Effect of Pre-Deformation on Fatigue Crack Propagation Life of X60 Pipeline Steel

Author(s):  
Xinwei Zhao ◽  
Jinheng Luo ◽  
Rong Wang ◽  
Maosheng Zheng ◽  
Baosheng Dong

It is impossible to keep oil and gas pipeline free from defects in fabrication, installation and serving processes. Mechanical damage is one of import causes of pipeline failure accidents. Mechanical damage might endanger the safety of pipelines and even shorten their service life. Pre-tensile deformation of X60 steel is employed to experimentally simulate the influence of dents on the fatigue crack initiation life. The investigation indicates that the fatigue crack propagation life of pre-deformed X60 pipeline steel can be predicted using a previously proposed equation, i.e., da/dN = B(ΔK − ΔKth)2. The threshold ΔKth for fatigue crack propagation decreases with the pre-deformation. The fatigue crack propagation coefficient B increases with the pre-deformation. So pre-deformation accelerates fatigue crack propagation and shortens fatigue life. The result is expected to be beneficial to the understanding of the effect of dents on the safety of pipelines and fatigue life prediction.

2012 ◽  
Vol 538-541 ◽  
pp. 1716-1719 ◽  
Author(s):  
Yu Rong Jiang ◽  
Mei Bao Chen

It is impossible to keep pipelines free from mechanical damage in the manufacturing, installation and servicing processes. In this paper, the geometric model for fatigue life of pipeline steel was introduced. The local plastic deformation was considered to imitate the mechanical damage on the pipe. The estimation models of the fatigue crack initiation life and the fatigue crack propagation life were proposed according to the plastic deformation. The result is expected to be beneficial to the understanding of the effect of damage on the safety of pipelines and fatigue life prediction.


2015 ◽  
Author(s):  
Niu Song ◽  
Cao Jun-wei ◽  
Ren Hui-long ◽  
Feng Guo-qing

Fatigue damage is one of the main causes responsible for the destruction of ship structures. The traditional methods of the fatigue strength check are based on S-N curves and Miner linear cumulative damage rules. But different fatigue lives of the same node are obtained, because the disadvantages of S-N curves could not be avoided, such as neglect of initial objection of material. The method of fracture mechanics to assess the fatigue life of ship structures has become a trend now. According to the relevant fracture mechanics theory, this paper brings forward a set of methods on the fatigue life of ship structures under random sea state. This method takes into account the non-linear effect of stress distributed along the crack surface, and the stress intensity factor is calculated through the weight function method. The crack extension is calculated in each cycle of stress according to the stress response history of ship in actual sea state so as to attain the fatigue crack propagation life of ship structures in the random load.


2004 ◽  
Vol 126 (1) ◽  
pp. 77-86 ◽  
Author(s):  
Yanyao Jiang ◽  
Miaolin Feng

Fatigue crack propagation was modeled by using the cyclic plasticity material properties and fatigue constants for crack initiation. The cyclic elastic-plastic stress-strain field near the crack tip was analyzed using the finite element method with the implementation of a robust cyclic plasticity theory. An incremental multiaxial fatigue criterion was employed to determine the fatigue damage. A straightforward method was developed to determine the fatigue crack growth rate. Crack propagation behavior of a material was obtained without any additional assumptions or fitting. Benchmark Mode I fatigue crack growth experiments were conducted using 1070 steel at room temperature. The approach developed was able to quantitatively capture all the important fatigue crack propagation behaviors including the overload and the R-ratio effects on crack propagation and threshold. The models provide a new perspective for the R-ratio effects. The results support the notion that the fatigue crack initiation and propagation behaviors are governed by the same fatigue damage mechanisms. Crack growth can be treated as a process of continuous crack nucleation.


Author(s):  
Fatih Karpat ◽  
Oguz Dogan ◽  
Tufan Yilmaz ◽  
Celalettin Yuce ◽  
Onur Can Kalay ◽  
...  

Abstract Today gears are one of the most crucial machine elements in the industry. They are used in every area of the industry. Due to the high performances of the gears, they are also used in aerospace and wind applications. In these areas due to the high torques, unstable conditions, high impact forces, etc. cracks can be seen on the gear surface. During the service life, these cracks can be propagated and gear damages can be seen due to the initial cracks. The aim of this study is to increase the fatigue crack propagation life of the spur gears by using asymmetric tooth profile. Nowadays asymmetric gears have a very important and huge usage area in the industry. In this study, the effects of drive side pressure angle on the fatigue crack propagation life are studied by using the finite element method. The initial starting points of the cracks are defined by static stress analysis. The starting angles of the cracks are defined constant at 45°. The crack propagation analyses are performed in ANSYS SMART Crack-Growth module by using Paris Law. Four different drive side pressure angles (20°-20°, 20°-25°, 20°-30° and 20°-35°) are investigated in this study. As a result of the study the fatigue crack propagation life of the gears is increased dramatically when the drive side pressure angle increase. This results show that the asymmetric tooth profile not only decrease the bending stress but also increase the fatigue crack propagation life strongly.


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