Analysis report clarification 3

[sivasooriyan]

Hi all.
Designed a grip hoist mounting set up to lift a load of 30000 N in autodesk inventor and I simulated it. But I cannot figure out with the output that whether the designed mounting device could withstand the said load. I have attached the sketch of the mounting device and the simulated results with this thread. the dimensions of the C-channel used in the fabrication of this mounting device are as follows.

C channel - ISMC 100 x 50
length - 1650mm
wire rope pulley dia. - 100mmm

Please share your ideas.
Thanks.

 

[rb1957]

if the minimum safety factor is 0.42 it could be ok ... if safety factor is margin of safety and if you've provided good allowables and if it (or you) understand crippling (compression failure). this is lifting something ... is there a required Factor of Safety (to protect someone underneath it) ?

but there are lots of things that need to be checked before you can say it's good ...
fastener (or joining) loads ?
deflection (is 19mm deflection acceptable ?)
constraint loads.

Generally I would not use Inventor stress module for "serious" stress analysis. It is ok for design sizing, but it is too limited IMHO (for example, it is very limited in the control it gives you to constrain the model) for final analysis.

another day in paradise, or is paradise one day closer ?

 

[jhardy1]

So ... we have someone using a CAD / FEA "Black Box" to design a hoisting system, and they don't know how to interpret the stresses and Factors of Safety ...

What could possibly go wrong?

(Hint: You have specified a yield strength of 207 MPa, and the maximum reported von Mises stress is 494 MPa; 207 / 494 gives a "safety factor" of 0.42. I won't even get into other issues such as buckling / crippling of thin-walled sections, weld details, pin details, etc.)

http://julianh72.blogspot.com

 

[rb1957]

is it common for safety factor to be allowable/applied ? like our (aerospace) old "reserve factor" (>1 is good). We've gone over (pretty universally) to Margin of Safety (>0 is good).

another day in paradise, or is paradise one day closer ?

 

[IDS]

We've gone over (pretty universally) to Margin of Safety (>0 is good).

Who are "we"?

Given the ambiguity, I would suggest not using the term "factor of safety" unless it is clearly defined.

Doug Jenkins
Interactive Design Services

http://newtonexcelbach.wordpress.com/

 

[ThomasH]

Hi

If you have a reported stress 494 MPa and allowed stress is 207 MPa, then I would say that the utilistion is 494/207 = 2.33 = 233%. Not good.
In the report the peak stress is reported as negative, 3rd principal. Buckling?

The device masss is 16 kg so it is probably fairly slender with length 1.65 m. And the maximum displacement is 19 mm. Don't you think that is fair warning?

If I understand the figures correct the design is basically a cantilever channel beam in bending and compression. Why not start with a simple hand calculation to check the results?

Good Luck

Thomas

 

[rb1957]

"we" in aerospace

another day in paradise, or is paradise one day closer ?

 

[gravityandinertia]

Your going to have problems. You have 16kg of steel, supporting the weight of an F350 hanging from it. Just from gut, doesn't that seem off to you?

Add in that you've significantly passed the yield strength and I don't see any mention of stress-strain curves, or bilinear material models being applied and I would say you are going to have serious issues. If this is a linear static analysis, it is likely over predicting stresses, and under predicting displacements by huge margin. I think this part will have significant permanent deformation after being loaded this amount, is probably going to buckle, and ultimately would likely fail, though that can't be said for sure without a non-linear analysis, but keep in mind based on the geometry, as the beam deflects, it increases the moment arm further increasing the stresses yet again. Once it yields, I find it highly unlikely that this won't create a loop that leads to catastrophic failure at the given design load.