Effect of changing slope of grain on ash, maple, and yellow birch in bending strength

The presence of slope of grain (SoG) in wood can severely reduce the bending strength in wood. Failure to recognize the degree to which SoG can reduce strength can be catastrophic if wood is in single member use. In the United States, a growing concern in the sport of baseball relates to the high frequency of multi-piece broken wood bats. It was observed that hard maple bats tended to break explosively, whereas white ash bats were more likely to stay intact. An examination of bats collected during the last three months of the 2008 baseball season indicated that for that time period the majority of catastrophic multi-piece failures (MPF) involved SoG failures. This paper reports the edgewise loading results of a study conducted to investigate the influence of SoG on wood properties for three species (white ash, sugar maple, and yellow birch) that are commonly used in baseball bats. The study conducted 2,200 tests to investigate the changes in bending strength with five different slope of grain (0, 2, 4, 7, and 10 degree) angles painstakingly manufactured from the same board for three different (21.4-, 23.9-, 26.6-mm- (0.84-, 0.94-, 1.04-in-)) diameter category 457-mm- (18-in-) long dowels. Results show that in general, edgewise MOE and MOR for all three species is reduced by a similar amount as SoG increases. Maximum reduction in MOE was 20–25% at a SoG category of 10 degrees. Maximum reduction in MOR was shown to be about 25–30% at a SoG category of 10 degrees. Density changes affected the three species differently in the density range of interest to baseball manufacturing. For maple, MOE is less sensitive to changes in density than for the other two species, whereas maple’s MOR is affected most by changes in density. Face-grain loading of diffuse porous maple and yellow birch at higher SoG angles had higher MOR values than matched edge-grain loaded samples. Finally, SoG may have slightly less effect on yellow birch bending properties than on ash and maple.