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Thread: BLACKOUT vs BE Meyers -- drop test

  1. #31
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    This is all fine and dandy, but what I want to see is this item installed on a gun, put into a M1950 weapons case, Jumped, lowered, PLF completed.

    Then same as before but ride the weapon in on a tree landing, lower equipment and drop it, pop your reserve and take precautions to climb down the outside of the chute.

    Then Jump weapon exposed from 800 Feet AGL, do a PLF on the weapon.

    All this computer simulations crap is just that, CRAP. You cant hit Control, Alt, Del on your weapon in real life.
    Life is too short to deal with Blonde women, or carbine barrels over 10.5 inches

  2. #32
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    I see your point, but I do not completely agree in regards to computer modeling....it SOP in every industry now, and is extremely reliable, more so than many older testing procedures. But, to ease your mind...the Blackout flash hiders are approved and in service with super-badasses in the nastiest parts of the world.

  3. #33
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    Quote Originally Posted by kevin/aac View Post
    I see your point, but I do not completely agree in regards to computer modeling....it SOP in every industry now, and is extremely reliable, more so than many older testing procedures. But, to ease your mind...the Blackout flash hiders are approved and in service with super-badasses in the nastiest parts of the world.
    Wheres that Cockheaded Owl pic when I need it. Feel free to pm me some POC's that I can talk to on the SIPRnet.
    Life is too short to deal with Blonde women, or carbine barrels over 10.5 inches

  4. #34
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    I do not mean to be difficult but if I were you I would not be posting that Von Misses stress comparison showing the deflections. Without more details on the meshing type you used and the element resolution at the areas of maximum strain, the three prong unit is in a fatigue condition, and if the materials you quote are correct then there will be a reasonable percentage of failures under that load condition.

    For my own interest, why did you represent the model output as a stress; strain is usually more useful? Also did you check the element flexibility for that load patern, your deflections look a little high for a simple bending calculation and that will drive the Von Misses energy calculation.

    May I suggest that if this is indeed one of the loads that this item absorbs that you run a series of cyclic loading tests.

    Bill Alexander

  5. #35
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    Quote Originally Posted by kevin/aac View Post
    I see your point, but I do not completely agree in regards to computer modeling....it SOP in every industry now, and is extremely reliable, more so than many older testing procedures. But, to ease your mind...the Blackout flash hiders are approved and in service with super-badasses in the nastiest parts of the world.
    SOP and will extremely reliably get you about 50% right, perhaps.

    Talk to any of the aerospace modellers and they will always model out a design "before" they make a prototype and test it anyway. Those who are experienced will get close to the real world, Those who are very experienced will tell you to run the tests before they will give an opinion.

    Did not notice the post about FEA being like a ruler, yes quite true and about as accurate when you are trying to measure either 17 microns or 1700 yards.

    Bill Alexander
    Last edited by Bill Alexander; 02-27-08 at 13:36.

  6. #36
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    I agree it is hard to get absolute results from FEA. For the relative difference between the two geometries though, it is pretty useful, and can help you pick which geometry to go with.

    As for strain, I gave a prediction of max deformations in mms. While I don't feel these absolute numbers are useful on their own and cannot be taken literally, I think they are useful to divide one with the other and see the difference (one has 3.6x more deflection than the other). But yes, there are many ways to run the analysis and a lot more output options. If the report was generated for an engineer it would need to be more complete but I am trying to make this as simple as possible. As it was the first images I posted were immediately misread so I simplified them.
    Last edited by rsilvers; 02-27-08 at 16:47.

  7. #37
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    Unless you can control your element size and deformation percentage across the differing geometries, particularly in the areas of greatest deformation, what you are attempting is quite dangerous and can be misleading. Still we are only dealing with a flash hider not an engine mount.

    My question about strain was related to the Von Misses energy result. Von Misses is a representation of the strain energy or node deformation within each element. Again I am at a loss for the code that you ran just as the element type but the stress is a calculated result from the input material properties.

    The elegence of the strain in this analysis is that it accounts for the failure state of the material from all three principle strains induced in the element. I forget the exact approach but I recall it calculates the principle shear strain energies (hence the Von Mises)

    Deformation in this analysis if your figures are correct is irrelevent. Deformation is a result of strain and is dimensional and positional. Strain is the failure criteria for the material. Deformation is only of interest if the deflection influences the function of the part.

    The result however shows that there is a likelyhood of a fatigue failure in this part if the load condition exists. If the load condition does not exist why waste valuable analysis time.

    Bill Alexander

  8. #38
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    Quote Originally Posted by scottryan View Post
    FEA is scientific fact. Like using a ruler to measure something.
    No it isn't, it is a computer simulation and analysis.

    Here is an example of how Boeing stress tested the 777 after completing design and computer modeling. Boeing 777
    Also take note, Boeing did not apply the test to an Airbus and include it in the video.

  9. #39
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    My goal was to apply the same virtual force to two models and determine the potential difference in deflection. It does not represent the strain within each node, but is not irrelevant because it is what I sought to model. Deformation can lead to fatigue and I have seen this induced in actual parts. This is really a 'no duh' outcome. Take a four prong model where each prong is thinner and longer, and one would expect it to deflect more. My results are just a way to illustrate what we would intuitively know.

  10. #40
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    Quote Originally Posted by Trim2L View Post
    Here is an example of how Boeing stress tested the 777 after completing design and computer modeling.
    That was awesome. The software predicted the exact location of the break.

    Also take note, Boeing did not apply the test to an Airbus and include it in the video.
    That would cost a lot.

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