CTE Errors in CW?

[frankjconway]

Because I don't trust myself using FEA entirley yet, I try to do a few simple examples that I can hand calculate to compare results. I'm getting a problem with thermal expansion of a part.

I'm a newbie to CW and having trouble with a few things. If I go into the material properties of 6061, SW/CW lists a CTE of 2.4x10^-5/deg C.

Using that CTE (the same one that SW/CW uses) to do a hand calc for a 2" long piece and a 40 deg. C detla, I get an expansion of .00192 inches. The FEA model shows an expansion of .00215 inches.

Now ~.0002 doesn't seem like much, but its a 10% error. And I'm working with optics. I checked and the SW CTE value is constant over temperature.

Does anyone have any insight on this? Thanks in advance.

 

[frankjconway]

I now have insight! (Answering my own post). I was viewing the resultant displacement instead of the z-axis displacement! I changed to view the z-axis and the results agree perfectly with my hand-calculations. I knew there had to be something to it!

 

[gfbotha]

The fact that you first analyse some benchmark problems and also do some hand calcs by far compensate for the little oversight!

Regards!