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Author Topic: Free Body Loads and Stress Calculation for Simple Panel  (Read 2990 times)

jsanc

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Free Body Loads and Stress Calculation for Simple Panel
« on: March 12, 2018, 01:32:06 PM »
New to HyperSizer and trying to understand the various inputs with a simplified case before proceeding to more difficult geometry.

Component type: foam sandwich w/ 0.50" upper and lower panels. Thickness of foam core is set to be very small 0.0001". 2nd area moment is calculated by: (1/12 bh^3)*2 (b=2, h=.5"). Since the foam core is intentionally very small, the area moment reduces to 2/48 in^4 (or 0.042). [see attached calculation]

In the Free Body section, the panel is unconstrained with the total Mx load of 10,000 in-lbs. The panel dimensions (a=1", b=2") are entered, but do not appear to be related to the stress??

Calculating the average stress at the neutral axis of the top plate gives: 10,000 in-lb * 0.25" / (2/48 in^4)) = 60,000 psi.

Hypersizer is calculating a stress of ~30,000 psi.

My answer is 2x larger than Hypersizer. I thought that I should unitize the bending load, but this would only make the difference increase.

Help appreciated. Thanks.

Stephen

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Re: Free Body Loads and Stress Calculation for Simple Panel
« Reply #1 on: March 12, 2018, 02:11:34 PM »
Hi jsanc,

It looks like there are two things going on here.

Moment of intertia calc
First, since this is effectively a rectangle with width 2" and height 1", the moment of inertia about the centroid of the cross-section is 1/12*(2in)*(1in)^3 = 1/6 in^4. If you do use the parallel axis theorem with two 0.5" plates, the offset of each, y, should be 0.25", since this is the distance from the midplane of the section to the centroid of each plate. Of course these two values should come out the same.

Moments applied in HyperSizer
When we apply moments in HyperSizer, we do so using running load. That means that any moment you apply has units of "in*lb/in", not just "in*lb". In this case, Mx is defined in terms of in*lb of moment per inch of x-span. So your Mx for verifying the calculation should be (10000 in*lb/in)(2in)=20000 in*lb.

Feel free to respond if you need clarification on anything!