Neutrons prove ‘Bond villain’ did not cause Arecibo telescope collapse
ornl.gov
ornl.gov
So this failure was easily predictable. I assume that the cables have been designed for a much shorter lifetime, so it was expected that either the cables would be replaced or the radiotelescope would be decommissioned many years ago.
Nevertheless, the choice of pure zinc for the cable sockets is somewhat weird, because it guarantees a short lifetime. Had a zinc alloy been used, like ZAMAK (Zn-Al alloy), the flowing speed would have been much less and the lifetime of the cables would have been greater.
Alloys are much more resistant to plastic deformation and flowing than pure metals, because the atoms with different sizes cause defects in the crystal structure that prevent the easy slipping of the atom planes over each other.
(Not a materials engineer so I’m not sure what to search for)
The handbooks from immediately after WW2 already included such a chapter, but I believe that the first studies of this problem must be much older.
When any metallic structure is designed, it must be verified that it will not fail in any of the possible modes, including due to flow over the intended lifetime.
See in:
https://en.wikipedia.org/wiki/Creep_(deformation)
at "Temperature dependence".
By the approximate rule mentioned there, zinc begins to have non-negligible creep already above minus thirty Celsius degrees, so at normal ambient temperatures you must always compute the creep of zinc for any structural design.
On the other hand, metals like iron or copper have negligible creep at room temperature, even when pure.
Aluminum and magnesium begin to have non-negligible creep at temperatures only a little above normal ambient temperatures.
Hard alloys can have much lower flowing speeds than the metals included in their composition.
In integrated circuits, the metal connections are affected by electromigration, which is the flowing of the metal due to electrical current instead of mechanical stress.
The electromigration properties and creep properties of a metal are closely related. In the beginning, the ICs used pure aluminum for interconnections, but when their size was reduced, the connections began to fail after a too short lifetime.
The first solution for this problem was the replacement of pure aluminum with harder aluminum alloys, including small quantities of copper and/or silicon.
When the ICs became even smaller, the aluminum alloys had to be replaced with a metal having a higher melting temperature, i.e. copper, which fortunately also has a lower resistivity.
Sometimes it’s worth pausing a moment when seeing a “It’s well known that…” to check the timeline because the construction of Arecibo might well have taken place (or planned) before it was known (let alone well known).
Edit: a bit more searching suggests that this was studied in 1947 (Andrade’s Creep Law and the Flow of Zinc Crystals, by AH Cottrell)
https://royalsocietypublishing.org/doi/10.1098/rspa.1910.005...
They show the zinc doesn't continue to creep if the load is below a threshold-- technically the zinc doesn't creep if it's not subject to persistent shear forces, which is won't be if the cable load is below a threshold as the wires take up the load. This essentially results in a long term capacity which is different from the short term capacity. Unfortunately the ratio between the two depends on the wire splaying geometry which isn't well controlled, resulting in wide differences.
The report concludes that if it had been built to a safety factor of 3 rather than 2, the issues wouldn't have been experienced. Alternatively, the failure could have been avoided by reacting to flow over some threshold (which was noticed well in advance, but not reacted to)
Presumably we don't see similar failures in sockets in suspension bridges because they're built at a safety factor of 5+ and usually that's a SF over their rarely reached maximum load rather than a factor over their 24/7 load.
I always thought that it was more a thing for objects like jet engine turbine blades, that get very hot as well as having very great forces acting on them.
It stood for as long as it did, and had more weight added than the original design called for: thats a pretty good win for the original design, i think.
Usually not an issue at room temperature, but it can happen - solder has a low melting point.
In the case of the observatory, the failure happened in zinc components, which has a fairly low melting point.
Turbine blades are just one of the most extreme examples, it's really hard to make a metal that resists creep in that environment.
Phase changes, on the other hand can happen abruptly wrt T (first order, melting/boiling ice), or gradually (second order, curie transition, boiling mixtures).
Of course, first order transitions require a pure substance that doesn't actually exist since the chemical potential is infinite at infinite dilution. But that's entirely academic.
EDIT: I forgot to mention that creep has many proposed mechanisms and their relative contribution is not fully understood; however most depend on a transport phenomena, typically diffusion.
Why does squishing things together AND warming them up cause the particles to stick together more than when you just squish them together or just warming them up?
>> The equations describing these laws are special cases of the ideal gas law, PV = nRT, where P is the pressure of the gas, V is its volume, n is the number of moles of the gas, T is its kelvin temperature, and R is the ideal (universal) gas constant.
>> https://pressbooks-dev.oer.hawaii.edu/chemistry/chapter/rela...
The laws of thermodynamics describe how gases work, those laws cause the effects you’re asking about.
The above is a bit much for a primer on the topic, but provide enough key words for a Google-dive into the subject.
The ideal gas law is very nice but hardly applicable to describe things like creep in metals under stress, let alone things like the grain boundary diffusion mechanism for sintering metal particles together.
Put two solids together with no intervening medium, and heat everything up, and you'll see some mixin' and mingling. Often, the reason you don't see more of that sort of thing is because everything is immersed in an oxygen rich fluid with a tendency to create large, relatively reluctant to mix and mingle oxide coatings before anything fun can happen. Hence why another word for cold welding is vacuum welding.
Materials, when you really look at em' are not as 'solid' and 'stable' as you may think. Hence why I have a mechanics of materials book I peruse from time to time.
Well there are two first degree phase changes to consider.
Then there are those pesky mtls that dont even follow the general trend of gases, like water that expands when cooled.
You might also be interested in cold welding. https://en.m.wikipedia.org/wiki/Cold_welding
Its not hard to understand once you see the mechanism in full (vacancies, interstials, etc) but its hard to write as txt.
Suffice to say, there's plenty of room to squeeze.
"Squeezing"
When you squeeze you get rid of air bubbles, right? Well, when you squeeze you get rid of boundaries which are really volumes at small scales.
Well nature hates surfaces, so if you squeeze surfaces close enough together and hot enough you'll give the material an opportunity to rearrange atoms to get rid of boundaries.
"Ostwald ripening"
If you thought sintering and diffusion are hard, I had a respected mechanical engineering professor working on a refractory materials project claim, when he first encountered it, that Ostwald ripening cannot occur.
The mtls Eng guys rolled our eyes...
Dislocation motion looks cool too. Fun math behind these strings of holes in the atomic structure.
This should be rebuilt with far lighter weight carbon fiber composite structures for the suspended equipment and far higher-strength and lighter weight carbon fiber rope/cable.
Both technologies are very well developed and proven. Structural carbon fiber is used in everything from aircraft [2] to buildings to bridges [1], and it is only carbon fiber ropes that allow elevators to work in new kilometer-tall buildings [0].
Merely reducing the weight alone reduces the stresses involved in supporting the required equipment, and even greater benefit and safety margin is gained with the higher strength of engineered composite materials.
Time to rebuild with the next generation of technology.
[0] https://www.compositesworld.com/articles/in-super-tall-build...
[1] https://www.compositesworld.com/products/creative-composites...
[2] https://hexagon.com/resources/resource-library/composite-mat...
The most common carbon fiber composite is carbon fiber reinforcing an epoxy matrix. The carbon fiber, as individual fibers 5-10 microns in diameter (vs human hairs ~20-180 μm), and as tows or yarns of 3000-24,000 fibers are actually very flexible. I can take fibers or yarns and fold and crush them back on themselves without breaking (of course, other high-performance fibers such as Kevlar or Dyneema, can take even more such abuse).
It is the epoxy matrix that is brittle, and when it finally breaks under load, the load is concentrated at the fracture and breaks the fibers.
This is not an issue in high-performance fiber ropes, as they do not use an epoxy matrix. They have much higher fiber ratio (so much less matrix) and the matrix is of course highly flexible, e.g., some urethane formulation, and often a wear-protective jacket; the matrix is basically a binder to keep the rope/cable together. This is why composite fiber cables have replaced steel in high-performance yachting, tall elevators, racecar wheel tethers, and many other applications. The entire point is that they are much MORE resistant to breaking and wear than steel (and in some applications will work in long-length when the steel cables would literally break under their own weight).
That said, while I haven't done a full analysis, it is possible that Kevlar or Dyneema or even Zylon as the main cable reinforcement, sacrificing some strength-weight for increased toughness, may be better in that particular application. But any of the high-performance fibers will outclass steel.
Similarly, for the structure housing the suspended instruments, composites are a win on every parameter. First, reducing the suspended weight pays benefits across the whole system — lower weight to suspend reduces the requirements of the cables, which reduces their own weight, which reduces the loads on and so the weight of the towers, etc. This alone may overcome any initial cost differences. Moreover, lower weight means lower momentum generated fighting high winds, etc., composites are better vibration-damped, and more. Plus, composites don't corrode the way metals do. And, this is not a structure where we need to worry about impacts and brittleness (which can also be managed by reinforcement and matrix selection).
Doubt all you like, but composites would be a huge improvement in this application (and don't need active blow-drying, which seems unlikely to have been able to prevent the creep failure).
Source: I founded & run a high-performance composites design & mfg firm, with 20 years of direct hands-on experience designing & fabricating advanced composite components & products for motorsport, defense, aerospace, subsea, sport, & architectural applications.
My (slightly) tongue-in-cheek proposal for Arecibo: drones. Instead of trying to hold one big antenna up with huge cables, you use an array of antennas flying above the dish on drones. This allows for low cost, easy beam steering (within the limits of the shape of the dish), adaptation for different frequencies, quick stowing when weather arrives, etc. Even station-keeping to the required accuracy doesn't seem that hard (you might have to do some active phase correction). Disadvantages are that you'd need to digitize on each drone (which might bust the whole scheme, SNR-wise), and that drones are quite electrically noisy.
More here: https://brooker.co.za/blog/2021/08/11/arecibo.html
We don't need a roaring 20's prohibition-era jiggly jazz fest on our energy packets, this sounds absolutely nightmarish for anyone below a management position having to work with it. :(|)
If you could make a suitable receiver that weighed 6 kg or even 600kg, you could just suspend it from motorized plastic cables on space frame towers. Drones aren't going to make it cheaper or easier.
I dunno.
I played the N64 game so much as a kid I can probably name almost all of the characters in Goldeneye.
My friend still to this day says he would have preferred to go in blind, not knowing who the bad guy was. It would have been an epic reveal.
Rumored, but proven not to be, invincible.
hahaha Not by far... I used to work with an Erlang programmer (probably not really the reason he was so eccentric), and this guy was by far so full of oddity that was almost impossible for anyone else in the office to tolerate him. A brilliant programmer, but utterly incapable to having other humans around.
Or we ask Pierce Brosnan, I have the feeling he was involved in this somehow...
> ...eventual cable failures would not have occurred if the cable system had been designed with a safety factor of at least 3.0...
Reaction 1: Sounds nice...but having a much-larger safety factor in something the size of the Arecibo telescope costs a lot of money. And there really is no safety factor large enough to for-sure protect you from shoddy workmanship. For far less money, they could have hired a couple workmen who really knew what they were doing, to handle the critical socket/zinc/cable joints.
Reaction 2: If you're stuck with so-so workmanship in those joints, then increase the safety factor - but only in those joints. Use larger sockets, with more zinc in contact with a greater length of splayed cable (within the sockets).
Metallic Bonds' that is.