Composite or laminated
Composite or laminated
(OP)
Two 1/8" aluminum plates are glued together with a 1/8" thick silicone.
When computing deflection should I conceder it as a combined shape or laminated ?
When computing deflection should I conceder it as a combined shape or laminated ?






RE: Composite or laminated
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Composite or laminated
RE: Composite or laminated
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Composite or laminated
...at least in my world, one 'laminates' in order to achieve 'composite' action, .... and the laminating connection must resist horizontal shears, that is the tendency of the individual laminates to slide past each other in the horizontal plane under loading, in order to be considered 'composite'. your 'way more elastic' connector won't accomplish compositeness.
RE: Composite or laminated
Let me recap just to make sure that all of us are on the same page.
Two statements that have been advanced are:
1) the loss of partially composite action is indicative of failure
2) your 'way more elastic' connector won't accomplish compositeness
As part of my research I refer to MIT Open Course Structural Mechanics, Paragraph 7.5:
Link
It is stated that in sandwich plates the Young's modulus of the "core" material is usually two orders of magnitude smaller than that of the face plates. Now in my particular example I am dealing with aluminum plates and a silicone core, that have the following shear strengths:
Silicon - 100psi
Aluminum - 30000psi
Since this is a difference of a magnitude of two (as described above) then again should I consider my section as composite or independent layers ?
RE: Composite or laminated
RE: Composite or laminated
RE: Composite or laminated
RE: Composite or laminated
Sounds like a good research project.
RE: Composite or laminated
In the cited document, the disparity in moduli is presented as justification for ignoring the core contribution to flexural stiffness. It is not presented as justification for treating the face plates as acting non-compositely. In fact, EQ 7.49a, by it's form, assumes 100% composite behavior.
Without running any numbers, I suspect that you'll have a high degree of composite behavior here as well. While the disparity in modulii is a couple orders of magnitude, the shear stresses are also usually a couple of orders of magnitude less than your flexural stresses so those effects tend to balance out. To assess the situation simply, try this:
1) calc flexural deflection assuming composite behavior in the face plates.
2) calc shear deflection in the core with standard VL/AG techniques.
3) compare one and two to get a sense for how much shear deformation of the core matters.
Anecdotally, were composite behavior not achievable with disparite stiffness/strength materials, we would not have modern:
- skis
- airplane wings
- wind turbine blades.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Composite or laminated
RE: Composite or laminated
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Composite or laminated
RE: Composite or laminated
Two sheets of glass laminated together with PVB foil ( or similar)
In glass design it depends on the duration of the load
if the load is short, like wind, then the interlayer can take shear force and thus the section is a 'composite' section
if the load is longer, like snow or dead load, then the interlayer will creap and the system behaves like two separate glass panels
This is how glass design is done
RE: Composite or laminated
RE: Composite or laminated
This is not about the properties of silicone rubber as an adhesive. Is more about the structural properties of silicone rubber compared to structural properties of aluminum. Even if the silicone rubber is "perfectly" bonded to each of the aluminum sheets, I see this problem resembling a (hypothetical) beam where the flanges are metal and the web is rubber. IMHO, the silicone rubber layer is essentially structurally "worthless"... the two aluminum sheets are two independent layers, per comments given by others.
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RE: Composite or laminated
Similar to 2-ply 2x8 wood headers loaded in the weak direction, is (6)10d nails sufficient to make it act as one single 3"x7.25"... no, it takes a lot of shear transfer to actually work. I doubt the bond strength of silicone to clean Alum. is sufficient. but again, this is something calculable.
RE: Composite or laminated
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Composite or laminated
Your thoughts and opinion helped me understand the issue in much more details.
In conclusion, I feel more confortable with independent action then with composite action.