Fatigue behaviour of adhesive bonds in tensile CFRP-metal double-strap joints with puddle iron plates taken from a 19th century bridge

The use of adhesively-bonded CFRP crack-patching in old metallic bridges seems to be a promising fatigue strengthening technique, but the internal laminar structure of puddle iron could influence its efficiency, resulting in premature interlaminar failure within the metal before CFRP debonding. To investigate the fatigue behaviour of this retrofitting system, six double-strap joints with CFRP laminates adhesively-bonded to puddle iron plates taken from a 19th century bridge were tested. Three specimens were statically loaded until failure as control specimens, and other three were tested under tensile-tensile fatigue loading up to 2 million cycles at a frequency of 10 Hz, with stress ranges in the metal of 60, 75 and 90 MPa. An analytical model is used to compute the maximum principal stress range in the adhesive during fatigue loading, which is assumed as the governing fatigue strength parameter in the double-strap joint. Based on the experimental results of the present work, together with a database for joints with modern steel collected from literature, an S-N fatigue curve is obtained for CFRP-metal double-strap specimens, and a fatigue limit in terms of maximum principal stress range in the adhesive layer is proposed to be used in design guidelines.The research leading to these results has received partial funding from the European Union's Horizon 2020 Programme in the framework of the research project IN2TRACK under grant agreement n° 730841.Peer reviewe