Do carbon fiber chassis get lose rigidity?

[brutus]

I seem to remember suggestions that the IndyCar chassis from pre-2012 were very old physically, not just in terms of when the design was penned, and this was a contributing factor to injuries sustained. I think it was mentioned at around the time Dan Wheldon was killed.

Sure i've heard about tubs being bonded together in places because they were weakening. Wish I knew where that was.

Edit: Wow, just changed the above from 2014 to 2012. Cannot believe Dans been gone for over 4 years.

Champ car chassis are purchased by each team from a supplier, while F1 teams produce their own. Champ cars are heavier than F1 cars. But Champ cars also must be capable of handling impacts at higher speeds due to racing on speedways. Champ car teams don't have the financial resources that F1 teams have, so naturally they tend to run their chassis for longer.

However, even back in 2012, I'm pretty sure the composite tubs used in Indy car were single piece. Many years ago some composite tubs were two-piece (upper and lower halves) and adhesively bonded along a horizontal lap joint.

So, are current F1/Indy monocoques a single piece? I thought they were two halves bonded together. I recalled reading in a book that this is necessary because with a single piece you wouldn't be able to put a mold in the interior.

[Edis]

If a composite laminate is subjected to sufficient levels of stress to produce local shear failure or delamination, then the failure will likely continue to propagate thru the structure at lower stress levels. Structural failure of the laminate will become a problem long before there is a noticeable loss of structural stiffness.

Detecting small local delaminations in complex composite structures is not an easy thing to do. Much easier, reliable and cost effective to simply replace the composite tubs on a regular basis.

If the chassi is subject to stress that can cause delamination during normal operation, I would suspect that the chassi would have poor stiffness even in undamaged condition. There is after all a relationship between stress and strain.

So, are current F1/Indy monocoques a single piece? I thought they were two halves bonded together. I recalled reading in a book that this is necessary because with a single piece you wouldn't be able to put a mold in the interior.

Modern monocoques are made using female moulds, unlike early monocoques which were made using a male mould. So, adhesive bonding of the halves is required.

See page 28
http://www.speautomotive.com/SPEA_CD/SP ... f/k/K3.pdf

[SuperDrummer]

But a bit more ontopic, the big teams make a chassis for a smaller number of GP's, so they can be lighter before they have reduced stiffness because of fractures or delimitation what will happen eventually) then the smaller teams who will build usually just four (two race, one testing/spare and a crash test chassis).

So the question should be, does a chassis loose it's rigidity during it's calculated lifespan. Yes it does, because of vibrations hairline cracks will occur but the big teams change the chassis before it's noticeable.

That's what i was asking. But does the same cracks/delamination happen in road going CF supercars?

I would guess that road legal CF supercars use much thicker CF shells, so structural rigidity and safety shouldn't arise as an issue before other components of the supercar fail - like engine, gearbox, air conditioner or glass-holders.
If we look at junior formulae we can see the the tub there is ca. 10 mm thicker than F1 which lets the teams run the same chassis for several years with no performance decay. And I presume that tolerances for road legal cars are much higher than for racing cars used in feeder series.

[riff_raff]

I recall that one serious issue with cored composite structures used on aircraft early on was progressive delamination failures. It would start with an impact on a leading edge surface and local delamination. Moisture would then penetrate into the delamination voids, and after repeated freezing/thawing cycles over many flights it would cause catastrophic structural failure of the part.

[flynfrog]

I recall that one serious issue with cored composite structures used on aircraft early on was progressive delamination failures. It would start with an impact on a leading edge surface and local delamination. Moisture would then penetrate into the delamination voids, and after repeated freezing/thawing cycles over many flights it would cause catastrophic structural failure of the part.

This is why they now do BVID (Barely Visible Impact Damage) allowables. You pick the highest stress points of the aircraft then apply an impact that is just into the visible detection area and run all of your static tests and watch for damage growth. The good/bad thing with composites is that they don't always dent like a metal part. You can have rather serious damage behind a face sheet (as you point out) with no damage visible on the outside.

lots of good info on the niar site

https://www.niar.wichita.edu/niarworksh ... awcett.pdf

[f1showcars]

Well manorf1 ran (at least one) of the MR03 Tubs for two years . Never heard anthing about it effecting performance although i do wonder if they did act on the side of caution when racing just incase they needed a new tub .

[brutus]

But a bit more ontopic, the big teams make a chassis for a smaller number of GP's, so they can be lighter before they have reduced stiffness because of fractures or delimitation what will happen eventually) then the smaller teams who will build usually just four (two race, one testing/spare and a crash test chassis).

So the question should be, does a chassis loose it's rigidity during it's calculated lifespan. Yes it does, because of vibrations hairline cracks will occur but the big teams change the chassis before it's noticeable.

That's what i was asking. But does the same cracks/delamination happen in road going CF supercars?

I would guess that road legal CF supercars use much thicker CF shells, so structural rigidity and safety shouldn't arise as an issue before other components of the supercar fail - like engine, gearbox, air conditioner or glass-holders.
If we look at junior formulae we can see the the tub there is ca. 10 mm thicker than F1 which lets the teams run the same chassis for several years with no performance decay. And I presume that tolerances for road legal cars are much higher than for racing cars used in feeder series.

Yes, i assume road car components are not so close to the strength/reliability limit. But when you mention tubs that are 10mm thicker, i guess most of that would be the spacing between the inner and outer CF shells, which is usually filled with some honeycomb panel. 10mm of CF would be way too much, and very heavy.

[Per]

It is true that delaminations in a composite structure, once present, will grow at quite low stress levels, reducing strength and stiffness locally. But local damages will not really be measurable in the torsional stiffness of the whole tub. It's not as if a delamination will grow a metre long before it is detected or before the tub actually breaks.

If an F1 team replaces a monocoque I think it is more likely to be because local damages around suspension pick-up points basically translate into suspension compliance, which 'slows down' the response of the car and reduces driver control.

If a driver has a small 'moment' - it can be as simple as tapping the wall at Melbourne turn 2 with the right wheels - it may result in a small damage which is not initially detected but does grow over time, resulting in unwanted behaviour after a couple of race weekends.

[countersteer]

Indycar ran the Dallara IR-03/05 from 2003 through 2011. Many of the tubs were run the entire 8 years. The most famous was de Silvestro's "Pork Chop" so named because it had been crashed and repaired so many times it was heavy.

Can't find the reference but I remember reading a story about a tub run by Sebastien Bourdais that included its accident history. It had, in its lifetime, been "re-skinned".

Granted, a "spec chassis" can be built more robust (heavy) than a competitive chassis series.

[bill shoe]

Indycar ran the Dallara IR-03/05 from 2003 through 2011. Many of the tubs were run the entire 8 years. The most famous was de Silvestro's "Pork Chop" so named because it had been crashed and repaired so many times it was heavy.

Can't find the reference but I remember reading a story about a tub run by Sebastien Bourdais that included its accident history. It had, in its lifetime, been "re-skinned".

Granted, a "spec chassis" can be built more robust (heavy) than a competitive chassis series.

Interesting info for sure. I'm guessing the Dallara Indycar chassis had a very large markup, so it became more financially advantageous for teams to repair and rebuild them to the point of lunacy rather than write giant checks for new ones.

[ChrisF1]

Indycar ran the Dallara IR-03/05 from 2003 through 2011. Many of the tubs were run the entire 8 years. The most famous was de Silvestro's "Pork Chop" so named because it had been crashed and repaired so many times it was heavy.

Can't find the reference but I remember reading a story about a tub run by Sebastien Bourdais that included its accident history. It had, in its lifetime, been "re-skinned".

Granted, a "spec chassis" can be built more robust (heavy) than a competitive chassis series.

Sound similar to what I had heard and posted about previously with the old fatigued chassis having a negative effect on driver safety in the later years of that chassis.

[brutus]

Indycar ran the Dallara IR-03/05 from 2003 through 2011. Many of the tubs were run the entire 8 years. The most famous was de Silvestro's "Pork Chop" so named because it had been crashed and repaired so many times it was heavy.

Can't find the reference but I remember reading a story about a tub run by Sebastien Bourdais that included its accident history. It had, in its lifetime, been "re-skinned".

Granted, a "spec chassis" can be built more robust (heavy) than a competitive chassis series.

So, does "re-skinned" means that they stripped out the entire CF outer skin, which goes over the honeycomb, and then laid another CF skin over it? While the inner CF skin remained?