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An Investigation Into Residual Stresses Formed by Bending and Quenching Processes

Ja’afari Bahramabadi, Mohammad | 2011

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 42103 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Karimi Taheri, Ali
  7. Abstract:
  8. Various forms of springs are applicable, among which spiral and leaf springs can be named. Definition of leaf springs is conventionally applied to constant-width springs and is consisted of step-like leaves, each leaf having constant width. Leaf springs are largely used in vehicles, where they act as a part of suspension system supporting the weight of the vehicle along with connecting spots axles to the chassis. Springs so installed are capable of handling starting and stopping torques as well as sudden vibrations due to load carrying. Most Conventional method of manufacturing leaf springs is to bend strips of appropriate steel between curved dies, quench the strip while held between the dies and release of the dies. One of the outcomes of this process is the change in mechanical properties due to formation of mechanical and thermal residual stresses. A wide variety of investigations have been devoted to prediction and determination of residual stresses. In present work, a number of leaf springs of 51CrV4 spring steel and 316L stainless steel were produced using the aforementioned method. Then, commercial finite element software, ABAQUS, was utilized to more precisely study the involved parameters. It was found that initial temperature, part width and frictional conditions play a paramount role among other parameters in residual stresses distribution. Increasing temperature will result in an increase of tensile and compressive residual stresses, as well as causing a larger fraction of the part being affected by tensile residual stresses. A similar trend was observed for variation of the part width. It was also illustrated that equivalent plastic strain will be reduced if friction factor between dies and part is raised. This, in the first place, can lead to the reduction of tensile and compressive residual stresses. Ignoring the effect of phase transformation associated with 316L by ABAQUS caused the effect of heat transfer coefficient on residual stresses to be negligible
  9. Keywords:
  10. Residual Stress ; Variable Stiffness Spring ; Finite Element Model ; Hot Deformation ; Quenching

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