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Recent content by nagi

  1. nagi

    mass scaling

    I guess you mean that you are now using implicit analysis? In that case, you should reduce the load gradually instead of just removing it at once.
  2. nagi

    bending or shear?

    I think the best measure is to check the ratio of bending or membrane energy to total internal energy in the model, but I don't believe most FE codes give such output. One qualitative estimate would be to plot the stresses at the shell midsurface and the stresses at the top (or bottom) surface...
  3. nagi

    bending or shear?

    Hi Jsboy, Are you talking about a shell or plate problem? In that case, there are two types of loading: bending-dominated and membrane-dominated. Is that what you mean? Nagi
  4. nagi

    mass scaling

    I agree with Drej that it all depends on the specifics of the model which we don't have that much information about. For such a slow speed process implicit analysis (with the right contact settings) will usually work. In many cases, such as this one where mass scaling is significantly...
  5. nagi

    procedure to solve complex equation

    I believe NASTRAN uses a complex Lanczos eigenvalue solver. Nagi
  6. nagi

    mass scaling

    Why aren't you doing an implicit analysis?
  7. nagi

    FE exam specific to each State? (Indiana)

    Also check out this website: http://ppi2pass.com/catalog/servlet/MyPpi They have a lot of useful references for the FE and the PE exams, as well as links to state boards. I just ordered a 30 day access to their Internet based Exam Cafe (for the FE exam). Nagi
  8. nagi

    Are High End FEA Software Packages Worth The Investment?

    I believe that if you don't need any of the advanced features of high end FEA software, and you customer does not dictate the choice of FEA software then you might be better off with a cheaper FE software. But I would be careful before concluding that I don't need the advanced features. Let's...
  9. nagi

    gear mesh stiffness variation

    What is the stiffness K that you are referring to?
  10. nagi

    Axi-symmetric geometrically nonlinear in hoop direction

    Hi dollbulldog, In large deformation axisymmetric analysis the equation relating the hoop strain to the radial displacement changes, so that must be taken into account in the FE code. Nagi
  11. nagi

    post processing of results

    I would use the averaged stress since it is usually closer to the exact stress value. The difference between the non-averaged values at a node is a measure of the error. If it is too large I would use a finer mesh. Nagi
  12. nagi

    Stick-Slip in Rubber Analysis

    I'm not familiar with ABAQUS, but this type of problem is common to FE analyses involving friction. You should try making the frictional constraint "softer". This means that the stick slip distinction is smoothed out. I believe in ABAQUS the parameter to do is the called the...
  13. nagi

    maixmum principal stress greater than von mises stress

    You're right cb4 the principal stress can't be that much higher than the von Mises stress for a curved beam since it is unlikely that the 3 principal stresses in that case be all comparable in magnitude (and same sign). Meher, what was the value of the maximum principal stress, the v.Mises...
  14. nagi

    maixmum principal stress greater than von mises stress

    Hi Meher, That is perfectly acceptable. If the 3 principal stresses are S1, S2 and S3, the von Mises stress Sv = sqrt( (S1-S2)^2 + (S1-S3)^3 + (S2-S3)^2 )/sqrt(2). So, the principal stresses can be greater than the von Mises stress. Consider, for example, S1=S2=S3=1000. The von Mises...
  15. nagi

    stress is greater than yield but plastic strain is zero?

    Feadude, I don't recall the values for the quadratic tet, but is should be relatively straightfoward (to go from nodal values to integration point values). You find the r,s,t coordinates of the integration point and substitute them in the shape function for each node. You then multiply the...

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