Dada
hope Bryn doesnt mind
Did that work?
if not i have another cunning plan
WEST
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| Chassis Strength http://www.gtmdrivers.com/forum/chassis-strength-t116.html |
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| Author: | Henry [ Fri Jan 04, 2008 10:02 pm ] |
| Post subject: | Chassis Strength |
I remember someone posted up a wonderful stress analysis of the Coupe chassis on the old forum. (Brian was it?) Does anyone still have these images? It would be nice to get them back online! Cheers, Henry |
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| Author: | West [ Fri Jan 04, 2008 11:01 pm ] |
| Post subject: | Re: Chassis Strength |
Dada hope Bryn doesnt mind Did that work? if not i have another cunning plan WEST |
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| Author: | Tim Rowe (1130) [ Sun Jan 06, 2008 9:43 pm ] |
| Post subject: | Re: Chassis Strength |
Seems to me like the the rear frame accounts for half of the movement in the chassis. So I'm hoping that the improvements I've made to the rear of mine would result in less twist. I think the other thing to note is to try and make the tunnel as stiff as possible. I've added some box section to the area around the gear selector, to try and add some stiffness. |
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| Author: | Pantera2075 [ Mon Jan 07, 2008 6:56 pm ] |
| Post subject: | Re: Chassis Strength |
Note that movement in the chassis is not the prime aim of a finite element analysis - the twist shown is usually amplified to give an idea of the movements involved - otherwise you would hardly see them. The primary use of the diagrams are in the colours - as in the grading to the side. Red is bad, blue is good. There are a few places on the chassis giving large point loads - These are the areas that need beefing up or redesigning to spread the load - to avoid failure in these areas - not to stop the twist. If you stiffen the chassis to lessen twist you may induce point loads and cause failure. The thing to do if possible here is to get hold of the original analysis and try a few mods to lessen the point loads and possibly stiffen it up at the same time. Note the red bits around the aperture in the tunnel, and how evenly stressed the sills are! Phil (Still looking for a Coupe) |
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| Author: | Durbs [ Mon Jan 07, 2008 10:05 pm ] |
| Post subject: | Re: Chassis Strength |
The bit that interests me are the stress points at the bottom of the access hole to the engine in the rear bulkhead. It doesn't look massive, but I notice that my chassis is splitting slightly at these points due to the seperate metal sheets coming apart. There are some large stress points in the foot wells I notice, did West not have a problem there on his car (his must be a good test chassis due to the large mileage he has clocked up). Anybody done FEA with the body on? While all the literature in the sales said it was an unstressed fiberglass body, that is not strictly true, more semi-stressed as the chassis is an open monocoque. I've noticed with my bare chassis that it does flex a reasonable amount and was looking at putting a simple cage in to reduce this (just continuing the rear roll hoop forwards over the doors, down the A pillars to the front jacking point, plus a joining member across the top of the screen). |
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| Author: | West [ Tue Jan 08, 2008 10:21 pm ] |
| Post subject: | Re: Chassis Strength |
Durbs wrote: ........there are some large stress points in the foot wells I notice, did West not have a problem there on his car (his must be a good test chassis due to the large mileage he has clocked up). Anybody done FEA with the body on? While all the literature in the sales said it was an unstressed fiberglass body, that is not strictly true, more semi-stressed as the chassis is an open monocoque. I've noticed with my bare chassis that it does flex a reasonable amount and was looking at putting a simple cage in to reduce this (just continuing the rear roll hoop forwards over the doors, down the A pillars to the front jacking point, plus a joining member across the top of the screen). Someone remembers well  After a couple of track days I had noticed the areas in the foot wells, had been flexing, one advantage of painting your chassis in a colour other than black is you can see the cracks form in the paint if there is any flexing., This evenings top tip.. I also found the box section between the diagonal cross brace and rear shock mount on the space frame had been flexing massively, hence why my car now has a piece of 2x1 welded ontop from the shock mount foward a few inches [and Tim has built this part of his frame in 2x1 after talking to me], not the prettiest way but when you find the problem and your amoungst a weekend engine out grear ratio change, and back in time is short. Was found between track days and two days before the next which was paid for Will hopefully get around to doing a chassis model myself and adding a cage etc to see the difference, but probaly end up actually fitting the cage first at this rate. The Body does add torsional strength and this is why i strongly recomend you glass in your windscreen surport tubes and atleast PU your tub to the chassis at the rear when you fit it as this will stiffen up the chassis i have seen the difference when i did a simple lifting one corner test on my chassis when i had it sat on a jig during some work, nothing techincal just a visual test and it made a difference glassing in the window tubes.. Also may i add the diagonal plating under the dash between bulkhead and A panel, these are spot welded inplace, at least stitch weld these, three stiches extending the exsiting spots will do, as this panel did a surprising amount Enough of my dribble this evening I have done well over 40K miles with honda power now, plus the mileage I did before I even started this Honda Power fun. WEST [excuse any mistakes have had a couple of drinks this evening] |
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| Author: | Tim Rowe (1130) [ Wed Jan 09, 2008 11:35 am ] |
| Post subject: | Re: Chassis Strength |
WEST wrote: After a couple of track days I had noticed the areas in the foot wells, had been flexing, one advantage of painting your chassis in a colour other than black is you can see the cracks form in the paint if there is any flexing., This evenings top tip.. That is good news, as I've bought the paint for the tub and it definitely isn't black. WEST wrote: I also found the box section between the diagonal cross brace and rear shock mount on the space frame had been flexing massively, hence why my car now has a piece of 2x1 welded ontop from the shock mount foward a few inches [and Tim has built this part of his frame in 2x1 after talking to me], not the prettiest way but when you find the problem and your amoungst a weekend engine out grear ratio change, and back in time is short. Was found between track days and two days before the next which was paid for Can't beat taking an idea and building on it. Just ask Mclaren. WEST wrote: Also may i add the diagonal plating under the dash between bulkhead and A panel, these are spot welded inplace, at least stitch weld these, three stiches extending the exsiting spots will do, as this panel did a surprising amount I should have all the welding done on the tub this weekend, so I will have to put that little tweak on the list of things to get sorted. A good collection of drunken knowledge there Neil  
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| Author: | the other Tim [ Wed Jan 09, 2008 12:55 pm ] |
| Post subject: | Re: Chassis Strength |
I've been cutting around the box at the rear and although it looks rust free its surprising how much internal corrosion there is, the box is pretty thin to start with
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| Author: | West [ Wed Jan 09, 2008 2:04 pm ] |
| Post subject: | Re: Chassis Strength |
the other Tim wrote: I've been cutting around the box at the rear and although it looks rust free its surprising how much internal corrosion there is, the box is pretty thin to start with Yep most coupes seem to have 18swg tubing which is 1.2mm thick to start with, was shocked my self when i first found this as always assumed it was 16 swg 1.6mm. Quote: A good collection of drunken knowledge there Neil JD and Dr pepper went down well last night  WEST |
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| Author: | Durbs [ Wed Jan 09, 2008 3:31 pm ] |
| Post subject: | Re: Chassis Strength |
WEST wrote: Also may i add the diagonal plating under the dash between bulkhead and A panel, these are spot welded inplace, at least stitch weld these, three stiches extending the exsiting spots will do, as this panel did a surprising amount Noticed my chassis has gone in this place as well, so will definitely be stich welding down there as well as round the rear access panel. West, how did you strengthen the chassis round the footwell, if I remember rightly you changed the shape slightly as well? Was this to reduce the stress or just to give you more room round the pedals? |
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| Author: | the other Tim [ Wed Jan 09, 2008 7:12 pm ] |
| Post subject: | Re: Chassis Strength |
I'm hoping my cage will negate most of the above problem areas apart from near the rear shock mounts. 
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| Author: | Starmag [ Sun Dec 21, 2014 1:14 am ] |
| Post subject: | Re: Chassis Strength |
Does any still have the pictures from the thread saved that they could re-upload? Also, West, what do you mean by the below? pictures would be a great help thanks WEST wrote: I also found the box section between the diagonal cross brace and rear shock mount on the space frame had been flexing massively, hence why my car now has a piece of 2x1 welded ontop from the shock mount foward a few inches [and Tim has built this part of his frame in 2x1 after talking to me], not the prettiest way but when you find the problem and your amoungst a weekend engine out grear ratio change, and back in time is short. Was found between track days and two days before the next which was paid for |
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| Author: | West [ Sun Dec 21, 2014 11:04 pm ] |
| Post subject: | Re: Chassis Strength |
As if by magic a picture speaks a thousand words Attachment: spaceframe.jpg [ 38.38 KiB | Viewed 22653 times ] The bits in red are what I am talking about, and the black line is where I experienced the signs of flexing. On some chassis the diagonal going down to the bulkhead is in a slightly different position I have noted on a couple of cars. If you think about it the whole weight of the rear of the car is on the tower mounts. The little bit of box section between the diagonal and the tower mounts is quite stressed hence the additional brace. Neil |
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| Author: | Starmag [ Wed Dec 24, 2014 8:04 pm ] |
| Post subject: | Re: Chassis Strength |
That's perfect, and a great explanation! Thank you Neil. Whilst we are on the subject, is there anywhere else which would benefit from strengthening, apart from that what is in this thread? James |
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