Steve, W3AHL wrote:
> If all you want to do is determine deflection under a static load,
> yep, that's all you need to do -- hang a weight on it. But that is
> the least of the issues. What is the composition of the steel? How
> brittle is it, will it fatigue with cyclic stresses?
Good points.. I would think that fatigue failure in a *steel* antenna
mast application would be unusual. It's not like the classic railroad
axle problem with millions of cycles. Maybe if you had an aeolian
vibration?
Presumably, you're not loading the mast to within a hair of it's failure
limit repetitively... It's been a while since I had to deal with
fatigue, but isn't there a limit below which loading can't cause fatigue
failure.
>
> But the major issue in pipe is the weld joint. In electrical
> resistance welding, there is no high tensile strength filler used.
> The joint is made of what the pipe is made of. If the machine speed
> is too fast (to cut costs) and the current too high (because the
> speed was increased) then you have poor penetration, a brittle weld
> because of the impurities of the base metal and the improper heating
> / cooling gradients, porosity due to cheap flux and martensite
> formations if it wasn't annealed properly. After a few tens of
> thousands of cycle swaying back and forth the weld joint develops
> microfractures. One strong gust splits the seam someday, ruining a
> couple of thousand dollars worth of antennas,coax and installation.
ok..now i understand the fatigue issue.
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