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TOPIC: Honeycomb Beam Equivalent Thickness Calc Error
#3428
tobij (User)
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Honeycomb Beam Equivalent Thickness Calc Error 1 Year, 11 Months ago Karma: 0  
Hi Guys,

First-time poster.

For the Honeycomb Beam and Panel Calc file, fourth tab (Centre), bottom of page, the equivalent plate thickness, teq, = SQRT(6*tf*h).

However, according to Niu (Stress Analysis and Sizing, 2nd Ed., Chapter 7.0, page 217), for equivalent plate thickness, teq^3 = (6*tf*h^2), therefore teq = (6*tf*h^2)^(1/3). In other words, the term is the cube root, not square root. The h term is also squared.

This is derived from I value for plate = t^3/12 versus I value for Honeycomb beam = tf*h^2/2.

Am I missing something?
 
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#3429
JohnDoyle[Admin] (Admin)
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Re:Honeycomb Beam Equivalent Thickness Calc Error 1 Year, 11 Months ago Karma: 492  
Hi Tobij. Thanks for your question this particular part of the calculation is to determine both and equivalent plate thickness and an associated Equivalent Young's modulus. I can use these as plate element properties in a finite element package to determine both face stress and deflection. I derived it myself but validated its applicability by comparison with classical calculations.

The calculations shows a deflection of 42.59mm compares to 42.86mm this is because the plate element considers only bending deflection and does not include shear deflection (which is negligible in any case 0.26mm)

Not shown in the calculation is the face stress which for the case would be:
My/I = 750000*(8.8/2)/(500*8.8^3/12) = 116.22MPa compared to 115.83MPa shown in the classical calculation.

I have used this method on many occasions for quickly assessing complex geometries and loading which cannot be adequately assessed as beams or plates. I hope this explanation helps.
 
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#3430
JohnDoyle[Admin] (Admin)
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graph
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Gender: Male MoreVision Location: LEEDS, WEST YORKSHIRE, UK Birthdate: 1965-02-24
Re:Honeycomb Beam Equivalent Thickness Calc Error 1 Year, 11 Months ago Karma: 492  
Actually the face stress calculation worked out even better when calculated in the sheet because there are no rounding errors. Now a plate element face stress of 115.83MPa compares exactly with 115.83MPa from the classical calculation. See below:
 
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