Here's a question from the July/August 2000 issue of RodMaker magazine:
"The article in RodMaker dealing with rod breakage fascinated
me. What I am wondering is what happens when an undamaged rod
is simply loaded past the point of failure and breaks of its
own accord. Where does the break start? On the top or on the
bottom and is there any way a rod builder can make a blank
stronger?. . .Matt, Westwood, MA
"A lot of things happen when you load a rod blank. The structure
tends to change shape from round to oval and the fibers on top are
forced to stretch while those on the bottom are forced to compress.
The fibers on the sides do some of either depending upon their
particular location in the structure. Generally, if the rod
blank has not been damaged and there are no inherently weak spots
to contend with, failure will occur on the bottom, or compression
side of the bend as these fibers "blow out" of the matrix and
the structure then collapses. Remember that these graphite fibers
will resist compression more so than elongation so it is the
compression side where such a normal failure under load would begin.
One of the common signs of a rod or blank that has broken due to
simply being taxed beyond its design limits is the tendency for
breaks to occur at several areas instead of just one. Here you
have an initial break that suddenly results in a tremendous shock
being transmitted through the rest of the structure, often resulting
in multiple breaks at various locations along its length. And
please remember, these scenarios refer only to rods or blanks that
have not been damaged due to impact or fracture in which case the type
and location of failure can be quite a bit different.
As a rod builder, you can do little to further fortify your
blanks against breakage due to overload. Probably the most
prudent thing you can do, however, is to fully inform your
customer why it is important to understand and carefully
follow the line weight ratings listed for the blank.
Blanks are designed around certain parameters and one of them
is the maximum load that a blank is expected to endure.
Exceeding the maximum rated line category listed for any
particular blank suddenly makes the rod the weakest part
of your combination. By staying within the listed line
weight rating you ensure that the line, not the rod, is
the weak point in the chain. Hopefully you and your
customers are also aware of the dangers and likely failures
caused by any sort of impact or crushing forces on a blank
or rod as well. ~ Tom Kirkman
Publishers note:
If you have any tips or techniques, send them along! Help out your
fellow rodmakers!
~ Publisher, FAOL
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