On 2019-10-14 3:45 AM, JF Mezei wrote:
On 2019-10-11 07:25, Jeff Findley wrote:

But, as Musk also said, raw materials for carbon composite structures
cost a *lot* more than commonly available 301 stainless steel.

Caveat: the comparison was the cost per pound of material not the cost
to build a part of X strengtn with one or the other.

Since you need fewer pounds of carbon fibre to achieve the same strength
as steel, the extra cost of carbon fibre is _not as bad_ as Musk made it
look. Steel is likely cheaper, but you end up with it being heavier.


That is really a remarkable comment. Not as bad? How do you know? You
building Starships?

Here's some interesting figures quoted from Tim Dodd:

https://everydayastronaut.com/stainless-steel-starship/

"With carbon composite, you need to cut the fabric, impregnate it with
high-strength resin, which can be difficult and then make 60 to 120
layers! There’s also approximately a 35% scrap rate of material too,
which makes it so carbon composites are terribly expensive. As a matter
of fact, the advanced carbon composites cost about $180 per KG by the
time you factor in the scrap material. So how’s that compare to
stainless steel? $3. $3 per KG….

Uhhh yeah… 60 times to cheaper to manufacture. SIXTY TIMES CHEAPER. I
don’t care what business you’re in, when something is 60 times cheaper,
readily available today, and outperforms the other material, you’d
better hop on it! Which makes me wonder how the heck does Rocket Lab get
away with it, they make it look so easy! Well, these two vehicles aren’t
in any way shape or form comparable… so let’s not even do it haha"

....and there was this comment at the end of the article by Bruce Dunn:

Bruce Dunn
January 30, 2019 at 2:09 pm
Reply

"There is a further reason for using stainless steel rather than carbon
composite – fracture toughness. Carbon composites are typically very
brittle, and small flaw can initiate cracks which rapidly spread and
destroy the structure. This means that extreme care needs to be taken
not to mar the surface of carbon composite structures. On January 17
1997 there was a failure in the carbon composite case of one of the
solid rocket boosters of a Delta II launch vehicle. This caused the
spectacular loss of the vehicle shortly after takeoff. A subsequent
lengthy investigation determined that the case of the booster had likely
been slightly damaged during ground handling, providing a flaw which
initiated a crack which rapidly spread."

Here is the video of that anomaly:

https://www.youtube.com/watch?v=z_aHEit-SqA

Note the debris field. An issue raised later during the development of
Aries I / Orion (The Stick). It wasn't clear the nylon chutes of the
Orion would have survived contact with any burning solid fuel remnant
debris field from an exploded SRB should it be so unlucky as to descend
through it after launch abort.

If I were a betting person, I'd prefer to take my chances on
characterization of thermal reactions of stainless and iterate on that...

Dave