04-14-2012, 08:21 PM | #57 | |
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04-15-2012, 12:17 AM | #58 | |
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The original Saturns and 4th Gen F-Bodies, as well as a few GM Minivans were made of "composite" body panels, which is a generic term that doesn't mean "carbon fiber". As I said above, carbon fiber is a great lightweight and strong material, but it is very brittle and is prone to damage and failure from fatigue, etc. This is well documented in the field of aircraft design. It also costs a LOT more to produce than metal alloys. For the most part it doesn't pay for itself in weight savings and the manufacturing process for the material has a rather beefy "carbon footprint". Once everyone is fully committed to building cars with it, someone will figure out that it must be helping kill polar bears and we'll be back to square 1 with some even more expensive process making cars even more unobtainable. |
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04-15-2012, 07:14 AM | #59 | |
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I spent years of research in the crashworthiness of composites for structural components. Number 3 misses the point about composites usage in automotive. Up to now, composites have been used mainly as non-structural components and you can only reduce so much weight with this stuff, body panels, interior, bumpers....ALL of the crash structural parts are still metal. Strong light weight metals are being used. A few manufacturers are experimenting with composites (CF) structural parts but they are not cheap and they are certainly not ready for cheap mass produced cars. The major difference in the design requirements of cars versus aircrafts and others is: the structural parts must be able to dissipate energies during the crash to protect the occupants. The ductility in metal allows for this plastic work (converting kinetic energies into the crumbled metals). This ductility in metal is a huge advantage that composites do not have. In aircraft design for example, the composites can be used to up to its brittle failure limit minus the safety factor and engineers do not have to worry about post brittle failure, i.e. if the stresses in the composite parts are exceeding the brittle failure, you already have a failure. In cars, we have to continue to work with the metals post yield because plastic flow and work hardening are what we rely on for energy dissipation. Personally, I believe we will have to come up with more active safety systems so that we can keep the occupants safe without completely relying on the plasticity of metals before we can truly have composite structural components in cars. Got up too early this morning to run some "blast on composites" simulations and couldn't stay away. I have spent way too many years doing this stuff and it's still as interesting as it was when I got started in the 80's I love getting paid for doing stuff I enjoy doing anyway.
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04-15-2012, 07:57 AM | #60 | |
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CF just happens to be the poster child for two reasons I believe 1) generally it's the biggest mass savings and 2) show carbon like I have on my Ducati looks sweeeeeeet Most of the composites you are thinking of have one big benefit and that is low tooling costs. A door inner panel for example would take 5 dies to make it from steel or aluminum (4 if you are lucky, good or both). And aluminum isn't cheap either so that is also one of the reasons composites (plastics) are favored on low volume applications like Corvette or special runs vehicles. The CF materials used in the automotive applications won't be sensitive to fatigue. They are in fenders or roof panels that aren't stressed very much. In the Boeing Dreamliner though, the CF is structural and that may be what caused the brief recall. Also SMC is much cheaper than CF and that works well in structural applications as well, it is just not as light. Injection molded plastics also have applications for fenders. They were used on the Gen IV Camaro fenders and also on the old G bodies. The problem with those was thermal expansion. Similar to the old Saturns your door gaps change with temperature and to allow for expansion you have to have larger gaps than is considered good today. I think the Saturns had 6+ mm gaps all around the car. You are absolutely correct in your point that they won't pay for themselves, at least in my opinion. Many of the OEMs as well as the dealers this past week have been telling us that the high cost of FE will drive many people out of the market costing millions of sales per year. Yes, you can save 100, 200 or even 300 pounds on a car using composite materials but at a PREMIUM price relative to steel, or conventional materials. So how much? A bunch and we can leave it at that but it isn't a few hundred $ as the Group of Concerned Scientists will try to tell you. (BTW, did you know they aren't Scientists and I'm not sure they are Concerned about the same things we are) Now if you add a hybrid battery into the equation, you have to save even more weight just to be even. So back to the original point on the Mustang weighing 300 pounds less sure it is possible. With downsizing and clever engineering it should be no problem. And if you do it well, you can make a car smaller and maintain a roomy interior. The 3 Series is a good example of that. I think they actually made the new one a little bigger and still cut some weight out over the previous model. Look at the weight of the Hyundai Sonata, I think it's about 3200 pounds or so and yet it is roomy and does a lot of things very well. Just watch out for the weight savings that comes from simply having a base 4 cyclinder engine. That alone with the smaller transmission you can use and the smaller axle can result in a good chunk of that 300 pounds.
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04-15-2012, 08:02 AM | #61 | |
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As I also have done crashworthiness in my career we can have that discussion as well so if you want to throw engergy management into the discussion we can. Just remember that the steel doesn't just crumple and absorb energy. If you look in detail you will see crush initiation points that are designed in to manage where the steel folds and hidden you will see many extra reinforcement and doublers and inserts to add strength in crush to other areas. This can also be done with SMC and CF as well. That just wasn't the topic of the post. Every material has it's plusses and minuses. Walk your way simply from low carbon steel to the higher strength steels and you suddenly find yourself with materials that are also harder to form and cut. And those too behave differently in crash. So not every material lends itself to any application. It isn't as simple as how much you want to pay.
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04-15-2012, 11:54 AM | #62 | |||||
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Remember that composite tooling costs less, but the fabrication process is a lot more complex, so this offsets some of the tooling advantages. It takes a lot less time to stamp sheetmetal than it does to cure composites, which often need to be made in a vacuum and cured in an autoclave and possibly heat treated as well. Quote:
A good grade of fiberglass can get close to the tensile strength of carbon fiber with just a slight increase in weight. This could easily replace carbon fiber in fender wells and roof panels and would save a lot of the cost, it just wouldn't be useful as a "shiny thing" to make people buy the car. Quote:
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04-15-2012, 12:11 PM | #63 |
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Holy walls of text batman
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04-15-2012, 03:58 PM | #64 | |||
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04-16-2012, 07:43 AM | #65 |
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Well, with the MY2013 details released yesterday...
This comes in at just over 3400 lbs in V6 form.
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04-16-2012, 09:02 AM | #66 |
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The new Mustang will probably still weigh less than Camaro and certainly Challenger. Even if Chrysler gets rid of Challenger and make Barracuda, i dont see them as being able to find a platform small enough to be lighter than Mustang.
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04-16-2012, 09:46 AM | #67 |
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The CTS came in at about 100 lbs more than the camaro. I doubt the ATS will be 100 lbs more than the 6th gen camaro, but I would anticipate that we see some weight savings to put the car in at slightly under 3400 lbs, about the size of a new altima.
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04-16-2012, 12:30 PM | #68 | |
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All I meant from the 3,100 lb Altima comment is that GM and Ford should also be able to build similiarly equipped Camaros and Mustangs around that weight...so by that, yes I mean a 4 cylinder Camaro and Mustang. I did not say I wanted a 4 cylinder lol. I'd take a 3357lb V6 Camaro any day!! Again...this is good news and hopefully means we will see a next gen Camaro V6 comming in right at this weight!
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04-16-2012, 12:56 PM | #69 | ||
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I too welcome lighter versions, but for some reason cars right now have become extremely heavy. It's not just the camaro. |
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04-16-2012, 01:37 PM | #70 | |
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Didn't mean to offend you, but I worked on a small team that started the crash simulation technology via computers at GM in the mid 80s and subsequently, I worked for the software company that developed and sell that piece of software that is being used by most auto makers today. Before the crash by computers was available, the crash design was an arduous task for any new platform.
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