3 ms·

Sounds like it was a blind spot for the engineers due to the normally bulletproof service history of zinc spelter cable terminations in structures.

potato3732842 2y ago
>normally bulletproof service history of zinc spelter cable terminations in structures. They're relatively new, they're relatively expensive (which saves them from being used in the worst of the applications) and like most things inherent to steel cable and whatnot they tend to get employed in situations where safety factors are generous. Don't count your chickens before they hatch.
- nick3443 2y ago
  I am not an expert, I read this in the report: The long-term zinc creep failure of the Arecibo Telescope sockets and the subsequent cable pullout has never been documented elsewhere despite a century of zinc-filled cable spelter sockets use. 17 The type, size, length, and fittings of the cables used in the Arecibo Telescope (whether the original cables constructed in the 1960s or the auxiliary cables installed in the 1990s) were catalog-selected items, not at all unusual, with decades of proven performance. Exten-sive structural modeling of the Arecibo Telescope, independently confirmed by laser cable sag surveys, validated that under all static and cyclic loading conditions, the cable loads barely exceed half the nominal cable strength. While PLC can occur at stresses well below yield, such a creep failure has never been reported in spelter socket zinc.
  - hinkley 2y ago
    I think we might need to send some microbiologists to do their own forensics. You have a mechanical failure that can’t be seen in the labs and isn’t reproducible at other sites. Suggests something environmental. Like when natural fiber army gear starts dissolving in the jungles of Vietnam. Could be direct action, or a side effect of a chemical in plant or animal detritus. Like pigeon poop on car paint.
    - madaxe_again 2y ago
      The paper posits that it’s due to low frequency electromagnetic induction in the tethers from the observatory operations, which is a pretty unique environmental factor.
      - hinkley 2y ago
        Oooh. Active galvanic action will ruin your day.
        madaxe_again 2y ago
        Not galvanic action, apparently, but rather a sort of phase creep within the zinc as a result of putting some of it in an excitation state. They aren’t sure though, as there hasn’t been much research on the topic.
  - londons_explore 2y ago
    > Exten-sive structural modeling of the Arecibo Telescope, independently confirmed by laser cable sag surveys, validated that under all static and cyclic loading conditions, the cable loads barely exceed half the nominal cable strength. I have a feeling such measurement and modelling might have been wrong. It's easy to miss some oscillation mode, particularly high frequency longitudinal wave's in the cables, which couldn't be picked up by a laser survey due to the kilometers per second these waves travel.

potato3732842 2y ago

>normally bulletproof service history of zinc spelter cable terminations in structures. They're relatively new, they're relatively expensive (which saves them from being used in the worst of the applications) and like most things inherent to steel cable and whatnot they tend to get employed in situations where safety factors are generous. Don't count your chickens before they hatch.

nick3443 2y ago
I am not an expert, I read this in the report: The long-term zinc creep failure of the Arecibo Telescope sockets and the subsequent cable pullout has never been documented elsewhere despite a century of zinc-filled cable spelter sockets use. 17 The type, size, length, and fittings of the cables used in the Arecibo Telescope (whether the original cables constructed in the 1960s or the auxiliary cables installed in the 1990s) were catalog-selected items, not at all unusual, with decades of proven performance. Exten-sive structural modeling of the Arecibo Telescope, independently confirmed by laser cable sag surveys, validated that under all static and cyclic loading conditions, the cable loads barely exceed half the nominal cable strength. While PLC can occur at stresses well below yield, such a creep failure has never been reported in spelter socket zinc.
- hinkley 2y ago
  I think we might need to send some microbiologists to do their own forensics. You have a mechanical failure that can’t be seen in the labs and isn’t reproducible at other sites. Suggests something environmental. Like when natural fiber army gear starts dissolving in the jungles of Vietnam. Could be direct action, or a side effect of a chemical in plant or animal detritus. Like pigeon poop on car paint.
  - madaxe_again 2y ago
    The paper posits that it’s due to low frequency electromagnetic induction in the tethers from the observatory operations, which is a pretty unique environmental factor.
    - hinkley 2y ago
      Oooh. Active galvanic action will ruin your day.
      - madaxe_again 2y ago
        Not galvanic action, apparently, but rather a sort of phase creep within the zinc as a result of putting some of it in an excitation state. They aren’t sure though, as there hasn’t been much research on the topic.
- londons_explore 2y ago
  > Exten-sive structural modeling of the Arecibo Telescope, independently confirmed by laser cable sag surveys, validated that under all static and cyclic loading conditions, the cable loads barely exceed half the nominal cable strength. I have a feeling such measurement and modelling might have been wrong. It's easy to miss some oscillation mode, particularly high frequency longitudinal wave's in the cables, which couldn't be picked up by a laser survey due to the kilometers per second these waves travel.