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  • Calculations using Tensile test data on a hybrid composite laminate

    Discussion in 'Calculations' started by AlexSch, Aug 7, 2013.

    1. AlexSch

      AlexSch New Member

      Jun 2013
      Likes Received:
      I am busy doing research on the properties of a certain Carbon Glass laminate.

      I am tasked now with finding the interlaminar stresses in the sample. To do that, I have conducted a tensile test using a load cell and strain gauges.

      The data that I have is as follows:

      Strain Longitudinal - e1
      Strain Transverse - e2
      Force longitudinal - F
      Cross sectional Area - A

      Ok... my problem is how to go about this:

      Consider this matrix:


      -v12/E1 and -v21/E2 are interchangeable due to the relation:

      v12/E1 = v21/E2

      so I can then get the formulas:

      e1 = s1/E1 - s2v12/E1
      e2 = s2/E2 - s1v21/E2

      (s1 = Sigma 1 and s2 = Sigma 2)

      v12 is easy to find, -(e2/e1) = v12
      s1 = F/A

      Now the issue. If I calculate the elastic modulus (E1) from s1/e1, then I cannot substitute it into:
      e1 = s1/E1 - s2v12/E1

      reason being that e1 = s1/E1, so you will have a value that is equal to itself minus something, which is invalid. So the question is, if F is the force reading from the load cell and e1 and e2 are the readings from the strain gauges, would it be correct to say that:
      E1 = s1/e1 ???

      Or should I calculate E1 from the formula:
      e1 = s1/E1 - s2v12/E1

      as this is a bidirectional analysis and not unidirectional. It is also an orthotropic material, which means that E1 will not equal E2.

      At present I have 3 equations and 4 unknowns.

      e1 = s1/E1 - s2v12/E1
      e2 = s2/E2 - s1v21/E2
      v12/E1 = v21/E2

      so either I need to find a fourth equation or if I calculate E1 directly from the test data, how will I substitute is correctly?

      Am I making any sense at all? ;)

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