Interpretation of FEA Results, a little help please?

What is the goal(s)?

That is the question you need to answer before the FEA even starts. Use the tool to then see how you are preforming toward achieving the goal(s). You commrads are more or less generally correct, it is often more difficult to achieve a stiffeness/deflection goal(s) than strength, but, I don't know what your design is doing.

Also, part of the goal(s) set should include a consideration for fatique if there is any cyclic loading being applied.

Need more info for a good answer.

Captn

It's a simple part, a platform that holds a motor. The question is will the part fail if we switch to this material?

So many questions come to mind... You've left out so much information I hardly know where to begin.

You say that your "fellow engineers" are most concerned about the deflection. Why? Is the deflection localized (i.e., stress concentration at a mounting point?) 

I don't see any problems, but here it is for your opinion. It is mounted and secured in the 4 outside corners, and the engine is mounted to the slots.

Would you change anything based on this?

I am curious - are "they" worried about deflection due to the dynamics of the motor - thus causing vibration problems?

We have already dampened the motor using think rubber grommets, so the is no vibration to worry about, I think the lead engineer is worried that someone may drop the assembly from a height of 3 or 4 feet, (1 to 1.2 Meters) and having the platform fail...

To that end, he had the FEA done using 2.23 Kn of force for a 25 lb. motor.

What form of coupling is on output? That much motion could wreak hell with gear mesh or chain/belt tension/alignment; forces might go up a great deal in that condition.

What is proposed lifetime? I can see a fatigue fracture in the future.

to check our FEA result whether it is safe or not then go for SCL option.

it will give you membrane stresses.

It's hard to tell much from the small photo, but the area in the center at the ends of the slots looks like it's worth a second glance. Is this a drop test or what? Give us a little more detail, please. Is this static? Is there a dynamic component?

Hi Labyguy

First, to answer your question: Conformity to preset criteria is necessary and sufficient for the results to be acceptable.

From what I gather, you already addressed the basic criteria (strength, vibrations, weight etc etc)

Max deflection (of the order of magnitude you calculated) is never a criterion by itself, unless it impairs functionality.

After looking at the data you posted:

1. As you well know, max deflection (as opposed to strain) by itself does not cause failure. If you are confident about your calculated stresses, then the part you designed will NOT fail.

2. BUT if this deflection causes other machine elements to become misaligned in a way that will stress them more (effectively redistributing the equillibrium across the machine), then THEY might fail. I.e. in your case, if the motor output shaft is not connected via a flexible coupling, then this shaft might bend and fail under fatigue. Do make sure that you have a flexible coupling in place.

So basically, if you check for such things like point 2, then you will be totally covered.

By the way, if your boss insists on making it thicker, let him by all means! Make your sound recommendations and keep your tail out. This is a trivial thing not worth arguing about.

Thanks for the reply, the alignment issues have been addressed but sense the posting, it become a point of contention and I now beleive I'm right, but this is not a fight I can win.

So, as so many of my good ideas, this will be shelved for now.

Thank you all for the advice and help.

Laby