JOM, Vol. 64, No. 3, 2012 DOI: 10.1007/s11837-012-0288-2 Ó 2012 TMS Feature Materials in Action Design Implementation of Baseball Bats: Reinforced Bats—A Case Study N.M. Ravindra, Ivan Padron, Priyanka Singh, Bhumi Bhatt, Vishal Singh, and Kevin Fritz An analysis of the physics of base- advance, rules were implemented by The rules that have been implemented ball bats is presented in this study. organized baseball leagues to main- are not completely consistent and of- In particular, the analysis focuses on tain a competitive balance between ten vary from one league to another. the safety of various types of baseball the teams and the players. These rules In Little League and collegiate base- bats and the numerous approaches were more focused on achieving com- ball where metal bats are prevalent, that have been taken in the industry to petitive balance than increasing safe- more and stricter rules have been improve their safety. In order to evalu- ty, largely because the equipment was implemented. The Little League As- ate their safety, several factors have not advanced enough to cause major sociation of America, for example, been analyzed including the baseball safety concerns. recently outlawed all bats made of EDWFRHI¿FLHQWRIUHVWLWXWLRQWKHWUDP- Starting in the 1970s, metal base- composite materials and also has rules poline effect, the durability of the bat ball bats, especially aluminum bats, regarding the maximum length of the and its constituent materials. In this became increasingly popular due to bat as well as its maximum diameter.2 study, a novel, patented, reinforced their extreme durability and improved The NCAA has gone even further re- wooden baseball bat has been exam- performance over traditional wooden garding rules for the safety of baseball ined to determine its durability and bats. More recently, bats made of bats. In addition to length and diam- safety relative to traditional wooden composite materials, which offer even eter restrictions, there are also rules EDWV5HVXOWVEDVHGRQD¿QLWHHOHPHQW better performance, have also become regarding the difference between the analysis using ANSYS software have common. As the metal and composite length and weight of the bat as well demonstrated that this reinforced bat performance continued to improve as the bat’s moment of inertia.3 Until bat reduces the stress of impact with over the years, the competitive bal- recently, the National Collegiate Ath- a baseball, increasing the useable ance between hitters and pitchers was letic Association (NCAA) also had a lifespan of the bat. Furthermore, af- increasingly disrupted, and more im- rule which required that all approved ter thorough and consistent use, re- portantly, safety began to be a major bats be tested to determine the ball sults suggest that the reinforced bat is concern. For example, given an av- exit speed ratio (BESR), which com- both more durable and safer because erage pitch speed and bat speed, the pared the speed of the ball before and it takes longer to break than a tradi- pitcher could have as little as 0.33 sec- after collision with the bat. Bats with tional bat and, when it does break, it onds to react to a ball hit back at them a BESR of more than 0.728 were not cracks instead of splintering and be- in little league baseball, and as little allowed in play.4 Recently, however, a coming a projectile. as 0.26 seconds in major league base- new, more stringent statistic called the ball. Another safety concern is that EDVHEDOO EDW FRHI¿FLHQW RI UHVWLWXWLRQ INTRODUCTION when wooden bats break during play, (BBCOR) has been implemented by Baseball is one of the oldest sports they often splinter, and a large chunk the NCAA which also takes into ac- in America, dating back to the mid- of the bat becomes a projectile which count the “trampoline effect” caused 1800s. As would be expected with any can potentially come very close to one by metallic and composite baseball sport that has been around for more RIWKH¿HOGHUV,QIDFWSHRSOHZHUH bats. Bats with BBCOR ratings of than 150 years, there have been many killed playing youth baseball between more than 0.50 are not allowed in advances made in baseball through 1987 and 1996 and there were over competition.3 the years. Probably the biggest ad- 29,000 injuries, including over 15,000 In Major League Baseball as well vancements have been in the area of ball-related mishaps.1 as professional Minor League Base- equipment. In the early years of base- As these incidents grew in frequen- ball, where wooden bats are used ball, there were not very many rules cy, more rules about baseball equip- exclusively, fewer rules are present regarding equipment, as most equip- ment, especially regarding baseball regarding baseball bats. While this is ment was generally very rudimentary. bats, were introduced at various levels understandable in the sense that these However, as the equipment began to of play to help make the game safer. leagues do not have to be concerned 359 360 Ravindra, Padron, P. Singh, Bhatt, V. Singh, and Fritz with the negative effects of metal and a number of factors to determine the composite bat at the moment of con- composite bats, it still poses the po- reasons for better performance of tact with a ball.3 To determine a bat’s tential danger of a broken wooden bat metal bats. BBCOR rating, the NCAA has devel- LQMXULQJD¿HOGHU In regards to the studies attempting RSHG D VSHFL¿F WHVWLQJ SURFHGXUH3 A In this paper, the impact of the new to improve aspects of baseball bats, EDOOFDQQRQ¿UHVUHJXODWLRQEDVHEDOOV rules regarding metal and composite Ashley13 developed two predominant- at a stationary bat, and the velocity of bats on bat performance is analyzed. ly composite bats, one of which had the ball before and after impact is re- A new reinforced wooden bat aimed performance similar to hardwood bats corded, similarly to the BESR statis- at improving the safety of wooden but with improved durability and the tic. The difference, however, is how EDWV LV SUHVHQWHG $ ¿QLWH HOHPHQW other with performance that exceeded these velocities are used in the respec- analysis (FEA) using the ANSYS even that of aluminum bats. Both of tive calculations. The equation for the software is performed to compare the these bats contain a high-strength in- BESR statistic4 is given by the follow- stress experienced during collision by ner core made from resin-impregnated ing expression: a regular wooden bat as well as the V\QWKHWLF ¿EHUV DQG \DUQV VXUURXQG- Vv−δ reinforced bat. ed by a wood outer surface. Axtell, BESR = R ++05. <>ε (1) 14 Vv+δ Smith, and Shenoy also developed a I REVIEW OF THE composite reinforcement for wooden LITERATURE bats to improve durability. This com- where, VI and VR are the ball inbound There have been a number of ar- posite reinforcement consisted of an e- and rebound speeds, ε is a correction ticles analyzing the physics of base- glass braided sleeve which was placed factor, and ball bats with a variety of motivations around a regular laminated wood bat. δν and applications. These articles can be However, the main problem with = 136 mph – VContact (2) separated into three distinct catego- both of these studies is that since they ries: articles that try to understand the use composite materials, they would The BBCOR statistic is represented bat-ball collision, articles comparing not be allowed in leagues that permit as: metal and wood bats, and articles that only traditional wood bats. V present ways of improving various BBCOR = R (1+++rrC ) (3) THEORETICAL ball characteristics of baseball bats. VI BACKGROUND Among the studies attempting to where, VI and VR are the ball inbound understand the bat-ball collision, a ma- There are several important factors and rebound speeds respectively. The r jor topic of interest was the so-called to consider when analyzing both metal and Cball values are calculated from the “sweet spot.” Cross tried to locate the and wooden baseball bats. These fac- following formulae: sweet spot in terms of vibration nodes WRUVLQFOXGHWKHEDW¶VFRHI¿FLHQWRIUHV- 5 or a center of percussion while Noble titution, its moment of inertia, and the Cball = 0.528 – BBCOR (4) also attempted to quantitatively de- mechanical properties of its constitu- scribe the location of the sweet spot ent materials. For metal and composite ⎡ 1 ()LBPz−−2 ⎤ as a combination of vibrational fac- bats, the so-called “trampoline effect” rm=+ ⎢ 2 ⎥ (5) tors, the center of percussion, and the is also important. ⎣W 16−−WBP()⎦ FRHI¿FLHQW RI UHVWLWXWLRQ6 Another Coefficient of Restitution study which sought to understand the where, m is the mass of the ball in bat-ball collision was Nathan, Rus- Beginning in 2005, the NCAA im- ounces, z is measured in inches from sell, and Smith, which analyzed the plemented the BESR statistic to limit the barrel end of the bat, W is the WUDPSROLQHHIIHFWXVLQJWKHFRHI¿FLHQW the performance of metal and com- weight of the bat, L is the length of of restitution.7 Finally, Drane and posite bats by placing restrictions on the bat, and BP is the balance point Sherwood (2004) found that there was the ratio of the ball speed before and relative to the knob of the bat. a 4% decrease in performance when after collision. This statistic, however, The results of this new rule have WKHEDVHEDOOZDVFRROHGVLJQL¿FDQWO\ did not provide enough safety, and EHHQ YHU\ VLJQL¿FDQW ZLWK VFRULQJ prior to use.[8] several pitchers were seriously injured dropping by over 1 run per team per The studies that focused on com- after it was implemented. In response, game and batting average dropping paring the performance between met- the NCAA implemented the BBCOR from .305 to .279.15 al and wood bats unanimously agreed statistic in 2011, which represents the Moment of Inertia that metal bats gave better perfor- FRHI¿FLHQW RI UHVWLWXWLRQ EHWZHHQ WKH mance.