Jersey Tom wrote:There is no reason for carbon in "every day" cars IMO.
For a $10,000 econobox if you could make it from carbon for that price there would be efficiency advantages, however the only carbon you see on the average cheap Kia/Hyundai/Chery "every day" econobox car is 3M vinyl or other no use stickers. Occasionally there may be some carbon trim but yeah its of no use. However, when you say every day I would include moderate to high volume production cars that car be driven on the road every day.
In these cases, carbon vs steel, aluminum etc has considerable weight, tensile and compressive strength qualities, higher fatigue resistance as well as the ability to follow / be molded into complex curvatures all of which can increase survivability and increase power-to-weight- stiffness-to-weight which in turn has a significant effect on fuel economy (CO2 emissions is all encompassing in Europe and Asia) as well as performance.
As such, there are a myriad of reasons to use carbon fibre or other composites over steel because of the above.
The main reason it is not mainstream is simply cost of material and production difficulties. So IMHO there is every reason aside from marketing to use it in "every day" production cars based on its properties, however until the various costs come down it will not be a mainstream material.
The only other downside for production cars is the ability of CFRP, GRP etc to be recycled after lifecycle.
Jersey Tom wrote:Only reason it's used is for marketing.
That's a very cynical and myopic view of the situation I think.
If it gave no benefit other than marketing then its usefulness would be limited and we wouldn't be seeing the recent expansion in it use. Companies like Audi, Porsche, Mercedes and BMW (see a pattern there, cost and Euro based design where efficiency is the primary driver) now have used composites in their production cars. However as before, cost it the main barrier to further usage.
As an example, are you certain that the carbon composite roof used on the BMW M3 was done only for "marketing" and did not reduce the vehicles centre of gravity by removing 7kgs of weight from the highest point of the vehicle? Was it only "cosmetic" then?? Same opinion for the previous generation CSL?? The M3 is an "every day" car as its high volume and based on a four door saloon and in the numbers they sell they are not a limited production run or exclusive item.
However as an example of manufacturers investing in carbon manufacturing technologies for future prodcution, the Audi Group established the "
Automobili Lamborghini Advanced Composite Structures Laboratory" (ACSL) in the USA on the University of Washington campus in Seattle where they partnered with Boeing and moved the Lamborghini Gallardo LP570-4 Superleggera to a new carbon chassis production methodology pioneered by Boeing for the 787 Dreamliner project. This was not a marketing ploy and had everything to do with gaining a performance benefit as well as a better understanding of the technologies for mass production possibilities. Scalability and cost are the drivers for carbon.
It is interesting that the use of the Boeing techniques saw improved construction remove 40+kgs from the car (still just marketing??) so the LP570-4 Superleggera had a dry weight of 1340 kilograms (2954 lb) which would be impossible with steel or aluminum while retaining the stiffness required while the carbon construction provides for better power-to-weight and stiffness-to-weight ratios by reducing total mass which also is important for fuel economy and CO2 emissions in this era. This is the benefit of carbon.
Jersey Tom wrote:Composites manufacture is already quite well established outside of racing - it's not like F1 teams are "paving the way" or whatever.
Yes, production techniques and methodologies are generally well understood however new ones do filter filter down from aerospace and racing and provide more cost effective scalability for general production runs.
F1 in this area are more adopters than innovators due to cost of R&D, however they have certainly helped drive the technology faster than if they weren't involved.
marcush. wrote:one important point is:
for weight savings composite ,not carbonfibre is what is driving the weight down.
In fact a glassfibre skin can be made lighter than carbonfibre ,which is very hard to get a closed surface with no telegraphing ..
Telegraphing or print through is fairly easy to control if you use the right weight cloth and interfacing method.
So you may be able to make a lighter glass panel but it will not have similar or greater stiffness, tensile or compressive strength than a similarly weighted carbon panel. Carbon is simply a stronger fibre reinforcement than e-glass or s-glass. That's not to say that glass panels and layups are no good, its just carbon is stiffer and stronger for a given weight however these properties may not be required for certain applications.
Glass reinforcements, both s-glass and e-glass, are relatively inexpensive and have moderate tensile and compressive strengths while showing average stiffness when compared to carbon or aramid cloths. Glass variants show good fatigue resistance however and are therefore very tolerant of cyclic loadings.
Carbon Fibre has considerably lower weight, higher stiffness and tensile strength than the either of the glass fibres. Its downsides are cost and the more involved techniques required to properly achieve matrix suitability and application (such as resin penetration or wetting out).
Kevlar as an aramid fibre, has the lowest density of the most uses reinforcements high tensile strength and superior toughness (abrasion, cut and tear resistance). It toughness make it harder to work with and when used alone exhibits poor compressive properties. This is predominately why Kevlar is used in hybrid fabrics and layups with the various glass fibre or carbon to increase stiffness and compressive strength over Kevlar alone.
marcush. wrote:so a nomex paper core with glass skins is what you need to make a ultralight panel.
It may be lighter but would it have the same or greater strength, stiffness or impact resistance as a carbon, kevlar or hybrid panel??
In reality for production cars, if you want light non-weight baring panels simple thermoformed plastic is the easiest solution. It is light, can be pigmented, has great deformability resistance and is cheap and recyclable.
marcush. wrote:I´d guess most of the cf use in car production is just a matter of being fancy.It´s a bit like the EV vehicle hype.
I'd disagree with this. Glass variants are less stiff, have less compressive and tensile strength and therefore you need to make a thicker heavier panel to take the same loadings. Sure in some application you could substitute glass for carbon on a cost basis but I would not think a replacement based purely on weight or other properties would be made.
From my personal experience, the biggest difference in these fabrics is the techniques used for making parts of parts.
I use carbon (particularly spread tow fabrics), Kevlar and hybrid fabrics in making various parts for my car and sailing equipment. So far I’ve managed a few splitters (with soric core mat, balsa wood and nomex cores), guards, bonnets (Hood), flat panels (Kevlar cored anti intrusion side protection panel to attach to the roll cage, floor panels and dash panels etc), as well as a few tubes (using sleeves and wound tapes on styrene and water soluble cores).
I ever tried a 9’6” carbon / Kevlar sail board using a foam blank!!
However, I can only use wet layups with vacuum bagging where possible due to having no access to or the cash for a $100,000+ autoclave. The biggest difference in wet vs. dry is component weigh due to excess resin and the associated strength loss you get due to the larger resin pockets in the layups. I tried using a pre-preg fabric and vacuum bagging it however the warm weather and short shelf life makes it simply too costly.
Print through of the bleed ply and/of the fabric weave can be an issue if not bagged correctly with pin holes or poor surface finish the result. Incorrect wetting out of the fabric or core with the resin also can be an issue when your DIY’ing.
Never approach a Bull from the front, a Horse from the back, or an Idiot from any direction
I've mentioned many times that for most parts, they no longer use the Autoclave. 
