
Super-Strong Graphene Has an Achilles' Heel - velodrome
http://www.livescience.com/45216-graphene-weak-link-discovered.html
======
icegreentea
GAHHH. They messed up the units! The stated numbers (4 MPa for imperfect
graphene) are wrong! They are meant to be fracture toughness (which is
measured in Pa/m^0.5), not just Pa. The paper is at [0]

Table 1 is where you want to look at. It places the fracture stress of pre-
cracked graphene in the 1-10 GPa range(which should be compard to the stated
100 GPa for perfect graphene).

I don't have the full materials properties of graphene with me, and I'm not a
materials guy, so I may have done something wrong above (so please correct
me), but I'm fairly certain that at a minimum, the article messed up the
units.

[0] [http://www-old.me.gatech.edu/zhugroup/paper/NC14.pdf](http://www-
old.me.gatech.edu/zhugroup/paper/NC14.pdf)

EDIT: replaced the link to a copy of the paper hosted by the author from the
original nature (paywalled) link.

EDIT2: some changes after actually reading the paper instead of going off the
abstract and supplied figures.

------
dfc

      > Perfect graphene can take ~100 Gigapascals (14 million pounds per square
      > inch) of force before it breaks...imperfect graphene...~4 Megapascals (580
      > pounds per square inch).
    

Can anyone put these numbers in perspective? I understand that 100 Gigapascals
is a lot, AKA more than anything I personally own. What items does the common
person interact-with/own that require > 4 megapascals? I have to imagine that
my old titanium lacrosse shaft could handle more than 4 megapascals.

CONTEXT ADDENDUM: Graphene hammer handle versus Hickory Handle?

~~~
analog31
I love Google unit conversion. Just enter "100 psi to pascals" as a search
phrase and you get an answer. Based on this, it's possible to note some
typical things converted into Pascals:

Bike tire pressure 100 psi = 690 kPa

Tensile strength of 6061 aluminum (the most common alloy) = 45000 psi = 310
MPa

~~~
dfc
Whenever people say that they like google's unit conversion I like to mention
GNU units. I would be surprised if google does a unit conversion that units
can not handle.

After reading the aluminum statistic it seems that graphene is not going to
replace my titanium shaft (that replaced the aluminum shaft).

~~~
ewillbefull
Can GNU units or anything like it accept a string such as "100F to C" and
understand what I'd like? If so I'd love to use that instead.

~~~
dfc
Temperature conversions are a little goofy because they are nonlinear.
Google's 100F to C is:

    
    
      dfc@ronin:~$ units
      2866 units, 109 prefixes, 79 nonlinear units
      
      You have: tempF(100)
      You want: tempC
              37.777778
    

The full explanation is here:
[https://www.gnu.org/software/units/manual/units.html#Tempera...](https://www.gnu.org/software/units/manual/units.html#Temperature-
Conversions)

~~~
Tloewald
I followed the like because I thought maybe i've been doimg temperature
conversioms wrong all my life. Temperature conversions are so linear. They
need to use a more correct term — e.g. simply proportional.

Having to add or substract a constant before or after scaling does not make a
relationship non-linear.

~~~
sixbrx
This may be getting pedantic, but the relationship is affine not linear -
linear would mean k times the original input would yield k times the original
output.

------
sudhirj
340 200-pound angels can dance on the head of an uncracked graphene pin (2mm
dia). Only about 3 to 35 on cracked graphene.

------
Theodores
So it is a bit like carbon fibre then? There is a surprise.

Anyone familiar with carbon fibre will know how some people are scared of it
breaking in a catastrophic failure, as in it gets a scratch and then, under
load, it breaks completely. In reality this is not much of a problem, however,
this failure is very different to what you can expect from other materials
such as steel and aluminium. I look forward to the 'high graphene content
steel', which should be a perfect material for handy things like making tanks.

~~~
stcredzero
The ductility of metal has been a tremendous boon to fabrication of large
machines. If parts don't quite fit, they deform to fit. This caused problems
when carbon fiber started to be used to build large airplanes. Those parts
don't bend and retained the internal stresses caused by mismatches. I read
this happened to Boeing.

Glass and ceramics are harder than steel. The reason that glass is fragile, is
that one can use its own strength against itself. The material itself acts as
a lever to concentrate enormous stresses at the tips of fractures. This
doesn't work nearly as well when materials are ductile.

Disclaimer: not a materials guy.

------
fit2rule
Phew. I thought the Achilles' Heel was going to be something more along the
lines of: its great and everything, but:

    
    
        The Grey Goo Will Kill Us All - File Next To "Asbestos".
    

')

------
politician
"Zhu, working with Jun Lou at Rice, found that graphene with cracks is 10
times more prone to breakage than steel, and closer in fracture toughness to
aluminum oxide or silicon carbide-based ceramics."

How does this compare to fracture toughness in silicon wafers? Does this
result mean that graphene-based ICs would be more or less difficult to
manufacture than silicon-based ICs?

~~~
icegreentea
I'm not a materials (or IC) guy, but my guess is that fracture toughness isn't
going to be huge issue. Once the wafer is made, they're all going to be
treated pretty gently. The tricky step is actually making the wafer. My
understanding is that silicon wafers are normally manufactured by growing a
giant silicon crystal ingot, and then basically slicing them into wafers. My
understanding of graphene is that since they more or less have to be grown in
sheets, then there isn't much of a subtractive process to put high stress on
the material.

~~~
akiselev
Most of the stress comes from expansion and contraction of the graphene when
it's heating up and cooling back down again, which can be more or less
pronounced depending on the substrate (glass, SiO, etc.). With chemical vapor
deposition for example, often the substrate needs to be heated and the
graphene has to be transferred from one substrate to another so there is still
plenty of room for stress during the process. At this point any poor
alignments of graphene sheets or individual atoms (I think there's three
classifications for the edge of the sheet alone) can cause cracks.

~~~
BugBrother
How much stress would radiation outside the Van Allen belts add?

(I could probably find this out myself, but it was quite a few years ago. I
assume a sheet would be damaged by gamma?)

~~~
akiselev
I don't think there is a known material that wouldn't be damaged by gamma rays
but it's a statistical process and we just don't have that many gamma rays on
our surface.

~~~
BugBrother
I was wondering about space applications.

A sheet might maybe self heal after gamma radiation, that is why I asked
(depending on environment, there might not be much else to happen?). Most
other radiation is charged and might be kept away with strong magnetic fields.

But, as I wrote, this was a long time ago.

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BuildTheRobots
Slightly off topic, but Professor Sir Andre Geim (the original inventor, I
believe) was the very enjoyable guest on Radio 4's Desert Island Discs last
month.

[http://www.bbc.co.uk/radio4/features/desert-island-
discs/cas...](http://www.bbc.co.uk/radio4/features/desert-island-
discs/castaway/20e3bf76)

------
EGreg
[http://www.extremetech.com/extreme/163997-carbyne-a-new-
form...](http://www.extremetech.com/extreme/163997-carbyne-a-new-form-of-
carbon-thats-stronger-than-graphene)

Use carbyne!

~~~
m_mueller
Sorry for OT, but.. Jeremy Clarkson has ruined all carby.* names for me - I
can't stop thinking about his joke.

