## 4 Results and Discussion
### Effect of Structural Compliance  
In this test series, three levels of structural compliance were employed, corresponding to natural frequencies of 135 Hz, 145 Hz and 173 Hz for the C1, C2 and C3 systems. Nominal pressures are plotted against time in Figure 15 for tests T1_10_18_C1_25, T1_10_17_C2_25 and T1_10_15_C3_25 for an indenter size of 10 cm and a constant ram speed of 2.5 mm/s. Although there were minor variations in ice temperature between tests, the differences remained within \(\pm\)3 \({}^{\circ}\)C.  
Assuming that compliance constitutes the primary distinction among these cases, it is notable that the variance in structural compliance does not exert a significant impact on peak failure pressure; however, it does notably influence the failure frequency. In the  
Figure 14: Comparison of results for tests T1\(5\)19_C1_2.5, T1_10_18_C1_2.5, T1_15_18_C1_2.5 and T1_15_18_C1_2.5; (**Left**) nominal pressure plotted against time; (**Right**) average failure frequency plotted against indenter size.  
Figure 15: Comparison of results for tests T1_10_18_C1_2.5, T1_10_17_C2_2.5 and T1_10_15_C3_2.5; (**Left**) nominal pressure plotted against time; (**Right**) average failure frequency plotted against the natural frequency of the beam.  
case of compliant system 1, only two major spalling occur, whereas for compliant system 3, seven failure events can be identified. A similar observation was made by [23] at a small scale where the failure frequency showed a linear relationship with structural compliance. The pressure drops following failure were more pronounced for C1 compared to the other two beams, attributed to the amount of stored energy in the beam at the point of failure. By comparing the events A, B and C for the three compliant systems with similar peak loads (Figure 15), the rebound of the indenter was found to be 0.98 mm for compliant system 1, 0.71 mm for compliant system 2 and 0.4 mm for compliant system 3. These results highlight the significant influence of the rebounding process on the extrusion of the damaged layer and associated vibrations within this layer, consistent with observations from small-scale experiments [24].  
For the most compliant system, given the larger rebound distance that follows a failure event, it is expected that nearly all of the damaged ice would be extruded during the rebound process (e.g., very little of the damaged layer survives the extrusion phase of the oscillation cycle), resulting in the indenter being in contact with much more 'intact' ice at the beginning of the next cycle of loading. On the other hand, for the stiffest configuration, a lower rebound distance suggests that a more significant part of the damaged layer survives between subsequent'sawtooth' cycles, highlighting that the ice contacting the indenter at the onset of each loading phase of an oscillation cycle is in a much more damaged state. This has important implications for modelling the behaviour of ice in the contact zone, since it implies that stiffer structures may be less likely to'reset' the damage layer formation process during each subsequent load cycle, which may give rise to more periodic layer oscillation. By comparison, more compliant structures would extrude most of the damaged ice from the contact zone during each cycle, making such interactions more likely to take on a sawtooth character. Since the behaviour of the ice (e.g., damage rate, fracture behaviour, strain rate dependence and temperature effects) in turn govern the rate and depth of the damaged layer formation, this work further highlights the need for a coupled treatment of dynamics ice-structure interactions.