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Study of Mechanical Properties of Polypropylene in Local and Global Scales: Effect of Crystalline Structure and Testing Conditions

Lesan-Khosh Monfared, Rasool | 2011

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 41833 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Bagheri, Reza; Asgari, Sirous; Naimi Jmal, Mohammad Reza
  7. Abstract:
  8. In this study, mechanical properties of neat isotactic polypropylene (iPP) were evaluated on local and global scales. Depth-sensing indentation with nanoscale resolution (nanoindentation) and traditional macromechanical tests were incorporated for this purpose at different temperatures and strain rates. Various morphologies and crystalline structures of iPP was obtained via changing processing conditions in melt state. A certain relation was found between the local and global mechanical properties, i. e. yield stress, modulus of elasticity and hardness. Moreover, developed yield models were evaluated on the local scale. The results showed that while crystal plasticity theory is not valid for yield prediction of iPP on local scale, lamellar cluster model is appropriate for both local and global scales. However, Johnson’s model was valid only for local measurements. In addition, a new modified model was developed for yield stress prediction of semicrystalline polymers on local scale. The relation between bulk and surface (hardness and scratch resistance) mechanical properties of iPP was also investigated. It was found that the scratch rsistance of polypropylene was only affected by mechanical properties of a specific layer beneath skin layer in injection molded samples
  9. Keywords:
  10. Nanoindentation ; Yield Stress ; Scratch Rsistance ; Polypropylene

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