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Old 9th May 2011, 13:41   #1
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Question Flexural Stresses on Jeep Hardtop

I'm planning a half hard top for my upcoming jeep.
It'll basically be a rally style top:
Name:  Hard top.jpg
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It'll either be made of metal or aluminum. Most likely metal.

Now my questions are:

- will the hard top be able to take the flexing stress or will it crack?
(i don't want leakages happening)

- anyway to prevent this?

I will be adding an external roll cage.

The side may or may not have the small window. At the back i will be fixing a plane of gypsy windshield glass.

According to allan who's doing up the jeep, since we are extending the top behind the 'B' pillar by approx a foot, there could be more stresses.

Last edited by Tejas@perioimpl : 9th May 2011 at 13:43. Reason: added last line to the post
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Old 9th May 2011, 13:48   #2
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Default Re: Flexural Stresses on Jeep Hardtop

Tejas,
Aluminum is more flexible compared to sheet metal (advised).
The flex stress will act upon a hard top but a roll cage inside, should minimize the twist impact.
Regards,
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Old 9th May 2011, 16:51   #3
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Default Re: Flexural Stresses on Jeep Hardtop

Tejas check the hard top design, Amit Gaud has made.. the guy who drives the really huge green mahindra 540! He's got a hard top made for a clients jeep in pune. Maybe a look at that will help you!
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Old 9th May 2011, 18:33   #4
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Default Re: Flexural Stresses on Jeep Hardtop

Quote:
Originally Posted by fazalaliadil View Post
Tejas,
Aluminum is more flexible compared to sheet metal (advised).
The flex stress will act upon a hard top but a roll cage inside, should minimize the twist impact.
Regards,
Thanks.

Quote:
Originally Posted by SunChaser View Post
Tejas check the hard top design, Amit Gaud has made.. the guy who drives the really huge green mahindra 540! He's got a hard top made for a clients jeep in pune. Maybe a look at that will help you!
I want to take feedback from people who use it for offroading not daily drives. I've seen the white 550 with black top you are talking about. It's good, but i want a half top.
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Old 9th May 2011, 18:45   #5
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Default Re: Flexural Stresses on Jeep Hardtop

Quote:
Originally Posted by Tejas@perioimpl View Post
I'm planning a half hard top for my upcoming jeep.
Tejas, are you doing this on a 540?

Quote:
- will the hard top be able to take the flexing stress or will it crack?
(i don't want leakages happening)
If a well done FRP / Injection molded part can withstand abuse then no doubt about a sheet metal part. All depends on what is done, there are very simple techniques to make a flexible sheet stiff. Observe the roofs of vehicles and you will understand, moreover you will have to add strengthening ribs for added strength. Incorporate gutters for water drain.

Quote:
It'll either be made of metal or aluminum. Most likely metal.
Aluminium is also a metal. I understood though.

Quote:
Originally Posted by fazalaliadil View Post
The flex stress will act upon a hard top but a roll cage inside, should minimize the twist impact.
Whats this? Didn't understand.

Spike

Last edited by SPIKE ARRESTOR : 9th May 2011 at 18:48.
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Old 9th May 2011, 19:09   #6
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Default Re: Flexural Stresses on Jeep Hardtop

Tejas,

Irrespective of what you finally decide, how about getting an easily removable hard top? And for the times that you remove the top, and still need protection from the sun, have a temporary bikini soft-top made.
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Old 9th May 2011, 19:24   #7
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Default Re: Flexural Stresses on Jeep Hardtop

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Originally Posted by SPIKE ARRESTOR View Post
Whats this? Didn't understand.
Spike
If a roll cage is added internally along side the A and B pillar, and the pillars fastened to the rigid roll cage, the flexibility should be reduced due to a stiff roll cage as compared to its non existence, no?

Therefore, my humble recommendation was the internal roll cage.
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Old 9th May 2011, 19:34   #8
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Default Re: Flexural Stresses on Jeep Hardtop

Quote:
Originally Posted by fazalaliadil View Post
If a roll cage is added internally along side the A and B pillar, and the pillars fastened to the rigid roll cage, the flexibility should be reduced due to a stiff roll cage as compared to its non existence, no?

Therefore, my humble recommendation was the internal roll cage.
Oh you were talking about an internal roll cage? Ok, but I feel connecting the A and B pillar to the roll cage would make it more stiffer not allowing it to move, why do you think so? Typo?

I would also prefer an internal roll cage any day, of-course personal opinions may differ.

Spike
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Old 9th May 2011, 20:42   #9
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Default Re: Flexural Stresses on Jeep Hardtop

the only concern here is the chassis twist happening in our old 550's
as a result you see cracks in the rea tail gate side and under the front doors.

a roll cage internal or extrernal straight to the chassis at 6 points can reduce this chassis twist to tolerable limits,
but then you compromise on articulation
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Old 10th May 2011, 09:55   #10
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Default Re: Flexural Stresses on Jeep Hardtop

Quote:
Originally Posted by Tejas@perioimpl View Post
I'm planning a half hard top for my upcoming jeep.
It'll basically be a rally style top:
==============
Now my questions are:

- will the hard top be able to take the flexing stress or will it crack?
(i don't want leakages happening)

- anyway to prevent this?
Tejas, I have the exact same style (without the side windows) on the Gypsy. Now I don't know what would be the difference of the body-flex on Gypsy vs the Jeep but my hard top has been holding very well. No issues of any rattle, leaks or vibrations/squeaks.

And yes, it is made out of metal sheet.
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Old 10th May 2011, 11:04   #11
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Default Re: Flexural Stresses on Jeep Hardtop

Quote:
Originally Posted by SPIKE ARRESTOR View Post
Tejas, are you doing this on a 540?
Ex army 550. (non NGCS)

Quote:
All depends on what is done, there are very simple techniques to make a flexible sheet stiff.
Won't a stiff sheet crack under stress rather than a flexible one? During flex, the left and right parts of the body will bend in opposite directions. A flexible sheet will twist and reform to original shape. A rigid one will resist bending until a critical stage after which it will either give way at the welding joints from the body or crack itself.

Am i correct?

Quote:
Observe the roofs of vehicles and you will understand, moreover you will have to add strengthening ribs for added strength. Incorporate gutters for water drain.
Please elaborate how many ribs are required? On the phone behram said to make a frame using hollow 1" x 2" square pipes to make the frames and then weld the sheets over it.

Can you give a schematic of what the frame would look like. Eg: a square first then maybe and X pattern inside?

Quote:
Aluminium is also a metal. I understood though.
Lol. Ya sheet metal steel.


Quote:
Originally Posted by GTO View Post
Tejas,

Irrespective of what you finally decide, how about getting an easily removable hard top? And for the times that you remove the top, and still need protection from the sun, have a temporary bikini soft-top made.
I'd love to have a concept like that but it's not possible to do. I've many times toyed with the idea of bringing down the tub of a CJ7 or some other Jeep body so that i can get direct bolt on hard tops and other fittings for it. The cost factors are prohibitive though.

Quote:
Originally Posted by xtreme power View Post
the only concern here is the chassis twist happening in our old 550's
as a result you see cracks in the rear tail gate side and under the front doors.

a roll cage internal or external straight to the chassis at 6 points can reduce this chassis twist to tolerable limits,
but then you compromise on articulation
True. Let's find a solution.

Quote:
Originally Posted by khan_sultan View Post
Tejas, I have the exact same style (without the side windows) on the Gypsy. Now I don't know what would be the difference of the body-flex on Gypsy vs the Jeep but my hard top has been holding very well. No issues of any rattle, leaks or vibrations/squeaks.

And yes, it is made out of metal sheet.
Nice to hear that. But i think the gypsy flexes less than the jeep. I may be wrong though.

What is the chassis section of a gypsy? C or box?

Last edited by Tejas@perioimpl : 10th May 2011 at 11:08. Reason: typo
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Old 10th May 2011, 11:29   #12
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Default Re: Flexural Stresses on Jeep Hardtop

Not 100% sure, but will a floating/semi floating cabin (rigid) help resolve the issue?

I've seen lots of trucks (commercial) that have a their front cab section floating independently of their chassis (ladder frame).

I believe that the Freightliner P4XL has this application.

You might have to experiment with the body mounts or something else.. It can be a "first" in Indian offroaders in case it hasn't been done already.
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Old 10th May 2011, 11:40   #13
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Default Re: Flexural Stresses on Jeep Hardtop

Shouldnt one be strengthening the chassis (ladder frame) instead of making the Hardtop flex resistant?

Does the chassis of the MM550 flex so "badly"? Surprising.

The Classic's tub never had any issues.. yet..
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Old 10th May 2011, 11:46   #14
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Default Re: Flexural Stresses on Jeep Hardtop

Quote:
Originally Posted by R32_GTR View Post
Not 100% sure, but will a floating/semi floating cabin (rigid) help resolve the issue?
Not sure about it but won't a floating/semi floating cabin give crazy body rolls?

Quote:
Originally Posted by Spitfire View Post
Shouldnt one be strengthening the chassis (ladder frame) instead of making the Hardtop flex resistant?

Does the chassis of the MM550 flex so "badly"? Surprising.

The Classic's tub never had any issues.. yet..
The issue is that if we make the the chassis flex resistant, we loose articulation. I don't want to make the hardtop flex resistant, i want to make it capable of withstanding / absorbing the stress.

Classic is a short and narrow wheel base that's why.
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Old 10th May 2011, 16:08   #15
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Default Re: Flexural Stresses on Jeep Hardtop

here some more pictures of the hard top.
Name:  1009_4wd_042007_jeep_wrangler_JK_unlimitedavenger_titeTop_half_cab.jpg
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Name:  1009_4wd_052007_jeep_wrangler_JK_unlimitedopen_tailgate.jpg
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Name:  1009_4wd_062007_jeep_wrangler_JK_unlimitedclosed_tailgate.jpg
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Size:  25.9 KB

Name:  Raider Moab_3.JPG
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Size:  55.5 KB

Name:  RaiderMoab037.jpg
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Size:  53.4 KB

Name:  RaiderMoab226.jpg
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Name:  RaiderMoab285 Medium.jpg
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Size:  71.5 KB

there is a internal roll cage as well.
Name:  photo51.jpg
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rgds,
Nikhil
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