HW5 - SwiftCompt Comparison

1. 

   Imad Hanhan @ 4:20 pm on 25 Oct 2017

   Hello everyone,

   My elastic constants are very similar to the elastic constants I computed in SwiftComp. However, my CTEs are off by quite a bit:

   I calculated (based on both the stiffness derivation and the compliance derivation) a11=-0.013, and a22=a33=17.18. In SwiftComp I computed a11=a22=2.1 and a33=33.85.

   Anyone else ran into this in their calculations? Can anyone comment on why this might be happening?

   Thanks,
   Imad

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2. 

   Fei Tao @ 4:53 pm on 25 Oct 2017

   Hi Imad,

   You can double check whether have you transformed your CTEs in each layer to the global coordinate correctly. For example, for the bottom layer, the orientation is 45 degrees. Then you should transform it to the global coordinate with an angle -45 degrees. You should get exactly the same result with Swiftcomp. 

   Fei

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3. 

   Imad Hanhan @ 1:33 pm on 26 Oct 2017

   Hi Fei,

   Thanks for the advice, I have double checked my rotation matrices and rotations, they seem correct. Any other suggestions?

   Thanks,
   Imad

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4. 

   Fei Tao @ 2:01 pm on 26 Oct 2017

   You Swiftcomp result looks good. Have you checked the R_eplison you used?  Attached is the R_eplison I used to get alpha_e and alpha_t. 

   

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5. 

   Imad Hanhan @ 2:22 pm on 26 Oct 2017

   Thanks Fei, my mistake was that I used the rotation matrix you named R_epsilon_e_1 to rotate both alpha vectors. Using the different rotation matrix to rotate alpha_t, my script now works. Can you comment on the rotation matrix R_epsilon_e? Why do we rotate the two alpha vectors using different rotation matrices?

   Thanks again for your help.
   -Imad

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6. 

   Fei Tao @ 2:55 pm on 26 Oct 2017

   This is because of the matrix partition. In our case,  alpha_e =(alpha11 alpha 22 alpha 12); alpha_t =(alpha33 alpha 23 alpha 13). Therefore, when do the coordinate transformation, the corresponding rotation matrix are different.

   I have attached a picture to help you better understand it. 

   

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