Definition of "composite"

I wonder if the aircraft enginners of yesteryear were worried about repairing metal aircraft after years of looking after wood and canvas ones!!!

An interesting point – i bet many aircraft engineers of yesteryear had many serious concerns over the reliability of those new-fangles “rivets”……

Billy Boeing tells us he’s got a repair scheme that’ll cope with any damage, so you have got to belive him!
The American pilots have tried to blame the AA airbus A300 accident at JFK on a dodgy repair to is composite fin. How are they going to cope with the entire fuselage and wings being composite?

Rgds Cking

I agree with Mr Murray, it is going to be VERY interesting when they drive a catering truck into the side of a 787!.
Repairing composite material is a specialist task. The only repairs I have been involved in were on fairings and flaps. They were horrible, messy things that, although done in accordance with the repair manual I would not say that I was proud of them!. Repairs are best done in the fibreglass shop were they do them all the time! I would not want to do a repair to a serious structural part without specialist guidence.
As for the fidelity of a repaired composite part, the repair and jointing area is stronger than the original part. The difficulty with any composite repair is cutting out all of the damage, you never get all of it out. In fact the cutting proccess will cause damage it’s self. Also you have to keep the damaged area dry because any moisture trapped in the repair will freeze at altitude and cause the composite to split. This is called De- lamination. This will weaken the item and can remain undetected as it is internal.

Rgds Cking

I wonder if the aircraft enginners of yesteryear were worried about repairing metal aircraft after years of looking after wood and canvas ones!!!

But that would depend on how the strength of mended material compares with the strength of newly built material, or perhaps intact worn material. For example, a lot of metals are joined by welding in the first building, so welding in a patch would give about as much strength as the intact material had.

How would you strengthen the spot where original fibreglass is joined to the patch?

I dont know about the fidelity of repaired composites etc – we are now into “proper” engineering and its not my specialist field, so i cant help you

Broken carbon fibre looks exactly like broken fibre-glass. I believe it can be patched in a similar manner, although i suppose the question of repair feasability will depend on how load-bearing the broken bit was – same as using other materials in engineering.

But that would depend on how the strength of mended material compares with the strength of newly built material, or perhaps intact worn material. For example, a lot of metals are joined by welding in the first building, so welding in a patch would give about as much strength as the intact material had.

How would you strengthen the spot where original fibreglass is joined to the patch?

Ah, I see.

Can it be said that the kevlar/carbon fibre composites, while perhaps having a greater absolute strength than composites based on silken, hempen or cotton cloth or paper, have the same strengths and weaknesses and, once broken by excessive force, look like each other? And therefore can be mended in a similar manner?

Broken carbon fibre looks exactly like broken fibre-glass. I believe it can be patched in a similar manner, although i suppose the question of repair feasability will depend on how load-bearing the broken bit was – same as using other materials in engineering.

I also suppose that common sense dictates that the cost and complexity of carbon composites are only tolerated for areas of high stress – less stressed parts of an aircraft are presumably made of lesser materials.

Michael

quite a lot of composites used in aircraft are just ordinary fibreglass, and not carbon fibre or kevlar.

Yes – a “composite material” is any material which has been formed by combining 2 or more other materials to create a new material.

However – In terms of aviation and modern technology, “composite material” generally refers to a material using carbon and/or kevlar fibres woven into a sheet and then bound together using a resin.

Carbon and Kevlar fibres have massive tensile strength in terms of stretching under load, but are fairly easily cut.

Using them in composite materials involves laying down sheets of the woven material with the fibres running in alternate directions (like a mesh) and then using a high strength flexible resin (like epoxy) to bind them together and to take up any required mould shape.

The finished material is then massively strong in all directions as the dried epoxy (or matrix component to be accurate) gives flexibility to the inner weave and stops it buckling, whilst the inner cross-weave resists tension and shearing forces.

I think this is all correct, but stand by to be corrected by any super-techs out there 🙂

Ah, I see.

Can it be said that the kevlar/carbon fibre composites, while perhaps having a greater absolute strength than composites based on silken, hempen or cotton cloth or paper, have the same strengths and weaknesses and, once broken by excessive force, look like each other? And therefore can be mended in a similar manner?

If you break metal, like aluminum, it behaves differently. Aluminum can be bent out of shape, and if bent back, it can be, e. g. welded… I suppose that a mesh cannot be reconnected by welding the same way aluminum could… and a kevlar composite might perhaps have too strong and rigid epoxy matrix to allow a patch to be properly sewn on to the mesh, so as to provide a good strength…

Yes – a “composite material” is any material which has been formed by combining 2 or more other materials to create a new material.

Usually, composites are made to create a material which has better or different physical properties to the individual materials used to create it.

Often this involves the composite material comrprising of inner strands of one material woven together into a mesh to give strength, which is then covered in a liquid outer second material which sets hard in the final shape and gives additional strength.

When people in ancient times created straw and mud huts, they created a composite material !!

Concrete reinforced with steel rods in bridges and buildings is also a good example of composite material.

Plywood is also a good example of this – each layer of wood is laid with the grain at right angles to the one below it, giving the finished plywood much greater resistance to splitting than a piece of individual wood of the same thickness.

However – In terms of aviation and modern technology, “composite material” generally refers to a material using carbon and/or kevlar fibres woven into a sheet and then bound together using a resin.

Carbon and Kevlar fibres have massive tensile strength in terms of stretching under load, but are fairly easily cut.

Using them in composite materials involves laying down sheets of the woven material with the fibres running in alternate directions (like a mesh) and then using a high strength flexible resin (like epoxy) to bind them together and to take up any required mould shape.

The finished material is then massively strong in all directions as the dried epoxy (or matrix component to be accurate) gives flexibility to the inner weave and stops it buckling, whilst the inner cross-weave resists tension and shearing forces.

I think this is all correct, but stand by to be corrected by any super-techs out there 🙂