Hydrogen embrittlement in pre-loaded sharply-notched samples of cold-drawn pearlitic steel wires for prestressed concrete structures: a fractographic analysis

Abstract

[EN]Hydrogen embrittlement (HE) is a primary cause of in-service failure of pearlitic prestressing steels, compromising the long-term durability and safety of prestressed concrete structures. This fracture process causes a material brittle fracture due to hydrogen-assisted micro-damage (HAMD). The main stage of HE is hydrogen transport by diffusion towards critical locations, a process highly sensitive to hydrostatic stress and plastic strain gradients. Accordingly, different HAMD scenarios to analyse HE in prestressing steels are defined in this study by modifying the stress and strain fields through sharp notches and mechanical preloading to induce residual stress and strains. To achieve this goal, two sharply-notched geometries were considered varying notch depth, shallow notch and deep notch. Both preloaded (90% of in-air fracture load) and un-preloaded notched samples were tested under a constant loading (70% of in-air fracture load) up to final fracture in the presence of an environment (saturated solution of Ca(OH)2 with 0.1 g/l NaCl) under electrochemical conditions (pH =12.5, E = −1200 mV SCE, saturated calomel electrode) promoting HE. Fractographic analysis via SEM of the fracture surfaces was performed to analyse the variations on the HAMD scenarios. The obtained results reveal different HE behaviours: shallow notches exhibited highly localized hydrogen damage and shorter time-to-failure, whereas deep notches resulted in more distributed damage and extended fracture lives.