## 4 Results and Discussion
### Effect of Temperature  
For slow tests (\(\approx\)2.5 mm/s ram speed), a significant difference in the failure behaviour can be observed for all indenter sizes and compliant systems when the ice temperature was above \(-\)3 \({}^{\circ}\)C. Figure 9 shows the comparison between tests T1_10_17_C2_2.5, T1_10_6_C2_2.5 and T1_10_2_C2_2.5. The indenter size, ram speed and structural compliance were kept constant for the three tests and the ice temperatures were varied. It is assumed that the nominal indenter area remains constant after the initial full envelopment and the nominal pressure was calculated by dividing the force recorded by the load cell by the indenter area. For the tests at \(-\)17.5 \({}^{\circ}\)C and \(-\)6 \({}^{\circ}\)C, the pressure-time plot shows a similar'sawtooth' pattern described in the previous section although the peak failure pressure was significantly higher for colder ice for most of the peak pressures (Figure 9 (Left)). It should be noted that, in general, the peak failure pressure varied significantly within each test, and, therefore, not all peaks of the colder ice were higher than the warmer ice. However, the pressure associated with the first failure event was consistently found to have a significantly higher value for colder ice. Figure 9 (Right) shows the average failure frequency (i.e., the number of failure events over the interaction period) as a function of ice temperature. It is observed that when the failure is in the brittle domain, the frequency of the'sawtooth' failure is not strongly influenced by ice temperature. However, for 'warm' ice, the failure frequency is significantly lower. Figure 10 shows a closer look at the ice failure processes near the indentation area at the end of the tests and the effect of ice temperature on failure behaviour. For ice at \(-\)2 \({}^{\circ}\)C, the continuous extrusion of highly damaged ice which resulted in the continuous nonlinear pressure-time series can be clearly visible. For 'colder' ice, the failure surface looks very similar suggesting the similarity in the failure processes. However, for ice at \(-\)17.5 \({}^{\circ}\)C, the  
Figure 9: Comparison of results for tests T1_10_17_C2_2.5, T1_10_6_C2_2.5, T1_10_2_C2_2.5; (**Left**) nominal pressure plotted against time; (**Right**) average failure frequency plotted against ice temperature. spall area was much larger compared to ice at \(-6\)\({}^{\circ}\)C, which is consistent with the observed load drop in Figure 9.  
For high-speed tests, the failure behaviour was slightly different for both the 'warm' ice and 'cold' ice. Figure 11 (Left) shows the nominal pressure and beam displacement at the centre vs. time for tests T1\(5\)3_C2_16 and T1\(5\)9_C2_16 where the ice temperatures were \(-3\)\({}^{\circ}\)C and \(-9\)\({}^{\circ}\)C, respectively. The pressure-time and displacement-time trace shows similar behaviour in this case with the failure being a mixture of both continuous extrusion and large load drops. The average failure frequency shows a similar trend to slow speed tests; the failure frequency is considerably high for colder ice (Figure 10 (Right)). The maximum pressure, load drops and maximum displacement were similar in nature; however, the acceleration data shows that the dynamics associated with the two cases were completely different (Figure 12). As shown in Figure 12, dynamic responses of the beam associated with ice failure were recorded in both cases. For the ice at \(-3\)\({}^{\circ}\)C, the maximum value ranged only between \(-0.05\) g to \(+0.05\) g, whereas for \(-9\)\({}^{\circ}\)C the value ranged between \(-20\) g to \(+20\) g. This has important implications for ice-induced vibration since the results suggest that for colder ice the failure process is sudden, and the rapid release of energy can significantly excite the structure.