Breakage Sequence

By Tom Kirkman, (RodMaker Magazine)

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

RodMaker Magazine

"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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