Carbon fibre-reinforced polymer for the repair of fatigue cracks in steel structures

Abstract

Fatigue cracking can occur in any complex steel structure. The user is generally unaware until the crack reaches a length that can be observed with the naked eye. At this time repair is needed: in some situations the repair may not require welding and can be relatively easily carried out. Carbon composite patches applied over the crack represent a possible choice. This paper describes an experimental investigation of the fatigue crack growth rate in welded steel details with carbon fibre-reinforced polymer (CFRP) repairs. Three types of specimen were tested, including a cruciform section and a longitudinally stiffened plate. Both plain steel unpatched specimens and patched specimens repaired with CFRP composite to extend the fatigue life were tested. The test results were used to validate the three-dimensional (3D) finite-element models, (FEM), which were used to predict crack growth in both the plain steel and repaired plates. The analysis was based on linear elastic fracture mechanics (LEFM) and the Paris law and was carried out using Abaqus in conjunction with Zencrack. The FEM were found to give an accurate predictions of the crack growth rate in both the unpatched specimens and patched specimens. It is concluded that the patching technique using CFRP can give a useful extension of life and that the finite-element analysis described could be used in practice to design such repairs with confidence.