Originally Posted by
BananaTugger
The Modulus of Elasticity (I'll just call it modulus), is how much the material stretches when stressed. This value is directly related to how stiff the material is. A high modulus material like Toray's M40 carbon fiber is very elastic and resilient compared to Toray's M30S carbon fiber, which is much stiffer and stronger in tension and torsion. Because the M30S fibers are stiffer, they are more likely to break when they are stressed to much. The M40 fibers will continue to stretch while not breaking when they reach their threshold. It is possible to deform high modulus fibres however.
1) M40 has a higher modulus than M30S -
http://www.toraycfa.com/pdfs/Torayca...yDataSheet.pdf
2) You say that M30S is "much stiffer and stronger in tension and torsion". Incorrect. M30S is less stiff, but stronger (see above). It is meaningless to say that it is stronger in torsion; the individual fibers are not stressed in torsion.
3) "Because the M30S fibers are stiffer, they are more likely to break when they are stressed to much." This is incorrect. All carbon fibers are brittle. They do not have any meaningful plastic deformation.
4) "The M40 fibers will continue to stretch while not breaking when they reach their threshold. It is possible to deform high modulus fibres however." I am not sure what you mean by "their threshold"; it seems you are getting confused with the behavior of metallic structures (yield and plasticity). Carbon fibers do not plastically deform; they break when their threshold (ultimate strength) is exceeded.