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Beth Stackpole
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Safety and cost issues?
Beth Stackpole   11/29/2011 6:35:40 AM
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Ann, you raise the issue of crash-optimized composites. That got me thinking, how safe is a vehicle if it's designed with this lighter weight material? Beyond safety, what about maintenance costs given that most vehicles are involved in some sort of minor fender bender if not a full-blown accident over the course of their lifetime. Is it much more difficult to repair a composite structure vs. steel door panels, for example?

Jerry dycus
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Gold
Re: Safety and cost issues?
Jerry dycus   11/29/2011 8:40:15 AM
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   Hi Beth, Ann and All,

             If correctly done lighter composite bodies can be a lot safer than steel ones.

              Take the  F1 racecar whiich can hit a wall at 200mph a yr or 2 ago and she walked away from it because of the composite tub/frame plus other energy absorbing features using tires, suspension, structures, etc.

               My vehicle designs use the same tech plus more and can easily out perform steel for safety.

              As for repairs in composites is fairly easy. In many cases you just soak the break in epoxy, let cure and grind of anything that doesn't look like a car  ;^P.  Then finsh sanding, paint.  Bigger just buy a replacement part and have it installed.  Not hard though different from steel. Most bodymen already have composite experience in finishing that should help them with fibers.  There are many boat/FG shops that can do it too.  Even better it's rather easy to do yourself saving much money.

                As for the new material it doesn't sound that useful as other things like foam, plastics are lighter, more cost effective. Kind of depends on it's cost.

               And generally to cut weight, thus cost, one want more stiff fibers/components, not less as we already have less stiff ones that cost less.

Beth Stackpole
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Re: Safety and cost issues?
Beth Stackpole   11/29/2011 8:44:36 AM
Thanks for your comments, Jerry. While there are marine shops and hobbyists versed in composite finishing, I would think there will eventually need to be a wholesale retraining of body shops and automotive maintenance suppliers (even at dealerships) to keep up with demand for repairs on composite-based vehicles as the use of these materials become more widespread. As for my safety concerns, your comments about the durability and structural integrity of fiber-enforced composites are a comfort. It's surprising to me, but definitely a comfort.

 

Alexander Wolfe
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Re: Safety and cost issues?
Alexander Wolfe   11/29/2011 9:16:26 AM
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Jerry, I'm wondering what the F=ma situation is when a composite car hits a steel-cage vehicle. So in other words, do we have a situation like today, where people want SUVs because they don't want to be in a small car that's hit by an SUV? (They want to be in an SUV.) When every car is composite, it'll be an equal "battle," for want of a better phrase. But when there are some composites mixed in with a legacy fleet of steel cars, what are the crash dynamics?

Jerry dycus
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Gold
Re: Safety and cost issues?
Jerry dycus   11/29/2011 4:09:19 PM
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  What happens as they say, depends!  
   Much depends on how it is designed. My style is soft ends and extremely hard cabin shell with 4 point seat belts in a safety designed seat like racecars do. I have other things that are likely patentable that cut forces by 50-75% on top of F1 style above.

I build a frame/rollcage of composite bars between the skins along with kevlar type cloth as the most inside layer keeping any breakage together and spread loads.

Now when hit instead of crushing it's going to get knocked around but I'm good with that, already having one accident that totaled the compact car that hit my composite one and mine only needed $40 in materials to put back on the road.

 One good thing about low mass is you can only put as much force on it as it weighs. Anymore than that it just squirts away. 

As for SUV's it takes those into account.  I expect that the safety will be overall as good as the better, if not  best cars.  And in the same size of vehicle, Composites would win easily. My new vehicles are only 500 and 1300lbs.

It's not like this is new as it's rather old hat in raceboats, aircraft and racecars for 4 decades now.

There is a vid of an Audi 100 hitting a composite car called the City head on and the Audi lost is another example.  Can't remember the name of the German composite company who made a bunch of prototype composite cars that set a bunch of records.

Once I'm in production I'll crash some but have to make some money before I can afford that.

TJ McDermott
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Re: Safety and cost issues?
TJ McDermott   11/29/2011 9:52:39 PM
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Attachment means also come to mind.  Should a part need to be replaced, rather than repaired, will it be attached with screws?  Snap posts?  Thread inserts seem likely, at added costs.  Threaded fasteners may add to the cost of the vehicle, but definitely make it easier to maintain.

kurturethane
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Iron
Re: Safety and cost issues?
kurturethane   11/30/2011 9:52:09 AM
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I appreciate the perspective regarding cost to repair. My company makes products body shops use to repair plastic, so I'm familiar with this area. A 50% glass fiber nylon composite strutural component is not something that shops would or should repair. For the most part, mineral-filled PP/TPO cosmetic parts (like bumper fascia) can be repaired, but often are not. Most shops today don't have plastic repair skills and prefer to replace parts. Insurers are applying some pressure to reduce the cost to repair and now some shops are looking at plastic repair more seriously.

Rob Spiegel
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Re: Safety and cost issues?
Rob Spiegel   11/29/2011 10:48:11 AM
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The steel industry has been fighting the growing use of composites. The most recent argument has been around the entire lifecycle (materials, use, recycling) emissions of steel versus composites. When it comes to crash optimization, steel may lose the argument.

Dave Palmer
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Platinum
Angles are not measured in Celsius or Fahrenheit
Dave Palmer   11/29/2011 10:42:45 AM
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@Ann: I think you mean "endure static distortion of up to 240° without damage," not "endure static distortion of up to 240°C without damage." Thankfully, angles are not measured in Celsius or Fahrenheit; 1° is just 1/360 of a full rotation - no matter what country you are in! For a 15% glass filled nylon injection molding compound to be able to withstand this much twisting without breaking is pretty incredible.

@Jerry: The point is not that the material is less stiff.  According to the press release, it's actually more stiff than comparable injection molding compounds - in other words, if you apply the same amount of torque, it will twist less than other compounds.  However, unlike other materials, if you keep putting torque into it, it won't break.  It's stronger and/or more ductile.  Since the press release doesn't say how much of the twist is recoverable, it's not possible to determine which.  It would be interesting to have a third photo showing how much it untwists when it is unloaded.

According to the press release, it took 35 N·m of torque (about 26 ft·lbs) to twist the test specimen 240°, but since the dimensions of the test specimen are not given, it's impossible to translate this into units of stress, which would be more useful.

It's also not quite clear from the press release what the benefits of the unusually-shaped test specimen are. (And there are some real disadvantages to doing your testing on a non-standard test specimen - you can't compare your results to anyone else's!)

Still, this does appear to be a significant advance in injection molding compounds.  It would be good to see datasheets for these grades.  Here is a datasheet for Ultramid B3WG6 CR, which was BASF's first crash-resistant nylon formulation.  The tensile modulus, tensile strain at break, and impact strength are all quite high, compared to "plain vanilla" 30% glass filled nylon-6.

By the way, many people would not think of this type of material as a composite, even though that's exactly what it is.  Since it's made by injection molding, most people would just consider this to be a plastic.

Ann R. Thryft
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Re: Angles are not measured in Celsius or Fahrenheit
Ann R. Thryft   11/29/2011 12:30:40 PM
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Thanks, Dave, the addition of "C" was a copyediting error. Yes, I was talking about angles, not temperature.

And that was a good summary of the benefits of the material and the relationship between torsion and strength/stiffness. This material is specifically targeted toward items such as steering wheel components, body inserts and seat structures, as noted in the photo caption. In other words, items that need to withstand a crash without breaking, and "bounce back." 


Jack Rupert, PE
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Platinum
Safety Only or Vehical Protection Too?
Jack Rupert, PE   11/29/2011 5:46:38 PM
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Maybe this is obvious to the mechanical and material engineers out there, but when you are talking about optimization and distortion does that mean that the materials return to their original shape after the distortion or does it just mean that the don't have a catastrophic failure.  I'm trying to get a perspective as to whether this is an improvement on some of the current designs that are "safe" but you end up totaling your vehicle after a minor collision

Dave Palmer
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Re: Safety Only or Vehical Protection Too?
Dave Palmer   11/29/2011 6:45:27 PM
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@Jack: Actually, it's not obvious at all.  Neither the story nor the press release indicate how much of the distortion is actually recoverable.  That's why a third photo (showing how much the test specimen un-twists when the load is removed) would be so helpful.

As you point out, materials which permanently deform under low loads would be undesirable.  That being said, materials which have the ability to bend rather than breaking can absorb a lot more impact energy than materials which simply break when they are overloaded.  If I were in an accident, I would much rather that the energy of the collision be absorbed by a piece of plastic or metal than that it be absorbed by my body.  After all, if I live to see another day, I can always fix my car later!

We want materials which are both strong (require high loads to permanently deform) and tough (can absorb a lot of energy without breaking).  It looks like this latest batch of Ultramid nylons fits that bill, at least as far as injection molding compounds go.

Ann R. Thryft
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Re: Safety Only or Vehical Protection Too?
Ann R. Thryft   11/30/2011 11:49:47 AM
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Good summary, Dave. The information provided, including the press release, was not as clear or complete as we'd like. However, it did imply that the biggest value to these materials is the safety issue, more so than vehicle protection, and that they can return to their original shape after that much distortion.


Charles Murray
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Re: Safety Only or Vehical Protection Too?
Charles Murray   11/30/2011 11:02:30 PM
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I second Dave Palmer's comment. These materials appear to offer strength and toughness. Would a stress-strain curve give us a better understanding of how they fail?

Dave Palmer
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Platinum
Re: Safety Only or Vehical Protection Too?
Dave Palmer   12/1/2011 3:48:13 PM
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You can find stress-strain curves for the previous generation of Ultramid CR here. They compare a 30% glass filled Ultramid CR grade to a regular 30% glass filled Ultramid nylon 6. What I like about these curves is that instead of just giving you one curve per material, they actually give you four: two different strain rates (slow and fast) and two different orientations (parallel and perpendicular to the fiber direction). This gives you a much better picture of the behavior of the material.

Unfortunately, even with the stress-strain curves, you still can't necessarily tell how much of the deformation is recoverable.  For linear elastic materials, such as metals, you can easily estimate how much of the total deformation is recoverable just by looking at the linear part of the curve.  For nonlinear elastic materials, such as most plastics, the curve is never linear to begin with, so this approach doesn't work.

I sent an e-mail to BASF at the address listed in the press release to ask about elastic recovery.  We'll see if they write back.

Ann R. Thryft
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Re: Safety Only or Vehical Protection Too?
Ann R. Thryft   12/7/2011 1:11:53 PM
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Dave, thanks for taking the initiative. I hope BASF answers your email and we can get some more info.


bob from maine
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Platinum
Composite Repair
bob from maine   11/30/2011 12:15:34 PM
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From a marine standpoint, composite repair is as much art as science, particularly with carbon fiber. Most carbon fiber assemblies are built to be as light and stiff as possible, but are expected to flex in a specified direction and for the most part smoothly over their lentire ength. Make a repair and 99 times out of a hundred you will create a hard spot that will fracture under future loads rather than flex. Secondary adhesion is also a significant issue. The original parts are typically infushed so the fiber to adhesive ratio is carefully controlled, secondary bonds to other parts is carefully engineered and specified. Making repairs to these parts so they meet the original design parameters is almost impossible. I wouldn't want to drive a car that had "minor" crash damage and was "fixed" in a body-shop. It doesn't make sense to make a safety-critical part out of exotic material at high cost and then allow trowell on smoodge, grind away the excess and hope it meets the original design criteria. Imagine a wing section of a  Dreamliner getting dinged and repaired. I'm guessing Boeing would have issues with not replacing the entire assembly.

Jerry dycus
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Gold
Re: Composite Repair
Jerry dycus   11/30/2011 2:43:32 PM
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          Hi Bob and All

                     While much of what you say is true, the repair part is rather off.  A decent trained composite repair person can make most repairs without causing structural problems.  I personally can and have made repairs for decades without hard spots in critical areas. Yes it takes more work but easily doable with training.

                      Your example of a 787 wing doesn't hold water. Little of the wing is critical and very resistant to battle, other damage and one of composites big advantages.  About the only critical area is the wing spar/s and even there it's not as hard to repair as a metal wing.  Damage other parts and all you are likely to get is a fuel leak.

                     As the other poster asked about fasteners, not hard either using glues, epoxies, double sided tape  along with screws, bolts, etc. You can make threads, etc into composites or just wet out a bolt and hole with epoxy/glue, etc and you have a threaded hole.

                       One thing I rarely do is put metal in the layup as it's always a hard point and usually delaminates sooner or later.  I instead put it outside the composite and glue/bolt, etc it on.  If you need strength instead of metal for attachment points, I just do it in composites instead with far better, lighter results. 

                            Nice now on the design side I can engineer these problems out.

Dave Palmer
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Platinum
Re: Composite Repair
Dave Palmer   11/30/2011 3:10:37 PM
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@Jerry dycus: The repair techniques you are referring to make sense for the type of composites you are using for car bodies, which I assume mainly use thermosetting resins.  But, as kurturethane pointed out, in this case we're talking about a 30 - 50% glass filled nylon injection molding compound.  How would you repair that? I would imagine that the sort of repairs you're talking about would be more difficult where thermoplastic resins are involved.

Tim
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Re: Composite Repair
Tim   11/30/2011 6:53:07 PM
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As far as I know, there is no real repair for glass filled nylon.  There are ways to weld the material, but fixing cracks or tears are not feasible.

Jerry dycus
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Gold
Re: Composite Repair
Jerry dycus   11/30/2011 8:56:44 PM
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  Hi Dave and All,

               You certainly wouldn't use these composites in aircraft as they weigh too much and cheaper, lighter  ways like foam to absorb energy over time.  Nor can they be repaired, replaced nstead. 

                My kind of composites is whatever the job needs.  I see little use for this other than boat cleats, cases, gun stocks, etc.   Depends on price mostly but who needs a high priced moderately strong material?

               



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