## 3 Results
### Failure Type  
After the SHPB test, each specimen is examined and is regarded as having failed if a fissure on its surface and sliding along its planar joint or triangular sawteeth joint are observed, if the specimen is fractured into many fragments, or if it is crushed into pieces. The specimens have various appearances after the test. Figure 5 shows six typical samples following the test. Figure 6 presents the three-dimensional (3D) appearances of some specimens. Obviously, the loading rate and the angle of the base plane (\(\beta\)) and the asperity (\(\alpha\)) of a jointed specimen affect its failure. After the tests with low loading rates, an intact specimen may remain integrated with or without tiny flakes (Figure 5a), but the two parts of each jointed specimen in a test can slide relative to each other, with both parts remaining intact (Figure 5b) or only minor scratches on their surface (Figure 5c,g,h). Most specimens lose their integrity at a high loading rate (Figure 5e,f). The specimens with a small magnitude of \(\beta+\alpha\) at a low loading rate are prone to slide failure, while the specimens with a large magnitude of \(\beta+\alpha\), or subjected to a high loading rate, are typically crushed. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Gas Pressure** & **No** & **Intact Specim** & **Planar Joint Specim** & **Sawteeth Joint Specim** \\ (**kg/cm2**) & **Specimen** & **Front PMF** & **Rear PMF** & **Front PMF** & **Rear PMF** & **Front PMF** & **Rear PMF** \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Illustration of red patches on pressure measurement films (PMFs) used between interfaces of embedded specimen and incident and transmitted bars in a SHPB test. Medium-pressure types are used except low-pressure type is used in the four on the right of the last row, with gray background. Figure 7 plots the distributions of the sizes of particles in some of the specimens after testing. Based on the distribution of particle sizes in Figure 7, Table 2 classifies the types of failure of the specimens after the SHPB test as follows: (A) intact with or without tiny flakes, (B) slide failure, (C) fracture failure, and (D) crushing failure. Type C can be divided into the following two subtypes: (C1) broken along the concave of the sawteeth, and (C2) complete fracture. Table 3 lists the types of failure of all tested specimens based on the classification in Table 2. Specimens with \(\beta=39^{\circ}\), \(45^{\circ}\), and \(51^{\circ}\), apart from the intact specimen, have two parts that can slide  
Figure 5: Images of specimen after the SHPB test: (**a**) integrated without any flaking of intact specimen, (**b**) two parts of specimen, with \(\beta=39^{\circ}\) and \(\alpha=0^{\circ}\) slide relative to each other, without any tiny flakes, (**c**) two parts of specimen, with \(\beta=51^{\circ}\) and \(\alpha=3^{\circ}\) slide relative to each other, with tiny flakes on both parts, (**d**) fractured specimen, with \(\beta=39^{\circ}\) and \(\alpha=18^{\circ}\), break along concave part of sawteeth can be observed, (**e**) completely fractured specimen, with \(\beta=45^{\circ}\) and \(\alpha=15^{\circ}\), (**f**) crushed jointed specimen, (**g**) scratches on joint surface of specimen in (**c**), (**h**) depicting (**g**) with an emphasis on scratches on joint surface. relative to each other until failure. At a particular loading rate, the two parts of a specimen that have a smaller \(\beta\) are more apt to slide relative to each other and are severely fractured if it happens. A specimen that has greater \(\alpha\) is more likely to be fractured or crushed to failure. Among specimens with similar total angles of the base plane and asperity (\(\beta+\alpha\)), only those with \(\alpha\leq 6^{\circ}\) have two parts that slide relative to each other and have irregular fragments if fractured. In contrast, those with \(\alpha>6^{\circ}\) do not exhibit sliding but break to failure.