Stress analysis of quadcopter part

[sciencerocks]

Hi Everyone,

I am a student studying civil engineering and want to do a stress analysis on a part I have made in Solidworks (CAD software). However, it is somewhat complex for handcalculation purposes, so I have simplified it down. I want to run a full ansys simulation on the part, however I need a basis from the handcalculation to determine if the ansys analysis is credible or not. If anyone can give me some input onto if my assumptions are right that would be great.

I initially tried to use a plane stress approach 2d analysis, however this assumes the whole cross section is fixed. It is only fixed at the spots indicated. Attached is the part geometry with support and loads.

The fixed support holes I am concerned that the material will fail there, and at the beginning of the square cross section due to the bending moment.

I can't thank you enough for the help.

 

[sciencerocks]

some work

Hey guys,

I did a force and moment balance and did a quick FEA in cad. I was expecting the max stress to be within regions B-C because this would have the highest bending moments. However, FEA shows otherwise. Anyone know why?

Thank you,

Sciencerocks

 

[sciencerocks]

here are the pictures

Please put in your input guys. I am very curious.

Thank you

 

[256bits]

Usually a part like that will fail at a cross section transition ie the rectangular meeting the round due to stress concentrations. You might want to put a fillet where you have now a sharp corner.

BC might have more shear stress, but especially CD will have more flex.

Your dimensioning is off - there is no way to determine AE or CD.

 

[sciencerocks]

BC might have more shear stress, but especially CD will have more flex.

How will CD have more flex if the moments are not nearly as large as the one between B-C, more specifically at C.

 

[256bits]

Just takes your moment around C for example. They both are equal or you would have an unbalanced forrce.
30 BC = 6 CE
Isn't CE longer than BC. so E would show more displacement relative to C than B would relative to C.

 

[The Jericho]

Hey sciencerocks

It depends what you're trying to calculate. What is it that you want to know? If it's the max stress in the part then SolidWorks will be able to tell you that more easily and accurately than by hand calc. Since the lower section is an extruded circular plate with a varying I value, your section constants (Area and I value) are important if you want to go into much detail. Determining (qualitatively) how it will fail and then calculating the most critical load case may be sufficient. I'm assuming this is a metallic part?

So your process should be:

Find loads

1. Sum of horiz and vertical loads, each = 0
Take moments about any point. Since its not "simply supported", make sure you don't make the common error of underestimating the reaction at the end fixture if you're taking moments about the lower fixture.

2. Find a data sheet with Ftu (ultimate tensile strength) and Fty (yield tensile strength) For the material you are using. e.g 2024-T4 Al alloy has a Ftu of circa 74ksi and Fty of circa 62ksi. A conservative assumption can be made to average these two values for your "allowable tensile stress".

3. Your margin of safety, MS = allowable stress/applied stress - 1

4. Your loads may give you a large MS if its a metallic part. If composite, then you will have to go into slightly more detail due to its isotropic material properties.

5. Just remember to keep it simple.

Let me know how you get on.

 

[sciencerocks]

Hi Jericho,

I do appreciate your help and realized my mistake. I just wanted to make a moment diagram to see how the loads would vary throughout the length of the beam. I did take sum of moments around the fixed supports to find the force reactions, however, i did not include moment reactions at the fixed supports. When moment reactions are taken into account, sadly this becomes a statically indeterminate problem. Should I just rely on the solidworks?

Thank you,

sciencerocks

 

[The Jericho]

Hey,

You absolutely could purely use SolidWorks, you'll just have to explain the most critical load case and how it determined where you applied the constraints/loads to the model. (Sometimes it's obvious, sometimes not so, but you still need to show you addressed each point.)

(When determining the maximum stress location, keep I value in mind and especially any sudden changes in section constants like I value and Area, as local changes in these values sometimes suggest that a region of local high stress is in the vicinity. You could say something along those lines, in fact, when you explain critical load cases.)

This is generally standard practice to perform a stress analysis on a part like this, it just requires you address the way the loads are applied and then how you made conservative assumptions on the criticality of the load case.

Let me know how you get on.