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ANSYS Workbench contact problem

  1. Mar 17, 2017 #1
    I'm currently working on my bachelor's thesis in mechanical engineering.

    A part of my thesis is conducting a FEM-analysis on a sump for sewage.

    I've applied a load on the upper face of the lid for the sump. As a result, the upper layer of the lid has been "pushed through" the lower layer of the lid.

    How can this be prevented? 5D - trykket igjennom.png
     
  2. jcsd
  3. Mar 17, 2017 #2

    JBA

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    From the diagram it is not possible to see how you have meshed the cover to represent a disc with thickness and interlacing elements between the upper and lower faces.

    At the same time, are you sure that the top face is pushed through rather than compressed into the lower face and both faces stretched and deformed downward as seen in this diagram.

    The configuration of the deflected disc would imply you have used a load that is concentrated in the center region of the cover. Is that correct?
     
  4. Mar 21, 2017 #3
    The entire model was automeshed. I've also tried several different meshes.

    Yes, I'm quite sure the top surface was pushed through. I've played around with several different contacts, but I cant seem to make the program understand that the top surface should "connect" to the bottom surface as loads are applied.

    Yes, in this configuration, the load is a remote load applied to the center of the lid of the container. This is not a correct representation of the real load, but I decided to try to solve the contact problem first.

    Any tips?
     
  5. Mar 21, 2017 #4

    JBA

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    How much of the displayed center section is protruded through the bottom layer and are the stresses in the protruded region all below the elastic stress limit for your selected material strength?

    Have you tried varying your load, plate thickness, and material strengths to see what effects those have on your results?
     
  6. Mar 21, 2017 #5
    I've tried varying the loads, but as I'm trying to simulate a car running over, it limits the loads that can be applied.

    I'm sure plate thickness and material strength would alter the results, bit I'm running simulations on a already designed product.

    I don't have access to the results at this time, but I seem to recall that the stresses in the portruded region exceeded the linear-elastic yield limit of the material.

    I've also tried to choose both the top of the top layer and the top of the bottom layer when applying the load, and this prevents any portrusion, but this wont be representative for the real load-situation.

    I think my problem is in the connections bar, where I'm able to "connect" the elements through contacts, but whatever combination I try, I cant seem to get the results I want.
     
  7. Mar 21, 2017 #6

    JBA

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    Sometimes the answer you want is just not the one that is correct considering that your analyses are showing that the existing plate is exceeding its specified yield strength.

    By how much is it exceeding its specified yield strength. Published "min yield" values are generally the suppliers guaranteed minimum for a material and the actual average yield strength of that material can be up to 10% to 15% above the certified minimum value.

    Is the top layer exceeding specified tensile strength as well?

    What type of geometry is being used for the element structures connecting the top and bottom layers this internal structure should transfer the load between the two surfaces regardless of the amount of applied loading. Have you structured this as a short round cylinder?

    Just for my information, are you applying your load as a distributed load over a tire contact patch area?
     
  8. Mar 24, 2017 #7
    As shown on the attached picture, the lid of the container is automeshed, but refined on the surfaces of the top and the bottom parts.

    Yes, I'm planning to distribute the load over a contact patch, but this has not been done at this stage in the process. lokk - pumpkum.png
     
  9. Mar 24, 2017 #8

    JBA

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    I the above a true representation of your cover where the top and the bottom of the cover are separated by a space between them with no intermediate supporting web plates between them?
     
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