Fatigue Reliability Analysis of Tunnelling Boring Machine Cutterhead with Cracks

The cutterhead of tunnel boring machine is a large-scale metal welding structure, which is prone to problems such as wear and cracking during the tunnelling process. For the issue, the fatigue crack propagation rate model of cutterhead under different reliability was established, based on the damage tolerance of cutterhead. Its dangerous position of cutterhead failure was determined by using finite element method. According to the fatigue load spectrum, the fatigue propagation life of cutterhead under different reliability was calculated, the main factors affecting the reliability of cutterhead were analyzed and the engineering experiment is carried out. The results show that three dangerous positions of the cutterhead failure are the junction of the split plane, the maximum deformation of the block and the central cutter seat. The load stress amplitude and initial crack size are the main factors affecting the crack propagation life and the reliability of cutterhead. With the increase of load stress amplitude and initial crack size of cutterhead, the fatigue crack propagation life of cutterhead decreases and the reliability is worse. When the initial crack size of cutterhead is greater than 0.5mm, the fatigue crack propagation life of cutterhead decreases obviously. The research results provide a scientific basis for crack detection, life prediction and reliability evaluation of cutterhead structure.

Effects of Drive Side Pressure Angle on Gear Fatigue Crack Propagation Life for Spur Gears With Symmetric and Asymmetric Teeth

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.

The Fatigue and Fracture Analysis of Steam Turbine Rotor Shafts Containing Defects

In this study, the assessment and calculation methods for the crack propagation life of steam turbine rotor shafts containing defects are presented. The analytic methods for estimating the average stress and the alternating stress amplitude of the steam turbine rotor shafts are introduced. The defects on/in the rotor shafts were regularized by the method of fracture mechanics, and the high cycle fatigue crack propagation life and low cycle fatigue crack propagation life of the rotor shafts are estimated from Paris formula. Taking the 60MW turbine rotor shafts containing an initial surface defect and an initial internal defect as the examples respectively, the crack propagation life of them were calculated. The results indicated that the assessment method for the crack propagation life can preliminarily be both used to estimate the safety-operating life and to analyze the fracture reason of a steam turbine rotor shaft containing defects. This paper can provide reference for periodic maintenance and safety evaluation of turbine rotor shafts.