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Experimental and Numerical Study of Pulse Shaper Geometry Effects in Split Hopkinson Pressure Bar Test

Ashrafi Habib Abadi, Mohammad Javad | 2010

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 40234 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Naghdabadi, Reza; Sohrabpour, Saeed
  7. Abstract:
  8. Split Hopkinson pressure bar (SHPB) test is one of the tests used for characterizing the mechanical behavior of materials at high strain rates between and s -1. A SHPB test consists of a gas gun, a striker bar, an incident bar, a transmission bar and a specimen which is sandwiched between the incident and transmission bars. In order to achieve constant strain rate during the test which is necessary in SHPB test, the incident pulse should obey the stress-strain curve of the specimen. For shaping the incident pulse usually a thin deformable disk -called pulse shaper- is placed between the striker and incident bars. In this thesis, first we designed, implemented and calibrated the measuring system of SHPB test which consists of four strain gages, two amplifiers, an oscilloscope and a velocity meter. Also, we wrote a program for processing the signals measured by the strain gages. In this program after finding the start and end points of each signal, we perform dispersion correction and compute stress-strain curve from one dimensional wave propagation theory. Then, using the results of simulation in LS-DYNA and performing test with pulse shaper, we studied the parameters that affect the incident pulse. These parameters include pulse shaper thickness, pulse shaper diameter, striker length and striker velocity. Finally we tested copper and cast-iron specimens with and without pulse shaper to show the effect of pulse shaper on the results of Hopkinson test. The results show that the variation of strain rate during the test decreases with pulse shaper. For instance, using proper pulse shaper reduces the strain rate variation to in the test of copper specimens and to in the test of cast-iron specimens.

  9. Keywords:
  10. Wave Propagation ; High Strain Rate ; Signal Processing ; Pulse Shape ; Split Hopkinson Pressure Bar (SHPB)Test

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