My father and I are arguing about which would be stiffer.
We’re only talking about stiffness.
.75" foam core with two layers of carbon on the ouside or
3x .25" foam core with one layer of carbon on each side.
Thanks
hey look at that first post! hah well I’ve been reading in the background for quite sometime.
Stiffness comes from thickness. In this case thickness is about the same.
In that case bring your fibers more outside, and you are stiffer.
In which case the one with 2x carbon on the outside is thicker.
they would be the same thickness
C C core C C
vs
C core C core C core C
Joeu3,
There are some VERY experienced composite tech’s here in this forum that have probably done side by side comparisons of your exact question. Although I have never done a side by side… I will say that at a composite department that I used to work they would stack core regularly in some of their more complex pieces.
I will be watching this thread to see what others say, and I may very well be wrong in this… but from some past experiences, my last engineers stacked cores in their layup schedules.
This is an interesting question that I never through to ask… thank you for bringing it up!
-C
CC core core CC is thinner than C core C core C core C
The CC nests better. I must admit that it is only marginal.
There can be good reasons for getting fabrics between cores. For instance when using Soric in stacked configurations, or when infusing the whole lot at once.
If the total thickness of the panel is the same then C C core C C will be stiffer and stronger in a bending load. The center carbon layers in the second option (C core C core C core C) will undergo much less stress in a bending load than the outer carbon. As the panel bends the fibers toward the outside of the bend undergo tension while those toward the inside of the bend undergo compression. The outer layers have to stretch and compress further/more than the layers nearer to the center. The outer layers will reach their elastic limit before the inner layers begin to take on much stress. If you put more layers of carbon on the outside of the panel there are more fibers that will resist being stretched and compressed. This makes the panel stiffer and stronger in a bending load. Also, the fibers in thin walled sandwiches that are under compression are very prone to buckling before the fibers under tension fail. Increasing the skin thickness with more than one layer of carbon will increase the flexural stiffness of the skin. This reduces it’s propensity buckle while under compression. This will typically increase the bending strength of the sandwich.
No need to EVER test this.
This is a fairly common engineering stiffness problem,
wyowindworks is 100% correct with a great physical explanation
You can actually calculate the difference quite easily. If you’re interested, Look into bending stiffness and geometric moment of intertia. This is KEY to understand when designing and building lightweight composites . You’ll find the difference is quite significant. As an exteme, adding carbon to the middle of a sandwich does almost nothing for strength or stiffness in bending.
Moved to Engineering Talk due to content.
I use the attached diagram I drew to teach students the basics of why a core is stiffer. This is numerically what wyowindworks was saying, so increasing the distance between the skins and increasing skin thickness makes the panel stiffer,
WyoWind,
I’m so glad you answered! I really should have questioned the engineers of past employers in more ways than one… fail.
-C