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post #1 of (permalink) Old 08-24-2000, 02:31 PM
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First roll bar analysis picture

Here is the first analysis. I basically hit the drivers side of the roll bar with 20,000 lbs of force, coming from a 45 degree angle from the ground, up and in toward the middle of the cage.

the picture shows the stress concentrations in the cage. Anything red is above the yield point, and has started to deform and absorb energy. Any other color is under the yield point and will return to its original shape. The bar is deformed in the pic. The deformation has been exagerated 10% so it could be seen better.

This program treats all materials as if they are linear, so if you are farmiliar with stress vs strain of steel, this program just takes the linear section (below yield point) and extends that line into infinity, and follows it for the calculations. In real life the material starts to "neck" and the stress vs strain plot begins to level off, and become non-linear. This allows the material to deform and absorb energy. My program doesn not accurately depict this. I wish I could expalin it in easier terms, but I can't do it and still make sense.

I short terms, the displacement of the cage will be larger than the .25 inch shown, but the max stress will be much lower than the shown max. In real life the max stress will bebelow the UTS of the steel.

This is 1018 steel.

the picture just shows the parts that are going to give first. These parts will deform. I am going to try some other things tomorrow.

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post #2 of (permalink) Old 08-24-2000, 03:16 PM
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Re: First roll bar analysis picture

[img]/wwwthreads_images/icons/smile.gif[/img] Pretty good work, Jesse. That's a very graphic way to see how the cage "works" with the stresses. Matt 1911 may be posting a "C" cab style ROPS later today; if he does, will you take a look at it also and see if it can be analyzed as well. I got to thinking about that when I noticed a power roller with a "C" cab ROPS. The "C" cab design seems to solve several problems associated with entry and exit and getting the front bars to hold up.[img]/wwwthreads_images/icons/smile.gif[/img]

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post #3 of (permalink) Old 08-24-2000, 03:28 PM
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Re: First roll bar analysis picture

That is interesting. I like the depiction and the gradients, very easy to follow. Hit it again! Hit it again! Sorry, just in one of my destructive moods.

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post #4 of (permalink) Old 08-24-2000, 03:31 PM
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Re: First roll bar analysis picture

Yeah, depending on what system he is using to design the bar, it may be really easy to analyze.

Most likely it will involve me redrawing it in Pro-E and then analyzing it, but that is not a big deal either. Seeing somone else model it will help me visualize it alot better too, for the analysis model. I will check back a few times tonight to see if I can spot the post.

I forgot to mention. I left the gussets off my analsys model for simplicity, and I am also using the gussets as a factor of safety.

Jesse

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post #5 of (permalink) Old 08-24-2000, 03:44 PM
 
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Re: First roll bar analysis picture

You can see that the frame mounts had better be solid. Very intersting. Good to see my physics class helping me understand this. Is this a roll situation with a 9.8m pr sec constant gravitational pull on the total vehicle weight with any frictional force? Is your program that complete? Looks real good though and im interested to see the next batch. Max

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post #6 of (permalink) Old 08-25-2000, 11:20 AM
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Re: First roll bar analysis picture

Looks good so far, but we need more, more, more. I would like to see a couple more shots, namely a top hit, and an angle hit to the side near the upper radius to simulate the pivoting action the cage sees during a slow or moderate roll.

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post #7 of (permalink) Old 08-25-2000, 12:04 PM
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Re: First roll bar analysis picture

Yeah, I know I want to do some more analysis too. We only have one license of Mechanica here, and it is shared between engineers and designers. It has been pretty busy with work stuff, so I am hoping to get a run in over the weekend, and post another on on Monday. I plan on hitting it from several angles, and multiple angles.

I do have another picture, with the basic CJ 7/YJ shape "faked" in around the bar. Basically I sort of drew the body in from memory, and a picture of my jeep at my desk during lunch today.

I also learned how to output the 3d model as a VRML file, to view with cosmo player 2.0 (and other programs, I am sure). That means you can download free software, and spin, zoom, rotate the model as if it were 3d, if you have a fast machine and a good graphics card.

I am posting the picture here, but the zipped up vrml file is too big. If someone has an FTP site or something I can send the vrml file to for you to post for download, then I will.

Then we can download it and see the bar, and basically where it will be in the body from any angle.

This picture does not show the gussets, and the ones it shows are gonna change to the outside of the bar, not the centerline.

Jesse

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post #8 of (permalink) Old 08-25-2000, 12:21 PM
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Re: First roll bar analysis picture

I got one VRML, zipped up to just fit under the size constraints here at ORC. It is just of the rollbar, but pretty cool none the less. I like computers more and more, the more I learn about them.

You will need a viewer to see it once you download.

I am using Netscape (latest version I think) and Cosmo Player 2.0. I got it to work on my computer, and hopefully ya'll can get it to work on yours.

I will post it, and we will see how it goes. You will have to download it, and unzip it. Be sure to scan for viruses first, because this is my work computer, and the IS dept handles all the virus scanning and stuff.... not that I don't have fiath in them, but just in case,

Jesse

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post #9 of (permalink) Old 08-25-2000, 05:57 PM
 
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Re: First roll bar analysis picture

Looking real good!
By the time you add a little extra sleeve and sill mount for the cage attachment points, you won't have any problem areas at all.

You did one hell of a job Jesse!! Take a bow!

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post #10 of (permalink) Old 08-25-2000, 06:44 PM
 
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Re: First roll bar analysis picture

Jesse:

Can you "hit" it again either right at the top corner or just shy of the top corner of the cage? Maybe at 90 from the side (parallel with the top) rather than 45, kind of like the jeep flopped down while sidehilling? That's the roll that scares me the most. Thanks for the great work--I deal with a few people that use Pro-E and I'm always amazed at what comes out.

Ken

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