Carbon Fiber Fabrics 3k-135-8h 1

[Donovan88]

Hi

I am trying to predict the tensile strength of carbon fiber and glass fiber laminates. I will use the laminate theory and the maximun strength failure theory.

Since this is the first time that I will be working with fiber reinforced composites in my country, El Salvador, I am having a hard time in understanding fabrics.

I will use micromechanics to determine the mechanical properties of the laminae, then, using laminate theory, the generalized hooke's law for orthotropic material and the maximun stress failure theory, I will obtain the required uniaxial tensile stress that causes the first ply failure.

Can someone advice me on the subject. My primary reference has been "introduction to composite materials" Stephen Tsai Thomas Hahn.

In most of the books i have found, the laminate theory is explained for unidirectional, orthotropic materials. Does fabrics behave like orthotropic materials?

Where can i find the mechanical properties of a fabric (warp and fill)?

I will use 3k-135-8h carbon fiber and 7781-3800-f3 glass fiber.

Thanks

 

[cpinz]

...."Can someone advice me on the subject."...

"Simple" request for a (very) difficult answer in one or more posts..!

Just to start ...look at NASA Reference Publication 1351 titled " Basic mechanics of laminated composite plates"; you find it on internet.

Hope it will be useful.

Cpinz

 

[RPstress]

RP 1351 won't tell you much different from Tsai/Hanh, but it is a good compact summary, though it seems to have a couple of errors in it (eqns. 21 and 83; 83 seems to be a printing formatting issue, 21 says [Qbar]=[T]^-1[Q][R][T] and should probably be [T]^-1[Q][R][T][R]^-1). It has a minorly interesting alternative to fully inverting the laminate stiffness matrix (it uses determinates).

With regard to your basic question about 'is woven material orthotropic?,' yes. The 1 direction properties are very similar to the 2 direction, but other than that fabrics are very similar to unidirection (tape) materials and all the usual orthotropic issues apply. The 1 direction and 2 direction similarity actually makes things a bit simpler.

Others may advise you that using classical laminate theory (CLT) as you describe is likely to be wrong for predicting strength. This is good advice, but it may be that it's all you've got. CLT is often conservative for failure theories such as Tsai-Wu, especially when woven material is used. However, max strain can be problematic. Be very careful when multidirectional stresses are present; maximum strain works ok for carbon and unidirectional stress where the woven plies are failing the fibres in tension or compression, but if any plies are predicted to fail in matrix shear rather than fibres things are more complex, and glass is a little more awkward where the flexible fibres allow strains more damaging to the resin matrix. You don't mention your industry or anything about the part; try to make sure that a good deal of testing is done.

 

[cpinz]

RPstress,

much appreciated your pointing out the errors of document.

Thank you.