I am modelling a 3-D corrugated sheet as orthotropic plate 2-D shell element in APDL. For orthotropic model, I am using two constitutive models for bending and memberane properties. I am getting material inputs as Ex, Ey, Gxy Vxy and Vyx from the constitutive model, that I am assigning in the ANSYS model.
Further doing analysis in APDL, it is showing that your tangent matrix is coming out negative and you have to assign properties of Ez, Gyz and Gzx greater than zero.
How could I assign these values in APDL, if Iam not getting it from material model? Are there any constitutive model that provides these additional material inputs?
Currently what are you giving as inputs to Ez, Gyz and Gzx?
You need all the 9 material constants since you're working with a linear orthotropic material.
Of course, since you're concerned with your composite as a membrane, through the thickness properties would not impact the calculations severely. Just go ahead and feed in some random, but reasonable values. Experiment with a couple of them to see if they indeed aren't that important to the solution of the problem.
If you do not know those constants, then you should try to determine them from some sort of mathematical modeling of your composite. Or you could use something like the weighted rule of mixtures to estimate your orthotropic properties. This would be the simplest way forward.
If you want even better correlation to real life, you could go ahead with some sort of a second order model where in order to get all the elastic constants, you could use data pertaining to fibre fraction, fiber distributions and fiber, matrix properties to get a theoretical estimate.
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