I am trying to determine the natural frequency of different sets of woven fabric composites made from carbon fabrics. I am wondering if we can use the same relation (fn = C*sqrt(E*I/w*L^4) to calculate the natural frequency of woven fabric composites that is used for isotropic materials.
Further, do the constant values of C for modes remain the same for woven fabric composites. I mean, for fixed free conditions, C1 = 0.559, C2 = 3.5, C3 = 9.81, and so on. Does this pattern apply to the polymer composites or not? In literature, I found some papers where the modes match and in some they don't.
I guess woven fabric composites have a lower symmetry, like orthotropic or cubic as you imply. In this case, I don't think this equation hold in general. The question is how the longitudinal motion is coupled shear.
Dear Khizar,
I used finite element modal analysis to find natural frequencis of such orthotropic materials. I think the isotropic equation cannot be accurate for your purpose. Please check ANSYS and ABAQUS help.
At the very minimum, you need to use an effective bending stiffness for the homogenized composite. There is an example of calculation for the natural frequency of a composite shaft, in chapter 8 of Introduction to Design and Analysis with Advanced Composite Materials, by S. R. Swanson, Prentice- Hall, 1997.
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