GRP monocoque based on steel car?
Discussion
Anyone any thoughts on the idea of getting a steel-bodied car and making moulds to produce exactly the same thing only out of GRP. Obviously the panels would need to be thicker than the original steel ones, but is there anything inherently wrong with the idea? If all the external and internal panels were reproduced then it wouldn't need a steel chassis.
I'm not really looking for thoughts on whether the project would be worthwhile or not, just whether it would produce a viable car.
I'm not really looking for thoughts on whether the project would be worthwhile or not, just whether it would produce a viable car.
I can't see how something engineered to be made from steel will be strong enough if made from GRP. They are completely different materials with very different characteristics.
AFAIK the only all GRP mocoque car produced is the original Lotus Elite, but it's construction is very different to a steel mocoque car.
I think you'd need at least a steel backbone chassis to make it work.
AFAIK the only all GRP mocoque car produced is the original Lotus Elite, but it's construction is very different to a steel mocoque car.
I think you'd need at least a steel backbone chassis to make it work.
groomi said:
I can't see how something engineered to be made from steel will be strong enough if made from GRP. They are completely different materials with very different characteristics.
Not saying I disagree, but could you put some flesh on those 'bones'? I can think of a few cases where stuctures have been made in either material, and where the main difference is just the thicknessgroomi said:
AFAIK the only all GRP mocoque car produced is the original Lotus Elite, but it's construction is very different to a steel mocoque car.
I think you'd need at least a steel backbone chassis to make it work.
Oh dear, the PH kit car forum is suffused with GTM owners who will want to disagree with you about the Elite being the only one!I think you'd need at least a steel backbone chassis to make it work.
singlecoil said:
groomi said:
I can't see how something engineered to be made from steel will be strong enough if made from GRP. They are completely different materials with very different characteristics.
Not saying I disagree, but could you put some flesh on those 'bones'? I can think of a few cases where stuctures have been made in either material, and where the main difference is just the thicknessgroomi said:
AFAIK the only all GRP mocoque car produced is the original Lotus Elite, but it's construction is very different to a steel mocoque car.
I think you'd need at least a steel backbone chassis to make it work.
Oh dear, the PH kit car forum is suffused with GTM owners who will want to disagree with you about the Elite being the only one!I think you'd need at least a steel backbone chassis to make it work.
rhinochopig said:
Wouldn't it be very heavy though? GRP is very prone to stress fracturing around risers - just look at the bolt holes on kit bodywork to see the crazing and cracks - unless it is very thick.
I guess the idea would be to reinforce areas where the stress was concentrated, and thicken the GRP in those areas too.GRP is less sophisticated and less strong than carbon fibre/epoxy etc, but they make racing cars out of that stuff where weight is critical, and so it seems reasonable to think that a GRP car could also be sufficiently strong albeit heavier.
I've just rememebered, Murtayas are GRP monocoques too.
singlecoil said:
rhinochopig said:
Wouldn't it be very heavy though? GRP is very prone to stress fracturing around risers - just look at the bolt holes on kit bodywork to see the crazing and cracks - unless it is very thick.
I guess the idea would be to reinforce areas where the stress was concentrated, and thicken the GRP in those areas too.GRP is less sophisticated and less strong than carbon fibre/epoxy etc, but they make racing cars out of that stuff where weight is critical, and so it seems reasonable to think that a GRP car could also be sufficiently strong albeit heavier.
I've just rememebered, Murtayas are GRP monocoques too.
TBH I'm pontificating about something I know f
k all about really - GRP monocoque design. Curious now to see what benefits and detriments there from using GRP as a chassis material - obviously rust is a key benefit - but I'm not sure how without FEA you could predict crash performance, fatigue, etc. and how do you repair in the event of an off.Post up what you find out please.
singlecoil said:
groomi said:
AFAIK the only all GRP mocoque car produced is the original Lotus Elite, but it's construction is very different to a steel mocoque car.
I think you'd need at least a steel backbone chassis to make it work.
Oh dear, the PH kit car forum is suffused with GTM owners who will want to disagree with you about the Elite being the only one!I think you'd need at least a steel backbone chassis to make it work.
The bottom line is that it can be done, but it's not going to be the most efficient approach in terms of weight/stiffness, because a well-designed steel bodyshell will have been designed to exploit that particular material's strengths (pardon the pun); stuff like the fact that you can make something that's very stiff and light by spot-welding together a number of sharply folded sheets and pressings, whereas with GRP you want to minimise the moulding complexity, manage high point loads differently and avoid both sharp corners and flat panels if at all possible.
If you want an efficient design, it needs to have been developed with the sprecific characteristics of the materials its made from borne in mind from the outset.
Who said GRP wasn't tough?
30 MPH Crash test (In accordance with ECE12)
The composite monocoque successfully absorbed the impact energy with the damage restricted to the frontal box sections. Whereas a steel bodyshell would show compressive damage around the door apertures, the Midas shell maintained its integrity. The key requirement of the ECE12 test is that the steering wheel should not be displaced by more than 127mm. At the peak of the impact the steering wheel moved by 15mm, before returning to within a few mm of its original position.
30 MPH Crash test (In accordance with ECE12)
The composite monocoque successfully absorbed the impact energy with the damage restricted to the frontal box sections. Whereas a steel bodyshell would show compressive damage around the door apertures, the Midas shell maintained its integrity. The key requirement of the ECE12 test is that the steering wheel should not be displaced by more than 127mm. At the peak of the impact the steering wheel moved by 15mm, before returning to within a few mm of its original position.
I did it with my GTM coupe.
I replaced the steel chassis/tub with an exact replica made in GRP.
As you suggest I made it thicker than the original with kevlar reinforcement at all the pick up and mounting points.
It was also braced with wooden and RPU foam formers to produce box sections on all the flat panels.
When it was finished it was considerably stiffer (and straighter) than the original
I replaced the steel chassis/tub with an exact replica made in GRP.
As you suggest I made it thicker than the original with kevlar reinforcement at all the pick up and mounting points.
It was also braced with wooden and RPU foam formers to produce box sections on all the flat panels.
When it was finished it was considerably stiffer (and straighter) than the original
Edited by gtmdriver on Tuesday 2nd February 13:36
gtmdriver said:
I did it with my GTM coupe.
I replaced the steel chassis/tub with an exact replica made in GRP.
As you suggest I made it thicker than the original with kevlar reinforcement at all the pick up and mounting points.
It was also braced with wooden and RPU foam formers to produce box sections on all the flat panels.
When it was finished it was considerably stiffer (and straighter) than the original
That's really interesting. Do you have a build diary anywhere? And how did you manage with the suspension mountings etc?I replaced the steel chassis/tub with an exact replica made in GRP.
As you suggest I made it thicker than the original with kevlar reinforcement at all the pick up and mounting points.
It was also braced with wooden and RPU foam formers to produce box sections on all the flat panels.
When it was finished it was considerably stiffer (and straighter) than the original
FlossyThePig said:
Who said GRP wasn't tough?
30 MPH Crash test (In accordance with ECE12)
The composite monocoque successfully absorbed the impact energy with the damage restricted to the frontal box sections. Whereas a steel bodyshell would show compressive damage around the door apertures, the Midas shell maintained its integrity. The key requirement of the ECE12 test is that the steering wheel should not be displaced by more than 127mm. At the peak of the impact the steering wheel moved by 15mm, before returning to within a few mm of its original position.
As I recall they had to engineer weakness into the nose section of the Midas Gold, so that it absorbed energy in a controllable manner. 30 MPH Crash test (In accordance with ECE12)
The composite monocoque successfully absorbed the impact energy with the damage restricted to the frontal box sections. Whereas a steel bodyshell would show compressive damage around the door apertures, the Midas shell maintained its integrity. The key requirement of the ECE12 test is that the steering wheel should not be displaced by more than 127mm. At the peak of the impact the steering wheel moved by 15mm, before returning to within a few mm of its original position.
The original Quantum (Fiesta based) was a GRP monocoque, although later versions went to a chassis frame, but that may have been to make a convertible easier to engineer.
gtmdriver said:
I did it with my GTM coupe.
I replaced the steel chassis/tub with an exact replica made in GRP.
As you suggest I made it thicker than the original with kevlar reinforcement at all the pick up and mounting points.
It was also braced with wooden and RPU foam formers to produce box sections on all the flat panels.
When it was finished it was considerably stiffer (and straighter) than the original
It may be the angle of the photo, but what are the kevlar "sausages" for? I can't see what function they perform as they don't appear to be anchored to anything and kevlar's strength is in tension. I replaced the steel chassis/tub with an exact replica made in GRP.
As you suggest I made it thicker than the original with kevlar reinforcement at all the pick up and mounting points.
It was also braced with wooden and RPU foam formers to produce box sections on all the flat panels.
When it was finished it was considerably stiffer (and straighter) than the original
Edited by gtmdriver on Tuesday 2nd February 13:36
I have some build photos here.
http://s41.photobucket.com/albums/e254/gtmdriver/G...
The suspension mountings were as on the original. A small tubular extension at the back and integral mountings (in GRP on my car) at the front.
I made my own tubular subframes to replace the usual Mini versions and made my own inboard suspension operated by pushrods and rocker arms.
The 'kevlar sausages' are actually wood. Life is too short to go sawing dowel in half so I bought it as half round section. It has no strength in itself but is simply there as a former to be skinned in GRP. The box section formed by the GRP adds greatly to the rigidity of the panel. You can use half round paper rope, rigid polyurethane foam cut into strips or even rolled up newspaper to do the same thing.
http://s41.photobucket.com/albums/e254/gtmdriver/G...
The suspension mountings were as on the original. A small tubular extension at the back and integral mountings (in GRP on my car) at the front.
I made my own tubular subframes to replace the usual Mini versions and made my own inboard suspension operated by pushrods and rocker arms.
The 'kevlar sausages' are actually wood. Life is too short to go sawing dowel in half so I bought it as half round section. It has no strength in itself but is simply there as a former to be skinned in GRP. The box section formed by the GRP adds greatly to the rigidity of the panel. You can use half round paper rope, rigid polyurethane foam cut into strips or even rolled up newspaper to do the same thing.
dcoombes said:
groomi said:
AFAIK the only all GRP mocoque car produced is the original Lotus Elite, but it's construction is very different to a steel mocoque car. .
Not to mention the Rochdale Olympic, ALL GRP, not even sub- frames for the engine or suspension mountings.
Gnits said:
I could have sworn the S1 Elise was Aluminium monocoque - the vx220 certainly was.
Murtaya is indeed GRP and has a torsional stiffness of something like 14,000 nm per °
Elite, not Elise. Pistonheads, spelling matters, especially when it means it's a different car Murtaya is indeed GRP and has a torsional stiffness of something like 14,000 nm per °
http://en.wikipedia.org/wiki/Lotus_Elite
Edited by singlecoil on Friday 5th February 21:52
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