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Ann R. Thryft
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Blogger
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.


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.

Charles Murray
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Blogger
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?

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?

               

Tim
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Platinum
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.

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.

Jerry dycus
User Rank
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.

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.

Ann R. Thryft
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Blogger
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.


kurturethane
User Rank
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.

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