A study on crack front shape and the correlation between the stress intensity factors of a pipe subject to bending and a plate subject to tension

The use of a pipe subject to bending moment with an equivalent plate subject to tension has been tried by a few researchers to avoid the complexity usually involved with experimental crack growth investigations of pipes with initial surface flaws. This approach also minimizes the use of more sophisticated monitoring instruments, thereby offering significant cost savings. This equivalency has been done for both experimental and finite element investigations. This paper studies the validity of this approach and evaluates the ranges of the crack depth ratio and elliptical crack diameter ratio for which this approach would be admissible. A series of finite element analysis was carried out to both verify the values of the stress intensity factors reported in the literature, and verify the results of the interpolation function used in the computational simulation in this research. Based on the computational simulations and demonstrating that the crack front follows a semi-circular shape during its growth, a dimensionless relationship between the stress intensity factor of a pipe under bending moment and that of a plate under pure tension has been introduced. A series of experimental investigation was performed to verify the validity of the proposed computational simulation. The results show the rationality and admissibility of this approach when considering the fatigue crack growth of pipes under bending.