Print 33 comment(s) - last by Keeir.. on Jan 10 at 12:47 AM

CFRP will also make the BMW i3 more lightweight with extra space

BMW said the i3 will have lower repair and insurance costs thanks to the use of carbon fiber reinforced plastic (CFRP). 
According to a new report from Autoblog Green, the BMW i3's use of CFRP will make repairs easier because most bumps at a traffic light or a parking lot will only damage exterior plastic parts, which are easily replaced. But for bigger collisions that actually do affect the carbon fiber, the damage stays local to that one spot. 
"When we evaluated carbon fiber, we started doing the safety, crash and repair concepts right from the beginning because just deciding on carbon fiber and then, when we're done, looking at [the details] would be a huge risk," said Manuel Sattig, communications manager for BMW i.
"Carbon fiber is, of course, a new material. Our dealers need to be trained for that specific repair system. But, if you look at the i3, if the car has a small bit of damage, someone hits you at a traffic light or bumps into you in a parking garage, you don't hit carbon fiber, you mostly damage the exterior plastic parts. They can very easily be replaced because you click out the damaged part and replace it with a new one. If you have a stronger accident, then, of course, carbon fiber will be damaged. The interesting thing is that carbon fiber is not deforming, so the damage only happens locally and it breaks only at that specific area."

Sattig noted that BMW has already talked the U.S. National Highway Traffic Safety Administration (NHTSA) and the insurance industry about the use of the new material, and they've decided to go with a "very low" insurance system. 

CFRP will also make the BMW i3 more lightweight with extra space. 

BMW officially announced the all-electric i3 back in July, giving the new vehicle a price tag of $41,350 USD. 

The i3 will feature a 22-kilowatt, 450-pound lithium ion battery, which will provide power to a rear-mounted electric motor. The i3 packs 170 horsepower and 184 pound-feet of torque, allowing the single-gear i3 to accelerate from 0-30 miles per hour in 3.5 seconds and 0-60 mph in about 7.0 seconds. Its top speed is limited to 93 MPH. 
For those concerned about range, the i3 has an electric range of 80-100 miles, and the battery can be charged with a standard system in about three hours.

In October, it was reported that BMW may boost production of the i3 EV due to early demand. At that time, the automaker said customers reserved over 8,000 i3s ahead of the official launch in Europe. 
BMW has plans to sell 10,000 i3 units next year and previously announced that it would adjust build capacity according to market demand.

The i3 will go on sale in the U.S. during the second quarter of 2014.

Source: Autoblog Green

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By hughlle on 12/12/2013 2:41:18 PM , Rating: 2
I thought the whole point of deformation across the whole panel, crumple zones or whatever they are termed these days, was to absorb energy and better protect the passengers, even if in just a small way.

I'm also wondering, just because they're cheaper to repair for small bumps and dings, how does that cost translate to a more significant impact? Can they simply repair the break, or is it still a matter of replacing a panel? I'd have thought that it would be a lot more expensive to replace carbon fiber than it would be to replace a conventional metal.

In reality though, i know little to nothing about automobiles, i'm purely speculating.

RE: Deforming
By Keeir on 12/12/2013 2:53:14 PM , Rating: 2
So... yes, your right. The whole point of deformation is to "absorb" energy. In some ways its also to extend the length of a crash, which lowers the acceleration on tender human parts.

I believe what the guy is saying is that BMW designed in discrete points of failure that would approximate the typical "crumple" zone, but would not create massive wide spread failure. At least I hope so. Carbon Fiber is typically fairly stiff (Higher Young's Modulus) on the level of steel. This means that without gross deflections/failures, crash length would be very short.

Carbon Fiber has been used for years in Aviation. Typically repairs can be accomplished relatively cheaply. Car structure is somewhat different, with a greater empahsis on beams and not so much on panels. Either panel or beam however, it typically is cheaper to replace that repair a full severage, even if technically feasable.

RE: Deforming
By theapparition on 12/13/2013 10:35:05 AM , Rating: 4
Wow, so much misinformation. Not particuarly you, just replying to your post.

First off, let the Apple marketing esque begin. There is no magic to CFRP. It's just plastic with a carbon fiber filler. People have been using this for decades. When you design plastic parts, you can add various fillers to give the parts strength. Fiberglass is common, but both carbon fiber and stainless steel fibers are also used per the application. For example, in the automotive world, there is the misconception that the Corvette is fiberglass. While older models did used hand laid fiberglass, new models use plastic molded parts with fiberglass fill. No magic here, BMW is just using carbon fiber instead. Some benefits to that approach and some drawbacks. But make no mistake, the body panels are just plastic and would be replaced just as any other plastic parts would be.

The other issue is structural members, where they seem to be using actual Carbon Fiber. Thats a completely different animal. Carbon fiber is awesome, but comes with lots of issues. First off, its really carbon fiber "composite". Composite means using two or more materials as one. Pure carbon fiber is either unidirectional or woven and isnt much different than a bed sheet. The matrix is an epoxy like "glue" that gives carbon fiber its compressive strength. Carbon fiber by itself is very strong in tensile strength, but horrible in compressive. Think of a string. You can pull it very hard, but collapes instantly. The epoxy gives the composite its compressive strength. So any comparisons to steel need to be accordingly. Tensile strength can exceed steel, but compressive strength is much weeker.

In a failure mode where the carbon fibers have been damaged, you basically cannot repair it. You have to replace the entire part. Once the fibers are broken, no way to mend them. With metal, you can weld. No such repair with CF. Thats simplistic, but realistic considering how Joe's Autobody would be doing the repair. And before people jump in talking about repairing fiberglass, while the mechanism is the same, your not using fiberglass in a structural situation. Sure, you can add a CF patch, but its almost like taping a structural member together. Not going to happen. Structural damage will require replacing the part.

So what BMW is saying in this press release is that major structural damage will require significant repair, but they will use a lot of plastic body parts to minimize the cost for most minor body damage claims. Ignore the CFRP and other hype.

RE: Deforming
By Keeir on 12/13/2013 2:02:13 PM , Rating: 1
The epoxy gives the composite its compressive strength


For compression loading there are two things to consider.

1.) Compression Yielding, a material related property
2.) Compression Stability, a material and geometry related property

Carbon Filaments are very resistance to compression yielding. In the sizes typically used in CFRP, they have no/little compression stability. The epoxy is very weak in 1, but it allows carbon fibers to be loadshare/stablized each other. It changes the geometry of the situation, especially when plys are orientated in different directions such that the large minority of not oriented axially to the applied compression loading. It does this by transfer of shear loading. Epoxy in and of itself is typically quite weak, and a sheet of epoxy itself would be very weak in both 1.) and 2.) sitations.

Epoxy allows carbon fiber filaments to act as a (more) unifed sheet and develop significant 2.) to get closer to the theortical limit of the material as expressed by 1.). In and of itself, the epoxy add very little compression capability.

Tensile strength can exceed steel, but compressive strength is much weeker.

Strength and stiffness are two seperate issues. In the event of a "crash" event, the most important thing is to ensure that the acceleration applied to the occupants is low. Acceleration is change in velocity over the time period. Materials with high stiffness values (Young's modulus) shorten the crash duration increasing the velocity. This is the foundation of crumple zones. In place of finding/using low stiffness materials (which would create many secondary issues), automotive engineers use materials that deflect and deform by design, significant increasing the duration of a crash and reducing the elastic feedback of the material. The i3, if not properly designed, could work similiar to a billards ball. The structure could be very stiff and highly elastic, which would result is more change of velocity and shorter durations. Having worked with large scale composites, a CFRP part will typically deflect very little before complete failure. To resist the bending loads that likely drive the initial requirements for i3 structure would probably result in structural members that also resist axial compression from crash situations.

In a failure mode where the carbon fibers have been damaged, you basically cannot repair it.

Interesting. This is false.

A simple example. Even in the event of complete failure/severage, composite repairs can occur. It will likely not be economical, but there will be areas of the i3 that are not designed for economical part replacement either.

Sure, you can add a CF patch, but its almost like taping a structural member together.

Which is essentially all that epoxy is right? CFRP are essentially taped together fibers.

RE: Deforming
By Samus on 12/13/2013 10:32:13 PM , Rating: 2
Carbon fiber absorbs and distributed energy without deforming. Metal compresses through this process, where carbon fiber returns to its original shape (depending on epoxy.)

RE: Deforming
By theapparition on 12/14/2013 2:39:58 AM , Rating: 1
Sigh, you use a lot of textbook replies but obviously no experience.

Example 1, you still refer to CFRP in structural loading talking about deflection. CFRP is just plastic, so either you mispoke, or still lack the fundamental understanding. CFRP is NO different than what's being used on modern car body panels. CFRP is NOT Carbon Fiber. True carbon fiber panels get strenth from strand weave.

Example 2. Saying CF is just taped together by epoxy matrix anyway. The fibers are what gives carbon fiber its strength, and severing them would lead to a repaired part with the same strength as just epoxy matrix.

Example 3. I said quite explicitly that I kept the discussion simple. You went out of your way to get detailed, but still lack some of the basic fundamentals from experience. You think the average body shop will have the capabilities to repair? Yes, composite engineering is complex, and the dailytech readership only needs the cliffs. While the filament weave helps, the matrix still takes most compression loading.

So I ask you this. Have you ever done any design with composites?

RE: Deforming
By Keeir on 1/10/2014 12:47:07 AM , Rating: 2
Your suffering from some misconceptions.

With the i3, BMW is using CFRP from the entire body frame. They are using continuous fiber tape/sheets for many of the parts currently. Since multiple layers are required, they are using a epoxy type resin. BMW is not using "flake" filled molded parts for body structure . Sure for the body panels, and even some structural components, but a substantial portion of the underlying frame is composed of oriented plys.

In this situation, it is entirely possible to repair them. These type of structures have been used in aviation for years with repairs. It takes less than 3 days to be trained on the process. Its very simple. Maybe not quite as simple as welding steel, but still relatively simple. Taper sand damage. Lay in some adhesive epoxy sheet. Lay in some sheets/tape with some more epoxy. Cover with vacuum bag. Heat. Simple.

While the filament weave helps, the matrix still takes most compression loading.

Hmmm. So, how do you explain a nearly 20 fold increase in compression strength from a typical un-reinforced epoxy matrix to one filled with multi-orientated plys/tape runs? Yes, your right, in the flake filled situation, your stability will be limited by matrix. In an oriented sheet lay-up, the epoxy is not a matrix so much as a shear transfer/binding agent.

So I ask you this. Have you ever done any design with composites?

I'll ask you something in return. How many oriented ply layup panels have you had repaired and tested to failure? I've done several. You can completely repair oriented ply carbon fiber reinforced plastic composites. Simply scarf them.

RE: Deforming
By Argon18 on 12/12/2013 3:01:59 PM , Rating: 3
You're confusing the various parts. Crumple zones are part of the unibody, and yes they are designed to deform to absorb the energy of an impact.

The carbon fiber and plastic parts mentioned in this article are not part of the unibody. These are the exterior bolt-on panels and cosmetic trim. These parts attach to the unibody.

RE: Deforming
By soydios on 12/12/13, Rating: -1
RE: Deforming
By Solandri on 12/12/2013 3:18:24 PM , Rating: 2
This. The "crumple zones" are actually about 20-40 lbs of metal reinforcement which gets added to the car after the artistic design and mechanical components guys have had their say. One of the engineers who specifically designs these crumple zones for BMW gave a guest lecture at my school. Because of his weight budget, he really has to work to extract the maximum amount of deformation energy from the least amount of material. It has nothing to do with the cosmetic trim which gives the exterior shape and appearance of the car.

Like I've been telling people for years when they complain about "plastic" phones or laptops - that is the sensible way a structural engineer would design these devices or a car. You make a strong metal interior, and surround it with a flexible plastic exterior. The plastic exterior bends and deflects light impact forces, and can be replaced cheaply if there's cosmetic damage. The metal interior protects against larger impact forces from a more serious accident.

RE: Deforming
By Keeir on 12/12/2013 4:05:09 PM , Rating: 2

The i3 is one of the first car sold that used CFRP for the main structural elements.

that is the sensible way a structural engineer would design these devices or a car

Yes and no.... Given how cheap/light plastic is, the increase in cost and wieght usually is an acceptable trade for the consumer/service benefits.

The design of many of the items you are refering to would not be ideal from a structural point of view, but repersent an inflection point... and potentially not even the true optimal point for confluence of requirements.

RE: Deforming
By inperfectdarkness on 12/13/2013 2:36:16 AM , Rating: 2
Here's what I'm hoping for.

CFRP pieces/panels means that expensive tooling/die equipment to manufacture parts--is no longer required. It would be great if I could have my vehicle towed to a service-center & have them 3D print new body panels on the spot to replace the broken ones on my car.

I won't hold my breath on that, but it would be a terrific leap forward. It would also save MFG's money on having to generate large amounts of "spare parts" inventory and subsequently warehousing it until it was needed. I hope that someday, every component on a car--from a door panel to an engine block--could be 3D printed on demand by a repair shop.

RE: Deforming
By theapparition on 12/13/2013 10:47:55 AM , Rating: 2
No offense, but people need to come down to reality on 3D printing.

It only works where you can print and then melt those materials together. Plastic is obvious where you can get close, metal is possible, but not near the same strength as worked parts. Forget combining carbon molecules into forming fiber bonds, at least no process invented yet for that.

3D parts are no where near ready for most production, and they cost significantly more than reguarly fabbed parts. Gets me everytime i hear people talk about 3D printing like its ready to replace traditional manufacturing. Not going to happen in a long time, if ever.

RE: Deforming
By Keeir on 12/13/2013 2:16:49 PM , Rating: 2
3D parts are no where near ready for most production, and they cost significantly more than reguarly fabbed parts. Gets me everytime i hear people talk about 3D printing like its ready to replace traditional manufacturing. Not going to happen in a long time, if ever.

Errr... no and no. A few decades ago, it was the most economic to make forgings, then final machine these. Machining costs were high, material waste was high, and technical barriers existed. Now forgings are a relatively rarity, because despite the material waste, machining has advanced and material technology and processing have evolved to allow this..

Metal based 3D printing is advancing to the point where metal printed parts and machined parts have little difference in material strength. Costs have fallen dramatically. Often now, 3D metal printed parts would be cheaper overall to fab that assemblies made from traditionally fabbed parts. And 3D metal parts are in use already in multiple applications (especially military). Significant barriers to wide spread adoption still exist, but already parts are being designed in a wide range of industries with the intention of using 3D printing to make them. It probably will be 5-10 years (essentially 1-2 design cycles) to get widespread usage, because it doesn't make sense to replace already working parts and supply lines, but a review of the technology says we are nearly at the tipping point.

RE: Deforming
By Jeffk464 on 12/12/2013 3:11:28 PM , Rating: 2
I'm not convinced that carbon fiber is more environmental than aluminum. Aluminum is easily recyclable and is non toxic.

RE: Deforming
By Solandri on 12/12/2013 3:32:01 PM , Rating: 2
Aluminum takes a boatload of energy to refine. Its naturally occurring forms are at very low energy states, so you have to add a ton of energy to convert it back into elemental aluminum. That's the reason the Shuttle's solid rocket boosters used aluminum for fuel - it releases a whole lot of energy when oxidized.

Aluminum cans and aluminum foil are only stable because oxidation forms a thin airtight layer of aluminum oxide (aka corundum - same stuf as rubies and sapphires) which protects the remaining aluminum from oxidation.

So while the aluminum itself is environmentally friendly, making the aluminum is not.

RE: Deforming
By TheBlackbrrd on 12/12/2013 5:13:45 PM , Rating: 2
Making aluminium is environmentally unfriendly, but it's environmentally friendly to recycle, since there takes little energy to melt aluminium. It's one of the few materials that makes sense to recycle economically too.

RE: Deforming
By TheBlackbrrd on 12/12/2013 5:18:36 PM , Rating: 2
Regarding the energy required in the process, if it's in countries like Iceland or Norway that are mostly hydroelectric, it really doesn't matter that it takes a lot of energy.

On the other side, the refinement process prior to the melting process is anything but environmentally friendly. Aluminium is poisonous (until it's in it's pure form, when it's quite inert)

RE: Deforming
By ritualm on 12/12/2013 5:13:08 PM , Rating: 2
Aluminum requires LOTS of energy to produce. Elemental aluminum itself melts at 3600 degrees F, so refiners have to first convert bauxite ore into cryolite and then apply 1740-1800 degrees F of heat to get the metal out.

Ever wonder why most aluminum mills are situated next to major power generation installations? Because those mills will then have access to huge amounts of cheap electricity required to make the metal itself.

It's easily recyclable and non-toxic, but environmental friendly it is not.

RE: Deforming
By Jeffk464 on 12/12/2013 6:15:58 PM , Rating: 2
Interesting I wonder if the weight benefits of aluminum over steal pays for itself environmentally. One thing that's kind of mitigating factor is I believe the metal in cars is almost all recycled.

RE: Deforming
By Reclaimer77 on 12/12/2013 5:54:09 PM , Rating: 1
This is what we've been saying since the CAFE increases were proposed. It will lead to much smaller and lighter vehicles, which reduces passenger safety.

RE: Deforming
By Jeffk464 on 12/13/2013 11:51:20 AM , Rating: 2
You need to wait for the crash test results to come back before you say they can't be made to perform well.

RE: Deforming
By Jeffk464 on 12/12/2013 6:18:02 PM , Rating: 2
You know what's impressive is that this is the first largely carbon fiber car that's reasonably priced.

RE: Deforming
By Spuke on 12/12/2013 6:39:18 PM , Rating: 2
I think BMW's goal is to be able to mass produce CF (I think there some other automakers involved also).

By Hammer1024 on 12/13/2013 1:09:55 PM , Rating: 3
BS flag thrown!

Being in the composite aircraft industry, when a composite lets go, it shatters. It doesn't deform, and is not repairable in any conventional sense.

Yes, a plastic outer pannel is fine for a grocery cart, but so is steel.

When that vehicle gets torpedoed by an F-150, there will be nothing but a pile of carbon splinters and dust at best. Carbon fiber splinters make for fine spear tips two! So much for the occupants.

As to repair... just start a bonfire... it will be cheeper.

By Jeffk464 on 12/13/2013 8:13:10 PM , Rating: 2
Again, this car will be crash tested every way it can. We just need to wait and see if BMW engineers managed to pull it off or not.

By Reclaimer77 on 12/13/2013 9:11:33 PM , Rating: 2
It's already been crash tested and it did poorly. But then again, does BMW ever do all that great?

By Jeffk464 on 12/14/2013 1:04:28 PM , Rating: 2
yeah, your right it doesn't look like it performed very well.

By Spuke on 12/14/2013 3:06:03 PM , Rating: 2
It's already been crash tested and it did poorly. But then again, does BMW ever do all that great?
Has it been crash tested here in the US yet? I read it got 4 stars in Europe and only did poorly in the pedestrian part.

By Reclaimer77 on 12/14/2013 4:37:07 PM , Rating: 2
A 4 star in Europe would be like a 3 star here.

I thought Saturn...
By dnoonie on 12/12/2013 6:36:48 PM , Rating: 2
Didn't Saturn already try this and after many years decided it was a bad idea and went back to metal?

RE: I thought Saturn...
By Spuke on 12/12/2013 6:37:49 PM , Rating: 2
Saturn didn't use CFRP.

By Pandamonium on 12/14/2013 2:26:22 AM , Rating: 2
It's a BMW. Do you really think a BMW dealer is going to have a cheap repair for a body panel? Let alone the premium associated with carbon fiber...

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