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# Shear Modulus Estimation

## Shear Modulus Estimation

(OP)
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!

### RE: Shear Modulus Estimation

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.

### RE: Shear Modulus Estimation

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.

### RE: Shear Modulus Estimation

(OP)
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?

### RE: Shear Modulus Estimation

No, fabric is not isotropic.

### RE: Shear Modulus Estimation

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

### RE: Shear Modulus Estimation

(OP)
Compositepro, thanks! Yeah... I missed out Z direction...

### RE: Shear Modulus Estimation

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

### RE: Shear Modulus Estimation

(OP)
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

### RE: Shear Modulus Estimation

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

### RE: Shear Modulus Estimation

(OP)
@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?

### RE: Shear Modulus Estimation

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.

### RE: Shear Modulus Estimation

(OP)
@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.

### RE: Shear Modulus Estimation

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

### RE: Shear Modulus Estimation

(OP)
@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.

### RE: Shear Modulus Estimation

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.

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