Hi, I have been reading some about symmetry and I have a couple of questions that I hope you can answer.

1: when a layup is written +45/-45 why do you go about having minus and plus. Is that only applicable when using unidirectional fibers ? Or is it applicable when using a twill 2x2 as well (If yes, then why)? 

2. I have read that if you are doing a flat panel then symmetry can be important to mitigate warping. How are you thinking about symmetry of your layup ? For exempel when doing complex shapes ? I are you always striving for it in any layup ?

3. When doing flat parts with core I have read that it might be good to have more layers on the side of the core that will bend. If doing that won’t you disrupt the symmetry when the is core is counted as midplane ?

4. Does a two layer layup of 0/45 count as symetrical when there is no mid plane?

Thank you, 

Generally rotating layers isn't done to avoid a warp but to get more balanced mechanical properties by become a quasi-isotropic layup. Specifically on most flat panels, adding sheets at +- 45 improves torsional stiffness.  

A 400g is approximately 2 x 200g in general use.

There aren't any specific books I can recommend as a lot of this gets covered in various composites modules at colleges etc but there are a few books out there that may help.  Also watch videos on our site as some explain fabric basics etc. Composites Learning Area

Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant