Shear Modulus Estimation

[sarclee]

Hi, I would like to work out the shear modulus based on the test data given by supplier before placing order.

Is it reasonable to use the shear modulus formula G = E/ 2(1+V) for estimating shear modulus?

Thank you!

 

[Compositepro]

That only works for a homogeneous material. Composite properties are different in each direction. My answer is based on simple logic, not specific knowledge of the equations.

 

[SWComposites]

No, that formula is only valid for isotopic materials.

In-plane shear modulus for most carbon/epoxy materials is ~ 0.6 Msi at RTA. See CMH-17 Volume 2.

 

[sarclee]

Thanks to both CompositePro and SW Composites!

Even if it is fabric which the properties in fill and warp directions are about the same, we also cannot assume it is isotropic materials to use the shear modulus formula?

 

[SWComposites]

No, fabric is not isotropic.

 

[Compositepro]

Isotropic means same in x, y, and z directions.

 

[sarclee]

Compositepro, thanks! Yeah... I missed out Z direction...

 

[SWComposites]

Fabric is not isotropic in the x-y in-plane directions also

 

[sarclee]

In some of my limited experience, I often see E1 = E2 (at least close to) for fabric prepreg.

For the properties in thickness direction, we assume transverse isotropic but the table below shows that E3 /= E2 ... Should I assume E3 = E2 based on the assumption of transverse isotropic?

Courtesy: Design, Manufacturing and Applications of Composites: Proceedings of the Ninth Joint Canada-Japan Workshop on Composites; Kyoto Institute of Technology, Kyoto, Japan July 2012

 

[SWComposites]

For UD tape, E3 =~ E2
For fabric, E3 is not = E2 (much lower; use E2 for tape with same resin)

 

[sarclee]

@SWComposites, is it transverse isotropic not applied to fabric?

From '10.2.4.1 3-D lamina property determination' in MIL-HDBK-17-3F, I do notice the material properties given are unidirectional for illustrating the transverse isotropy.

I only have 2D data for running FEA. Is there any assumption we can make if no experimental data available?

 

[SWComposites]

Why do you need 3D properties? Why not just model with shell elements with 2D properties?

Post the specific material you are using and the property values you have.

 

[sarclee]

@SWComposites,

I usually use 2D properties with pcomp in nastran but I am now using ansys which no 2d orthotropic material card.

I only have the table below from Toray website.

 

[SWComposites]

What is the specific Toray material? Fiber and resin? Tape or fabric? The above values are for a tape.

 

[sarclee]

We are looking at T800H but still checking with vendor if the panel is fabric or tape.


Datasheet:

https://www.toraycma.com/wp-content/uploads/T800H-Technical-Data-Sheet-1.pdf.pdf

Related thread:

https://www.eng-tips.com/viewthread.cfm?qid=495675

*I should have created one thread for all the questions... hmmm

 

[SWComposites]

See page 3 here for tape and fabric properties

https://www.toraycma.com/wp-content/uploads/3900-PREPREG-SYSTEM.pdf.

Kind of hard to do an analysis if you don’t know what the material is.

 

[sarclee]

@SWComposites, thanks for the link. I did come across the spec you shared. Based on the spec, I suspect T800H is for fabric as the properties seems like fabric properties.

 

[tstanley320]

If it is a fabric, why don't you model a unit cell of the fabric using the properties of the individual fibers and matrix using micromechanics? That way you can load the unit cell to find the tensile properties, the poisson's ratio and the shear in the plane of the fabric. It has worked well for me.