## Need Opinion on Stress Analysis Procedure for Interior Monument Honeycomb Laminates

## Need Opinion on Stress Analysis Procedure for Interior Monument Honeycomb Laminates

(OP)

Hello,

In some of my previous aircraft interior monuments analysis which are constructed from Nomex or similar Honeycomb Laminates, I've modeled the laminates using smeared or equivalent PSHELL formulation (Ref: FEMCI NASA document). So Nastran will spit out stress values for the entire laminate instead of each individual layer if I had defined laminate using PCOMP/PSHELL formulation. I've used Panel long beam bending allowables obtained from long bending test to check against the Von Mises output from FE for the laminate. Similarly, one can extract the shear running forces from Nastran and convert them to shear stresses and compare against short beam shear allowables which are for core shear failures. Is the procedure is accurate? If no, can a more accurate method of check be suggested i..e how to use panel allowables from long beam & short beam test against FE results? Thanks

In some of my previous aircraft interior monuments analysis which are constructed from Nomex or similar Honeycomb Laminates, I've modeled the laminates using smeared or equivalent PSHELL formulation (Ref: FEMCI NASA document). So Nastran will spit out stress values for the entire laminate instead of each individual layer if I had defined laminate using PCOMP/PSHELL formulation. I've used Panel long beam bending allowables obtained from long bending test to check against the Von Mises output from FE for the laminate. Similarly, one can extract the shear running forces from Nastran and convert them to shear stresses and compare against short beam shear allowables which are for core shear failures. Is the procedure is accurate? If no, can a more accurate method of check be suggested i..e how to use panel allowables from long beam & short beam test against FE results? Thanks

## RE: Need Opinion on Stress Analysis Procedure for Interior Monument Honeycomb Laminates

- facesheet stress?

- smeared stress?

- bending moment?

## RE: Need Opinion on Stress Analysis Procedure for Interior Monument Honeycomb Laminates

## RE: Need Opinion on Stress Analysis Procedure for Interior Monument Honeycomb Laminates

Any input on my original question based on my response about how strength is defined for the laminates?

Thx

## RE: Need Opinion on Stress Analysis Procedure for Interior Monument Honeycomb Laminates

smeared stress as well as bending moment.? which one? you need to be very specific about how the allowables are defined. If the are based on a smeared stress, then exactly what equation was used to calculate them?Are these allowables from your own testing? or from a vendor or customer?

## RE: Need Opinion on Stress Analysis Procedure for Interior Monument Honeycomb Laminates

Short Beam Shear TestIn the short beam shear test, core compression failures were observed in the first samples. Load plates were added to the loading fixture and holding fixture to prevent this type of failure.

The following equation converts the load from test results to core shear stress:

σ = V/hb, where V = P/2, σ = core shear stress, V = shear load on the panel, h = height of the core and b = width of the panel. The shear load is half the applied load as external load is applied at the center between two supports.

Long Beam Bending TestThe bending moment allowable is quoted in both inch/lbs and lbs/sq. in. The following equiation translates the moment in in/lbs to lbs/sq. in

M = PL/8b

σb = M/tfh, where tf = thickness of facing sheet

Fs is in psi

## RE: Need Opinion on Stress Analysis Procedure for Interior Monument Honeycomb Laminates

## RE: Need Opinion on Stress Analysis Procedure for Interior Monument Honeycomb Laminates

http://www.stressebook.com/sandwich-panel-long-bea...

How the flexure stress equation is derived here:

http://www.stressebook.com/sandwich-panel-flexure-...

And a bit more about the concepts and test coupons here:

http://www.stressebook.com/sandwich-panel-flexure-...

The flexure allowable is at the top of the panel in compression on the facesheet in the middle.

So I suggest you use minimum principal stress from your hand calc or FEM results on the panels to compare against the allowable stress.

Aerospace Stress Analysis and FEA Courses

http://www.stressebook.com

Stressing Stresslessly!

## RE: Need Opinion on Stress Analysis Procedure for Interior Monument Honeycomb Laminates

## RE: Need Opinion on Stress Analysis Procedure for Interior Monument Honeycomb Laminates

MOHR1951, per my understanding, a honeycomb panel is made of two facesheets and a core. The facesheets themselves may be a laminate made of different plies. In smeared stress, the stress distribution is obtained for the entire laminate as opposed to stresses in individual plies/layers. As you can see, some of the panel allowables are provided for the entire panel rather than individual layers. Having a smeared output makes it easier to make direct comparisons.

## RE: Need Opinion on Stress Analysis Procedure for Interior Monument Honeycomb Laminates

## RE: Need Opinion on Stress Analysis Procedure for Interior Monument Honeycomb Laminates

I am in need of using pshell elements for modeling laminates. I am curious how did your analysis worked out. I did a quick study of results between plate modeling and laminate modeling and the results are not comparable. I compared shear stresses as well as vonmises and principal stresses. Do let me know where is your analysis standing and I will update you what my research findings are.

## RE: Need Opinion on Stress Analysis Procedure for Interior Monument Honeycomb Laminates

## RE: Need Opinion on Stress Analysis Procedure for Interior Monument Honeycomb Laminates

Brian

www.espcomposites.com

## RE: Need Opinion on Stress Analysis Procedure for Interior Monument Honeycomb Laminates

george_hobbs@msn.com

## RE: Need Opinion on Stress Analysis Procedure for Interior Monument Honeycomb Laminates

## RE: Need Opinion on Stress Analysis Procedure for Interior Monument Honeycomb Laminates

## RE: Need Opinion on Stress Analysis Procedure for Interior Monument Honeycomb Laminates

## RE: Need Opinion on Stress Analysis Procedure for Interior Monument Honeycomb Laminates

## RE: Need Opinion on Stress Analysis Procedure for Interior Monument Honeycomb Laminates

Sorry for the late response.

Please refer to this document on how to convert PCOMP to PSHELL in Nastran.

http://www.aersys.com/AERSYS-7001.pdf

I have tried the above and I was not able to obtain comparable results to approved hand calculated test cases.

Your query does not specify about the nature of the laminate panels i.e. if they are honeycomb sandwich panels or just plain composite laminates.

If it is the former, then I recommend following the procedure listed in this link: https://femci.gsfc.nasa.gov/hcplate/honeycomb_pshe...

I can vouch that FEMCI NASA procedure works correctly and I was able to get comparable & accurate results to an approved document containing hand calculations for simple test cases. Of course, please consult with your FAA DER or any other certifying agency approved signatory about the validity of using the above approach for your project/work.

Hope the above helps you.

## RE: Need Opinion on Stress Analysis Procedure for Interior Monument Honeycomb Laminates

Perfect 3-4 rows of hex elements between laminates to model the core structure. And then you can use the hex stresses to evaluate your core failure as you would define the material orientation with respect to a local coordinate system.

Just another approach to your case if the latter got too complicated on its way.

Spaceship!!

Aerospace Engineer, M.Sc. / Aircraft Stress Engineer