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,
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.
