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Analytical and Numerical Investigation of Stress Wave Propagation in Split Hopkinson Pressure Bar for Studying Viscoelastic Behavior of Polymers at High Strain Rates

Moghaddam, Fazel | 2012

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 43522 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Naghdabadi, Reza; Sohrabpour, Saeed
  7. Abstract:
  8. Studying the behavior of materials at high strain rate is necessary for design and analysis of structures subjected to impact loading. Therefore, design and construction of apparatuses that enable us for testing various materials under impact loading is very important. The split Hopkinson pressure bar test -one of the most important impact tests- is utilized for dynamic loading at constant strain rates ranging from 100 to 10000 1/s.
    In this thesis, first we explain about the behavior of materials at high strain rates and then focus on the behavior of polymers -that are widely used in different industries- under impact loading. Also, basic concepts of polymeric Hopkinson pressure bar and important cares for the design of the apparatus will be presented. To better understand dynamic behavior of soft materials and wave propagation through them a spectral analysis is used. In order to analyze the wave signals easily, the waves are transformed from time domain to frequency domain. The waves dispersion and attenuation effects can be considered in this method, which is difficult in time domain. Also, the experimental method was used to determine the propagation coefficient.
    In this project, the design and construction of a polymeric split Hopkinson pressure bar for studying viscoelastic behavior of polymers and rubbers was accomplished successfully. The experiments were conducted on samples of polyurethane and Teflon at different strain rates. In the Hopkinson tests of polyurethane specimens at strain value of 0.5 and the strain rates of 1460, 1810 and 3000 1/s, the stress values of 4.3, 5.1 and 9.8 MPa was measured, respectively. Also, for Teflon specimens at strain 0.5 and the strain rates of 460 to 1250 and 2430 1/s, the stress values of 10.9, 17.9 and 26.7 MPa was measured, respectively. Therefore, for polyurethane with increasing strain rates by 1.24 and 2.05 times, stresses increases by 1.35 and 2.28 times, respectively and for Teflon with increasing strain rates by 2.7 and 5.3 times, stresses increases by 1.64 and 2.45 times, respectively. According to the results, it’s observed that at the same value of strain, strain rate sensitivity of polyurethane is greater than Teflon.
  9. Keywords:
  10. Stress Wave ; High Strain Rate ; Stress-Strain Behavior ; Polymers ; Viscoelastic Behavior ; Split Hopkinson Pressure Bar (SHPB)Test

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