huangyhg

aluminum extrusion w/phenolic resin thermal break
i have an aluminum extrusion with a phenolic resin thermal break. the extrusion is an h shape to receive an aluminum and polyurethane sandwich panel on each side. the panels are 2.5" thick to match the slot between the flanges of the h shape.
the phenolic resin is poured into a cavity in the extrusion. after it hardens, a segment of the aluminum is cut away to provide a thermal break.
i need to compute the axial load and bending load structural capacity of this composite member. how should i compute the composite structural properties of this member? i am working on getting the resin properties.
steve...you didn't pick an easy one, didja?
i'm not sure which section of the aluminum will be cut. a sketch would be helpful.
phenolic is a thermoset material, with highly variable properties, depending on the mix. i would suggest you use the proprietary properties of the phenolic rather than generic properties.
there are several ways to approach this. here are a few suggestions.
for bending
1. neglect the contribution of the phenolic.
2. neglect the contribution of the aluminum.
3. analyze separately and superimpose, matching deflections. when the deflections match, the load capacity at corresponding deflections will give you the proportion of load sharing (and equivalent modulus by backcalculation).
for axial
1. neglect the phenolic.
ron,
i got some more information on the aluminum shape and the polyurethane polymer. i have the modulus of elasticity and the tensile strength of the polymer and all of the properties of the aluminum alloy. i can figure the section properties of the 2 aluminum pieces and the transformed section properties of the polymer, then i will combine these for the composite section. i assume that i can then use the aluminum assoc code to evaluate the composite section as long as the tensile stresses in the polymer are not exceeded.
the hatched area in the sketch is the polymer.
steve...yes, that is the proper approach, but you'll need to check for both tension and reversal to compression as the polymer might tend to move a bit more in compression.
i assume this is subject to wind loading?
just a quick comment (you probably checked it). how do the properties of the polymer change with time? i know some products will 'creep' with time, making them unreliable to take long term loads or resulting on large deformation.

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