Characterization of fatigue crack propagation of pitting-corroded rebars using weak magnetic signals

Abstract

In this study, mode-I high-cycle fatigue tests were conducted on smooth standard specimens manufactured from HRB400 steel bars, prefabricated with a semi-ellipsoid corrosion pit. Fatigue crack growth (FCG) behavior was predicted using the FCG model, based on linear elastic fracture mechanics (LEFM). During the fatigue process, an online piezomagnetic signals was detected, while the residual magnetic field (RMF) distribution near the corrosion pit was recorded after the specimen was unloaded. The range of the magnetic tangential induction ΔBt and the gradient of the normal component of the RMF distribution Gmax were selected as the characteristic weak magnetic parameters, which exhibited a three-stage evolution law with fatigue progression. Next, the evolution mechanism of the weak magnetic field during the FCG process of the pitting-corroded rebars was comprehensively explored. Subsequently, quantitative relationships between the stress intensity factor (SIF) range ΔK and ΔBt as well as the fatigue crack length a and Gmax were separately established. The errors between the predicted and validation experimental results of ΔK, a, and FCG life were all within 20%. Furthermore, the influence of the pit geometry and stress ratio on the variation of ΔBt versus ΔK, and Gmax versus a was investigated. The increments of ΔBt and Gmax in different 1000-cycle intervals during various FCG stages were recorded, which could help estimate FCG behavior of pitting-corroded rebars in practical applications.