General Mechanical

General Mechanical

How to define contact region?

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    • AnsysUser_101
      Subscriber
      Hello Everyone.nI am new to fea and I am having difficulties setting up the analysis. I am trying to simulate an acceleration acting on my body and I need to find out the stresses that develop on the body. My body consist of beams, brackets, nuts and bolts. The beam is held together by the brackets which in turn have bolts and nuts. (all solid bodies) The body is supposed to be fixed to another body.nMy questions are:nWhat should be the boundary conditions? I tried fixed joint to the ground where my body's faces should come in contact with the bigger body. Does this type of joint work for my body? I didn't use fixed support, as my asembly consists of solid bodies and as per my understanding I am not supposed to use fixed support for solid bodies. Please correct me if I am wrong. I tried 0 displacement support, but I didn't continue since I did not know very well how to properly assign the support.nShould I apply bolt pre-tensions for the bolts in my assembly? Is it mandatory? I tried defining that and due to the contact set requirements (frictional for contact regions of bolt heads etc) the solver is taking too long to run and the solution doesn't seem to converge. Can I run the simulation without defining the bolt pre-tensions? nI tried with all contacts bonded and the solver gives me results. But I am not sure of the validity of my results.nAny help is appreciated. Thank you.n
    • SaiD
      Ansys Employee
      Hi,nCan you add an image showing the problem that you are trying to simulate? Even a hand-drawn sketch will do. What does the geometry look like? What loads act on the geometry? Is it just the weight of the components itself or are there additional constraints?nYou can use Fixed Support boundary condition for solid bodies, no issues with that. You just need to remember that fixed support constraints the displacements of nodes (and rotations in case of beam and shell elements) in all the directions. You can also use displacement boundary condition and set it to 0 for all directions to mimic fixed support.nBolt pretension is used to simulate the case when the bolts are tightened. It is not a requirement to run a simulation. But in certain special cases, you may need it. E.g. if the assembly is such that without tightening the bolts, two components can rotate/move with respect to each other, then bolt pretension is required to ensure that rigid body motion does not occur (Static Structural analysis cannot handle rigid body motion).nChanging contact type from 'bonded' to 'frictional' changes the nature of the problem since frictional contact is a nonlinear contact. So the increase in computational time is expected. nHere are some resource materials that might be helpful:nHow to define contact etc. - https://courses.ansys.com/index.php/courses/fundamental-topics-in-contact/nWhen to use bolt pretension, how to define it etc. (see the workshops at the end of each course) - https://courses.ansys.com/index.php/courses/bolted-connections/nnHope this helps,nSain
    • AnsysUser_101
      Subscriber
      Hello Sai, nThank you so much for your response. nOnly the weight of the model acts on the body + an additional distributed mass. I am trying to apply an acceleration to the assembly to see how it behaves.nI have included the picture.nnAnd for the boundary condition, I fixed the vertices to the ground. (Body-ground joint) And ran the analysis. I am getting results and it looks somewhat ok. I tried then again with fixed supports on the vertices and 0 displacements on the vertices, but the stresses I get are significantly lower compared to the fixed to the ground joint method. What should be the most accurate fixture? Was I correct in fixing the vertices to the ground? The logic was to simulate the real bc, in which this body will be bolted to the bigger body (let's say in the corners, allowing the beams (profiles) to undergo stresses). Is my logic correct? Could this be an acceptable representation of the actual problem? nThank you again.n
    • AnsysUser_101
      Subscriber
      n
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