Hello I wanted to know if someone can enlighten me on the notion of buckling, indeed I want to study an automobile spar and for this I intended to make the analogy between a spar and a can in order to do simpler experimental tests. This analogy seemed relevant to me because the spar and the bobbin are buckled during a deformation. However, on the internet, some say that it's not really flambé. I now doubt my analogy and I would like to know if my analogy is really relevant and what are the different similarities between the bobbin and the spar, if not the differences. Thanks in advance
Hello
Basically, buckling is a bending deformation of a beam drunk at a compressive load, so you need a "big" slenderness.
https://image.slidesharecdn.com/12-poteaux-140902135348-phpapp02/95/12-poteaux-16-638.jpg?cb=1409666220
For a bobbin, or any other profile, you can have a local warping of part of the shells. Cf. https://image.slidesharecdn.com/courscm1chapitre1introductiongenerale1112-libre-150505044304-conversion-gate02/95/cours-cm-1chapitre1introductiongenerale1112libre-77-638.jpg?cb=1430819103
To be able to make the parallel spar / bobbin: are all the spars identical and if not does the bobbin have similarities?
Hello
Decidedly, car stringers and cans by analogy are in fashion, it's time.
As there are several needs or questions in your request for the can look at my comments here https://www.lynkoa.com/forum/solidworks-simulation/peux-ton-%C3%A9tudier-la-d%C3%A9formation-dune-canette-sur-solidworks-peut-ton-sim
The choice of the bobbin will bring you nothing more than the drawing of a spar and in addition it would distort the calculations if you managed to make this simulation (see the attached links)
and also here https://www.lynkoa.com/forum/solidworks-simulation/simulation-crash-automobile
As far as buckling is concerned, there is a fairly common definition which essentially aims, for the framework or good-sized frames, to predict the acceptable buckling (depending on whether or not it is recessed). In the standards of the structural beams, the supplier also directly gives the values.
But you have to be very careful about the very polysemic side of the word "Buckling" because as you will see if you read the two links above you always have to say if the buckling takes place in the elastic field or in the plastic field.
Coachbuilders frequently have flaming chassis and spars. In these cases, it means that these metal objects have passed into the plastic domain since the deformation has become permanent.
The important thing to remember is that buckling is a characteristic deformation well described in the basic literature.
What you can add without it changing anything in the debate is that buckling is often accompanied by twisting.
And it is for this reason that we can say that in the case of a crash it is not a pure buckling since there are several concomitant and simultaneous deformations, Buckling + Twisting + Accordion deformation + tear opening, etc...
Kind regards
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Good evening actually, even if the results on the bobbin are not exactly the same as the results on a spar. I intended to make a can/spar analogy only to know the behavior of the general spar. In fact, are the bobbin and the spar subject to the same physical phenomenon? The car spar is subjected, as you say, to buckling, twisting, accordion deformation, tear opening, etc., but if the can during an impact undergoes the same phenomena, isn't the analogy so stupid?
Another question attached is a video of an experiment I performed, For 4.5kg of weight when I repeat the experiment 10 times I have 10 times the same deformation but when I increase the weight to 9kg and repeat the experiment 10 times, it is impossible to have 10 times the same deformation. Why is that?
video-1546546402.mp4
Good evening
Does the square of speed speak to you.
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Good evening
Cf. Zozo_mp , you multiply the energy of the shock by 2, thus increasing the deformations and therefore the divergences due to the inaccuracies of your experimental set-up.
For your can/spar analogy, apart from the general principle, I have big doubts: you would have to take into account the scale factors (for dimensions, energies and speeds) and as a bonus you would have to find more information on viscoplasticity.....