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Old 10th May 2011, 20:43   #16
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Default Re: Flexural Stresses on Jeep Hardtop

Tejas,
If you can, order these (2nd pic post #15) LED tail lamps (also used on the IKON Dog). The ones you are proposing to order from Australia are common and not as good as these.
Regards,
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Old 11th May 2011, 07:36   #17
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Default Re: Flexural Stresses on Jeep Hardtop

Quote:
Originally Posted by Tejas@perioimpl View Post

I don't want to make the hardtop flex resistant, i want to make it capable of withstanding / absorbing the stress.
1) Achieving it with any metal body looks doubtful Unless you make the joints between two panels flexible enough.

2) Try non metal material , such as kinds of FRG/P , Plastics (HD) etc for panels bolted over thin metal frame ,

3) one wild suggestion, try some tough flexible material such as used in conveyor belts , or like wise bolted on metal frame ( made of sections from sheet metals )

Sudarshan

Last edited by Sudarshan : 11th May 2011 at 07:37.
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Old 14th May 2011, 08:22   #18
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Default Re: Flexural Stresses on Jeep Hardtop

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Originally Posted by khan_sultan View Post
..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.
Yours is officially not a Gypsy anymore Khan, its BIGGER, looks more brute, destroying things along its way!! Now all you need is no more roads!!


Quote:
Originally Posted by Tejas@perioimpl View Post
Won't a stiff sheet crack under stress rather than a flexible one?

yeah but if its a part of the body then does it matter!

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?

The entire body has body mounts on the chassis where the body is fixed onto the chassis. This will take care of the flexes.


Please elaborate how many ribs are required?

Atleast 3

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.

Ask him for a design

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

^^


But i think the gypsy flexes less than the jeep. I may be wrong though.

No you are right - Gypsies flex less than a jeep "normally"

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

Quote:
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3) one wild suggestion, try some tough flexible material such as used in conveyor belts , or like wise bolted on metal frame ( made of sections from sheet metals )
@Sudharshan: You are WILD
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Old 14th May 2011, 10:46   #19
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Talking Re: Flexural Stresses on Jeep Hardtop

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@Sudharshan: You are WILD
Thanks Yes I am , guilty as charged

but let me elaborate what I said about using thick sheets along with channels made from sheet metal .

Here is a drawing hope it serves the purpose . If these joints are made properly & using silicon sealant ( RTV ) I think a rugged & flexible top can be achieved

Flexural  Stresses on Jeep Hardtop-channel-sheet.png

Sudarshan

P.S. M 6 bolts must be used along with thick big flat washers ( or a continuous strip ) & both need to be of stainless steel .
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Old 16th May 2011, 13:23   #20
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Default Re: Flexural Stresses on Jeep Hardtop

When we take a jeep on an articulation ramp up to max articulation and then open one door, it's then impossible to close that door due to the body flex.

Thus, there is a lot of twist in the body which the body mounts are not able to compensate.

Now in such a case, either a strong hardtop will prevent max articulation or will crack.

I need to compensate for this.
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Old 16th May 2011, 15:32   #21
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Default Re: Flexural Stresses on Jeep Hardtop

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Originally Posted by Tejas@perioimpl View Post
When we take a jeep on an articulation ramp up to max articulation and then open one door, it's then impossible to close that door due to the body flex.

Thus, there is a lot of twist in the body which the body mounts are not able to compensate.

Now in such a case, either a strong hardtop will prevent max articulation or will crack.

I need to compensate for this.
Sirji, NO NO NO, the door will shut properly even if the jeep is wildly articulating.

Your problem appears to be a loosely put together piece. Please check the A and B Pillar alignments.

The stalwarts here could and will guide you in totality
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Old 16th May 2011, 15:42   #22
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Default Re: Flexural Stresses on Jeep Hardtop

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Sirji, NO NO NO, the door will shut properly even if the jeep is wildly articulating.

Your problem appears to be a loosely put together piece. Please check the A and B Pillar alignments.

The stalwarts here could and will guide you in totality
headersji,

Tried with 3 different jeeps. All same issue. This weekend will put the Thar up the ramp as well.

I don't want to wait forever or get confused by mumbo jumbo if i wait to be guided in totality!

However, BD last week told me that the major problem with the MM series is that the area below the door, i.e. where one steps to get into the vehicle (not foot rest, but the body tub) is poorly designed and should be reinforced from underneath with a box section pipe. Could it be that this area flexes the most? Next weekend i shall put up snaps once the jeep is on the ramp to show areas where the door is getting interfered with.

Last edited by Tejas@perioimpl : 16th May 2011 at 16:01. Reason: typo
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Old 16th May 2011, 15:53   #23
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Default Re: Flexural Stresses on Jeep Hardtop

Quote:
Originally Posted by Tejas@perioimpl View Post
headersji,


However, BD last week told me that the major problem with the MM series is that the area below the door, i.e. where one steps to get into the vehicle (not foot rest, but the body tub) is poorly designed and should be reinforced from underneath with a box section pipe. Could it be that this area flexes the most? Next weekend i shall put up snaps once the jeep is on the ramp to show areas where the door is getting interfered with.
If BD knows its weak and needs reinforcement, why can't they (M&M) do it in production, is it done in NGCS?
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Old 16th May 2011, 16:04   #24
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Default Re: Flexural Stresses on Jeep Hardtop

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If BD knows its weak and needs reinforcement, why can't they (M&M) do it in production, is it done in NGCS?
God knows! They'll need to alter the die i guess which will be a very expensive proposition.

BD or spike can answer it best.
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Old 16th May 2011, 16:32   #25
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Default Re: Flexural Stresses on Jeep Hardtop

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Does the chassis of the MM550 flex so "badly"? Surprising.
Quote:
Originally Posted by Tejas@perioimpl View Post
However, BD last week told me that the major problem with the MM series is that the area below the door, i.e. where one steps to get into the vehicle (not foot rest, but the body tub) is poorly designed and should be reinforced from underneath with a box section pipe. Could it be that this area flexes the most?
Oh wow. That's something.

So whatever you do to the (hard) top if the chassis flexes as much as it does you wont have a robust solution.

So you are going to get the chassis reinforced first? That probably would narrow down your HT issues with respect to dynamic forces acting on the chassis.
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Old 16th May 2011, 16:40   #26
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Default Re: Flexural Stresses on Jeep Hardtop

Reinforcing the chassis to prevent flex will affect the articulation. It's a toss between the devil and the deep sea!
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Old 16th May 2011, 16:46   #27
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Default Re: Flexural Stresses on Jeep Hardtop

How much articulation would one lose by preventing chassis flex (it cannot be eliminated totally anyways)?

I am thinking a flex free chassis would give a better platform for offroad based suspension. At least suspension travel can be computed better, considering chassis flex is a constant or not a variable.
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Old 16th May 2011, 16:51   #28
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Default Re: Flexural Stresses on Jeep Hardtop

Tejas,

In my assessment, the design flaw is in the flex of the C section chassis, particularly evident in the LBW, MM's with doors. The same flex, but lesser is inherent in SWB jeeps because of the shorter length between axles, also goes unnoticed due to the absence of doors.

If the design was flawed just 'under the door floor' and had that been reinforced it would twist again and again and tear, as the chassis would be causing a reoccurring twist due to the flexible C section design as compared to the more rigid box chassis.

During articulation it is the B pillar that swings most sideways, being more or less in the center of the length of chassis .

In short the twist originates from the chassis which is passed on to the tub.
Regards,

Last edited by fazalaliadil : 16th May 2011 at 16:53.
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Old 16th May 2011, 16:58   #29
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Default Re: Flexural Stresses on Jeep Hardtop

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Originally Posted by fazalaliadil View Post
In short the twist originates from the chassis which is passed on to the tub.
That's what i gathered too.

Is the chassis on the Bolero (old) the same as MM range?

I can do this ramp articulation bit in the slope leading to our parking lot. One wheel at a time and check the flex.

I am thinking if the chassis is well build the wheel should lift (beyond the maximum wheel articulation) but the chassis should not flex.

The point between which the doors start getting misaligned and when they are properly shut would be the optimal point of chassis strength.
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Old 16th May 2011, 17:23   #30
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Default Re: Flexural Stresses on Jeep Hardtop

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Originally Posted by Spitfire View Post
That's what i gathered too.
I can do this ramp articulation bit in the slope leading to our parking lot. One wheel at a time and check the flex.
Spitfire,
The best way to do a ramp test on a level ground, place one jack at the front left wheel and another at the rear right wheel, lift until the front right wheel and the rear left wheel are in the air and not touching the ground.

Have a thin vertical indicator rod placed just beside the C section of the chassis before and after the articulation for comparison.

It is very difficult to ascertain the flex by naked eye.
Regard,
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