numero25

J. Toribio et alii, Frattura ed Integrità Strutturale, 25 (2013) 124-129; DOI: 10.3221/IGF-ESIS.25.18 125 higher the cyclic load level, the stronger the pre-straining/stressing effect which delays environmental damage (metal dissolution in LAD or hydrogen entry in HAC) and improves material performance in a hostile environment. Young modulus E [GPa] Tensile Yield Strength  Y [MPa] Toughness K IC [MPa  m] Ramberg-Osgood curve  =  /E+(  /P) n (I)  p <1.07 (II)  p  1.07 P I (MPa) n I P II (MPa) n II 195 725 53 2120 5.8 2160 17 Table 1 : Mechanical properties of the steel. Figure 1 : Failure load during the EAC test as a function of the severity of the fatigue precraking regime. Fractographic analysis of the samples after HAC tests revealed the existence of a particular microscopic fracture mode (Fig. 2a) which is a signal of hydrogen assisted microdamage [3] in pearlitic steels as those used in the present work: the so called tearing topography surface (TTS) between the fatigue pre-crack and the final cleavage fracture. Measured TTS depth x TTS also depends on the pre-cracking regime, as plotted in Fig. 2b. Again this may be attributed to the cyclic plastic zones and compressive stresses near the crack tip due to fatigue. (a) (b) Figure 2 : (a) Fractographic appearance of the Tearing Topography Surface (TTS), (b) Depth of the TTS zone in the HAC tests (cathodic regime of EAC) as a function of the severity of the fatigue precraking regime (K max /K IC ). M ODELLING OF CRACK TIP MECHANICS o ascertain the effects of pre-cracking on EAC, the evolutions of mechanical variables associated with EAC are desired. In previous analyses [4] the Rice model [5] was applied. In this paper, a high-resolution numerical modelling of the crack tip stresses and strains during fatigue pre-cracking and rising load EAC test was performed T