BASEBALL BATS

[OLDDOG04]

Having spent 30 years making the world safe for steel and concrete <Grin> (Structural Engr., PE, & graduate degrees), one of my diversions for the past 20 years is to umpire baseball (not enough abuse in engineering – go figure). Here’s the issue, it should be fun – an interesting application of engineering mechanics.

All age groups - up to 18 years old - use metal bats. Visibly cracked metal bats are not allowed for play (makes sense) but dented metal bats have become an issue for controversy. Typically, umpires have not allowed dented metal bats for play after doing pre-game equipment inspections.

This year, Little League Baseball (Williamsport, PA), says that if a dented metal bat passes through a circular ring whose diameter matches the major diameter of the dented “tapered” metal bat (2-3/4” down to about 1” at the handle), the dented metal bat should be OK for play.

Without biasing the discussion, too much, with my own specific concerns that I’ve expressed to other umpires of various backgrounds and education levels, what are your thoughts as technical professionals? Would you feel comfortable addressing a safety issue by measuring only the major bat diameter when the dent can be anywhere along the bat? Is the lack of an outer surface crack sufficient? Bats are, typically, hollow, thin-walled aluminum alloys. And, yes, metal bats have been known break on impact although nothing close to the frequency of wooden bats.

 

[drawoh]

OLDDOG04,

What condition are the bats in when they break? Perhaps visible cracks are more of an issue than dents.

Have you any idea what aluminium grade the bats are made of?

JHG

 

[vmirat]

OK, I'll take a swing at this (couldn't resist!). I'm assuming that your primary concern is with dents that run transverse to the length of the bat, versus dents running with the length. If the dent is large enough, it would pucker the sides of the bat, making it larger than the diameter un-dented, and thus not pass inspection. I agree that's not a very scientific approach to the subject, but short of doing a flexural test, it's probably the best they can do. I would suggest measuring the depth of the dent instead of the effect on the diameter - the deeper the dent, the greater chance for an internal crack. They could also determine a "no-dent-zone" which would prohibit dents in the highest area of flexural stress - say the bottom half of the bat from the knob.

 

[PEinc]

OLDDOG04

Why don't you just call a bat manufacturer and speak to someone in their engineering department?

 

[btrueblood]

I've read (somewhere) an article that suggested that dimples in bats (like those on a golf ball) can result in longer hitting distances - the reduction in aero drag forces helps batters swing faster.

 

[jhardy1]

Shouldn't you post this in the "Finite Element Analysis" or "Abaqus" forums?

I am sure someone there could run you a nice non-linear transient dynamic analysis of an aluminium baseball bat (with and without dents, cracks, etc)

 

[BigH]

Aw for the love of the game, why oh why not wooden bats. A crack of the bat is more in line with the game than a thunk!
Call me old, call me a purist, but having used both, I love the wooden ones! especially the bottle bats of old.

 

[Ron]

Simple...follow BigH's suggestion. Go back to wood.

Not going to happen though. The "major diameter" test is not adequate, since baseball bats are tapered with the exception of a short distance on the barrel.

The dent work hardens the area and that can produce faster fatigue failure of the bat. Stresses sufficient to cause denting are likely causing deformation curvature in the handle as well.

My criteria...If dented, don't use it. If bent with handle curvature, don't use it.

 

[PSlem]

The point of the test is not safety, but fairness. If the major diameter is increased, so are the chances of hitting the ball. If it were flattened like a cricket bat, there would be very few strikes.

 

[AJUK]

Not knowing the complexities of baseball (I do know cricket though), on a side issue, in the UK you will see baseball bats on sale but never any baseballs!

 

[Ron]

PSIem...different bats have different barrel diameters, so denting doesn't necessarily offer an advantage. Might even be more of a detriment, since there is perhaps a greater chance to not connect cleanly with the ball due to the curvature, resulting in more foul balls.

Batter up!

 

[jheidt2543]

For those interested in this topic, I would suggest the book "The Physics of Baseball" by Robert K. Adair, Harper & Row, 1990, ISBN 0-06-055188-7.

The book discusses the physics of bats, both wood and aluminum as well as pitching, curve balls and the baseball itself.

Here is a quote to think about: "Very large forces, reaching values as high as 8,000 pounds, are required to change the motion of the 5-1/8 ounce ball from a speed of 90 mph toward the plate to a speed of 110 mph toward the center field bleachers in the 1/1000 of a second of bat-ball contact."

So, the condition of the bat, whether wood or aluminum, is a safety issue.

 

[Qshake]

I agree with what Ron has noted about work hardening and wish to express concern in the transverse dent. As it has been noted the diameter of the bat at the major axis of the dent (assume elliptical) will not fit the given criteria. And that is good because this style of dent presents a fatigue and fracture critical area right at the outer limits of the dent and the major axis of the dent. This area is typically "pinched" and becomes a stress riser that can quickly turn bad.

With dents whose major axis follows the longitudinal axis of the bat the above problem is only a minor issue as the radius at this location is relatively large. Moreover, the indention in the long direction is typically inward and not "pinched"

In summary, the transverse dent will not absorb and transmit energy like it once did. The working hardening and stress riser take care of that. It will crack and break in just a matter of time. The other indentation is not as likely to crack or split and will absord and reflect the energy (assuming the dent opposite to the side hitting the ball) but not as efficiently. Rather than get into many arguements about using bats that are dented about so and so axis, I recommend banning dented bats altogether.



Regards,
Qshake

Eng-Tips Forums:Real Solutions for Real Problems Really Quick.

 

[CRACKKILZ]

In the aerospace world we evaluate dents in aluminum structure by measuring the depth of the dent and the width of the minor axis. Generally speaking the "sharper" the dent or crease, the more concerned we are about cracking (on the inner tension side surface). Although there is a cold working effect, long smooth dents generally don't significantly reduce "B" basis allowables for the material, although there is a reduction in fatigue life.

To give you an idea, we use an A/Y ratio of 30 to evaluate dents in 2024-T3 aluminum. Any dent with an A/Y ratio over 30 is considered smooth and OK. If the A/Y ratio is less than 30, we cut out the damage and repair the structure (in your case reject the bat).

Example: dent depth .125" - Major axis 2.5 inches /Minor axis 1.5". A/Y = 1.5/.125 = 12 which is less than 30 so dent is no good.

Obviously the A/Y limit of 30 is based on testing and years of service experience with that particular alloy. It would not be appropriate to apply this limit to other alloys.

Another concern to investigate would be bat failure due to thin wall instability in compression. The dent represts an eccentric load path and will add another bending term to the beam equation. Without knowing the actual bending stresses on a bat, I would guess that the handle area would be most critical, with less concern at the upper end.

One more comment and then I'll quit. Visual inspection of the bat will not detect small cracks on the inner surface (where I would expect cracking to intiate). Other inspection techniques would not be practical. Banning dents altogether seems extreme since, in my experience, they get dinged up just throwing them in the bat bag.