Loading...

Simulation of Three Dimensional Crack in Spur Gears due to Misalignment

Ghassabzadeh Saryazdi, Maryam | 2009

920 Viewed
  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 39908 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Durali, Mohammad
  7. Abstract:
  8. Fatigue crack is one of the most important causes of defect for gear systems. This effect results tooth fracture and failure of other elements of the power transmission systems. As a result, much effort has been devoted to the modeling of fatigue crack and improving the methods of crack detection. Simulations of three dimensional crack growth in spur gears due to misalignment and examination of this effect on vibration response of gear system are the main goals of this research. To model the crack growth, a new method of gear meshing modeling was proposed. In this method, the effects of pinion on the gear and vice-versa are modeled by a finite set of virtual interconnected springs. The stiffness matrix of these springs is a function of each gear properties and its crack size. This matrix is calculated using a boundary element simulation. These matrices provide the distributed meshing force along the contact line which will be used for crack growth modeling and results the meshing stiffness for vibration analysis. Therefore, this method helps in simulating each gear individually in contrast to the conventional finite element contact model. As a result it is much faster than the other existing calculation methods. In search for a method to detect the crack initiation and growth, a vibration analysis was performed to find the effect of crack growth on vibrational response of the gearbox. It was shown numerically that the bending and lateral vibrations are negligible and torsional vibrations play a major role in the gearbox behavior. Using the aforementioned method, the crack growth path was determined for two cases of ideal and misaligned contacts in a pair of spur gears. It was shown that misalignment affects the position of initial crack, the crack growth path, and the force distribution along the contact line. Moreover, the crack growth reduces the meshing stiffness depending on the meshing position on the flank. The vibration response of a one-stage gearbox was determined for two cases of ideal and misaligned contacts at different stages of crack growth. Kurtosis number and the amplitude demodulation methods were employed to detect the fatigue crack from the gear vibration response. It was shown that in misaligned contact the kurtosis of residual signal is less sensitivity in detection than the amplitude demodulation since the kurtosis number detects the crack in its later stages than the amplitude demodulation. The amplitude demodulation method detects the crack in both ideal and misaligned contacts with the equal ratios of crack to tooth section area. However, the sensitivity of amplitude demodulation method in misaligned contact is less in ideal contact.
  9. Keywords:
  10. Spur Gear ; Crack Detection ; Misalignment ; Three Dimentional Crack ; Meshing Stiffness

 Digital Object List

 Bookmark

No TOC