Fiberglass Material Properties

I would call up a good marine archetect who designs boats in fiberglas and ask them.

Your question cannot be answered.

Fiberglass is not used alone; it is mixed with resin. The final properties depend on the fibers, the resin, and the skill of the person who laid up the sheet. If the glass layer is not wetted, it will have almost no strength at all. If there is too much or too little resin, the strength will be lowere than if applied correctly.

About all you can do is prepare a sample and break it. Then make sure that all following work is done to match the sample.

Absolutely right. No doubt about it at all.

This is how they all do it in prototyping or low volume production. Make a sample and test it.

I the high volume, mainly injected glass fibre or carbon fibre, they can control their environment so accurately that it is possible to predict and calculate.

All the rest of the industry works with experience (hey that dirty word again).

I agree with Harry. I've done some work with composites, and would have to say that one would be foolish to apply general mechanical properties to a particular layup that might be done in a different way than the test layup from which the general properties were obtained.

In hand layup, the resin ratio can vary fairly widely from one layup to another, so that one test coupon may be 50% resin and the next may be 70%. Thus the mechanical properties will vary accordingly (with the resin having very little strength compared to the fibers).

To highlight the differences, a carbon fiber pultrusion can be three times as stiff and strong as a careful hand layup. In the hand layup, the fibers are not equally straight, so all the load is accepted first by the straightest fibers which may break before the wavy fibers have much stress on them. Carbon fibers elongate by only 1.3 percent before breaking, so you can imagine that if some fibers take a path 5% longer than others, they never come into play before the straighter ones have failed.

Once you have a process down, you can get reasonably good estimates of finished properties, if you are using consistently skilled personnel. Fiber orientation, is, as you probably know, critical in determining properties -- in the most extreme case, there is unidirectional fabric, which has very high strength in line with the fibers, and essentially none perpendicular to the fibers.

You've really got to test, and as Harry said, then make sure that the following work matches the sample .

I would not think of fiberglass as rebar. Work has been done on that subject by Dr. John Murden at The Citadel in Charleston SC.