FEM Stress analysis with a simplified bearing

 Hello,

Following parts are available:

  • Shaft
  • Bearing blocks, representing the housing

However, the bearings are missing. 

Following Elements were applied:

  • Fixed constraint on the bottom of the two bearing blocks
  • Remote displacement on the other end of the shaft ( x rotation and displacement ramped)
  • Force on the end of the shaft
  • A group of four spring elements on each bearing block should add a stiffness, representing the bearing stiffness.

The shaft will be bent upwards in the positive Y-direction. I didnt get what I was looking for in the results. I wanted to see a force acting on the bearing blocks as well, but there was no deformation nor stress on them. Why?

The setup and results are seen below

Comments

  • peteroznewmanpeteroznewman Member
    edited June 2

    tuffaha,

    Were the springs of the type Body-Ground?  That would explain why there is no stress in the bearing blocks.

    I recommend you take two planes at +/- 45 degrees and split the cylindrical face of each bearing block into four pieces. Also take two more planes parallel to YZ through the center of each bearing block to split the face of the shaft. Create a Remote Point on each circular edge on the shaft. Then you can scope each outer end of each spring to a 1/4 face of the bearing block in a Body-Body spring configuration where the other end of the spring is connected to the respective Remote Point.

     

  • tuffahatuffaha Member
    edited June 2

    Thank you for your reply Peter, your posts have been a great help to everyone here.

     

    The faces of the shafts were already split. The springs are attached to the other body (Body - Body). The definition of the spring as seen in the picture:

    Following messages appear as well:

    I have also tried your approach by dividing the housing blocks, but it didnt work out, and the results came out the same.

    More info: Scope radius = 30, shaft radius = 9.

    Any other suggestions? Is there a way to upload the file so that you can take a look at it?

    Thank you Peter

  • peteroznewmanpeteroznewman Member
    edited June 3

    Analyzing stress in the bearing block using 4 springs is too simplified. You need a bearing outer race in frictional contact with the bearing block to get reasonable stress values in the bearing block.

  • tuffahatuffaha Member
    edited June 3

    so youre suggesting the following?

    • Adding a solid body which represents a bearing outer race (cylinder fo example)
    • Bearing outer raceshould be in a "frictional contact" with bearing block.
    • Attaching the springs from shaft face to bearing outer race inner face.

     

    Right?

  • tuffahatuffaha Member
    edited June 3

    I tried this approach. Unfortunately it did not work.

    I am happy to hear other suggestions.

    Here is also a download link to the file, in case there is a mistake that I did and that I did not know of:

    https://drive.google.com/file/d/1AAK_mU2Uqi5jaGp0EJfp7U815nesd0uF/view?usp=sharing

  • tuffahatuffaha Member
    edited June 3

    I have tried a new approach now. I reduced all the parts to small cylinders ( shaft, bearing inner race, bearing outer race, Housing). Spring were defined body - body between inner race and outer race. contacts were frictional for shaft - inner race and housing - outer race.

    The 4 springs were defined on faces and on edges. I got different results:

    Deformation:

    Stress (Von Mises):

     

    I am kind of confused what to use and what not to use.

    How would you model a bearing that is not there, and the only information you have abt it is its stiffness? Maybe there is an alternative.

    Thanks

  • peteroznewmanpeteroznewman Member
    edited June 3

    Springs can push down on a bearing block, but they also pull up, which is wrong.

    Frictional contact can only push, it never pulls because it separates instead.

    I haven't had time to look at your model to see what is wrong, but I stand by my recommendation.

  • tuffahatuffaha Member
    edited June 3

    No problem. Take your time to take a look at it.

     

    Yes the pulling makes this unrealistic. Your recommendation was to add a bearing outer race. This was added. But adding the outer race didnt change the results so much and it wont solve the pulling problem which is caused by the springs rights?

  • tuffahatuffaha Member
    edited June 10

    sorry to disturb again. did you find a solution?

  • peteroznewmanpeteroznewman Member
    edited June 11

    Some members here have the balls (or cylinders) between the inner race and the outer race. When you do that, there are no springs to pull up. It is all contact. The down side of this approach is the very long computation time.

  • tuffahatuffaha Member
    edited June 11

    Well, that is exactly why I did this post. I want an FEM analysis that includes the stiffness of the bearing, without having the bearing itself. A simplified bearing you can say.

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