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  1. aerostress82

    Dear all I have a 3D model with

    If you had a perfectly constant size and quality mesh (if your current tet size is 10mm, you could achieve this perfection with 1mm elements), this type of FEA model would give you the maximum "force" element as the maximum "stress" element. It is a little sci-fi, but it the only way you can...
  2. aerostress82

    Not apply bolt preload, is it conservative?

    If you were checking the fatigue life on your bolts somehow for a selection of fasteners from a group of vendors, then you might have needed it. If you are only checking the static analysis for a "limit" loading, then you might want to have it again if those areas are expected to be critical...
  3. aerostress82

    Fatigue life calculation

    There is no easy simple way to assess the fatigue life in such structure on such a large aircraft. Your fatigue life isn't only the static loads that undergo the concentration factors, but is also vibrational effects. I've done both for some time, they are totally 2 different things. If you go...
  4. aerostress82

    Free vibration of a folded plate.

    The stress police got me and he is right. Let me try to clean up the garbage from my previous comment then. My above explanation about cog location, and the relation between each mode's behavior and your error between FEA and Matlab is still something you need to look into to understand what...
  5. aerostress82

    Effect of pitch for Composite joints

    Thank you both for your comments gentlemen. I sincerely appreciate all the insight you provided on this. Spaceship!! Aerospace Engineer, M.Sc. / Aircraft Stress Engineer
  6. aerostress82

    Free vibration of a folded plate.

    This will sound "not so good", but trying to help you however I can. First of all I didn't do this in Matlab before, so I can't help much with that. But I sure did natural frequency and frequency response analysis. So I'm familiar at FEA level only. Your first 4 modes actually correspond to: 1)...
  7. aerostress82

    Effect of pitch for Composite joints

    But it is bound by 1.15 so far, right? Have you ever witnessed a higher fitting factor for composite joints? Spaceship!! Aerospace Engineer, M.Sc. / Aircraft Stress Engineer
  8. aerostress82

    Getting the in-plane shear modulus G12 of a weave composite...

    From what I remember in my composite materials master's course 10 years ago, I believe you need to get it experimentally. It is not isotropic material anymore.. Spaceship!! Aerospace Engineer, M.Sc. / Aircraft Stress Engineer
  9. aerostress82

    Effect of pitch for Composite joints

    oops :) 1.15 is about right. Thanks for the correction Sir! Spaceship!! Aerospace Engineer, M.Sc. / Aircraft Stress Engineer
  10. aerostress82

    Need Opinion on Stress Analysis Procedure for Interior Monument Honeycomb Laminates

    I understand why you are trying to model everything as shell elements including the core+laminates. Why wouldn't you consider modeling your core as hex elements? And at locations where your core is ending and you are left only with laminates, use wedge elements for these transition region cores...
  11. aerostress82

    Effect of pitch for Composite joints

    Depending on the behavior of your structure under loads (ie. bending/shear/tension/compression + direction of these behaviors), you will have fitting factors of 1.5 coming into effect in your joint calculations at these rows of fasteners with specific directions of loading (as mentioned in the...
  12. aerostress82

    Load Extraction Procedure in Bolted/Riveted Joints

    Thanks SWComposites for the additional explanations. Just a couple more comments and one correction with regards to what you mentioned about 4 elements at the fastener pitch: 1) Using 4 elements instead of 3 elements at every fastener pitch is a lot better approach actually. This will help you...
  13. aerostress82

    Load Extraction Procedure in Bolted/Riveted Joints

    Method 2 will give you the best accuracy on this, but you need to be careful: 1) Model each fastener one by one as CBUSH elements (with 6 dof, out of plane rotational stiffness being a dummy/small value just to avoid singularity in your model) 2) Have your coincident nodes CBUSH element located...
  14. aerostress82

    bearing strength vs. thickness

    I finally checked Al7075 T6 material bearing values for 0.1" and 0.2" (couldn't check it all day because of the busy workday). I remember the bearing strength values of sheets being different, but after your message now went ahead and checked it in detail. You are right. I remember significant...
  15. aerostress82

    bearing strength vs. thickness

    ESPcomposites Careful with the D/t. It is mainly related to bending of the fastener. (both for composite and metallic) Also careful with bearing knockdown factor for blind rivets. Blind rivets and Hi-Loks are also different in bearing behavior. Blind rivets have a knockdown factor to reduce the...
  16. aerostress82

    How many nodes/elements/DOFs do you work with?

    ...are SPCs applied at the cut nodes. you will get some extra stiffness if you cut the model too short for static analysis under mechanical loads. ***remembering Kirchhoff's Rule for structural analysis, try to maintain the structural circuit up to some level as much as you can - either by...
  17. aerostress82

    MPC (RBE2, RBE3) sol400 NASTRAN multi step analysis

    You are missing NLPARM card in step 2? Not so sure, but this is the only thing I can think of as I can't check your model at home without any FEA software. In the company, they won't allow me to look into this. So I'm just text reading your bdf file. Spaceship!! Aerospace Engineer, M.Sc. /...
  18. aerostress82

    bearing strength vs. thickness

    AB & BC: Both are bearing. CD: Fastener shear failure. The reason is your material billet thickness. Different billet thicknesses of the same material have different bearing allowables. And bearing always is linearly proportional to thickness for a constant billet size of any metallic...
  19. aerostress82

    MPC RBE2 SOL400

    Even if this is student post and this whole post will be deleted later, I want you to understand what you are doing. So copy paste it somewhere right away.. You most probably have all 6 degrees of freedom locked at your boundary nodes at the lower side of the panel. On the upper side of the...
  20. aerostress82

    hex to wedge elements

    I assume this is happening at the lovation where the matrix is touching the laminate ply. If this is the case, I understand your unknown and raise ypu one. In theory, the matrix will support out of plane forces, and there will be some interlaminar shear at the matrix faces. And then you will...

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