In most Natural Inquirer articles, this section is called “Thinking About Science.” However, engineers did the research in this article. Science and engineering are closely related. Science and engineering have some interesting similarities and differences. Sometimes scientists conduct research to solve a problem, and sometimes they conduct research to provide new information about a topic. Scientists study how nature works and generally conduct experiments using the scientific method. Engineers apply scientific and mathematical knowledge to help solve a problem. Engineers and scientists also create things to help them answer questions and solve problems. Engineers have a method they use to help them solve problems. It is called the engineering design process (figures 1a and 1b).

In recent times, different types of wood have been used to create baseball bats. One of the reasons different wood is used is because baseball players want to try different types of wood bats. They are interested to see if the design and type of wood will affect how far the ball is hit. However, some types of wood break easier than others resulting in an increase in bat breakage rates.

In this research, the engineers wanted to understand more about wood used to make baseball bats. Baseball bats can and do break. To help prevent baseball bats breaking, the engineers wanted to figure out a way to test wood for baseball bat manufacturing. This wood testing process could be used now and into the future to determine the suitability of different wood for baseball bat manufacturing.

Much of the white ash wood used to manufacture baseball bats comes from trees in Northern Pennsylvania and New York (figure 2). The white ash trees in these areas are experiencing problems. One problem is the emerald ash borer (figure 3). The emerald ash borer is a beetle that is native to Asia. The beetle was first found in Detroit, Michigan, in 2002. Since that time, the beetle’s range has spread. The range of emerald ash borer now includes Pennsylvania and New York, where much of the white ash for bats is harvested. The larval stage of the beetle feeds on the inner bark of white ash trees. Feeding by the beetles causes trees to have problems with transporting water and nutrients, which weakens the tree. Over time, the trees can become so weak that they die.

Another problem white ash trees are facing is climate change. Climate change refers to how Earth’s climate may be changing over time. In the past few years, most scientists have agreed that measured and recorded changes in Earth’s climate over the past 100 or more years point to a warming of Earth’s surface. Extreme cold temperatures in Northern Pennsylvania and New York help to kill the emerald ash borer and provide relief to the white ash tree. However, if the climate warms in this area, the emerald ash borer may be able to live through the winter. If more emerald ash borers survive the winter, the trees will be under greater threat and may not be able to survive.

Due to the challenges facing white ash trees, baseball bat manufacturing companies have tried new types of wood to make baseball bats. For more information, visit https://www.scientificamerican.com/article/baseball-bats-made-from-ash-may-fall-victim-of-climate-change/.

Over time, as baseball players have wanted to try different types of bats, various types of wood have been used to make the bats. Over 750 different types of trees are found in North America. Although most of these trees would not be suitable for making bats, the number of choices is large enough to need a consistent selection process.

Typically, northern white ash has been used in baseball bats (figure 4). White ash is native to North America and is known as a strong, light wood. The characteristic of the wood being strong but light makes it perfect for baseball bats. In the 1990s, baseball bat manufacturers started using sugar maple (figure 5). Some players thought that using bats made from sugar maple trees might increase the distance a batted ball would fly. Sugar maple is a very dense wood, but it tends to break easier than white ash. Other types of wood, such as bamboo, birch, and hickory, have also been used to make bats (figure 6).

Two different kinds of breaks are found in a baseball bat. These breaks are called either a single-piece failure (SPF) or a multi-piece failure (MPF). An SPF is when a bat breaks but stays in one piece. An MPF is when a bat breaks into two or more pieces (figures 9a-d).

In recent years, the number of baseball bat breakages has increased. Following this increase, people began to look at how wood was chosen for baseball bat manufacturing. A Wooden Baseball Bat Specifications list existed. The list, however, had not been reviewed and updated in a long time.

In 2008, the Baseball Office of the Commissioner and the Major League Baseball (MLB) Players Association appointed a team of wood and bat experts led by Forest Service Engineer David Kretschmann. The research team was asked to address the concern that more bats had been breaking in recent decades. Changes were implemented from the recommendations of these experts, and bat breakage rates declined by 67 percent.

The Wooden Baseball Bat Specifications list was updated to include the new recommendations and a list of recommended wood species. However, the updated list of recommended wood species was based on how a wood species had performed in the past. This list of wood specifications for existing wood species would not help identify whether a new wood species would be acceptable for bat manufacturing. Experts had not identified criteria for wood species to be considered acceptable for MLB bats. Therefore, the research team determined that a test for the suitability of wood species in bat manufacturing was needed.

The engineers looked at three main tests: a durability test, a clear dowel test, and a batted-ball performance test. The engineers did their testing in the University of Massachusetts-Lowell Baseball Research Center (figure 10).

The engineers first tested white ash because white ash has been the preferred wood to use for baseball bats for many years. The engineers used white ash as the benchmark. A benchmark is something with which to compare other things. In this case, a white ash baseball bat was the benchmark to which other woods were compared during the testing process.

To develop a testing process, the engineers tested yellow birch and compared it with white ash (figure 11). The first test examined durability. Durability for wood baseball bats is a product of several things: wood density, wood species, wood slope of grain (SOG), impact location, and impact velocity.

The wood SOG refers to the straightness of the wood grain along the length of the bat (figure 12a).

Straighter grain along the length of the bat means the bat is less likely to break (figure 12b).

Impact location refers to where the baseball hits the bat. Impact velocity refers to the speed in which the bat is hit by the baseball. To test durability, the engineers used an air cannon. The air cannon can be used to shoot baseballs at velocities of up to 200 miles per hour (mph).

The engineers measured the density of each wood species tested (table 1). Density is the relationship between the mass (weight) of a substance and how much space it takes up. If two items take up the same amount of space, the heavier item is denser. Two bats made from the same wood species may have slightly different densities, because the density of wood from the same species can be different.

Low-, medium-, and high-density versions of each bat were tested. Each bat was tested at four impact locations. An impact location is a place on the bat that comes in contact with the ball as it is hit. The impact locations were 2, 10, 14, and 16 inches from the tip of the barrel (figure 13).

The bats were tested at 5-mph increments up to the peak testing speed. A total of five impacts were made at peak testing speed if the bat had not broken during the process. The testing ended when the bat initially cracked or the testing sequence was completed. SPF (single-piece failure)-threshold and MPF (multiple-piece failure)- threshold velocities were established for each of the impact locations (table 2). Recall that SPF is when a bat breaks but stays in one piece. MPF is when a bat breaks into two or more pieces.

The engineers also tested the clear dowel and batted-ball performance for each type of bat (figures 14a and 14b). The clear dowel testing examined the wood before it was carved into a baseball bat. This test examined the strength and stiffness of the wood. The batted-ball performance test was used to determine if a particular wood species performed differently than the bat carved from white ash.

Based on their testing, the engineers created a process to evaluate different wood species for use in baseball bat manufacturing. For each wood species, the proposed testing process is as follows:

Background information is provided about the proposed wood species. The background information includes what type of tree the wood comes from and basic information about the tree.

A preliminary durability test is performed on 12 low-density bats. All bats are impacted at the 14-inch location. If the proposed wood species passes this test, then a dowel sample test is performed. As part of this test, 180 dowels undergo the test.

Next, a complete dynamic bat test is performed. A complete dynamic bat test includes durability testing of 15 low-, 15 medium-, and 15 high-density bats. Half of the bats are impacted at multiple locations. The engineers proposed that if more than 2 of the 15 bats tested experience SPF or MPF below the thresholds in table 1, then that bat density would not be suitable for baseball bat manufacturing.

Finally, a test is conducted to compare whether the proposed wood species performs differently than the white ash species, which is used as a benchmark. If all of these tests and comparisons are passed, then the proposed wood species is accepted as a suitable wood to use for baseball bat manufacturing.

The proposed testing process involves five main steps to determine whether a wood species is suitable for making baseball bats. The engineers used white ash as the benchmark species to compare other wood species because of white ash’s proven durability over time. When the engineers tested yellow birch using the proposed test protocol, they concluded that the durability, performance, and material properties were all similar to white ash. Therefore, yellow birch would be suitable for use in MLB bats. Engineers hope to see a reduction in the number of SPFs and MPFs now that this testing protocol is in place for determining whether a particular wood is acceptable for use in baseball bat manufacturing.