Numerical analysis on fatigue crack growth life of non-load-carrying cruciform welded joints repaired with FRP materials

Fiber reinforced polymer (FRP) materials were used to repair cracked non-load-carrying cruciform welded joints; and both the finite element method and the boundary element method were employed to study the fatigue crack propagation life of specimens repaired with FRP materials. The stress intensity factors (SIFs) were calculated for cracked welded joints that were unrepaired or were repaired with various FRP materials. The reduction of the SIFs for the repaired specimens was evident with the comparison of the control specimens. The fatigue life was then estimated with the NASGRO equation, which is modified from the Paris law. It was observed that the resulting fatigue improvement agreed with existing experimental data, indicating that fatigue strength can be upgraded with composite material repairs. The effects of various repair parameters on fatigue life were also examined. Single-sided repairs on cracked surfaces were more effective than double-sided repairs, due to the shift of the neutral axis. An increased modulus of FRP materials and adhesive achieved better fatigue performance. The use of more patch layers also had a positive effect, while increased adhesive thickness had a negative effect on fatigue life.