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Ann R. Thryft
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Re: Other problems with composites
Ann R. Thryft   11/30/2011 11:33:11 AM
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ScotCan, those are good issues you raise. They may dovetail into issues raised by the GAO report regarding repairability and maintenance of mostly-composite commercial planes:

http://www.designnews.com/document.asp?doc_id=235037

The report seems to conclude that the entire industry may have bitten off more than it can chew when it comes to the lack of data about repair and maintenance of in-service planes, versus the research done before they were built. That said, extensive research *was* done:

http://www.designnews.com/author.asp?section_id=1386&doc_id=235214

But as this current story points out, the use of composites in commercial aircraft and in military aircraft are two different situations with two different scales of usage. 


ScotCan
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Other problems with composites
ScotCan   11/29/2011 7:13:36 PM
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@DavePalmer some of the experienced aerospace engineers believe that Boeing may have bitten off more than it can chew. Following the 787 problems over the years at times it looked as if Boeing had forgotten how to build aircraft. The saga of the thousands of fasteners that had not been seated properly raised a lot of red flags. Hundreds maybe, but thousands no! Then, how do you organize ground returns in a non metal aircraft? Do you go back to a two wire system? In that case forget about the weight savings! When ARALL came out the old hands had a comfort zone...at least there was metal in the matrix and both manufacturing processes and electrical services followed similar patterns as the conventional construction in other words an evolutionary advance. The AirBus 380 uses a lot of ARALL. There was a rumour that manufacturers did not want to use ARALL because its fatigue resistance and corrosion resistance was so great that the structures would last longer than the projected 25 year lifespan so the economics in their minds were not practical. deHavilland's Dash 8 uses metal to metal bonded structures and some reports show that corrosion shows up in 2000 hours in competitors aircraft which only shows up in the Dash 8 at 20,000 hours...it's not uncommon to get 3 lifetimes out of a Dash 8 due to the bonded structure which is a quasi composite construction glueing (FM 73) a skin and waffle doubler together

Ann R. Thryft
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Blogger
Re: Fiberglass versus composites
Ann R. Thryft   11/29/2011 12:05:46 PM
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Alex, my understanding is that composites manufacturing is very messy, whether it's glass fiber-based materials or carbon-based materials. Most commentators are more concerned with time and cost issues, or material properties. Some manufacturers of materials used in the matrix are definitely making progress in improving curing times and/or laydown times in automated processes. And automation is certainly proceeding apace: it's a major driver in getting more composites use in primary aircraft structures.


Dave Palmer
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Platinum
Re: Design and Simulation Tools OK for Theory but not for Manufacture
Dave Palmer   11/29/2011 12:01:30 PM
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@Jerry: It's not a question of easy vs. hard, it's a question of familiar vs. unfamiliar.  It takes a certain amount of time for people to establish familiarity with a new technology. (Just because it's not new to you doesn't mean it's not new to a lot of other people).  Many people will need to be trained - not only in the U.S., but at places like Aeroman in El Salvador, where many U.S. airlines increasingly send their fleets for repair.

This isn't an argument against using composites, it's just a fact of life with any new technology.

Jerry dycus
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Gold
Re: Design and Simulation Tools OK for Theory but not for Manufacture
Jerry dycus   11/29/2011 8:11:48 AM
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  On repairs they really are not hard at all with many just being done by injecting epoxy to rejoin any broken fibers, fill any gaps restoring it's strength.  Just drill a few holes as needed into the delamination, suck on it then let the epoxy get sucked into it.

  Otherwise simple technics not that different than alum but using glues instead of rivets.  We have been doing these repairs for 60 yrs so yes we know how to do it. Or whatever nessasary depending on the part being fixed. 

Bigger damage just layup another section from the production molds and replace it.

While automation is ok for some production, hand layup can be fast and economical unless really large runs can be done.  I did costs on a production line building car bodies and it easily beat steel automatic body building on costs by a large margin, both setting up the line and running costs. 

Jerry dycus
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Gold
Re: Fiberglass versus composites
Jerry dycus   11/29/2011 7:56:30 AM
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  Sorry Ann but economics is the point of any business product.  Facts are very clear that various FG are better to other fibers in most composite jobs.

  As I said, FG can do the same job as CF for only a 10% weight penalty at 10% of the cost of CF.  Anyone who disregrads such should be fired. Only very few caes is CF worth it'd cost.

  Unlike those here I actually do composite design manufacturing and building composite 2 seat sportscars, etc that are stronger than steel by a good amount while being 50% of the weight, 235lbs for a sportwagon body/chassis unit that in steel is 450-550lbs.  My costs are about $2k/body which I'd bet costs less than in steel production.  All done without CF and lower /unibody costs than steel.

The mentioned parts failures were the result of QC, mamufacturing problems CF has as it's extremely hard to get good resin coverage/wet out leaving pockets of air bubbles and dry fibers leading to problems.  This is why Boeing has such problems early on and another strike against CF.  Though if done correctly and tested correctly it's very doable in places such a small weight advantage is worhwhile..

Now as I said CF can be useful in fishing rods, aircraft and other special things but for most, other less expensive fibers are the real future. 

 

 

Dave Palmer
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Platinum
Re: Design and Simulation Tools OK for Theory but not for Manufacture
Dave Palmer   11/28/2011 4:35:22 PM
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@ScotCan: I think you've hit the nail on the head.  Manufacturing defects are just one of the issues you encounter when you move from the computer screen into the real world.  Hopefully, some of the automated manufacturing techniques discussed in the article can help with this - but this is why structural health monitoring (which is being discussed in another thread) is such a hot topic.

Your point about maintenance crews being familiar with repair methods for aluminum but not for composites echoes the findings of a recent U.S. Government Accountability Office report, which has also been discussed here.

Dave Palmer
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Platinum
Re: Fiberglass versus composites
Dave Palmer   11/28/2011 4:19:34 PM
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From google.com, "fiberglass definition":

fi·ber·glass/ˈfībərˌglas/

Noun:
  1. A reinforced plastic material composed of glass fibers embedded in a resin matrix.

So the term "fiberglass" actually refers to all glass-fiber reinforced polymer matrix composites, not just a class of them.

Now that we've got that cleared up - the article actually discusses automated layup of composites.  Manual layup is still quite common, but CNC is making inroads.  For example, this article from Composites World discusses automation of composite wind turbine blade manufacturing.  The article notes that many of the techniques described have already been in use for some time in the aerospace industry.  

ScotCan
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Platinum
Design and Simulation Tools OK for Theory but not for Manufacture
ScotCan   11/28/2011 4:11:24 PM
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The general problem in composite use in aircraft is nonconformance during manufacturing and none of the tools mentioned during the design and simulation stages can predict what goes on. Carbon fibre laminating is a complex business affected by such things as humidity, cure cycle times, resin fluctuations etc. Liaison Engineering can fix aluminum structures and bring them back to the design intent using a number of ingenious solutions it's not so straightforward with composites. ARALL and GLARE (hybrids) are closer to traditional aluminum construction where repair procedures are concerned. Carbon fibre/honeycomb construction has failed explosively in the case of AirBus Rudders and Canadian tests on similar construction with undetected local delaminations cycled from sea level to altitude caused double the delamination in an explosive fashion. The consensus was that the rudder explosively delaminated (the pilots heard a bang from the rear of the aircraft), the rudder lost its structural stiffness and began to break up separating from the fin. The aircraft went into a series of Dutch Rolls and was only brought under control by reducing altitude into denser air. A pressurized fuselage if fabricated from the same construction would be disastrous since passenger cabin depressurization would injure people.

Alexander Wolfe
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Blogger
Re: Fiberglass versus composites
Alexander Wolfe   11/28/2011 2:19:17 PM
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Thanks for the update, Ann. So are carbon-based composites as messy to manufacture as I've long assumed them to be, mainly from what I've seen on Discovery-channel-like cable shows. Seems like it's labor intensive and messy -- almost like working with Fiberglass, but on steroids. Is that truly the case or is there an automation aspect to the manufacturing process that I'm missing?

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