## 3 Results
### Slope of Grain  
The Charpy data were sorted into three SoG groupings, specifically (1) \(|\)SoG\(|\)\(<\)1\({}^{\circ}\), (2) 1\({}^{\circ}\)\(<\) \(|\)SoG\(|\)\(<\)3\({}^{\circ}\) and (3) \(|\)SoG\(|\)\(>\) 3\({}^{\circ}\). Absolute values are used in the SoG grouping due to the symmetry involved in the Charpy Impact test. Because it is well-known that the stress-to-failure decreases with increasing absolute value of the SoG [16; 17], it was anticipated that the test data would show a similar trend for the strain-to-failure as a function of SoG for maple and for ash. Figure 7 is the same plot as Figure 5 where the ash and maple data have been sorted into three SoG groupings. It is challenging to see a clear decrease in the strain-to-failure with increasing SoG in Figure 7. However, upon review of the mean strain-to-failure and standard deviation of the  
Figure 5: Strain-to-failure as a function of wood density for ash samples impacted edge-grain and maple samples impacted face-grain. Figure 6: Failure energy as a function of wood density for ash samples impacted edge-grain and maple samples impacted face-grain. data set in Table 2 for each of the three SoG groupings, it can be seen that the mean for \(\mid\)SoG \(\mid\)\(>\) 3\({}^{\circ}\) is lower than the mean for 1\({}^{\circ}\) < 1 SoG \(\mid\)\(<\) 3\({}^{\circ}\) which is lower or equal than the mean for 1 SoG \(\mid\)\(<\) 1\({}^{\circ}\). However, this interpretation of the data may be a stretch due to the limited number of samples in each of the SoG groupings that span the range of densities. Without more data, it is difficult to make a definitive conclusion by using only the current research data on the relationship between SoG and strain-to-failure. Thus, in the absence of more data, the available results suggest that density has a greater effect on the impact failure properties of the wood than SoG for the range of densities and SoGs considered in this study. However, once the wood has begun to fracture, SoG dominates the direction of crack propagation of the wood, thereby determining if the pieces breaking away from the bat are fairly blunt or spear-like in shape. This phenomenon is highlighted in Figure 8.  
Figure 8: Charpy samples of varying SoG (**a**) 1 SoG \(\mid\) <1\({}^{\circ}\), (**b**) 1\({}^{\circ}\) < 1 SoG \(\mid\)\(<\) 3\({}^{\circ}\) and (**c**) 1 SoG \(\mid\)\(>\) 3\({}^{\circ}\). \begin{table}
\begin{tabular}{c c c} \hline \hline
**SoG Class** & **Maple Strain-to-Failure** & **Ash Strain-to-Failure** \\ \hline \(<\)1\({}^{\circ}\) & 0.026 \(\pm\) 0.0043 & 0.027 \(\pm\) 0.0025 \\ 1\({}^{\circ}\) \(<\) SoG \(<\) 3\({}^{\circ}\) & 0.025 \(\pm\) 0.0030 & 0.027 \(\pm\) 0.0020 \\ \(>\)3\({}^{\circ}\) & 0.023 \(\pm\) 0.0041 & 0.024 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Mean maple and ash sample strain-to-failure results sorted by SoG class. Figure 7: Strain-to-failure of ash samples impacted on the edge-grain and maple samples impacted on the face-grain. All samples are sorted by slope-of-grain (SoG). Figure 8 shows a maple wood species Charpy test sample from each of the three SoG groupings that were examined. The samples shown in Figure 8a have a density of 0.028 lb/in\({}^{3}\) (786 kg/m\({}^{3}\)) and a SoG measuring 0.3\({}^{\circ}\). It can be seen that the sample has not completely fractured through the width and this fracture surface is indicative of a brash wood failure. The samples in Figure 8b have a density of 0.026 lb/in\({}^{3}\) (709 kg/m\({}^{3}\)) and a SoG measuring 1.7\({}^{\circ}\). Theses samples exhibit more splintering of the wood at the fracture site in comparison to Figure 8a. The Figure 8b samples also did not completely split through the width. Figure 8c shows samples with a wood density of 0.026 lb/in\({}^{3}\) (722 kg/m\({}^{3}\)) and a measured SoG of 3.7\({}^{\circ}\). The high-SoG specimens split along the grain line during impact, thereby resulting in the formation of sharp edges on the fracture surface.