Composite Panel

1. You used the wrong equations/properties.
2. (Less likely because it is easier to measure than calculate) - You measure weight/deflection wrong.

Some more information would be handy.

Which equations/properties did you use?

Give us some more insight into the panel - thickness, material, cross-sectional area, how is it supported .........................

Hi:

Both core(1.5 inch thick) and face sheets(.063 inch thick) are aluminum. Face sheets 7075-T6 and core 6061-T6. Panel is 108 inch and 88 inch in length and width direction.

Actually deflections are more in hand eqations.a uniform pressure of 115 psi is applied on the panel for testing.

If I use from hand results, stiffness (Pressure* area /deflection)is not acceptable because sfiffness is small than required because high deflection.

thanks

Did you use equations for beams?

Because the equations for plates would be more appropriate.

How many sides are these plates supported? Are the simply supported or fixed?

Another thing - is this panel a honeycomb sandwich panel or similar?

HI

I used beam eqn. It is simpaly supported on 2 sides and its honey comb structure.

As I said before from hand results, stiffness (Pressure* area /deflection) I got is not acceptable .

thanks

Try to explain the problem so that we can understand it. What exactly is not acceptable? And, by the way, stiffness is not pressure*area/deflection.

If the material is elastic and is supported on two opposing sides separated by a distance "L" then the deflection is Δ=5wL⁴/(384EI). If you know the load, the span and you have measured the deflection, you can calculate the quantity EI. Where is the problem?

Hi,

for example Stiffness of a spring is elongation due to applied load which is applied load/deflection.So I do not understand how stiffness is not pressure*area/deflection.

I can understand it is also EI but isn't what I what I said above is also right.

Thanks

What is you said is partly correct (in principle that is) -

See this paper for a better explanation (note the beam arrangement is different, but the main point should come across):

http://www.brushwellman.com/alloy/tech_lit/feb01.pdf

The equation for a beam is linear like a spring - but you must also factor in other properties - thus you get a different equation/(spring constant)

Stiffness of a spring is load/deflection, but in that case, the entire load goes through the same deflection. In the case of a bending member, the load goes through varying amounts of deflection. The load at midspan goes through the maximum deflection, but at every other point in the span it goes through a lesser deflection. Near the supports, it goes through almost no deflection.

In structural calculations, say by the moment distribution method, the stiffness of a beam is defined as 4EI/L which is the moment required at support A to cause a rotation of one radian at support A in span AB when support B is fixed against rotation.

Hi,

As I said befoe in my question its composite panel and its restarined on all four sides also its bolted at the center at few locations to some other part and i have to calculate stiffness of panel at these bolted location. Loading is uniform pressure load.

In ur eqation 4EI/L which term is varing, if EI is constant then is stiffness same all all points. And where is the load coming in to ur eqution.Thats why I used simple way of spring theory to calculate stiffness.

Please explain.

Thanks

I believe that the equivalent spring stiffness of the composite panel at any point could be found by applying a unit load at that point, say one pound, determining the deflection at the unit load, then dividing the unit load by that deflection. This would give you the stiffness term you require.

You would then consider compatibility of deflections of the panel under uniform load and the bolted member which you have not described but which I assume is reacting elastically with the panel.