L profile bracket how to find the needed tickness?

[ellweenlive]

Hi all,

I designed the attached bracket and I made an analysis with ansys.The results show that it's enough safe. But i want to also correct myself with a hand calculation. But i dont know which calculation i have to do. First of all I think i need to see maximum shear stress to decide if the tickness is enough and maximum deflection. But i need your comments.

Thanks to all.

 

[dhengr]

Ellween:
There will be a bending moment and shear in the vertical leg extending down and picking up the load. That will induce a bending moment, shear and torsion in the horizontal portion going to the left, to the bolt. What prevents this whole bracket from just rotating about the axis of the bolt? Put some loads, dimensions, and cross sections on your sketch. It is difficult to know what the bracket shape really is, in cross section, and what the reaction system is. Is that a bolt circle or a single large bolt hole? Is the load a uniform, lbs./inch, line load at the end of the downward cantilever, or is it a triangular load part way up that canti.?

 

[ellweenlive]

Dhengr;
I attached two technical drawings to make it more clear. One of them shows where i ll use this part and why a this kind of force will act to the place on it.By the way the sketch before i put here, was half of the part now you can see how this part is actually. If you look to the assembly drawing you can see a nut, which a 3Nm torque will be applied on by a torque wrench. And this torque will produce forces on both sides of the part. But i think we can consider only half of it. This load will be 157N which is located on 6x6 mm2 area as a triangular force. If its not clear what im saying, ask me please more. I looked many beam problem examples from the books, but this case is not similar with anyone. And may be you can help me to make the similarity to the other cases.

Thanks.

 

[ellweenlive]

And the other technical drawing is here.

 

[dhengr]

Ellween:
That’s quite a different picture than your first sketch implied. While your first sketch showed some things correctly, imagine how it could be misinterpreted in comparison to your new sketches. This was exactly the reason for my first questions. Are you a student? Did you read the posting rules on E-Tips? We might get red flagged because of student posting, I’ll work with you though, but you have to do the work and the digging. You should also be discussing this problem with your Professor or boss, so that they know what you do know and what you don’t know, and where you need help from them. Get your Strength of Materials, Theory of Elasticity, Structural Design and Engineering Mechanics text books out and handy, or we can’t help you.

Do you really think the load pattern will be triangular? What has to happen for that load pattern to occur on the canti. arm/beam? What would be the most conservative way of applying that load? Where is the max. bending stress in the canti. arm? How is your loading reacted by the two bolts through the base plate? Write some simple moment balance equations between the load and the bolts. Do some free body diagrams and post them in pdf format, please. What materials are the bracket and the retained hex nut made out of? How tight is the tolerance between the canti. arms and that retained nut? Why does this make a difference?

 

[adamgnt]

dhengr is spot on with this reply. If these "conceptual" answers aren't immeadiately apparent, I'd be very hesitant to trust my own ANSYS results. In reality this is rather basic algebra, just needs some manipulation to be applied to your application. No worries this isn't a gang up, instead take this opportunity to improve your process of approaching problems.

 

[racookpe1978]

<i>"By the way the sketch before i put here, was half of the part now you can see how this part is actually. If you look to the assembly drawing you can see a nut, which a 3Nm torque will be applied on by a torque wrench. And this torque will produce forces on both sides of the part. But i think we can consider only half of it"</i>


No.

Draw the whole thing. If we (after reading your words and your drawings) cannot understand your description, then you do not understand your problem well enough to "assume" half of a solution is going to be correct.

 

[Twoballcane]

" I looked many beam problem examples from the books, but this case is not similar with anyone. And may be you can help me to make the similarity to the other cases."

Beam problem examples are just that…examples. Hopefully you still remember how to do this analysis since college. You will have break out your pencil and calculator and formulate the max principle stress equations (better yet Von Mises) to fit the design and then use the failure theories to determine if the design meets the requirement. Thickness can be manipulated by how you calculate the moment of inertia of the L bracket.



Tobalcane
"If you avoid failure, you also avoid success."
“Luck is where preparation meets opportunity”