and Innovation (MICINN; Grants BIA2008-06810, and BIA2011-27870) and Junta de Castilla y León (JCyL; Grants SA067A05, SA111A07, and SA039A08). R EFERENCES [1] Toribio, J., Lancha, A.M., Overload retardation effects on stress corrosion behaviour of prestressing steel, Constr. Building Mater., 10 (1996) 501-505. [2] Ford, F.P., Stress corrosion cracking of iron-base alloys in aqueous environments, in: C.L. Briant, S.K. Banerji (Eds.), Treatise on Materials Science and Technology, Embrittlement of Engineering Alloys, Academic Press, New York, 25 (1983) 235-274. [3] Toribio, J., Lancha, A.M., Elices, M., Characteristics of the new tearing topography surface, Scripta Metall. Mater., 25 (1991) 2239-2244. E T