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?