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Old Thu, Apr-06-2017, 11:49:58 AM   #44
Bubblegunz
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Bulgaria




Default Re: FEELER thread: CSL Front Bumper Group-Buy

Hi boyz,

I am Antony, the CEO of Streamline and I am here to give your minds a little bit of rest on the matters. This will be the only time I will schime in, because there is a lot of 3rd party info, going from 1 guy to the other and I would prefer for me to answer everything directly. I will try to be as theral as possible.

The people I work with are also creating elements for race-cars sutch as european rally-cars (where as you know nothing is left to chance and everything is tested/stress tested etc.), time-attack cars, hillclimb racers etc. The same people work at the moment for a team which has been an european hillclimb champion and has been on the european rally podium. They are currently building up the legendary audi S1 and has a lot of experience building race-cars. This means that these people know a lot more than me about what they are doing and because I want the highest quality items on the market I have these people in my team. Furthermore the exotic cars that have gone through these people's hands is insane - from the rarest possible 992 GT2 RSR to Lambo's, Porsche's etc. The point of this is not to brag, I couldn't care less about that. It is so you know that we are not just 2 people in a garage building carbon products. We are a team of people who test / create and for the most part - know what they are doing. And we are honest enough to not charge 4-5x the price of the item because we can...

Enough about us, I will begin by explaining each material as therally as I can by refering to its properties.

There is a huge misconception that Carbon is a "stronger" material than fiberglass. If you google the word "strength" this is what comes up:

"the strength of a material is its ability to withstand an applied load without failure or plastic deformation"

What will be a huge surprise to many people is that Fiberglass can withstand a higher ammount of load per area than carbon fiber - meaning it has a higher tensile strength. The highest quality fiberglass has about 35-40% higher strength properties than carbon for the same ammount of force applied at the same area. Lower quality fiberglass has about a 15-20% higher strength properties in this regards. High grade fiberglass is actually used in spacecarft where they need high-strength material which needs to be thin at the same time.

Kevlar is on par with the lower-quality fiberglass in terms of strength, and a not as strong as the higher-quality material out there.

Comparing this to aluminium, the carbon fiber is a lot stronger as a meterial per unit of area. So is Kevlar and so is fiberglass.

Actually the tensile strength of all these materials is a lot higher than steel. Again please understand that this is PER UNIT OF AREA not per KILOGRAM so weight is not the factor here! I will get into the weight of the materials a bit further down the line .

STIFFNESS
Okey so why are car manufacturers using CARBON rather than Fiberglass? There is a lot to the story. Talking about chassis dinamics is where it will sort of start to make sense. Further down the line I will explain the weight differences as well, which is another reason.

As I told Leighton Carbon fiber is a very very stiff material. In terms of chassis dinamics carbon is about 10% stiffer per unit of area than steel. It is why it is used by car manufacturers for chassis development - if you look at modern supercars all of them have a "carbon tub". It is why it is a great material to be used for a roof and we wouldnt sell a fiberglass roof for anything other than a race car .
Kevlar is about as stiff per unit of area as high-grade fiberglass. Both of them are about 50% less stiff than Carbon Fiber.
Now let us get to the weights which ties to everything. Carbon is not only 10% stiffer than steel per unit of area, but it is between 60-70% lighter. This simply because the material is a lot less dense than STEEL. Which means that for the same weight as a steel chassis your chassis will be about 72-75% stiffer and more durable (because when you go from lower to higher number percentages change, I hope you realise that).

Kevlar is about a bit less dense than carbon fiber and fiberglass is about 35% denser than carbon. Which is why you see FIBERGLASS items to be about 2x the weight of carbon fiber items.

So in terms of strength to weight KEVLAR IN TENSION will be about 25% stronger and Carbon will be on PAR with high-quality fiberglass and about 10-15% stronger than low-grade fiberglass. However to achieve the same weight the item will also be about 45% bigger. As you probably realize in a front bumper we do not have the space to put 45% more material in order to make the carbon item the same tensile strength.

So for the amount of material we can put, the weight difference comes from the fact that carbon is less dense as a material, but since the same amount of material is used – the item in FRP is actually STRONGER than from carbon fiber.

SO WHY didn’t BMW just use KEVLAR for the front bumper?

Well.. what I haven’t talked about yet is trength in compression. The problem with Kevlar is is that it is creat in tension, but very very poor in compression. The fibers in Kevlar buckle at about 20% the force needed to buckle a fiberglass item OF THE SAME WEIGHT and at about 30% of the force needed to buckle a carbon fiber item of the SAME WEIGHT. So Fiberglass in compression is about 10% stronger PER UNIT OF WEIGHT than carbon fiber. What this means is that if the bumper is 2KG from fiberglass and 2KG from carbon the fiberglass bumper will be the same strength in TENSION and 10% STRONGER in compression. However the FIBERGLASS bumper will be about 2x that weight, so effectively you will have a 2x stronger bumper .

SO to answer the question – WHY DIDN’T BMW USE KEVLAR? Well if you look at your brace, it has multiple angles so that the fibers always work in tension. Not only that but the fibers are connected in different directions. What this means though is that depending where the hit comes from, (from the side for example) if the force is in exact compression to the fibers that brace will have a 50% reduced strength from that impact, because these will fail very very early and only the fibers in tension will actually transfer. It is probably why my personal Kevlar bar failed from a small hit. A FRONTAL hit will make the bar work SOLELY in compression, which is not the issue here. However to adapt the brace with the bumper they would have had to have more fibers working in compression from more angles, which means the shape of the bumper couldn’t have been as it is… it will need more angles and will need a new engineering philosophy. One other thing is that one of the creators admitted that the bumper was taken straight out of one of their motorsport cars – where carbon is mostly used. I will get back to that in a sec.

TOUHNESS AND ELONGATION

One more thing is Toughness. The toughness of a material measures its ability to resist stress and strein. Which is basically its resistance to an impact. ELONGATION is an important factor here, it basically measures how far a material can strein before it fails. Well S-glass has the highest toughness per unit of AREA. BOTH fiberglasses do, where high-grade fiberglass comes first. This is because the material has the highest STRENGTH and highest ELONGATION between all these materials. Next is Kevlar, and the least tough is Carbon Fiber, because it is a very brittle material.

In order for you guys to understand what elongation is – think of a ceramic bowl and a plastic one. When dropped (a.k.a impact) the ceramic bowl although mutch stronger will brake, whereas the plastic one may not!


SO WHY DID BMW USE CARBON?

BMW used carbon fiber for a couple of reasons. The main concept for the CSL was lightness (and an FRP bumper will hardly be any lighter than OEM) and CARBON for a unit of AREA is as we said a lot LIGHTER as a material. If you read the interview for pistonheads of one of the creators of the CSL car he says that he asked his supervisor whether cost is a concern or the car should be as LIGHT as possible in terms of the front bumper and the supervision said – LIGHTNESS is our biggest concern. An FRP bumper would not have been that mutch lighter than the standard one – although it would have been stronger. Also they had these bumpers made and tested for their racecars and they copied the technology without further crash-tests and other testing. IT was a more effective – lighter and somewhat cheaper and more streight forwards way to go.


HOW DO OUR BUMPERS COMPARE?


The front brace is the item which took most of our time. We took appart a whole CSL bumper in order to figure out exactly how it is made. We thickened the brace a little bit as well, made it smoother. A lot of research and development went EXACTLY into that brace in order to make it the best possible product. We looked at the way it is reinforced and did the same exact thing to our bumpers. To do that you need people with a lot of experience and thankfully I have such people on my team which know a lot more about how an impact will affect the bumper then I do. We further researched the brace and as I said even thickened it at a couple of points where we thought that is needed!

The bumpers had to be out 1 month ago, however we needed 1 more month (on top of the 2 months before) for research and development SOLELY on the front brace. A test variant was made – modified, tested again, and the process was repeated until we made the final variant. It is how we work – it is what we do. After all this bumper is going on my car, and I will not risk my own life because of a bumper… especially since my car sees track duties and will see such even more often from now on – I do not have a cage installed.

P.S. One more thing I forgot to mention is that you can easily repair an FRP item with any FRP producer anywhere in the world. All you need to do is give it to them shortly after the impact and with most of the pieces that are collected. It can easily be made as good as new. Carbon is a bit different.

I hope this answers satisfies all of you guys. Sorry for my English I realize I might have made many grammatical mistakes.

Best regards,
Antony Nikolov

Last edited by Bubblegunz; Thu, Apr-06-2017 at 12:12:49 PM.
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