In this paper, we implement the combined method of drilling stop hole and FRP reinforcement to repair cracked steel plates subjected to cyclic tension. The crack initiation and growth are experimentally investigated. The stress distribution at the stop hole and the residual fatigue life are evaluated by the FEM. The effects on prolonging residual fatigue life are analyzed. The results show that the effectiveness of only using the stop hole is limited, while the combined method has dramatically prolonged the residual fatigue life. The effect mainly owes to the increasing of the crack initiation life from the stop hole.

In this paper, we analyse the surface crack growth in the Fibre-Reinforced Polymer (FRP) reinforced steel plates subjected to tension by means of the finite element (FE) method. Following the experimental study, a three-dimensional FE model is developed to evaluate the Stress Intensity Factor (SIF) of the surface crack, and the crack growth rate is calculated by using the Paris’ law. Then the FE model is validated by the experimental results. Afterwards, on account of the validated FE model, a parametric study is developed in order to guide the optimization design of FRP reinforcement accounting for different reinforcing schemes and multiple influential parameters. The results indicate that the single-side FRP reinforcement on the cracked surface is the most efficient method, owing to the generated out-of-plane bending moment. In addition, the optimum bond length and number of layers are indicated. Besides, surface crack growth is sensitive to the influential parameters including aspect ratio of the surface crack and crack dimension, while less sensitive to the Carbon-FRP (CFRP) tensile modulus, and the adhesive thickness. The analysis is of instructive value to facilitate the application of FRP reinforcement on the surface cracked metallic structure repairing domain.

In this paper, we experimentally studied the external surface crack growth in steel pipes reinforced with Composite System Repaired (CRS). CRS reinforced surface cracked API 5L X65 pipes were tested, containing three initial notch sizes and four reinforcement schemes. During the tests, the crack growth results, as well as the strain on the external mid-bottom composite laminate around the cracked area, and the vertical deflection of the specimens were recorded. The results showed that within the surface crack growth stage, the composite laminates were adequately bonded on the steel substrate, which significantly decreased the crack growth rate and prolonged the residual fatigue life. In addition, CRS reinforcement has increased the stiffness of the surface cracked pipes. Through the analysis on applying different reinforcement schemes, we indicated that increasing the amount of composite layers evidently facilitated the reinforcement effectiveness, while increasing the bond length did not; and the inversely diagonal wrapping pattern performance less effective.