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For A Novice, How Are Composite Materials Made?  
User currently offlineVC10er From United States of America, joined Feb 2007, 2897 posts, RR: 9
Posted (3 years 1 month 2 weeks 2 days 4 hours ago) and read 6420 times:
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I have only the most basic understanding of composite materials AND how they are used on aircraft? I believe I am correct in my assumption that the 787 will be the the aircraft (commercial) that has used and even pushed the envelope the most composite material.

A few questions from a novice:
How is it basically made?
What are composite materials composed of?
Is it true that the 787 fuselage is baked in a tube shape?
Is lighter weight it's primary purpose?
Is it equally as strong and flexible as aluminum or steel?
Any other things about composites a novice would fascinating?

THANK YOU SO MUCH!


The world is missing love, let's use our flights to spread it!
21 replies: All unread, jump to last
 
User currently offlinebristolflyer From United Kingdom, joined May 2004, 2297 posts, RR: 0
Reply 1, posted (3 years 1 month 2 weeks 2 days 3 hours ago) and read 6412 times:

From one novice to another...

I believe the 787 is the first all composite a/c. Others (eg some Airbusses) have stabilizers that are composite (the composite stabilizer was at the center of the investigation of the AA A300 that crashed just after 9/11 in New York).

I don't know a great deal about the mfr process, but it involves layering strands of fibers on top of each other in alternating directions (so the finished product is strong in all directions). Then you bake it to make the resin hard.



Fortune favours the brave
User currently offlineKELPkid From United States of America, joined Nov 2005, 6388 posts, RR: 3
Reply 2, posted (3 years 1 month 2 weeks 2 days 3 hours ago) and read 6411 times:

Quoting VC10er (Thread starter):
How is it basically made?

A fibrous, carbon-based material with high tensile strength is placed in a material which bonds the fibers together (like an epoxy), and then cured (usually under heat) to cause the bonding reaction to occur. This creates one layer. Then, another layer is sandwiched on top and bonded to the first layer, and another, and another...until the desired strength/thickness of the material is achieved.

Quoting VC10er (Thread starter):
What are composite materials composed of?

Carbon fibers + a bonding agent

Quoting VC10er (Thread starter):
Is lighter weight it's primary purpose?

Not always. Many times, it is cheaper to design complex shapes (like fairings) as a composite rather than using traditional metal working techniques.

Quoting VC10er (Thread starter):
Is it equally as strong and flexible as aluminum or steel?

I'm sure it depends upon the composite and thickness. I would imagine that, in fact, composite is more flexible than a traditional metal like aluminum.



Celebrating the birth of KELPkidJR on August 5, 2009 :-)
User currently onlineBMI727 From United States of America, joined Feb 2009, 15745 posts, RR: 27
Reply 3, posted (3 years 1 month 2 weeks 2 days 3 hours ago) and read 6403 times:

Quoting KELPkid (Reply 2):
A fibrous, carbon-based material with high tensile strength is placed in a material which bonds the fibers together (like an epoxy),

In principle, it can be thought of somewhat like paper mache, with the carbon fibers being like the paper and the epoxy being like the glue.

Quoting VC10er (Thread starter):
Is lighter weight it's primary purpose?

It can also cut down on maintenance significantly. When you get barrels or large carbon fiber panels instead of conventional aluminum panels you can cut down on the number of fasteners and joints, all of which need to be inspected.



Why do Aerospace Engineering students have to turn things in on time?
User currently offlinehorstroad From Germany, joined Apr 2010, 268 posts, RR: 0
Reply 4, posted (3 years 1 month 2 weeks 1 day 19 hours ago) and read 6335 times:

Quoting VC10er (Thread starter):
A fibrous, carbon-based material with high tensile strength is placed in a material which bonds the fibers together (like an epoxy), and then cured (usually under heat) to cause the bonding reaction to occur. This creates one layer. Then, another layer is sandwiched on top and bonded to the first layer, and another, and another...until the desired strength/thickness of the material is achieved.

almost correct, but you add all layers before baking it.

basically you have the fibre, which can be carbon or glass, and a matrix which is usually epoxy resin combined with a hardener. in aircraft manufacturing these two components are already brought together with the right ratio, to achieve an optimal bonding. so you add all layers of so called PrePreg and put it in an autoclave where it is cured with high pressure (something like 150psi) and high temperature.
the 787 fuselage is made of 3 major parts which is, in my opinion, a disadvantage to the A350 which is made of huge CRP panels. I think the panel solution is easier to handle in case of damage, as you can simply change them. repairing carbon fibre structures can be quite difficult.
light weight and high strength are the primary reasons.
I was told "its as strong as steel but lighter than aluminium". I made myself a mouse pad of about 8 or 9 layers of carbon fibre. this thin plate of plastic can carry my whole weight standing on it when I lay it over a gap only resting on two edges.

another type of composite material not mentioned before is glare. it´s a combination of glass fibre and aluminium


User currently offlineNorthwest727 From United States of America, joined Jul 2005, 491 posts, RR: 0
Reply 5, posted (3 years 1 month 2 weeks 1 day 18 hours ago) and read 6317 times:

Quoting KELPkid (Reply 2):
Quoting VC10er (Thread starter):
Is it equally as strong and flexible as aluminum or steel?

I'm sure it depends upon the composite and thickness. I would imagine that, in fact, composite is more flexible than a traditional metal like aluminum.

Carbon fiber is apparently stronger than steel.

I'm curious though, say the composite skin is damaged and repaired with a patch (standard practice)...is the patch now going to create a weak spot that is a nuisance to maintenance (ie, cracks)?


User currently offlinedlednicer From United States of America, joined May 2005, 544 posts, RR: 6
Reply 6, posted (3 years 1 month 2 weeks 1 day 13 hours ago) and read 6243 times:
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Common composites are fibers of glass, carbon, boron or an aramid such as Kevlar, embedded in epoxy or polyester resin. They can be cured at room temperature or at elevated temperatures (baked).

Composites usually have more tensile (pull) strength than metals, but less compressive strength (except rebar reinforced cement, where the opposite is case). Technically, they can be lighter than equivalent metal construction, but usually, when all is said and done, they come out the same weight or heavier. They have very good fatigue and corrosion resistance, but you can get problems with things like aluminum touching carbon composites, where you get corrosion from the dissimilar materials. Kevlar in particular, has moisture absorption problems, but is very abrasion resistant (and hard to cut). Most composites are not very abrasion resistant. Composites are easier than metals to form into shapes with complex curvature.

To me, the biggest drawback of composites is that no one has demonstrated a viable means of recycling them. There have been a lot of claims, but I have never seen a commercially functioning process. For example, when Beech destroyed the Starships, the incinerated them at very high temperature.

Composites won't completely replace metals, but are rather an alternative material.

BTW - wood is a composite, created by nature. Cement with steel rebar is a composite, as are automobile tires, with rayon cords and steel fibers embedded in vulcanized rubber.


User currently offlineVC10er From United States of America, joined Feb 2007, 2897 posts, RR: 9
Reply 7, posted (3 years 1 month 2 weeks 1 day 11 hours ago) and read 6216 times:
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Quoting horstroad (Reply 4):

Super THANKS to everyone, this is all very educational and I can talk about it at dinner and sound smart!

From you account it sounds like the Enterprise (the Starship) will be made of composite's - but probably not wood.

Any more input will help.

Is there like a big metal form to wrap the composites around for the 787?

...and if composites are not really lighter than metal, how is it the 787 will (hopefully) be able to burn less fuel? wings and engines?



The world is missing love, let's use our flights to spread it!
User currently onlineBMI727 From United States of America, joined Feb 2009, 15745 posts, RR: 27
Reply 8, posted (3 years 1 month 2 weeks 1 day 11 hours ago) and read 6208 times:

Quoting VC10er (Reply 7):
Is there like a big metal form to wrap the composites around for the 787?

I'm not sure about the 787, but use of a mandrel is one of the ways large composite pieces are formed. I want to say that is exactly how the Beechcraft Premier fuselages were formed.



Why do Aerospace Engineering students have to turn things in on time?
User currently offlinehorstroad From Germany, joined Apr 2010, 268 posts, RR: 0
Reply 9, posted (3 years 1 month 2 weeks 1 day 8 hours ago) and read 6169 times:

here is a video about the 787 assembly process... it may be interesting for you

http://www.youtube.com/watch?v=f07HpUAuWgk&feature=related


User currently offlinesoon7x7 From , joined Dec 1969, posts, RR:
Reply 10, posted (3 years 1 month 2 weeks 1 day 6 hours ago) and read 6147 times:

51% for the 787 will be carbon fibre. A composite is actually several materials cured to form one. Adobe bricks are actually composites. They are mud reinforced by straw. Boats, surfboards are composite. In aerospace, the first to be used in commercial transport was polyester resin and fibreglass. It is still used today however the polyester was replaced by epoxy resin. The fabrics involved are fibreglass, Kevlar, carbon fibre, carbon fibre w/ boron and carbon/carbon. Initially wing fairings, canoe fairings or "secondary surfaces" were the areas subject to its application. The spoilers of 747's from its inception were fabricated from aluminum honeycomb laminated between layers of aluminum. This method, also considered composite. During the design of the 757, 767, Carbon fibre entered the picture while its use or applications grew on the airframe design. The dive brakes or spoilers, wing fairings, wing lower panels, engine cowlings, rudders, ailerons, etc, saw all composite fabrication with obvious much success. The first Boeing "primary structure" to utilize composite technology was or is the 777 vertical fin. Most of the above mentioned structures are nomex honeycomb core or "resin impregnated paper". The honeycomb core is shaped and then layed up with the resin impregnated fabrics which may be individually , fibreglass, Kevlar, carbon fibre or a matrix of all of them at once...depends on the application. The resins used call for by design certain cure rates and cure temperatures. The parts will be cured in an autoclave the draws out any air and compresses the fabric layers while they cure out. This can take 1/2 hour to several. result is an incredibly light and very strong product.

Airbus led the way with composites in primary structures during the development of the A310. All the tail feathers were composite application. Next they redesigned the A300 tail grouping as compared to its alloy predecessor and yielded a weight savings of about 347 lbs. Not much but it allowed for more PX seats...more flight revenue. Airbus has also pioneered Aluminum lithium into their designs. This is a product Boeing rejected during the 777 development as it had inherent fracture characteristics during manufacture. While composites have amazing qualities they have draw backs including internal damage detection, composites are porous so the exterior topcoat must always maintain its protective integrity. Repainting these surfaces requires a different approach as they are easily damaged. They are also easily repaired. With the 787 as far as I am concerned the jury is open one this one. Not sure how fuselage damage repairs will be approached. Just because it is constructed of carbon fibre does not mean it is indestructible. The leading edges of the space shuttle Columbia were made from Carbon Carbon and we all saw what a block of lightweight foam did to it and the result that unfortunately followed. All in all, composites have made for intersting innovations in aircraft design...some good, some not.


User currently offlineVC10er From United States of America, joined Feb 2007, 2897 posts, RR: 9
Reply 11, posted (3 years 1 month 2 weeks 17 hours ago) and read 6071 times:
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Quoting horstroad (Reply 9):
Quoting soon7x7 (Reply 10):
Quoting horstroad (Reply 9):

Thanks to you both, I will watch the video. Also learning about the vertical fin is interesting. I recall a TV special (can't recall if it was a news story or documentary) when AA took delivery of the A300 and the fact that they would have to use a flat grey paint on the vertical tail vs shiny metal to paint it's AA logo onto and how the overall ac would look like as a mixture of really "almost chrome-like aircraft when clean" metal parts with other parts in grey. I hated the way it looked at the time- but now it seems like an actual part of the livery. The picture that always was stuck in my head was the AA 727 which seemed like 100% metal. Like the album cover of the beasty boys (dating myself)

Have there been discussion about their future 787 where the entire fuselage will need to be flat grey!

I wonder if the ac paint suppliers can develop a good silver for the composite parts?



The world is missing love, let's use our flights to spread it!
User currently offlinebikerthai From United States of America, joined Apr 2010, 2131 posts, RR: 4
Reply 12, posted (3 years 1 month 2 weeks 12 hours ago) and read 6010 times:

Quoting Northwest727 (Reply 5):
...is the patch now going to create a weak spot that is a nuisance to maintenance (ie, cracks)?

No, typically the patch is over built to avoid the weakening the structure. And crack or crack propagation is not a problem with graphite epoxy panels.

Quoting VC10er (Reply 7):
if composites are not really lighter than metal,

You really can't compare strength of composite vs. metal on a one for one basis. It depends on the complete design and how it's optimized for one material to another.

Typical industry design have shown that a good composite design will be 20% lighter than a comparable metal design. (My own experience included).

If you want to understand how it is made first hand, you can try making a composite panel yourself.
All you need is a fiberglass cloth and some two part epoxy from the hardware store.
Lay the fiberglass on a smooth metal surface, brush the epoxy on to it and let it cure.

For better resin and fiber you may try the local boat repair shop.

Of course the material they use for airplanes are more processed and better suit for rate production, but you will get a sense of how it works.

More samples of in-expensive composites can be found in tennis rackets.

bikerthai

[Edited 2011-08-09 11:58:42]


Intelligent seeks knowledge. Enlightened seeks wisdom.
User currently offlinesoon7x7 From , joined Dec 1969, posts, RR:
Reply 13, posted (3 years 1 month 2 weeks 6 hours ago) and read 5940 times:

West marine offers "vacuum bagging" technology through their epoxy systems. Just get the manual and read it...you will then have a great idea how composites are produced, generally speaking...good idea bikerthai!

User currently offlinedynamicsguy From Australia, joined Jul 2008, 873 posts, RR: 9
Reply 14, posted (3 years 1 month 1 week 6 days 19 hours ago) and read 5882 times:

A good layman's guide to composites, and pre-pregs in particular, can be found on Hexcel's website here. Hexcel is a material supplier to the industry.

User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 79
Reply 15, posted (3 years 1 month 1 week 6 days 7 hours ago) and read 5817 times:

Quoting VC10er (Thread starter):
Is it equally as strong and flexible as aluminum or steel?

A common issue is that people (in aerospace) often automatically equate "composite" with "fiber-reinforced plastic" which is just *one* type of composite, and even then it's a really broad category. *The* major advantage of composites is the ability to tailor their properties. It's easy to make a composite that's more or less strong or more or less flexible than metal. There are also metal composites that have properties better than any individual alloy.

Quoting Northwest727 (Reply 5):
I'm curious though, say the composite skin is damaged and repaired with a patch (standard practice)...is the patch now going to create a weak spot that is a nuisance to maintenance (ie, cracks)?

Permanent repairs need a damage tolerance analysis just like the original sturcture, so it needs to be at least as good at not cracking as the original structure. Usually the repair is overstrength just to make up for any discrepancies in the application of the repair, so it's more likely to be less maintenance prone than the original (but heavier).

Quoting VC10er (Reply 7):
From you account it sounds like the Enterprise (the Starship) will be made of composite's - but probably not wood.

I still have the Star Trek:The Next Generation Technical Manual...the Enterprise (at least NCC1701-D) is, according to cannon, in fact made from composite (some kind of fiber-reinforced ceramic). So is the warp core.

Quoting VC10er (Reply 7):
Is there like a big metal form to wrap the composites around for the 787?

Yes, it's called a mandrel. There are several for each fuselage section.

Quoting VC10er (Reply 7):
...and if composites are not really lighter than metal, how is it the 787 will (hopefully) be able to burn less fuel? wings and engines?

About half is supposed to come from engines, about a quarter from systems & aerodynamics, the rest from weight. A lot of the maintenance savings also comes from the composite, as well as a lot of the cabin comfort features.

Tom.


User currently offline474218 From United States of America, joined Oct 2005, 6340 posts, RR: 9
Reply 16, posted (3 years 1 month 1 week 5 days 15 hours ago) and read 5742 times:

Quoting tdscanuck (Reply 15):
Permanent repairs need a damage tolerance analysis just like the original sturcture, so it needs to be at least as good at not cracking as the original structure. Usually the repair is overstrength just to make up for any discrepancies in the application of the repair, so it's more likely to be less maintenance prone than the original (but heavier).


Composite on aluminum repairs where developed and approved years ago so I would think a composite to composite repair would be simple.


User currently offlinesoon7x7 From , joined Dec 1969, posts, RR:
Reply 17, posted (3 years 1 month 1 week 2 days 3 hours ago) and read 5580 times:

Depends on the nature of the repair. Vacuum bagging may be required on an AOG aircraft to a component that is not easily removed. In short it would be easy to the experienced tech w/ the proper evaluation and repair gear. To the less experienced, the evaluation will probably not be correct and the repair will ultimately fail. Composite manufacturing is typically performed in a very controlled environment but not always repaired in same.

User currently offlinePurdueAv2003 From United States of America, joined Dec 2005, 251 posts, RR: 2
Reply 18, posted (3 years 1 month 4 days 19 hours ago) and read 5362 times:

Quoting soon7x7 (Reply 10):
In aerospace, the first to be used in commercial transport was polyester resin and fibreglass.

I'm going to disagree with this statement. As was mentioned above, wood is a natural composite material and has been used since Kitty Hawk. Dope and fabric is also another early composite application.  
Quoting Northwest727 (Reply 5):
I'm curious though, say the composite skin is damaged and repaired with a patch (standard practice)...is the patch now going to create a weak spot that is a nuisance to maintenance (ie, cracks)?

I've talked with some people who are helping AB develop the A350 SRM, and one of the solutions they are working on is to use metal doublers (Al or Ti) installed with Ti Hi-Loks as a temporary repair solution for skin damage during line operations. Once the aircraft reaches heavy mx, the metal doublers will be removed and a precured patch will be installed.

As is key with any structural repair, the repair has to meet or exceed the original static strength requirements of the original part. Fatigue is less critical with composite structure, so the damage tolerance recheck requirements will, hopefully, be much more liberal.



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User currently offlineAutothrust From Switzerland, joined Jun 2006, 1596 posts, RR: 9
Reply 19, posted (3 years 1 month 4 days 15 hours ago) and read 5327 times:

Quoting bristolflyer (Reply 1):
I believe the 787 is the first all composite a/c.

Neither the 787 or the A350 are full composite a/c. Fighters /Bombers/ Helicopters have reached much higher CFRP percetnage.



“Faliure is not an option.”
User currently offlinesoon7x7 From , joined Dec 1969, posts, RR:
Reply 20, posted (3 years 1 month 3 days 6 hours ago) and read 5245 times:

Quoting Autothrust (Reply 19):

The 787 is 51% CFRP's. That is enough for an aircraft of its size. Airliners are designed for higher cycles than bombers while fighters and choppers are just smaller.

Quoting PurdueAv2003 (Reply 18):
I'm going to disagree with this statement

Of course you are and I would further disagree with you and myself...first composites were mud and straw bricks used in Scotland, Ireland, etc, to build homes...but we are splitting hairs here,...aren't we?...but then again, I'm wrong...I don't have any left!
Think the thread is concerned with contemporary type aircraft as in transports...again...the first used was fibreglass and polyester resin converted to to epoxy based resins. One of the first items that required composite use was the nose raydome. On the 727 wing fairings, access covers and horizontal stabs got the composites along with spoilers. Wing canoes were still alloy construction...the 737 started using composites on rudders, wing canoes, outer wing panels, spoilers, nose gear doors (also later 727's) and vertical fin caps. Carbon fibre started with the 757 and 767 series but still mostly figreglass/ kevlar. CFRP's were used on the engine cowls and spoilers. 747's have fibreglass rudder skins (nomex)with alloy ribs, elevators and h/trim tabs are fibreglass w/ alloy ribs. Belly and wing fairings are fibreglass nomex (3" thick). Wing canoes are nomex w/ outer layer of CFRP's on later models. Kruegar variable camber leading edge devices are fibreglass. The inboard highspeed aileron and low speed aileron are nomex skins over alloy ribs. 40% of the 747 is honeycomb composite, some aluminum honeycomb. All 747 wingtips are fibreglass while the main wing tips on 727,'s, 37's 57's and 67's are alloy. The 777 uses quite a bit more CFRP technology but not sure of its distribution through the airframe. I believe it is the first Boeing product to utilize a carbon tail feather grouping, floor beams, etc. While CFRP's increase use in the 777, the presense of fibreglass is still there and widely used...even on the 787. Guess in less critical areas...it is cheaper and easier to work with. Intersting is how the Kevlar seemed to be phased out as it is difficult to work with. You need some special tools and it creates some AOG repair issues. It doesn't like to be sanded, cut or drilled. In this regard, the other composites act more or less equally the same. Had enough?...I have...sorry for the rant but I like talking after 6 cups of coffee...                  


User currently offlinebikerthai From United States of America, joined Apr 2010, 2131 posts, RR: 4
Reply 21, posted (3 years 4 weeks 1 day 12 hours ago) and read 5077 times:

Quoting soon7x7 (Reply 20):
Kevlar seemed to be phased out as it is difficult to work with

Kevlar is only used now where ballistics is critical (fan blade containment). Though heavier, some fiberglass and toughened epoxy can fill in the niche without issues of water absorption attributed to Kevlar.

Quoting soon7x7 (Reply 20):
6 cups of coffee...

Oh, i thought they were beers.   

bikerthai



Intelligent seeks knowledge. Enlightened seeks wisdom.
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