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Investigation of Deformation Behavior and Stress Relaxation of Helical Springs

Soltani, Hossein | 2013

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 44718 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Karimi Taheri, Ali
  7. Abstract:
  8. Springs parts are widely used in many industries including the automative industries where the disability of the springs can cause damage. Spring forming processes induce residual stresses on the surface of spring. Residual stress is affected by various processes, such as heat treatment or shot peening. When a coiled spring is heat treated, depending on the temperature and time of heat treatment residual stresses are partially relieved, but they generally do not disappear.An important characteristic of spring steel is its resistance against stress relaxation at different temperatures and times. Stress relaxation in valve springs working at high temperatures causes some problems for internal-combustion engines. Few results on fatigue behavior and stress relaxation of helical springs are available in the literature, but there are very few results on the effect of heat treatment on fatigue properties and stress relaxation of springs. In this study, the effect of initial stress relieving on the loss of operation force of peugeot 206 car valve springs made from Cr-Si steel after coiling and shot peening is investigated. Also,the effect of initial stress and test temperature on the stress relaxation was dealt with separately. The springs after stress relieving at different times and temperatures, were grinded and shot peened and then experiements were conducted in static and dynamic stress relaxation tests. It was found that by Stress relieving process in temperature range from 370-410°C and 15 to 30 minutes duration, stress ralaxation is decreased to a minimum due to the continuous carbide films formation. By using Design Expert Software there lationships predict the percent drop in performance force and the percent drop of spring length regarding temperature and time of stress relieving were developed. The results showed that increasing test temperature and initial stress accelerate the stress relaxation percentage, more over with increasing the time of test the stress relaxation rate is reduced
  9. Keywords:
  10. Compression Helical Springs ; Operation Force Percentage Loss ; Free Length of Spring Percentage Loss ; Peugeot 206 Car Value Spring ; Stress Relaxation

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