Engineering & Analysis Methods > Miscellaneous Analysis & Methods
Use Non-Structural Core In HyperSizer
Jason_the_CA_surfer:
Does anyone know how to use nonstructural core in HyperSizer. I am trying to analyze a stuffed hat (monolithic panel with strips of sandwich panel stiffeners) in hypersizer. The intent is that the core is non structural, it is only there for manufacturing purposes and cannot be considered for damage tolerance reasons.
What I have done thus far is create a core material that has orders of magnitude less stiffness for a nastran run, generated pcomps that reference this material, and run with a model that uses shell elements that reference this pcomp. Nastran seems to run fine with this core. I then import it into HyperSizer.
In HyperSizer I created a new material for this non structural core; I did this by copying a traditional aluminum honeycomb core and then dividing all stiffness and stress allowables by 100. When I imported the model imported fine, it picked up the new core material. The problem comes when I run the MS check in HyperSizer. HyperSizer is applying load to the core and giving very negative margins. Somehow load is getting appllied to the core and the very low stress allowables are being referenced, causing these negative margins.
What I want is for all the shear load to be analyzed as transverse shear in the top and bottom facesheets. How can this be acheived.
Thanks,
Jason J
Goodrich Stress Engineer
Jason_the_CA_surfer:
I have found the following on core imports in HyperSizer. In order for hypersizer to recognize a material at import as a core it must satisfy the following:
HyperSizer looks at the thickness and the properties of the ply to determine if it should interpret the ply as a honeycomb. The rules that HyperSizer uses are:
1. This is not the last ply in the PCOMP
2. The thickness of this ply is greater than 10 times the thickness of the previous ply (i.e. if the ply is ply 5, then it says if thickness_5 > 10*thickness_4, then this is true)
3. The transverse shear stiffness (G1z) of the material is greater than the in-plane stiffness, E1 of the material. This should never happen for a composite ply material but is very common for a honeycomb which has very little in-plane stiffness.
Jason J
Goodrich A350 Stress
Phil:
--- Quote from: Jason_the_CA_surfer on July 24, 2008, 09:11:03 PM ---Does anyone know how to use nonstructural core in HyperSizer. I am trying to analyze a stuffed hat (monolithic panel with strips of sandwich panel stiffeners) in hypersizer. The intent is that the core is non structural, it is only there for manufacturing purposes and cannot be considered for damage tolerance reasons.
What I have done thus far is create a core material that has orders of magnitude less stiffness for a nastran run, generated pcomps that reference this material, and run with a model that uses shell elements that reference this pcomp. Nastran seems to run fine with this core. I then import it into HyperSizer.
In HyperSizer I created a new material for this non structural core; I did this by copying a traditional aluminum honeycomb core and then dividing all stiffness and stress allowables by 100. When I imported the model imported fine, it picked up the new core material. The problem comes when I run the MS check in HyperSizer. HyperSizer is applying load to the core and giving very negative margins. Somehow load is getting appllied to the core and the very low stress allowables are being referenced, causing these negative margins.
What I want is for all the shear load to be analyzed as transverse shear in the top and bottom facesheets. How can this be acheived.
Thanks,
Jason J
Goodrich Stress Engineer
--- End quote ---
Jason,
Is this truly a hat concept (with a web and a crown?) Or is this a honeycomb where there are facesheet separators in for manufacturing but don't actual contribute to the structural response? If I understand correctly, you are looking for a capability where the facesheets are uncoupled and the core material has no strength.
There are two ways I can think of doing this:
1) you can turn off all core analyses on the failure tab. This way, HyperSizer will ignore the core completely when doing failure analysis. The core will not contribute stiffness for in-plane loads at all. It will only contribute to bending stiffness in that it keeps the facesheets separated, therefore increasing the D matrix contribution of the facesheets.
There is no physical way to keep the core from taking transverse shear load. If the sandwich is loaded in transverse shear, then the transverse shear stress in the core must be the peak transverse shear stress. This stress value is approximately Qx / thickness and is independent of the core material. It must be this way to transfer shear from the bottom to the top facesheet.
2) If the core is truly non-structural and cannot take load at all, you could model this in the FEA with two separate CQUAD elements and then in HyperSizer just treat these two CQUADs as unstiffened laminates. This means that these two elements are completely uncoupled both in HyperSizer and in the FEA. In this case, any transverse shear is picked up in the two facesheets and none is transferred across the core.
It sounds like to me option two is what you are looking for.
Please let me know if this sounds correct.
Phil:
--- Quote from: Jason_the_CA_surfer on July 25, 2008, 11:32:23 AM ---I have found the following on core imports in HyperSizer. In order for hypersizer to recognize a material at import as a core it must satisfy the following:
HyperSizer looks at the thickness and the properties of the ply to determine if it should interpret the ply as a honeycomb. The rules that HyperSizer uses are:
1. This is not the last ply in the PCOMP
2. The thickness of this ply is greater than 10 times the thickness of the previous ply (i.e. if the ply is ply 5, then it says if thickness_5 > 10*thickness_4, then this is true)
3. The transverse shear stiffness (G1z) of the material is greater than the in-plane stiffness, E1 of the material. This should never happen for a composite ply material but is very common for a honeycomb which has very little in-plane stiffness.
Jason J
Goodrich A350 Stress
--- End quote ---
Jason, these rules are exactly correct.
Phil
Jason_the_CA_surfer:
Hi Phil,
Thank you for the response. The physical part I am analyzing is a stuffed hat panel (but for a damage tolerant requirement the core must not be considered structural, so for analytically I am analyzing a "hollow hat" or some call it a "skin stringer" configuration).
Ideally I would like to build a new model with the sidwalls of the hats modeled and top of the hat as there own quads; unfortunately all I have at this time is a sandwich panel model (quads on a midsurface) because the design change actually came during my PDR stress analysis. So I was looking for a quick and dirty way to transfer all the transverse shear than normally would be applied to the core to the facesheets. For now I have just turned off the core check, which will suffice for PDR analysis. I can just do a hand calc to superimpose the shear to the interlaminar shear M.S. check for now.
Thanks again,
Jason Joel
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