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Different values of shear modulus

  1. Apr 8, 2016 #1
    After completing two experiments to find the shear modulus of a beam, I found two very different results. For test 1, we twisted the beam slowly at very small angles (0.005 - 0.03 rad), only in its elastic form. The torque was found using a torsiometer . In test two a replica of the beam was used and twisted till breaking point (1 - 1274 degrees). Here the results were found using a digital load meter. However the torque, even for lower angles was much less in test 2 than test 1, even though the same method of twisting was used. For the steel beam G was 106GPa in exp 1 and 60 in GPA. Would anyone know why there is such a difference.
     
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  3. Apr 8, 2016 #2

    SteamKing

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    Well, what kind of beam was used? What did the cross-section look like?

    It's really hard to comment on experimental results when you don't have access to the procedure or the data obtained from the experiment.
     
  4. Apr 8, 2016 #3
    The beam was a cylinder
     
  5. Apr 8, 2016 #4

    SteamKing

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    This is going to be like pulling teeth. o_O

    What was the diameter of the shaft?
    How long was it?
    Why did you test it to destruction?
    What was the material of the shaft?
    What torque was applied to the shaft?
    What happens to G once the elastic limit is exceeded?
    Why do you think you got such different results?
     
  6. Apr 8, 2016 #5
    Diameter was 6mm
    Length was 76mm
    I tested it to destruction as that was what was required
    It was steel
    Torque came from turning it in degrees, and a reading was given either by a torsiometer or a digital load meter
    Once the elastic limit is reached hooke's law no longer applies and thus G can not be determined.
    I'm not really sure of the last one which is why I asked the question
     
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