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Aluminum Bracket Analysis

Question asked by Ameya Wadekar on Apr 15, 2013
Latest reply on Apr 17, 2013 by Jerry Steiger

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Friends and Solid Works Experts,

I have been trying to solve this problem since couple of days and i need some direction from you guys.

This is the bracket on which i am running a linear static study:

(Isometric View)

Front View

Given below is the schematic of assembly where this bracket is used:

Basically this bracket holds a part through 4 vacumm cups ( on one side) , the total mass of the part is 80 Kg and accelration forces are 270N acting horizontal through each of these 8 vacumm cups. ( I assumed that total mass is equally supported by all 8 cups hence 80/8=10Kg (100N) force acting through each cup)

I basically want to find out if the stress due to these forces are not causing the bracket weld to fail. ( Cause some of these brackets failed at our customer site)

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Ameya Wadekar Apr 15, 2013 8:13 PM
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I did a Linear Static Study and treated the forces acting through these 4 points as "Remote Loads-Direct Transfer" and attached them to the highlighted face below because that is where the assembly holding the vacumm cups is attached to (See Schematic Sketch Below)

Schematic Sketch of the whole Setup:
(4 Cups in Front and 4 Cups Behind the Plane)

Firstly
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Ameya Wadekar Apr 15, 2013 8:22 PM
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When i ran the Linear Static Analysis it is giving me very high stress values, i feel there is some thing i am doing wrong.

I am especially interested in the region marked below with line (on the circular face):

Can anyone guide me on how can i check (by hand calculation) if Solid Works is giving me right value.

Thanks in Advance,
Ameya
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- Jared Conway @ Ameya Wadekar on Apr 15, 2013 10:53 PM
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  its a good idea to check the stresses with hand calculations but i think before you go down that route you have to ask yourself what this problem looks like as a free body diagram?
  
  it seems like you're reversing the problem. fixing the end that is connected to the part and then applying the forces that are normally on the part on the side of the bracket that is held by the cup assembly. that is fine but you haven't told us anything about how you've restrained the model.
  
  i think once we know that, we'll have the information to guide you better.
  
  off the top of my head a few things i'd look at are the assumptions made with a remote load/rigid transfer. also, how is your mesh, do you have sharp corners? how many elements are actually affected by that high stress?
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  - Jared Conway @ Jared Conway on Apr 15, 2013 10:54 PM
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    also, before you rack your brain around stresses, ask yourself if the displacements and the way it is moving look good. then look at some of the recent posts about singularities and stress concentrations and mesh convergence.
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    - Ameya Wadekar @ Jared Conway on Apr 16, 2013 7:48 AM
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      Jared,
      
      Thanks for replying, i have restrained the bracket on the highlighted faces (Counter Bored Holes) shown below.
      
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      - Jared Conway @ Ameya Wadekar on Apr 16, 2013 12:28 PM
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        are those holes fixed then?
        
        can you show us the defintiion of your remote load? and how it relates to your assembly? (XYZ orientations and location of center)
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        Ameya Wadekar @ Jared Conway on Apr 16, 2013 3:01 PM
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        Jared,
        
        Thanks for the reply, yes these holes are fixed.
        
        I have attached remote loads as shown below.
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        Jared Conway @ Ameya Wadekar on Apr 17, 2013 12:37 PM
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        the setup looks reasonable if you're assuming that the part stays fixed in space, it is bolted to the bracket at the holes and that the part doesn't resist the deformation at all and then the cup bracket is mostly rigid (see help for description of direct transfer), and that there is a force at that point in the y and x directions.
        
        the high stress may be a result of a stress concentration or singularity. there have been some good conversations lately about this that i'd recommend taking a look at. (your model looks like it has sharp corners which points us in this direction)
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        Ameya Wadekar @ Jared Conway on Apr 17, 2013 1:18 PM
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        Jared,
        
        Thanks and appreciate you for helping out. But as a quick question, why do i see stress values drop when i use a rigid connection option.
        
        Yes there are lot of sharp corners and this going to be a weldment and hence i was interested in the stress values in areas of weld.
        
        Again i Appreciate you stopping by and helping out. Thanks.
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        Jared Conway @ Ameya Wadekar on Apr 17, 2013 1:53 PM
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        that question is pretty vague. i'd recommend taking a look at both displacements and stresses and if you havent' done so already, looking at the defintion of the different remote loads.
        
        http://help.solidworks.com/2013/English/SolidWorks/cworks/c_Remote_Load_(Rigid_Connection).htm
        
        regarding the sharp corners. i would check the standard simulation training and the discussion about singularities. the stress is infinite at the sharp corner, so you really can't look at stress there.
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        Jerry Steiger @ Ameya Wadekar on Apr 17, 2013 3:46 PM
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        Ameya,
        
        I am not familiar with the nomenclature in SolidWorks Simulation and also not familiar with remote loads, but I have seen discussions of something similar in ANSYS. Perhaps it will help you work it out. There may be two methods of attaching a remote load to a surface. The rigid method means that no deformation of the surface you are mounting to is allowed. The flexible method acts more like a distributed load on the surface, so the surface can deform. I would expect to see different stresses in the area around the mounting surface using the two different methods.
        
        Jerry S.
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Aluminum Bracket Analysis

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