Exploring the Crack of the Bat in the Lab: Performance and Durability
Rebecca H. Shaw
Graduate Research Assistant
James A. Sherwood
Professor
Baseball Research Center
Department of Mechanical Engineering
James B. Francis College of Engineering
One University Ave.
Lowell, MA 01854
ABSTRACT
Advances in material behavior and manufacturing processes can lead to enhancing the performance of the
equipment used in sports activities, e.g. tennis rackets, golf clubs and running shoes. However, these engineered
equipment can potentially change the original intent of the sport and blur how much of the performance is due to
the athlete and how much is due to the equipment. Is putting the equipment on “steroids” any different than
athletes using steroids? In 1998, the UMass-Lowell Baseball Research Center (UMLBRC) was founded with the
intent of evaluating bat and ball performances for Major League Baseball and the NCAA. The UMLBRC employs
four different machines for laboratory investigations of bat and ball performances. One of the challenges in
establishing a laboratory test is determining how the bat should be gripped so as not to compromise the modal
response of the bat from that in the field. This paper will discuss how the UMLBRC test machines are used to
evaluate bat and ball performance and how modal analysis is used to ensure their proper testing methodologies.
INTRODUCTION
The balance between offense and defense in the sport of baseball is particularly sensitive to technological
advances in equipment. Advances in bat technology favor the offense, and if hitters are given an advantage the
balance and spirit of the game is compromised. The dimensions of a baseball field were initially set based on
wood-bat performance and are set such that even the best players only occasionally hit homeruns when using
wood bats. If advances in bat performance, or lively balls are introduced into the game that balance is lost. In the
late 1990s concerns with technology arose in both Major League Baseball (MLB) and in NCAA baseball. MLB
was struggling with the “juiced ball” controversy. The NCAA was trying to determine a laboratory test
methodology that could be used to control the aluminum bats, which were out-performing traditional wood bats,
and to pull back the performance of these aluminum bats to a wood-like standard. These two issues led to the
creation of the UMass Lowell Baseball Research Center (UMLBRC) as a technical resource for MLB and the
NCAA. Since being established in 1998, the UMLBRC has expanded to become a resource for the academic
community and the sports industry to collaborate and to explore the game of baseball and the equipment being
used from a scientific perspective.
The Study of the “Juiced Baseball”
MLB depends on the UMLBRC to investigate the consistency of the baseball from year to year. Baseball has
statistics for every facet of its game, e.g. batting averages, homeruns, runs batted in, slugging percentages, and
on and on. Therefore, it is very important to ensure that the baseballs being hit today are no different than those
being hit in 1925 or 2025. MLB has specifications in place to regulate the performance of their baseballs.
However, until the advent of the UMLBRC, MLB had no independent testing facility in place to ensure that the
balls in play were actually in compliance with those specifications. In 1999, the UMLBRC established a set of
tests to be performed each year to ensure that the balls are within MLB specifications and to confirm whether or
not the balls were changing from year to year. Those tests include dynamic testing for the coefficient of restitution
(COR), static compression tests to study the hardness of the ball, and ball dissections for measuring layer by
layer dimensions and the properties of the constituents. COR testing is done using a pitching machine and a rigid
wall. Light gates are used to measure the speed of the inbound and outbound velocity of the baseball. Instron
machines are use to measure the ball compression and the tensile strength of the leather.
In April of 2000, a record number of homeruns had been hit. A controversy was growing in the late 1990s among
fans that the baseball had been “juiced”, and the statistics in April 2000 fueled the controversy further. Because
of the controversy, MLB was likewise concerned and wanted to know if there was a change in the baseball.
Extensive testing was performed on the 1999 and 2000 Major League baseballs, and the baseballs were found to
meet all MLB specifications. Assuming a nominal batted-ball distance of 400 ft, the potential range of batted-ball
distances for the balls tested in this study was on the order of 7 feet. This 7-ft range implied that the batted-ball
performances for the balls investigated in this study were essentially the same. Thus, the tested baseballs
indicated that the 1999 and 2000 baseballs fell within a tight range of batted-ball performance and that the 1999
and 2000 baseballs were for all practical purposes the same with respect to batted-ball performance.
To evaluate the effect of the ball weight and COR specification tolerances, the wall-test COR was investigated to
account for any potential difference in impact conditions. The result of the tolerance analysis, which includes the
acceptable extremes allowed by MLB baseball specifications, is provided in Table 1. The weight and COR
tolerances provide maximum distance differences of 8.7 and 40.4 feet, respectively. These tolerance ranges
mean that theoretically, two baseballs could meet the specifications but one ball could be hit 49.1 feet further than
the other could be hit. This 49.1 feet is the combination of the increased distance of 8.7 feet for the ball being on
the light side with respect to weight (i.e. 5.00 oz. as opposed to 5.25 oz.) and an additional 40.4 feet for the COR
being biased to the high side (i.e. 0.578 versus 0.514). The 49.1-ft value is purely academic.
Table 1 Major League Baseball Tolerance-Performance Analysis
Ball Wt (oz) Wall COR Batted-Ball Distance (ft) Difference in Batted-Ball Distance (ft)
5.11
0.551
400.0
--5.00
0.551
403.8
8.7
(due to weight)
5.25
0.551
395.1
5.11
0.514
376.8
40.4
(due to COR)
5.11
0.578
417.2
5.00
0.578
421.3
49.1
(due to weight and COR)
5.25
0.514
372.2
Controlling the Performance of Nonwood Bats
The problem for the NCAA in 1998 was the appearance of an ever widening gap between the batted-ball
performance between wood and nonwood (i.e. composite and aluminum) bats. The dynamics of the bat-ball
collision are complex and are still not completely understood to the level that credible computer models can be
used to evaluate the differences amongst bat designs. Therefore, a credible test methodology is required. One
of the biggest challenges in establishing a test method is replicating field playing conditions in a controlled
laboratory environment. The UMLBRC currently has three machines that are used to investigate baseball-bat
performance and durability. To investigate bat performance a patented testing machine that uses two
synchronized servomotors is used. One motor swings the bat, and the other motor “pitches” the ball. These two
moving objects simulate the bat/ball collision analogous to how the impact occurs in a game. Because batted-ball
speed varies with axial position on the bat, the batted-ball speeds are measured for impacts along the length of
the bat to isolate the sweet spot. Another machine to investigate bat performance uses an air cannon to “throw” a
ball at a stationary bat such that the field conditions of a pitched ball and swung bat are combined so as to result
in the same relative speeds between the bat and the ball. An automated data acquisition system measures the
bat performance and likewise isolates the sweet spot. The latter machine is not patented and has an approved
ASTM standard associated with its test methodology. In both test machines, bat performance is characterized by
comparing the batted-ball speeds off aluminum and composite bats relative to batted-ball speeds off solid wood
bats under the same test conditions.
An NCAA certification procedure was established in 1999 to regulate the performance of nonwood baseball bats.
A performance standard using a Ball Exit Speed Ratio (BESR) was established using a variety of solid wood bats.
In 2001, the National High School Federation adopted the NCAA certification procedure. Currently all bats that
will be used in NCAA or high school play must be certified at the UMLBRC. From October 1999 through
September 2005, the certification procedure was based on the use of the Baum Hitting Machine (BHM), the
machine that swings the ball into the swinging bat. It is now understood that the same results can be obtained
using the LVS air cannon that “throws” the ball into the stationary bat. The move from a limited availability
patented machine to an open standard will allow other labs to run the test and allow for a crosschecking of results
between labs.
Figure 1 shows performance results for a reinforced-handle wood bat tested in both the BHM and the LVS air
cannon. The error bars show the standard deviation of the mean for each test. The data points for the air cannon
fall within the error bars for the BHM for three out of four impact locations. Both tests show a parabolic
distribution for performance over the length of the barrel. In each test, the sweet spot of the bat is 5.0 inches from
the barrel end of the bat. Figure 1 also shows a clear difference in standard deviation between the BHM and the
air cannon. The error bars denote plus or minus one standard deviation. The air cannon has standard deviations
about half of those of the BHM, therefore the air cannon yields much more repeatable test results.
0.75
BHM
0.74
LVS
0.73
BESR
0.72
0.71
0.70
0.69
0.68
0.67
4.0
4.5
5.0
5.5
6.0
6.5
Impact Location (in.)
Fig. 1 BESR Comparison between BHM and LVS for a reinforced-handle wood bat
Bat Durability
A third machine, which is used to measure durability, also employs an air cannon to “throw” the ball at a stationary
bat. This machine is made by Automated Design Corporation (ADC) and uses an automated ball-retrieval system
to load the baseballs so that the operator needs only to monitor the condition of the bat. The durability machine is
capable of firing a baseball every five seconds at speeds up to 200 mph. The toughness and fatigue properties of
different bats can be examined using this machine.
One of the challenges in establishing a laboratory test is determining how the bat will be gripped. It has been
hypothesized that the grip mechanism does not play a role in bat performance testing as is done using the BHM
or the LVS air-cannon tests. Because the sound wave generated by the bat/ball contact does not travel from the
collision point to the grip before the ball leaves the bat, the ball is “unaware” of how the bat is supported.
However, the gripping method is important for durability testing. The sound waves traveling up and down the
length of the bat as well as across the diameter can cause the wood to crack. To evaluate the durability of a
baseball bat accurately, the modal characteristics of the bat must be representative of those in field play. The
natural frequencies and associated amplitudes excited by the ball are the primary driver of bat durability. To
ensure that lab and field conditions are comparable for durability testing, modal tests are performed on baseball
bats in field conditions and compared to various gripping methods.
Two accelerometers placed along the length of a bat were used to determine the first two natural frequencies in
the primary bending direction. Experimental data were taken using five different grips: three gripping mechanisms
in the durability machine and two person-held grips. The first machine grip consisted of four rubber rollers used to
hold the bat at two points as shown in Fig. 2. The second machine grip used a set of rubber rings to support the
bat inside a canister as shown in Figure 3. When the canister grip is used, the machine can rotate the bat
between hits.
Fig. 2 Rubber roller gripping method
Fig. 3 Rubber ring gripping method (canister grip)
The rubber-roller grip was tested two different ways: first with both pairs of rollers tightened and second with the
top pair of rollers tightened and the bottom pair only loosely touching the bat handle. To represent a player
swinging a bat, data were taken with the bat gripped very loosely by a student and gripped very tightly by a
student. The results are shown in Table 2. All of the accelerometer data were taken with the bat held stationary
(i.e. not swinging), either in the durability machine or by the student.
Table 2 Frequency response as a function of gripping method
Natural Frequency (Hz)
Gripping Method
Cantilever Mode 1st Bending Mode 2nd Bending Mode
Free Free
N/A
152
634
Roller Grip Tight
39.8
222
703
Roller Grip Loose
36.5
166
676
Canister Grip
42.4
168
704
Hand-Held Loose
N/A
155
628
Hand-Held Tight
N/A
148
638
Table 2 shows that each of the durability machine gripping methods are introducing a cantilever mode that is not
present in free-free or person-held conditions. The roller-grip-tight method shows a significant increase in the
natural frequency of the first bending mode when compared to the free-free and person-held conditions. The
roller-grip-loose method and the canister-grip method both have natural frequencies only slightly higher than the
person-held grips for the first bending mode. The results for the second bending mode show more separation
between the person-held bat and the machine-gripped bats. Similar to the first bending mode, the roller grip more
closely represents a player’s hands when the bottom set of rollers is left loose. The canister grip raises the
natural frequency of the second bending mode the same amount as the roller grip tight. Bat deflection shapes for
the first and second bending modes are shown in Figure 4. The roller-grip-tight method and the canister-grip
method both constrain the deflection of the bat at two points on the handle, thus changing the shape of the
second bending mode. The roller-grip-loose method allows some deflection within the lower pair of rollers, much
like a player’s hands would. From these modal data, the roller-grip-loose method and the canister-grip method
are concluded to be good representations in the lab of a player-held bat in the field, if the second bending mode is
of little importance in the bat/ball collision.
Fig. 4 Bat deflection shapes for the first and second bending modes
It is important to look at the bat under dynamic field conditions to conclude whether or not the lab test is
replicating field-service conditions. Strain gages were used to measure the strain on a bat in field conditions.
Two strain gages were mounted on an aluminum bat, both oriented along the axis of the bat but located 90o apart
(see Figure 5). Because the impact location cannot be easily controlled in the field, two gages were necessary to
ensure the impact was captured. Three college players were used for this study; each taking some soft-toss hits
(ball tossed from the side so zero incoming ball speed) and then hitting off live pitching from a batting-practice
pitcher.
Fig. 5 Two strain gages attached to an aluminum bat
Strain gage data were collected for several hits from each player, and the respective impact location was marked
after each hit. The same bat was then loaded into the durability machine, and the bat was impacted at the same
locations as the field hits using each of the three gripping methods. The impact speed was varied to try to match
the amplitude of the peak strain and the shape of the response with that observed in the field-test data. Estimates
for pitch speed and player swing speed were used for comparison. Figure 6 shows the strain-gage response for
one of the gages for a hit off live pitching for one of the college players. The strain response is also shown for a
similar impact in each of the three gripping methods used in the durability machine. In the strain response from
the live hit, there are clearly two modes present right after impact, and then the second mode damps out leaving
only the first bending mode in the response. A similar response is seen in each of the grips in the ADC. However,
there is less overall damping present in the ADC responses; a player’s hands absorb more of the vibration than
the rubbers used in the ADC grips. The peak strain seen in a field hit where impact occurred about 9 inches from
the end of the barrel was matched in each of the three ADC grips with impacts of about 100 mph. The strain
results for each of these hits are shown in Figure 6. The shape of the strain response is matched closely for all of
the grips, but is best matched by the canister grip for the aluminum bat used in this study.
Fig. 6 Comparison of strain gage responses for hits off of live pitching and in the ADC
at an impact location 9 inches from the end of the barrel
A study by Crisco, Greenwald, and Penna [1] shows an average swing speed for college players to be 66 mph at
a point 5 inches from the barrel end of the bat. Because each player is different, it is assumed that the players
swing speeds range between 60 and 70 mph. Assuming the axis of rotation is at the knob of the bat, bat speed at
9 inches from the end of the barrel is approximately 52-60 mph for a 34-inch bat. It is assumed that the batting
practice pitches were coming in at about 50 mph at the point of contact. Using these assumptions the impact
velocity of the field hit was approximately 102-110 mph. The impact speeds in the ADC that resulted in similar
peak strains were at approximately 100 mph. These results show that the peak strain seen by a bat in the ADC is
in the same region as what would be seen in the field. It is reasonable to assume that impacts in the ADC at a
certain velocity result in a similar peak strain to what would be seen in the field at the same combined velocity.
Fig. 7 shows two different soft-toss hits from one of the college players compared with two impacts in the
durability machine with the canister grip. The two hits from the player resulted in a peak strains of 800-1000
microstrain. Similar peak strains were seen with hits in the durability machine for impact speeds between 67 and
75 mph. The two impacts in the durability machine were probably not at the exact same location which may
explain why the strain was higher for the 67 mph impact than the 75 mph impact. Using the swing speed model
described above, an average college player would have a swing speed of approximately 57-67 mph at a point 6
inches from the end of the barrel. This agrees well with the ADC results of 67 and 75 mph. Because these hits
were soft-toss hits, there may have been a small component of ball velocity which could explain why the ADC hits
were slightly higher than the estimated range of swing speeds.
Fig. 7 Comparison of strain gage responses for soft toss hits and in the ADC at an impact location
6 inches from the end of the barrel
The accelerometer and strain gage data support the conclusion that the ADC machine can be a good simulation
of field-service conditions for durability testing in a lab environment. Of the three grips tested, the roller-grip-loose
method and the canister-grip method are good representations of a player’s hands. Based on experience, the
roller-grip-loose method is less time-consuming to load a bat than is the canister-grip method. When testing wood
bats, which typically crack in the handle region after only a few hits, the roller-grip-loose method is the preferred
gripping method because a bat can be loaded and unloaded relatively quickly and a crack in the handle can be
easily observed in comparison to the canister grip. When testing aluminum bats, which tend to fail in the barrel
region of the bat, the canister grip is the preferred gripping method as it allows the bat to be rotated as the bat
would be in the field between impacts.
Conclusion
The UMLBRC is able to examine the performance and durability characteristics of baseball bats and balls through
the use of four laboratory test setups. Using modal analysis, the credibility of these machines to simulate fieldservice conditions has been demonstrated. With these testing capabilities, governing bodies can establish
specifications and regulations to control the equipment used in the game of baseball. With the proper regulations
in place, the game of baseball can be played with aluminum and composite bats without compromising the
integrity of the game.
References
1. Crisco, JJ and Greenwald, RM, Penna, LH, “Baseball Bat Performance: A Batting Cage Study”, Draft Report,
July 14, 1999. http://www.nisss.org/BBSPEED6a.html