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  1. sdm919

    Aircraft Loads Simplification

    I agree with rb1957's comments. Skin buckling and wing loads are more like two separate and large subject areas. You may be making your study too complicated by combining them. If your study is more about buckling of the skin panels, you could assume ranges of loads as rb1957 suggested...
  2. sdm919

    Nastran sol 106

    What type of behavior are you expecting? If you're just testing the nonlinear capabilities of Nastran, you would probably be better off using one of their example problems. Is Nastran trying to iterate at all? Check the f06 file for the convergence information. It might be converging right...
  3. sdm919

    Buckling with Inertia Relief

    Glad to hear your static runs with inertia relief are running. I am not sure why the buckling run does not work. I can only suggest more tests. As you found, the test case with a ring of CBARs is not necessary for the static run, but it still might be a worthwhile test to see if it helps the...
  4. sdm919

    Buckling with Inertia Relief

    Sorry I don't have the software to look at the model, I can only read the text file. So I am still "only guessing". If possible, the idea of supporting the model at only translational DOFs at 3 distinct points might work. Note that SUPORT and SUPORT1 are different cards. My first question...
  5. sdm919

    Buckling with Inertia Relief

    Just a guess: Does your SUPORT1 node have the ability to take moments? The 456 on the support card basically require that point to have that ability. Does your model have solid elements? Is the SUPORT1 node attached to only solid elements? That might be the problem. Solid elements cannot...
  6. sdm919

    Bruhn C10.18

    My interpretation is that "c" is the width of the space between the holes and "h" is the height of the web.
  7. sdm919

    Bruhn C10.18

    In reading L-323, they state that the formula is empirical. It appears that they took sort of an average between 2 shear buckling loads, fsh and fsc. fsh is the shear buckling load for a long rectangular plate with width "h" and length "long". fsc is the shear buckling load for a long...
  8. sdm919

    Composite Anisotropy

    I believe the effect can be minimized by using fabric plies instead of tape (recall SWC said the effect matters for TAPE materials). In a laminate made of tape plies, a given +45 ply is balanced by a -45 ply, but they are at different distances (in the z-direction) from the mid-plane. Being...
  9. sdm919

    TABLES1 limited number of stress/strain entries for SOL 401 Using FEMAP 24.06

    No problem. By the way, the when I plot the data in Excel, it looks a little "bumpy" to me. I don't think anything is technically wrong, but jobs might behave better if the curve is smoother. I assume the slope for aluminum alloys would be decreasing all the time, whereas this curve has a...
  10. sdm919

    TABLES1 limited number of stress/strain entries for SOL 401 Using FEMAP 24.06

    I am not aware of limitation of number of points in the table. Your points 6 and 7 seem to be the same point: 0.03 strain, 35100 stress. That may be the problem.
  11. sdm919

    Composite Anisotropy

    I found this figure in the book "Structural Analysis of Laminated Anisotropic Plates" by James M. Whitney, Technomic, 1987 (page 155) It shows the difference in buckling load under positive and negative shear loads for [(+/-45)n]sym laminates. The difference becomes smaller as the number of...
  12. sdm919

    Composite Anisotropy

    one more thing I should have added... An for any given laminate, if you interchange the +45 and -45 plies, you will change the sign of the D16 and D26 terms, but not the magnitude. Again, looking at the ADB matrices of lots of sample laminates should be instructive.
  13. sdm919

    Composite Anisotropy

    Yes, and what you have noticed is what makes the difference between "orthotropic" and "anisotropic" analysis. In the bending stiffness matrix, the bend-twist coupling terms D16 and D26 make the difference. When D16 and D26 are not zero, the D matrix is "fully populated" and referred to as...
  14. sdm919

    Looking for the Royal Aeronautic Society Data Sheets from the 1940s.

    Sorry, here's the Cook & Rockey data table... https://files.engineering.com/getfile.aspx?folder=8115ad36-5757-4d50-a512-228528e6fb59&file=Cook_and_Rockey.jpg
  15. sdm919

    Looking for the Royal Aeronautic Society Data Sheets from the 1940s.

    Yes, I had the wrong exponent for one of the terms in the Galambos equation for that case. With that correction, the 4 curves in my version of the Data Sheet agree fairly well with the 4 curves using the Galambos equations. Also, the Cook & Rockey data for the case of long simple/short fixed...
  16. sdm919

    Looking for the Royal Aeronautic Society Data Sheets from the 1940s.

    My copy of the Data Sheet says "Third Issue June 1963" The most recent reference referred to by the data sheet is: Shear Buckling of Rectangular Plates with Mixed Boundary Conditions I. T. Cook and K. C. Rockey The Aeronautical Quarterly Volume XIV, November 1963, Part 4 pages 349-356 I have a...
  17. sdm919

    Looking for the Royal Aeronautic Society Data Sheets from the 1940s.

    Sorry I just saw this. I have a copy of Data Sheet 02.03.01. I can confirm that nu is built into the buckling coefficient, with an assumed value of 0.3. I did a quick comparison using the equations from Galambos as a baseline (Guide to Stability Design Criteria for Metal Structures, Fifth...
  18. sdm919

    Help Understanding Limit Load and Margin of Safety

    Maybe it's confusing because we're using the word "load" for both internal and external loads. The load P at the end of a cantilever beam is the external load, which causes internal loads and stresses at various locations inside the beam. The MS is written based on internal loads/stresses at...
  19. sdm919

    Help Understanding Limit Load and Margin of Safety

    I won't discuss your particular examples, but I will provide some general information. You can think of limit load as the highest "actual" load the part will ever see. To ensure the part is safe at that load, we design it to the ultimate load, which is the limit load times a factor of safety...
  20. sdm919

    Which Type of Stringers cross section is most preferred in aircraft wing and fuselage

    here is the second picture I intended to send in the previous post https://files.engineering.com/getfile.aspx?folder=1bf7b842-13d9-452f-84fe-9e1374ae30c2&file=pic1.JPG

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