Anisotropic Properties

General Composites Discussions Engineering Talk
#1

Hello,

How to get the anisotropic properties ,(D1111, D1112, D2222 … etc) which are 21 engineering constants , for composite laminate.

are these the elements of ABD matrix???

#2

Hi,

first post here.

I’ve looked into this for my ongoing project that requires me to input the engineering constants of the material on ANSYS. Engineering constants, stiffness matrices… oh boy, there is a lot that can be said!

  • First of all, that matrix you are referring to is the stiffness matrix which is not the same as the ABD matrix. The ABD matrix is derived from the Q matrix, which is a simplification of the stiffness matrix to the plane stress condition of each lamina.

  • Now, if you can live with the plane stress condition and uni-directional lamina, you can use the reduced stiffness matrix Q. In this case, you have 4 independent constants you need to calculate E1, E2, v12 and G12. More information here:
    http://info.firehole.com/blog/bid/265319/Composite-Engineer-s-Pinboard-Reduced-Stiffness-Matrix-Q-Matrix

  • If you need more than the Q matrix, the next step is to treat your lamina using the transverse isotropic formulation, which is a special case of orthotropic material. This means that the material has isotropic behavior in the place normal to the fiber direction. The stiffness matrix, let’s just call it K, is 6x6 and has 6 independent engineering constants E1, E2, v12, v23, G12 and G23. For more on the transverse isotropic stiffness matrix:
    http://www.efunda.com/formulae/solid_mechanics/mat_mechanics/hooke_iso_transverse.cfm

  • If you can’t treat the material as transverse isotropic, then you can use the orthotropic stiffness matrix. The only difference now is that E2 is not equal to E3, v12 is not equal to v13 and G12 is not equal to G13. You can figure it out. More info:
    http://www.efunda.com/formulae/solid_mechanics/mat_mechanics/hooke_orthotropic.cfm

The anisotropic stiffness matrix (full 21 constants) is not needed to define the behavior of a UD lamina.

To calculate the mechanical constants necessary to assemble the stiffness matrix, you have to resort to the rule of mixtures, the Halpin-Tsai semi-empirical model and sometimes… witchcraft :stuck_out_tongue:
I usually follow the rules described by the NASTRAN documentation:
http://www.mscsoftware.com/training_videos/patran/Reverb_help/index.html#page/Functional%2520Assignments/materials_forms.5.6.html

I hope this post helped you!

#3

many thanks for your reply… it has surely helped