## 4 Results and Discussion  
### Observations during the Tests  
Most of the tests showed some regular patterns which can be identified as the characteristics of the ice failure process during the indentation of the confined ice specimen. Figure 7 shows the force, displacement and acceleration obtained from test T1_10_17_C2_2.5. The ice force shows a periodic'sawtooth' behaviour, which is observed during intermittent crushing. The first failure event usually generates a lower force due to lower initial confinement for spalls that ran to the free surface. Each load drop is associated with a transient vibration of the beam which damps out quickly. The synchronized displacement of the LVDT suggests that the beam was deflecting as a simply supported beam and its first mode was excited during the associated vibration.  
At the beginning of each ascending part of the loading curve contact area increases as the load accumulates. The load keeps increasing until failure occurs even after the contact area reaches its local maximum value. The failure process was found to be associated with a competition between damage and fracture, the ratio of which is highly influenced by test parameters. Damage refers to the pulverization and extrusion of ice beneath the indenter whereas fracture refers to the propagation of cracks initiated at the contact zone which  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Test ID** & \begin{tabular}{c} **Indenter** \\ **Diameter (cm)** \\ \end{tabular} & \begin{tabular}{c} **Ice Temperature** \\ **(\({}^{\circ}\)C)** \\ \end{tabular} & \
\begin{tabular}{c} **Beam Stiffness** \\ **(N/m)** \\ \end{tabular} &
\begin{tabular}{c} **Ram Speed** \\ **(mm/s)** \\ \end{tabular} \\ \hline T1\_5\_16\_C1\_2.5 & 5 & \(-\)16.5 & C1 (2.67 \(\times\) 10\({}^{7}\)) & 2.5 \\ \hline T1\_5\_1  
results in the removal of larger pieces of ice. By synchronizing the video with the obtained data, the effect of the interaction parameters on the ice failure process can be observed. For most of the tests, as the load increases, extrusion of pulverized ice and propagation of cracks occur simultaneously, suggesting the initialization of both damage and fracture processes. However, for warmer ice with a small indenter size and slow ram speed, the rate of pulverization and extrusion dominates over spalling crack propagation. The loading curve at this point shows a'smoothed-out' peak usually followed by a dip. After that, the load might increase for a few moments eventually followed by a spall and sharp load drop (see Figure 8 (left)). On the other hand, for colder ice, especially with larger interaction areas, cracks develop very quickly and failure is associated with a sharp peak and large load drops (see Figure 8 (right)).  
Figure 8: Damage and fracture dominated failure in two tests: (**Left**) Test ID: T1\(5\)7_C2_2.5, showing extrusion process of ice with loading curve; (**Right**) Test ID: T1_15_6_C2_2.5, showing initiation of cracks which results in sharp peak during load drop.  
Figure 7: Results from T1_10_17_C2_2.5 showing force, displacement and acceleration against time.  
During each load drop, a large part of the contact area is usually removed and the indenter surges forward with the energy stored in the beam. Although the total force is less, due to the reduction in the contact area, the pressure in the contact zone becomes very high and the stored energy causes a rapid pulverization and extrusion process. The rapid extrusion process is often accompanied by pressure melting and dynamic recrystallization [22; 25]. Eventually, due to the increase in the contact area and the release of strain energy stored in the beam, the process reaches a point where the load of the indenter can be borne by the ice, and a new cycle is initiated.