Abstract
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.
Highlights
Assisted cracking (EAC) of metals is usually evaluated by testing of pre-cracked specimens prepared by fatigue loading in laboratory air that produces a redistribution of stresses and strains as a consequence of cyclic plastic deformations
The rising load Environmentally assisted cracking (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
For the two regimes of environmental cracking (HAC and localized anodic dissolution (LAD)), Fig. 1 plots the failure load during the EAC test as a function of the severity of the fatigue precracking regime
Summary
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. 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 FEAC to the failure load in air FC) as a function of the severity of the fatigue precracking regime (expressed in dimensionless terms as the maximum stress intensity factor during fatigue precracking Kmax divided by the fracture toughness of the material KIC). For both LAD and HAC, heavier pre-cracking is beneficial for the EAC resistance of the steel. This stress component is focused since it is determinant for HAC controlled by stress-assisted hydrogen diffusion driven by the gradient towards maximum stress locations [8, 9]
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