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  1. astro808

    Simply Supported Boundary Conditions

    Brian, When you say "soft springs" what do you exactly mean by soft? I have tried them as you suggested, but do not understand how they are changing my buckling eigenvalues. (running implicit global buckling in ls-dyna) For example, I am using lbf/in for units and applying unit loads to a...
  2. astro808

    Combined Compressive-Shear Buckling

    Yes that was a typo error. Thanks for the input. I have noticed you are always the one who answers my questions. Thank you. BTW I am anxious to see your book.
  3. astro808

    Combined Compressive-Shear Buckling

    From Bruhn, eq.C5.11: Rs + RL^2 = 1 is the criteria for combined shear and longitudinal stress. This is from NACA-ARR-3K13 "Critical stress for an infinitely long flat plate with elastically restrained edges under combined shear and direct stress", this is for constraints against rotations on...
  4. astro808

    Simply Supported Boundary Conditions

    CORRECTION My BC's for uniaxial loading is: unit load at A (distributed to all nodes along A) SPC's (applied to all nodes along boundary) A - 13 B - 3 C - 123 D - 3
  5. astro808

    Simply Supported Boundary Conditions

    I am attempting to model the buckling of a plate subject to the following loading conditions Uniaxial loading Biaxial loading Shear loading Uniaxial-Shear loading Biaxial-Shear loading See attached image (shows Biaxial-Shear Case)...
  6. astro808

    Stealth and Supersonic Aircraft - Buckling????

    rb - lol... I was leaning towards the later, self included :) BTW this is my second thread, first one was over the summer is a different forum. You are somewhat correct about my reasons for looking although the person I am trying to check is myself. I believe that this is true, just curious if...
  7. astro808

    Stealth and Supersonic Aircraft - Buckling????

    Sorry the post seems to vague. Let me pose the question this way. When designing a commercial aircraft, do companies ever decide that it is acceptable to allow for buckling below limit? Ans: YES, effect on aero performance can be minimal. When designing a stealth aircraft, do companies ever...
  8. astro808

    Stealth and Supersonic Aircraft - Buckling????

    @IRstuff Wing panels can carry additional load beyond the initial buckling load. It is common practice to utilize this additional load bearing capability, even for below limit load cases. I included one quick ref from an online search. "In a typical wing structure the skin panels are...
  9. astro808

    Stealth and Supersonic Aircraft - Buckling????

    I was thinking about limit loads. You make a good point by asking under what condition the critical load occurs. I was just looking for a general answer. I am trying to justify if the panels are designed to account for load carrying capabilities beyond initial bucking (ie post-buckling) under a...
  10. astro808

    Stealth and Supersonic Aircraft - Buckling????

    I was wondering if anyone could tell me for sure if skin buckling is permitted to on stealth or supersonic aircraft? I assume it is not allowed on a stealth plane because the skin buckling would cause a change in the skin shape which is important to the stealth characteristics of the plane...
  11. astro808

    Tri-element geometric stiffness

    Hi everybody, I am trying to write a small script to determine the total geometric stiffness matrix of a FE model containing only triangular plate elements with bending stiffness similar to the NASTRAN TRIA3 elements. I found several definitions of the geometric stiffness matrix (3x3) of such...

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