Relationship of density and laminate modulus

[sgdon]

Dear all

Given a laminate of areal density 50 oz/yard sq and a 25 GPa modulus in the fibre direction, can i extrapolate the results to obtain the modulus of a laminate with 25 oz/yard sq density? Assume the 2 laminates have the same fibre volume fraction. Any crude estimates will also be appreciated.

Regards
sgdon

 

[Gerrd]

if i understand your question correctlly then the answers yes.

so long as the fibres are the same,
the weave is the same,
the matix, the curing and handeling then yes the modulus will be the same.

the flexural stiffness will of caurse change with the secondmonent of area.

if however what you are talking about is a change fabric to a lighter finer weave, then tecknicaly you will get some difference. the basice factor which will change is the crimp angel caused by the weave, (if its woven?).

in essence though you will be hard presed to spot the difference in a real structure.


to sumises, if all the variables stay the same, the modulus will remain the same as it is a fundimental propertie of the material that is indipendent dimensions.

please excuse the spellings

hope its usfull, and please come back if it needs clarification

 

[sgdon]

Dear Gerrd

Thank you so much for your response. Maybe i do not really understand the definition of areal density. Is it a measure of the amount of fibres in a given area of the density? What is the difference between areal density and fibre volume fraction then?

If assume that the fibre is indeed more finer (25 oz/yard2) comepared to 50 oz/yard2 (with modulus 25 GPa), can i crudely estimate the modulus of the 25 oz/yard2 laminate be 12.5 GPa? I refer here the modulus as tensile modulus basically. How can i estimate the change in flexural modulus then?

Regards
sgdon

 

[Gerrd]

ok, no worries

yongs modulus of elasticity (E) is inherent to the material
it will not change - for carbon it is in the regon of E=240GN/m2
this is a constant for the "fibbre"

if you have half the numbers of fibbres then the stress (load/Area) will double as the area is now smaller for a given load.


as for areal density, i beleave its the same as areal weight, however your working in an american system where as i'm useing S.I unites. not sure these though
The unites are Grams per square meter. which is a system used in fabrics and paper. there are formulars to give you what you want though.

i sergest you look up the basic "rules of mixtures" which are used to determin properties of composites.
these are relationships between volume fraction areal weight, modulus, thickness and other stuff, dead simple and easy to use.

if you cant find them i'll wright them out and put them on here some where.

happy hunting

 

[sgdon]

Dear Gerrd,

I agree with you E is a material property of fibre and matrix and would not change (disregard the effects such as strain rate of course). But the modulus i concern here is to the laminate, which you have also referred me to the rule of mixture. So the question is does the areal density affects this laminate modulus. I had tried to look up books on mechanics of composite where they mainly discuss with fibre volume fraction rather than fibre areal density of the laminate. It seems to me there must changes but im not sure though. If there is a relationship between areal density and fibre volume fraction, then i would be more confident in adjusting the modulus for it.

Thanks for your valuable inputs again.

sgdon

 

[abygupt]

The modulus of laminate will not change with changing the density, because
Ec = Ef*Vf+Em*Vm

So, for the same matrix, fiber and volume fraction of fiber, modulus will not change even by changing density.

 

[sgdon]

Thanks Abygupt. Can you explain further on why the modulus would not change. My thought is that volume fibre fraction is a measure of the amount of fibre in a unit volume of composite. Assuming i interpreted it correctly, the areal density is another measure of the amount of fibre in a unit area of composite. So if we consider unit thicknesses, are not both directly related?

Regards
sgdon