Going to a baseball game engages all the senses. There’s the green of the field and the flash of the scoreboard. The feel of the hard plastic seat and the crunch of fallen popcorn underfoot. The smell and taste of the ballpark hot dog. The sound of the thump of the ball in the catcher’s
glove. And every now and then, a loud crack as a bat, swung towards a ball hurtling 90 miles per hour or more, snaps in two.

A broken bat isn’t an uncommon experience in a Major League Baseball game. For a while in the early 2000s, there seemed to be an increasing number of bat fractures. Some speculated that recent innovations in bat engineering might have something to do with it. More wood species were being made into Major League Baseball bats, and the previous wood specification guides hadn’t been updated in a long time. Major League Baseball decided it was time to call in the engineers.

In the early days of baseball, baseball bats were usually thick and made of heavy woods like hickory. As the game evolved, batters looked for different woods and bat styles to improve their swings and hitting capabilities. Bat handles are much thinner now than they were in the 19 and early 20 centuries, and bats are made of different woods like ash, maple, and birch, as well as hickory.

One challenge of powerful swings with thinner-handled bats was an increase in bat breakage depending on the type of wood. Bat breaks are classified as either single-piece failures, meaning the bat broke but stayed in one piece, or as multiple-piece failures, meaning the bat broke into two or more pieces. Multiple-piece failures are the more dangerous of the two types of failures. Pieces of a broken bat can fly into the infield or into the stands and can injure players or bystanders.

In 2008, Major League Baseball commissioned a study to reduce the number of multiple-piece failures, and in 2012, a team of engineers from the University of Massachusetts Lowell Baseball Research Center and the Forest Service’s Forest Products Laboratory created a testing protocol for certifying new wood species as acceptable for Major League Baseball. Here’s how they did it.

Though maple bats became more popular starting in the late 1990s, white ash was the most commonly used wood in bats for Major League Baseball until the turn of the 21 century. White ash had always performed well as a bat, being lighter and more flexible than hickory. The engineers’ preliminary tests were performed with ash wood bats, setting a baseline for comparing other wood species.

First came durability testing. The durability of a bat is determined by a combination of several factors: wood species, wood density, the slope of grain, the impact location, and impact velocity. What do all these terms mean for testing?

Wood species is just what type of wood the bat is made out of. Different woods have different properties. Properties include flexibility, whether they tend to snap, and weight. In this study, the engineers compared white ash (the baseline wood) and yellow birch (a potential new bat wood).

Density is the relationship between the mass of, in this case, a bat and how much space it takes up. If two bats are the same size but one is heavier, the heavier bat is more dense. Even bats made of the same wood can have different densities, which is why the engineers tested low-, medium-, and high-density versions of the bat materials.

The slope of grain refers to the straightness of the wood grain along the length of a bat. The straighter the grain along the length of the bat, the less likely the bat is to break.

The impact location is where the ball hits the bat. Engineers chose four different locations along the length of each bat: 2, 10, 14, and 16 inches from the tip of the barrel. They used an air cannon to fire baseballs at each of the impact locations on each bat. They tested more bats at the 14-inch location because impacts at that spot tended to cause larger bat fragments to fly into the field or the
stands.

Finally, the impact velocity is the speed at which the baseball hits the bat. Using the air cannon, they launched baseballs at each bat starting at a baseline speed. They increased the speed by 5 miles per hour until they reached the peak testing speed at each impact location. They attempted to hit the bat five times at peak speed at each location. The testing stopped when either the bat broke or they had completed the five impacts at peak speed.

The impact velocity that resulted in a single-piece failure (SPF) or a multi-piece failure (MPF) on white ash bats at each impact location set the threshold. In other words, new wood candidates, like yellow birch, would have to meet or exceed these impact velocities at each impact location to be approved to move on to the next test.

Engineers also tested the wood species using a clear dowel test. Dowels of different densities of each wood type (ash and birch) were tested on their flexibility (how much they could bend) under controlled circumstances.

The batted-ball performance test measures the velocity at which a baseball rebounds off the bat. Engineers tested different impact locations along the bat’s barrel to determine the bat’s “sweet spot.” A baseball hitting that sweet spot will achieve the maximum exit velocity while causing a minimal amount of vibration down the bat to the batter’s hands. Maximum exit velocity means longer hits at higher speeds.

Engineers tested 12 ash and 12 yellow birch bats, half low density and half high density. The bats were impacted at three to five locations along the barrel to find their sweet spots, and engineers documented the exit velocities of the balls at these locations.

Based on their results, engineers came up with a proposed testing process for new wood species. After gathering information about the type of wood and where it came from, bats would be subjected to three phases of testing: a preliminary durability test, a complete dynamic bat test, and finally a performance test. These tests would be like those run during the experiment, and engineers made recommendations about how many samples should be tested at each phase. At each phase, bats would have
to perform at least as well as the white ash benchmarks established in the experiment. And, by the way, the yellow birch bats passed their tests, establishing the material as a viable alternative for white ash.