Thanks TET, Riff, that’s the kind of basic info amateurs like me appreciate!
It’s a good topic. Something not many people take into account.
does prepreg also bow?
pre-preg is only fabric with the matrix in it already. After all is said and done, it’s the same as VARTM, or wet layup with a bag.
epoxy pre-preg might not have a clean and perfect surface though. but I think that can be fixed with processes.
How much does storage effect bowing of composite panels?
Also how much does the core thickness account for twist?
I have a few 3/4 divinycell epoxy and biax panels that I made to rebuild a xxxxpit in a boat that have been stood up on edge flat against a wall. Some of them have a twist, others don’t…
I put the mat side towards the foam and laid up both sides at the same time.
3/4 Coosa board done the same way went wild after I glassed it, though it was almost 8 feet wide and a giant semi-circle.
Cheers,
Zach
flat panels are always a pain in the arse. Sometimes the only difference is how fast one side heats up and cools down faster (prepreg, hot infusions, etc), or your fabric is NOT balanced in the warp/weft directions, and you mess up which way the fabric is cut. Balanced laminate is VERY important, in both direction, and material.
All of mine are mat side down 45/45 biaxial cloth, 1708 single layer on each side.
By balanced, would I need to turn the cloth 180 degrees on the back side, even though it is a 45/45?
Thanks
Zach
so if your current stack is: 1708, mat/45, mat/45, 1708, you need to change it to: 1708, mat/45, 45/mat, 1708
There is a “mid-plane” where the middle of your panel has to mirror.
ie: 0, 90, 0, 90, | 90, 0, 90, 0
pretend the mid-plane ( the |) there is a mirror. When you have one side, do the opposite after that.
Now, when making complex parts, it’s not always needed. Some areas might have more layer than others. But for flat panels, you need to be symmetric.
YES!
I use a lot of thin unbalanced laminates, and they all bow.
And with the system I use, there is a light layer of glass on top of the weave, to prevent pinholes. Did some tests on it, glass crimps a lot more than the CF, so the higher the cure temperature, the more the panel wil bend.
My Panels are 1708, foam, 1708.
Both 1708’s are placed mat side down.