baseball bats

huangyhg

baseball bats
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 鈥?go figure).  here鈥檚 the issue, it should be fun 鈥?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 鈥渢apered鈥?metal bat (2-3/4鈥?down to about 1鈥?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鈥檝e 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.
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
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.
olddog04
why don't you just call a bat manufacturer and speak to someone in their engineering department?
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.
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)

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.
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.
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.
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!
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!