Influence of fatigue loading mode on the crack initiation mechanism of pipes

Abstract

In this study, we developed a finite element model for fatigue fracture to investigate crack initiation in pipes under fatigue fracture. Under eccentric wheel loading, the stress concentration positions on the V-notch cross-section of the pipe varied continuously. Owing to the V-notch, stress concentration primarily occurred on the pipe’s outer surface. Thus, crack initiation occurred on the flank of the V-notch and was influenced by the applied load. Experiments under different loading modes revealed that under alternating and linear loads, the crack initiation and propagation faster, with the outer side expanding more quickly than the inner side. Additionally, constant tensile and monotonic loads affected the degree of crack opening and axial stress, accelerating crack expansion. The pipe diameter, clamping force arm, and loading force arm influenced the crack initiation position. At a constant outer diameter and clamping arm, the crack initiation angle of the pipe increased with the loading arm, promoting the precise separation of the pipe.