# Silicon Anisotropic elasticity

Amin1372
Member
Posts:

**16**
in Structures

Hi,

Can anyone help me to read this table? it's for Silicon Anisotropic elasticity

## Comments

67Member140Forum CoordinatorHi Amin1372

What do you mean by read? Explain the tables values? If so please see the following:

ANSYS Help -> Mechanical APDL -> Material Reference -> Chapter 3.3 Anisotropic Elasticity

Bit too much in the help to copy/paste here.

Mike

118MemberHi Amin,

The 1.66E+05 is your elastic modulus

The 80000 is your shear modulus

the 64000 is related to poissons ratio, 64000/1.66e05=0.3855

Isotropic elasticity is a linear material model with a symmetric matrices. The D values can be read as x, y, z, xy, yz, xz. If you change the values for any one of these the element orientation becomes important as you are changing the stiffness for a given direction.

https://ansyshelp.ansys.com/Views/Secured/corp/v195/ans_mat/anel.html

67MemberHi Benjamin,

Thanks for your help. Well, if Silicon is Anisotropic material, why the elastic modulus in all directions of X, Y and Z are the same(1.66E+05)? and should the poisson's ratio be the same too?

Thanks

118MemberI actually do not know why the material is included with Anisotropic Elasticity as default. It may just be a handy exmaple of when/how to use it. It would be presumptive, and possibly risky, for ANSYS to include the Anisotropic property and then have a user implement it in a project without checking element orientations.

Even the wood material that has been included in Granta Design Sample Materials is included with linear elasticity.

It is better the user implement any anisotropic, or orthotropic, material properties and take responsibilty for understanding the matrix and applying element orientations.

For the material to be anisotropic, as you have mentioned, the elastic modulus and poissons ratio can be different for each axis.

15MemberHello Dear,

Did you find the solution? if yes please share with me. I am doing wood material simulations.

Thank you.

6MemberHi Benjamin,

I was just wondering if you could clarify how you calculated that poissons ratio? Just because I am not sure it is correct and therefore do not understand where the 64000 has come from. Any help appreciated!

Em

118MemberThe calculation is in my comment. Although something I am not entirely sure of is whether this value should be halved? Either way poissons ratio is the linear relationship between a load applied in a certain direction, and the strain experienced in a direction orthogonal to the direction of the load, which is what that calculation of 6400/1.66e5 is describing.

If it is not clear to you I would recommend starting with structural steel, setting up two definitions, one that uses isotropic definitions, and one that use anisotropic definitions, and applying a unit load to a cube, or prism of some nominal shape. Adjust the anisotropic values until you see correlation with the isotropic definition.

11,486Member@BenjaminStarling @g_empo @user8179 @Amin1372

I found a good reference for the Anisotropic properties of single crystal silicon.

https://sites.engineering.ucsb.edu/~sumita/courses/Courses/ME141B/HopcroftJMEMS.pdf