Does my theory of hitting the ball high and towards the heel, ie. at or very near the hosel, hold any water?
Al
At 11:49 AM 7/27/2003, you wrote:
At 11:43 PM 7/26/03 -0700, Alan Brooks wrote:In principle, I agree with Dave T. A plug of epoxy on the inside of the shaft will cause a stress concentration. That said, however, I find it unlikely that effect is significant. The modulus of elasticity of the epoxy is so much lower than that of the steel hosel and the graphite reinforced composite shaft that it's effect is going to be negligible.
Offhand, I'd have thought so too. An article in Golfsmith "Clubmaker" a few years ago claimed otherwise. They said that their observations of broken shafts suggested that an epoxy plug at or above the tip (1) increased the chance of breakage substantially, and (2) when breakage occurred, it was always at the top of the plug.
As I said in my other post, I think this breakage is either due to the shaft tip reinforcing never being designed for this club head speed, or something in the assembly process that is reducing the amount of reinforcing above the hosel. And, again, if the shaft is breaking off straight across (as opposed to a spiral fracture)
Interesting point about the spiral fracture. If y'all don't know what Alan is talking about, try this experiment. Take two sticks of round chalk:
* With one stick, bend it till it breaks. It will be a jagged but mostly straight-across break.
* With the other stick, TWIST it till it breaks. Twist it about its own axis. The break line will spiral around the stick at a 45-degree angle.
Anyway, if it were a metal shaft (or other anisotropic material) and if the break were not right at the hosel, I'd certainly agree. I'm not as sure in this case because:
* The material definitely has strength-aligned directions. This might affect the spiral. But more important...
* There is a definite discontinuity at the top of the hosel. A long, well-graded cone filled with epoxy will minimize its effect. But if the coning is too short or filled with air, there will be a decided stress concentration there. I could be convinced that a torsional stress combined with a concentration point at the top of the hosel could result in a straight-across break rather than a spiral.
That doesn't mean that that the impact stress that causes the break is torsional. It certainly could be the clubhead bending backward due to the impact. But it could also be torsional, as originally suggested.
it is a consequence of bending or tension in the shaft and if it is consistently breaking just above the hosel, it's most likely bending from the centrifugal toe down forces that is initiating the failure, with tension finally separating the head and shaft tip from the rest of the shaft.
I have a lot of trouble with this. The reason is that the forces due to impact with the ball are much greater than the forces due to the swing alone (toe down due to centrifugal force. I've never EVER heard of a shaft that broke at the hosel during a practice swing that didn't hit anything. It always involved contact, either with a ball, the ground, or something else (a tree?). If it were the centrifugal toe-down forces, then a practice swing is as likely as a real swing to cause the problem.
Cheers! DaveT
