Strengthening of cracked DH36 steel plates by CFRP sheets under fatigue loading at low temperatures

Abstract

DH36 Shipbuilding steel plate is widely used in marine applications, which undergo fatigue loading at low temperatures. This paper suggests using carbon fiber reinforced polymer (CFRP) sheets to strengthen this steel under fatigue loading in the −60 to 20 °C temperature range. The mechanical properties of the steel and adhesive were analyzed, eight bare steel plates and eight strengthened steel plates were tested under fatigue loadings at different temperatures, and a theoretical calculation was conducted. First, the elastic modulus and strength of DH36 steel and the elastic modulus of the adhesive increased with decreasing temperature. Second, the temperature decreasing from 20 to −60 °C increased the fatigue life by 113% for the bare specimens and 190%–254% for the strengthened specimens due to the high elastic modulus of the adhesive at −60 °C. The fatigue life of the strengthened specimens was 1.62–4.74 times that of bare specimens, which proved that CFRP-strengthened DH36 steel with good efficiency in the temperature range. Finally, by considering the influences of temperature on DH36 steel, adhesive and CFRP composite, a relatively accurate prediction of fatigue life is achieved using fracture mechanics theory.