Acoustic Emission Assessment of Fatigue Crack Growth from a Transverse Weld Toe

Acoustic emission (AE) has been increasingly used for assessment and prediction of fatigue cracks in steel bridge members. Fatigue cracks develop at the transverse weld toe of stiffeners, attachments, and cover plates in steel bridge members. Effectiveness of AE to assess fatigue crack initiation from weld toe is investigated in this study, and an attempt is made to predict the crack growth behavior using AE signal features. Cruciform specimens consisting of a single tension pull plate with transverse fillet-welded plates attached at midspan are tested in this study. The transverse plates represent stiffeners and/or short attachments typical of welded steel bridge details. The specimen provides realistic initial conditions of fatigue crack initiation and growth from high stress concentration regions. Consequently, AE waveform characteristics representative of those expected on bridge structures are produced. Accurate stress intensity factor values are difficult to obtain because of the small, nonuniform crack growth conditions at the weld toe. Finite-element method analysis for welded geometries capturing stress fields at the weld toe of stiffener details is performed, and numerical results are incorporated into an existing analytical stress intensity factor framework. Procedures for assessing the crack size and predicting remaining fatigue life of the specimen using absolute energy feature of AE signals are demonstrated.