numero25

J. Toribio et alii, Frattura ed Integrità Strutturale, 25 (2013) 124-129; DOI: 10.3221/IGF-ESIS.25.18 124 Special Issue: Characterization of Crack Tip Stress Field Plastic zone evolution near a crack tip and its role in environmentally assisted cracking Jesús Toribio, Viktor Kharin University of Salamanca, Spain A BSTRACT . This paper analyzes the effects of crack tip plastic strains and compressive residual stresses, created by fatigue pre-cracking, on environmentally assisted cracking of pearlitic steel subjected to localized anodic dissolution and hydrogen assisted fracture. In both situations, cyclic crack tip plasticity improves the behavior of the steel. In the respective cases, the effects are supposed to be due to accelerated local anodic dissolution of the cyclic plastic zone (producing chemical crack blunting) or to the delay of hydrogen entry into the metal caused by residual compressive stresses, thus increasing the fracture load in aggressive environment. K EYWORDS . Plastic zone; Near-tip stress-strain fields; Environmentally assisted cracking. I NTRODUCTION nvironmentally assisted cracking (EAC) of metals is usually evaluated by testing of pre-cracked specimens prepared by fatigue (cyclic) loading in laboratory air that produces a redistribution of stresses and strains as a consequence of cyclic plastic deformations. Compressive residual stresses generated at fatigue load release, together with plastic strains, affect the stress corrosion behavior of materials [1]. This paper deals with the mechanical effects of pre-loading on the posterior EAC in a pearlitic high-strength steel wire used for prestressed concrete structures. The rising load EAC experiments are considered in combination with numerical modeling of the elastoplastic stress-strain field near the crack tip subjected to fatigue pre-cracking and subsequent monotonic loading during EAC tests. E XPERIMENTAL AC experiments were performed with a series of K max /K IC = 0.28, 0.45, 0.60 and 0.80, where K IC is the fracture toughness of the material and K max the maximum stress intensity factor during fatigue precracking. The experiments were rising load tests of pre-cracked specimens in aqueous solution under anodic and cathodic potentials to evaluate the two main mechanisms of EAC [2]: localized anodic dissolution (LAD) under the anodic regime and hydrogen assisted cracking (HAC) under the cathodic regime. The full experimental details are described elsewhere [1]. The tested high-strength steel has the properties given in Tab. 1. For the two regimes of environmental cracking (HAC and LAD), Fig. 1 plots the failure load during the EAC test (evaluated through the ratio of the failure load in aggressive environment F EAC to the failure load in air F C ) as a function of the severity of the fatigue precracking regime (expressed in dimensionless terms as the maximum stress intensity factor during fatigue precracking K max divided by the fracture toughness of the material K IC ). For both LAD and HAC, heavier pre-cracking is beneficial for the EAC resistance of the steel. This may be attributed to the cyclic plastic zones and compressive stresses near the crack tip due to fatigue. The E E