Hi everyone. I do need to replace a thick steel plate with a composites (Kevlar+Carbon) plate. I do not have the strength of the composite material, so how I could know the strenght of the composite (without testing) to get the equivalent thickness

Thanks in advance!

This is much more difficult, compared to the metal part. The strength of a composite part varies with the fibre content and orientation, as well as with the used fibres (there are different types of carbon and kevlar). Additionally you have to think about the fastening points, wich can easily become the weak point. So even a simple plate can be quite difficult to calculate.

The obvious question is why?

What is the application?

A thick steel plate sounds like it might be a structural component. And as you are willing to get the weight down, it will likely be under dynamic load. Under this circumstances I would advice against a crp construction. There are many steps to master (mechanics, dynamical mechanics, material sciences, material science of composites, as well as the practical side of composites), before you can really say you are ready for such projects.
A forum might not be the right place for such questions, as this isn't an easy question, and you might not be able to tell, if the "most pleasant answer" comes from a 20 year old, who just skinned his first automotive console, and caught up something like "carbon is 7 times stronger than steel" from television.

Intrigued now :-) What is the actual component you want to change?

I agree with oekmont, but it does depend what the application is. Your opinion of a ''thick" steel plate could be quite different to our opinion of a ''thick" steel plate. There's also every chance it doesn't need to be as thick or structural as it is, so it's possibly premature to just say forget about it without actually knowing what it is you're trying to replace. 

If its a race car floor pan, then that's certainly possible to build in composites and I'm certain there is enough knowledge on this forum to help you do it. If it's a bullet proof shield, then yeh... Forget about it.

The easy way:  Just copy the "Thick Steel Plate" in Grade 5 Titanium -- Done ... 40% lighter --  The work that would go into working out a composite replacement would probably be more expensive that buying the Titanium plate in China .. And contrary to popular beliefs Titanium is not that hard to machine -- as a bonus you will get extreme corrosion resistance, and if its purpose is to stop bullets, Titanium is much stronger than ordinary steel. You will need specially hardened and tempered steel to match the extreme toughness of Titanium.

https://www.youtube.com/watch?v=FeVTZlNQfPA




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