Why ASTM F2219?

1
Why ASTM F2219?

• SGMA Annual Meeting
• Dallas, Texas, October 2, 2003
• Lloyd Smith, Washington State University

2
ASTM F1890

• Fire ball at 60 mph
• impact the bat at its COP
• record the ball pitch speed and bat recoil speed
• calculate performance metric (BPF)
• compare against associations limit

3
ASTM F2219

• Fire ball at 110 mph
• impact the bat at the COP, 6 in from tip, or
  multiple locations
• record the ball pitch and ball rebound speeds
• select a performance measure (BBCOR, BPF, BESR,
  BBS)
• calculate the average performance at each impact
  location
• compare the bats highest performance with the
  associations limit

4
Motivation For Change

• Science
• increased understanding of the bat and ball
• increased understanding of test methodology
• Field Study Results
• Montgomery, Alabama (November 2002)
• ASA Championship play, A D level

5

• Some science results

6
Impact Location

• bat performance depends on the impact location
• the highest performance was thought to occur at
  the bats COP
• models and experiments show that the sweet spot
  and COP do not necessarily coincide
• (COP depends on the location of the pivot point)

7
Bat Scanning

• scanning
• measure impact from the pivot point
• impact at ½ inch intervals
• scanning interval should encompass the maximum
  performance measure
• each location impacted with 6 balls (once each)
• bat performance vs. impact location is relatively
  constant near the sweet spot

8
Normalizing Performance

• Fundamental dynamics allow variation in ball
  weight and COR to be accounted for
• Performance is normalized to the properties of a
  nominal ball selected by the governing
  association
• ???Normalizing relations will be proposed for
  adoption into ASTM F2219???

9
Normalizing Performance

• No current proposal to normalize for ball
  compression or diameter
• Normalizing for variation in ball compression
  requires further study
• The effect of variation in ball diameter in
  laboratory tests is small
• short ball flight distances

10
Experimental Accuracy

• ball-out vs. bat-out
• ideally, performance from bat-out and
  ball-out measurements would be equivalent
• momentum is used to find the unmeasured quantity
• mvir Iwi mvor Iwo

11
Experimental Accuracy

• consider a 1 variation on the out speed in the
  test of a 10,000 MOI high performance metal bat
  at 110 mph
• change in bat-out measurement
• 1.2 BBS, 2.6 BPF
• change in ball-out measurement
• 0.2 BBS, 0.5 BPF

12
Experimental Accuracy

• ball-out measurements require light curtains
  (rather than point measurements), rebound angle
  should be within 5o
• bat-out measurements can be affected by bat
  vibrations that increase for impacts away from
  the sweet spot

13
Bat oscillations from impact
14
Measuring Bat Speed
15
Boundary Conditions

• in the laboratory
• the bat is constrained to rotate about a fixed
  center
• the bat is held in a rigid grip
• in play
• the bat motion is described by an instantaneous
  center that is constantly moving
• during impact the hands of the player impart
  relatively little force to the bat (i.e. free)

16
Boundary Conditions

• the bat-ball contact duration is short (1ms)
• constraint forces are small (negligible) during
  impact
• only the bat motion during impact (not before or
  after) is needed to represent performance

17

• Montgomery Field Study

18
Pitch speed (slow pitch)

• Was thought to be 10 mph
• from high speed video
• measures in-plane speed
• average 23 mph
• standard deviation - 2 mph
• predicted speed from projectile motion
• (in-plane/total)
• 50 ft, 12 ft arc ? 22/28 mph
• 50 ft, 6 ft arc ? 34/36 mph

19
Swing Speed

• Was thought to be 60 mph

20
Field Study Observations

• the 60 mph ball speed currently used to certify
  bats is significantly below the relative bat-ball
  speed observed in play (110 mph)
• swing speed should scale with bat MOI not weight
• bats should be tested at their sweet spot (found
  by scanning) not the COP

21

• Laboratory Observations

22
BBS vs. BPF

• many results are presented as BBS
• there is a strong correlation between BBS and BPF
• similar trends should be observed using BPF

23
Does Test Speed Matter?

• The trampoline effect increases with impact speed
• a ball dropped on a wood and hollow bat would
  rebound to similar heights
• Test speeds representative of play conditions
  will improve the comparison of the relative
  performance of bats

24
Does Test Speed Matter?

• the performance of a solid bat would be constant

25
ASTM 2219 vs. ASTM 1890
26
ASTM F2219 era study
27
Effect of bat MOI
28
Ball Compression (90 mph)
29
Ball Compression
Results from Charlotte field study, 2002
ASTM F2219, 2003
30
Ball Conditioning

• Increase RH by 20
• Ball compression decreases 40 lbs

31
Summary

• Test speeds should represent play conditions
• Impact location should be found experimentally
• Ball-Out measurements reduce experimental
  variation
• Ball compression can be used to control the ball
  speed in play