Analysis of Oil Tube Fatigue Fracture
Cui Xuming(1),He Fujun(1),Tan Yun(2),Yang Xiaoxang(3),Luo Min(1),Zhang Yonghon(1)
(1 Daqing Petroleum Institute, Anda 151400) (2 Maoming college£©(3 Fuzhou University, Fuzhou, 350002£©

Abstract: Fatigue fracture is one kind of oil tube failure. In this paper, the fractures of oil tube (J55, 2 1/2" in) under cyclic loading are investigated by theory and experiment. Such kind of oil tube is widely used in the well of suckerrod. The elasto-plastic finite element method is used to compute the inner strain and stress field for the oil tube thread on the base of load spectrum and strain spectrum measured on site. Then the fatigue experiments concerned are completed to get the fatigue resistance. As the root of the first engaged thread on oil tube bears the maximum stress and strain, the s tress may reach yield limit. The oil tubes often run in a condition of heavily stress and strain level with low stress and strain amplitude. If the stress is large enough to make the material get in to its strengthen phase (the equivalent strain is more than 0.01¦Å) , and the plastic strain amplitude surpass 4¡Á10^-5 ¦Å, fatigue fracture will occur.
Keywords: oil tube, fatigue fracture, elastic-plasticity , finite element, experimental mechanics.