EPS Aluminum Skin Sandwich Panel

[omoreno1]

I am reviewing some composite theory to better understand sandwich panels so that I may compare tested results to theoretical results. I am having diffuclty obtaining the relative density of EPS. Also, in exploring the limit states of panel stiffness, face yielding, face wrinlking, core shear, core fracture, and bond failure. I am finding that the core shear values tend to control the capacity of simply supported panels. The skins are made of Fy = 33ksi 26 gage steel, 4" or 6" thick panels. I applied safety factors related to material strength per AISC specification for steel and safety factors for bond and shear stress per ICC AC4 for Sandwich Panels. I am using the panels in a building application. There is not much literature out there, so I was looking for some more background information, I believe there is a book by H. Allen out there, but I am unable to locate a copy.

 

[Demon3]

EPS is not one material and can have a range of densities, hence your trouble in finding a definitive, accurate value.

Density of EPS 25–200 kg/m3

http://en.wikipedia.org/wiki/Polystyrene

Chris DeArmitt PhD FRSC CChem

http://www.phantomplastics.com

Consultant to the plastics industry

 

[RPstress]

Howard Allen's book ("Analysis and Design of Structural Sandwich Panels") is out of print but it's worth looking for a second hand copy. Zenkert is probably the current 'standard' reference for sandwich design, but he's perhaps a little bit academic in his approach. (Allen was good enough to write an approving intro for Zenkert.) I believe Tom Bitzer also has a book out there.

If you want a reference but don't want to buy a book try for MIL-HDBK-23 or the Hexcel and Diab design guides.

http://www.hexcel.com/NR/rdonlyres/...-CC15967A4B05/0/4547_Sandwich_Fabrication.pdf

http://www.hexcel.com/NR/rdonlyres/...B3-7EFF685966D2/0/7586_HexWeb_Sand_Design.pdf

http://www.diabgroup.com/europe/literature/e_lit_man.html

 

[PanelGuy]

The Hexcel guides are good...Bitzer wrote them and they are the "cliff's Notes" for his "Honeycomb Technology" book. Broutman wrote a great book that includes alot of the matrix code. I found it friendlier that Zenkert or Tsai's. I have always defaulted to the Hexcel TB that RP notes, it is the most succinct...plus I have derived those before.

Quite a few of these are available on Scribd.

Or - for EPS we use
2 pcf, Comp Strength 35psi, Comp Mod 500 psi, Shear Str 33 psi Shear Modulus 625 psi.

You can probably adjust up or down about 50% on the density and change the properties the same amount...good luck finding hi density EPS. As well, Dow has a wide variety and publish a lot of the mech values.

Once you get over about 5/8" the skins rule the equations in the shear properties. It is great to try to balance them, but it will (guaranteed) become a local point load or impact issue...My experience is that in EPS Foam panels, you chose the thickness to fit insulation or assembly and the skin to match a local loading and visual requirement...once you are over 1" the structure takes care of itself. Besides, Ya gotta test it anyway.

Good Luck.

 

[omoreno1]

Thank you for all the responses, I looked up a few of the links and found some good information. The EPS steel skin panels I am dealing with use and adhesive to bond the EPS to the metal skins. Based on my research one of the failure modes could be the adhesive used to bond the EPS to the steel skins. Anyone know typical strain energy release rates for adhesives used in this type of application? Also the panels are ribbed or stiffened, I believe this affects the capacity of the panel in comparison to a flat sheet. Is there anyone in Europe that can lead me to find the European Recommendations for Sandwich panel design, I am unable to find this document and it seems like it may have some design guidance. I want to be able to compare the test panel values to a rational analysis to get a better feel of the numbers.

 

[RPstress]

You should find that the EPS fails well before any reasonable adhesive.