I thought this was a good read: wire rope failure forensics.
Nice photos for a lot of failure modes. From a guy whose career is analyzing
Some nice stuff about lightning issues, pictures of heat melting etc
But in terms of failure modes and inspection, I liked this comment:
"visual rope inspection = 20% evidence + 80% hope"
(he was talking about internal wire breaks, and how the outer wires only
represent about 40%
of the metallic cross section, in most ropes)
Also: how can you tell if a replaced cable needed to be replaced? You would
have to test it
to failure...and that's along all parts of the cable?
I've replaced rusty cables, that are clearly brittle, and strands broke when I
cable sharply. And I agree with the author above, that it's difficult to
inspect a cable
It would be interesting to test cables from towers that have failed. i.e. was
the rest of
the cable perfectly good, and only one exact spot weak? If so, then the risk is
the one weak spot?
For people thinking stainless steel cable is better, here's an interesting page
an interesting story from there:
Flight Control cable failures have occurred even though the cable was inspected
the book. An Aileron control cable failure on a Boeing 737-3TO on takeoff at
September 27, 1997 just six weeks after the cable was inspected for wear. The
consisted of checking for visible wear (external wire wear). However, the NTSB
the internal wires were 90% worn. A Boeing 737-100, Flight 169 lost aileron
control when the
aircraft cable broke. The NTSB found that existing inspection methods could not
breakage of 98 of the 133 strands in the cable! The broken strands were not
the prescribed method of drawing a cloth rag over the cable. Only until
released from the cable were the broken strands detectable. Thus the need to
tension to better detect broken strands.
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