How to choose a replacement cloth

[phoenix221]

Hi all,

I have a challenge to reduce the overall weight of a sandwich construction using E-Glass (style 7725 9 oz. BID). I will use vacum-bagging to ensure little or no excess resin in the layup. Also, in order to keep the costs down, I was contemplating using S-Glass instead of the E-Glass.

Given that S-Glass is generally thought to be 20% stronger and somewhat stiffer than E-Glass, is it reasonable to assume that I can use as a replacement S-Glass that is say 7-8 oz., while keeping the same layup schedule, without compromising the mechanical properties of the resulting sandwich composite?

I understand that the mechanical properties of the S-Glass cloth would have to match that of the original E-Glass cloth, however what I am trying to get at is if the weight of the cloth has some impact on mechanical properties that is not apparently obvious by just looking at the numbers?

Any help is appreciated.

Thanks.

 

[EdCollinson]

Hi Phoenix,

Your assumption that S-glass is significantly stronger than E-glass is correct (the AGY website can give you actual values). It is however, much more expensive than E-glass and you will need to factor this into your calculations. As a guide, the S-glass fabric we use is approx 6 times more expensive than the E-glass equivalent (this is for fabric not a pre-preg).

Best regards,

Ed

 

[phoenix221]

Yep... I knew the price difference can be substantial... depending on the cloth as well... I am not so much concerned with price at this point... weight reduction is my main focus...

Thanks,

 

[amorrison]

Somewhere i read that bidirectional does not "pack" as well as unidirectional.
If you use uni the increased glass density will require less resin =less weight?
Also if your object has a lot of "height" while curing the stack effect of the liquid resin will produce a "bulge" at the bottom of the vacuum "bag" =more resin to fiber ratio than at the "top" of the vacuum bag.

 

[Compositepro]

Thinner skins buckle more easily than thicker skins. So, yes, the change you are proposing could have significant effects on strength and stiffness that are not immediately obvious.

 

[NCSUMAN]

I thought you wanted to keep the cost down? S-glass may be double, but I don't think 6 times the price. But either way you are adding costs.

Anyway, decreasing thickness will decrease your section and make for a less stiff sandwich, all other things being equal. Strength should be the same. Buckling may come into play depending on skin thickness and loading.

You may decrease impact performance and damage tolerance slightly if you are dramatically reducing skin thickness. Although the change to S-glass may offset. If this is a concern, you should verify through experimentation.