>>>As an example, take a laminate of 50% carbon and 50% Eglass. the modulus of "standard" T-700 type carbon is 33 million. and the glass is about 1/3 of that. In other words, the glass will stretch about 3 times as much before it fails. So if you pull a rope made of the stuff to where the carbon strarts braeaking, the glass has only contributed 1/3 of its ultimate to the rope. It may add a lot of toughness thoug so there are potentially synergistic effects but you need to test it.<<<
The elastic modulus, or Young's Modulus, to which you are referring has no relation to breaking strength what so ever. It is simply the ratio of stress to strain for a given material and only tells us how "stiff" the product is. Also, the typical values given in reference tables apply only below the proportional limit for the material.
In the 50%/50% laminate you describe, the Carbon would experience 3 times the stress of the glass at any strain up to it's proportional limit (normaly the beginning of failure). If you pull a rope made of the stuff to where the carbon strarts breaking, the rope will quickly fail unless you have found an e-glass with more than 4/3's the ultimate strength of carbon. The glass will add virtually no toughness. Its main contribution to the rope will be increased weight. (I haven't looked it up, so I am assuming that the elastic strain limit of e-glass is at equal or greater than that of carbon otherwise the glass breaks first)
Conversely, if you made a laminate of mild steel and e-glass and applied the same physical loading, the glass would break long before the steel. Although steel has a much higher modulus than e-glass, its elastic strain range is also greater. Steel is also much more ductile and hence vastly tougher than e-glass, so the failure of the e-glass portion of the rope would not result in instant failure of the steel.
Moral: when mixing materials of significantly different moduli in simple tension and compression applications, the contribution of the lower modulus material to the strength of the part will usually be negligable. BE CAREFUL!
Rob