Hi, Doug,
I still can't find the actual reference but it was a
paper by Aviva Brecher long ago. Oddly enough,
there's not much materials testing on meteorites
(maybe because it's destructive testing!), but
John S. Lewis reports on ten irons which yielded
crush strengths of 2.7 to 4.2 kiloBars (Gibeon was
3.2 kiloBars). This scarcely more than achondrites
(2.5 to 4.0 kiloBars). Wrought iron (or a mild
steel) measures 7.0 kiloBars. Cretaceous igneous
rocks from Greenland average 4.5 kiloBars, for
example. Terrestrial rock is stronger than iron
meteorites, in other words.
Crushing strength of stone once very important.
Why is the Washington Monument the tallest stone
structure ever bult by man and probably the tallest
that ever can be built? You go up much further and
the load on the lowest trace of stones exceeds the
crushing strength of the stone. Bad news. You couldn't
built it out of iron meteorites -- too weak. Even so,
the other problem is that tall stone structures tend
to sink straight into the Earth because they exceed
the crushing strength of the crustal bedrock.
Whoops! That's why the Washington Monument
sits on a 140-foot cube of the hardest granite
known to man, which you never see, but which that
big stone plaza around the Washington Monument
is the top of!
I love good engineering...
Sterling K. Webb
--------------------------------------------------
----- Original Message -----
From: <[EMAIL PROTECTED]>
To: <[EMAIL PROTECTED]>
Cc: <[email protected]>
Sent: Tuesday, June 13, 2006 12:04 PM
Subject: Re: [meteorite-list] Norway Meteorite Impact Site Believed to be
Found
Hola Sterling,
Turns out meteoric iron is often weaker than igneous
rock while terrestrial iron is like, well... like iron!
That is an interesting idea you have (and of course has nothing to do with
temperature). On-the-surface, the crystalline structure giving rise to the
Widmanstatten, and other figures, does seem like it could introduce planes
of
cleavage, especially when oxidation starts along the interfaces, but as
sexy
as a thought as that might be (and limiting to planar-'seeded' fractures)
I'll
definitely look forward to your posting on the issue not have an opinion
until at least I read what you and that link have to say on this subject
subject
of iron meteorite brittleness. What is ringing and resonating in my ear as
I type this, though are thoughts of the Tucson Ring and no shortage of
other
meteoritic irons like Zacatecas (1969 )in history that have be favored to
be
used as anvils specifically for their superior properties vs. other
materials
when struck with a hammer. Also the arduous chiseled inscription on the
iron meteorite La Morita (apparently dating back to at least 1821) comes to
mind: "Only God with His power --- this iron shall destroy --- because in
this
world there won't be --- another who can undo it." So field evidence and
the
difficulty of even meteorite hunters getting a piece of iron to take home
as a
specimen might be at odds with that...
OK, here's the link you asked for:
_http://www.diogenite.com/met-temp.html_
(http://www.diogenite.com/met-temp.html)
Remember the meteoroid shield failure (not due to a strike) of Skylab in
the
mid 70's? Here is another link for fun, related to the coldness of space
(NOT) for those who forget we have a Sun in the neighborhood and why skylab
could reach 165 deg C:
_http://history.nasa.gov/SP-4208/ch14.htm_
(http://history.nasa.gov/SP-4208/ch14.htm)
_http://history.nasa.gov/SP-4208/ch14.htm#t3_
(http://history.nasa.gov/SP-4208/ch14.htm#t3)
(actually all the links provide a great primer coat for thermal control in
space:-)
Extracted from the link text: "The power shortage drew most attention at
an
evening press conference; little was said about an even more serious
problem, the apparent loss of the micrometeoroid shield. No one was
particularly
worried about damage from a meteoroid strike, since the chances of a hit
were
slim. i But the shield's secondary function, thermal control, loomed large
in
the aftermath of the launch. The shield had been designed to keep the
workshop
on the cool side of the comfort zone, heating being easier than cooling. The
outside of the shield was a black-and-white pattern designed to absorb the
desired amount of heat. The inside of the shield and the outside of the
workshop were covered with gold foil, which regulated the flow of heat
between the
two. It was an admirable system as long as the shield stayed in place.
Without
it, the gold coating on the workshop would rapidly absorb excessive heat,
making the interior uninhabitable.4
The shield had failed to deploy at the scheduled time and subsequent ground
commands had no effect. While officials were debating further action, Saturn
engineers discovered flight data indicating an anomalous lateral
acceleration
about a minute after liftoff. The data, coming just before the space vehicle
reached its maximum dynamic pressure, suggested some structural failure. A
short time later, workshop temperatures began rising, strong evidence that
the
shield was gone. Within a few hours, readings on many of the outside
sensors
exceeded 82°C, the maximum scale reading. Internal temperatures moved above
38° C. Working from the thermal model, Huntsville engineers figured that
workshop temperatures would go as high as 77°C internally and 165°C on the
outside, endangering food, film, perhaps even the structure itself. Mission
Control
therefore began maneuvering the exposed area out of direct sunlight, and
some
cooling occurred.5
Saludos, Doug
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