Composite NanoStaples: Ideas for composites repairing.

7/17/2019 Composite NanoStaples: Ideas for composites repairing.

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Composite NanoStaples:

Ideas for composites repairing.

When we talk about carbon fiber repairing or any other composite material, there is not

much you can do nowadays, once you got a part that have an important crack we can doseveral things, these two are the most common:

• “Adhesive layer”: Add another layer and apply heat so we can fill up the hole on

the structure with a new layer of carbon fiber, this is expensive and not very useful

in many applications.

• n Aircrafts, or other applications where we need good mechanical properties, is very

common to use this kind of patches to repair the structures, this brings us some

structural problems on the material due to the drilling that is necessary for this kind

of repairing.

!o what is the deal with this patches and why we are losing mechanical properties, the

problem is the kind of "oint that is made between the two parts# we are not going to explain

it very deep this, because we have studied it on another sub"ect, but we know that these

fastened joints, due to the drilling and more things bring up a large stress



concentration, even though this kind of repairment is prefered in high added value

applications.

$ow we can see the effect on the stress concentration of "ust one fastened "oint, now

imagine the effect of %& or '& of them, not critical tough but we are losing properties.

And here we present you our idea, we would like to mixed the good properties of the

bolted repair and the good microstructural structure of the bond repairs, because

this last one doesn(t introduce stress concentration.

)ut how we are going do this* e would try to ta!e advantage of the nanoscience of

the gec!o adhesion properties and using as a nanotechnology on the repair of

composite parts.

And where is the Nanoscience in the gec!o"

geckos has the ability of +run up and down a tree in any way, even with the head

downwards(. eckos, the world-s supreme climbers, are capable of attaching and detaching

their adhesive toes in milliseconds while running. We know that this properties are given by



a hierarchical micronanostructured filaments on their feet.

/uring some studies we are now reaching to understand how this work and the strong it is,

two front feet of a gec!o can withstand #$%& N of force parallel to the surface 'of

##( mm#)* in the two feet we have &+.+$$ filament,mm#, that makes a 0,'10 $ per

filament.

Another interesting property is that the deeper we go on the hierarchical structure the

better properties rise, here we can see a graph of the stress that can withstand and the

surface area of different parts of the gecko, from the total gecko to the spatula 2the

filaments3, in different tensional test.

At least seven possible mechanisms for gecko adhesion have been discussed over the

past &(- years: glue% suction% interloc!ing% friction% static electricity% capillary

forces and van der aals adhesion. All but the latter two mechanisms had been

re"ected by %404.

Which one of those two is the most important* We run a test on a hydrophobic surface and

on a hydrophilic surface, there were no great variations on the results, so the capillary



adhesion forces are not dominant, so the an der aals adhesion forces are the !ey

ones.

an der aals force is largely independent of surface chemistry and highly

dependent on the distance between surfaces# thus it can be said that gecko adhesion

depends more on geometry than on chemistry. 5his discovery paved the way for fabricationof synthetic gecko adhesives from a variety of materials. ecko keratin proteins are not

re6uired for fabrication of geckolike adhesives# which is great, so other materials can be

used to fabricate the first prototype synthetic gecko spatulae that exhibited limited gecko

like adhesion at the nanoscale.

5he discovery that gecko adhere by van der Waals forces does not preclude an effect of

water under some conditions. ater is li!ely to alter contact geometry and adhesion

energies. t(s concluded that humidity 2i3 modifies the contact geometry, increasingadhesion and 2ii3 decreases the van der Waals 7amaker constant, reducing adhesion. 5hese

two effects counteracted each other to yield an increase in adhesion from ( nN at low

humidity to &# nN at high humidity.

8nowing this, that is a 9an der Waals driven mechanism and helped with water humidity is

good because we can take advantage of this at higher altitudes, where the planes are

flying, and where the mechanical properties have to withstand high tensions.



or airplane applications is good that is 9an der Waals driven mechanism because the

humidity at high level of the atmosphere is lower.

7ow is this applied as an adhesive*

;sing a nanostructure to create an adhesive is a novel and bi<arre concept. eckolike

synthetic adhesives 2!As3 are under rapid development and with each generation more

geckolike properties will emerge.

)ut in our case we are not loo!ing for an exactly gec!o0li!e adhesive% because the

gec!o can attached to a surface as easy as it can be detached from a surface, this

for structural applications could be very dangerous, so for our prototype we would only like

take advantage of the attaching properties.

1rototype:

2or our prototype we will use as filaments 'or also called setae) the 3ultiall

Carbon Nanotube 4echnology, that is a promising technology for development of ecko

like !ynthetic Adhesives.

5ach nanotube grown to a length of =&>%&& @m with a diameter of %&>'& nm could

function as individual spatulae. $anoscale adhesion measurements of a ultiWall



Barbon $anotube based eckolike !ynthetic Adhesive produced nanoscale detachment

stresses up to %0 Ca, D= times the adhesive stress measured in a single gecko seta, %0Ca

only one filament or seta, imagine the properties of placing a few hundreds in a common

adhesive, imagine the mechanical properties.

!o we will create a some kind of gel solution in which it will be full of carbon nanotube

place in the desired directions, and we will use this as an adhesive film that will connect the

composite material with the structural damage and the new composite material, making a

new continuous material saving the material from structural damage.

)ut, how could we orient the B$5(s in the desired direction*

Eecent studies have discovered that applying an electric field could be the answer. Barbon

$anotubes show alignment to AB electric fields when they are inside a solventFgel. 5he

main aspect to obtain a great orientation are the si<e 2diameter and length3 and number of

walls of the nanotubes, and the fre6uency of the applied field.

Advantages and 6isadvantages:

5he main advantage of this prototype is that is a solution for bro!en composites that

can reach high stress structural applications, without using patched with bolted "oints



that decrease enormously the mechanical properties due to introducing distortion on the

matrix of the material.

5he main disadvantage of when we use adhesive repairing for composite is that we can(t

allow the material to break through the adhesive, so we have to run up test to prove

that the using of ultiWall Barbon $anotubes increase as much as we think the mechanical

properties, the failure stresses and the direction of the critical tensions 2not the same

charging perpendicular or parallel to the surface for the filaments3.

Conclusions:

As a conclusion we think that this prototype of using nanotechnology to improve the

macrostructural properties is very interesting, due to the high increase of the mechanical

properties, and even more important the gigantic increase of using composite material 2as

carbon fiber3 on our day to day life, and if this prototype of eckolike !ynthetic adhesive

works it can be a ma"or breakthrough for many applications, from the aeroespacial, that is

already been said, to simple tennis rackets, or bikes, and much more.

Composite NanoStaples: Ideas for composites repairing.

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