## 4 Summary of Results and Discussion
### Fracture Mode of Ice at Moderate Strain Rates  
The fracture mode of ice in compression tests at the employed strain rates is not similar to that under quasi-static conditions or that in very high strain-rate range. In quasi-static uniaxial compression tests, ice samples fail with a large number of cracks in the ductile-failure strain-rate range (<10\({}^{-4}\) or 10\({}^{-3}\) s\({}^{-1}\)), or in longitudinally splitting mode with a small quantity of cracks in the brittle-failure strain-rate range (10\({}^{-4}\) or 10\({}^{-3}\) s\({}^{-1}\)) to 10\({}^{-2}\) or 10\({}^{-1}\) s\({}^{-1}\)) [16]. In high strain-rate uniaxial compression tests, ice samples crush into a large number of small fragments. While, in moderate strain-rate uniaxial compression tests, ice samples show features of longitudinal splitting failure but with a large number of small fragments, just like that in crushing failure mode. According to the fracture feature of hard ice and soft ice, a sketch of the ice compression fracture mode at moderate rates is summed (as shown in Figure 19). The following failure processes are observed: (a) cracks firstly emerge at the top and bottom ends of sample; (b) cracks propagate vertically or approximately vertically, triggering quick formation of a vertical full-height crack; (c) crack density increases and several vertical full-height cracks appear at the same time, accompanied with load increase; (d) as more and more cracks nucleate and propagate, more intersections and link-ups among cracks occurs; the width of vertical full-height cracks increases; at this moment, cracks are uniformly distributed in the specimen, the crack density reaches a high value, and load reaches its peak value; (e) sample begins to expand obviously in the horizontal direction, and fails in a longitudinally splitting mode in appearance, along those vertical full-height cracks; there are  
Figure 18: Uniaxial compressive strength results of present and some previous work. Solid marks denote results of the present work and hollow marks denote results of some previous studies of other researchers.  
a large amount of expansion and slip among different small fragments, and load decreases quickly; and (f) more and more large-width cracks appear and sample crushes into small fragments.  
Failure process observed in the present study exhibits some similar features as that of splitting failure mode described by [PERSON] (1966), such as the formation of full-height vertical cracks and the link-up of of cracks. While, there also exist some differences. In splitting failure mode, a few cracks forms and ice sample is divided into several large blocks when the peak load is reached. However, observation of present experiments shows that a large number of cracks forms and ice sample becomes milky white when the peak load is reached. The appearance of ice sample is similar to that in ductile failure under quasi-static conditions though the forming rates of cracks in these two failure processes are obviously different. Post-peak failure characteristics are similar to that of impact failure described by [PERSON] et al. [PERSON] et al. (2011) and [PERSON] et al. [PERSON] et al. (2015). It seems that the failure process is a combination of splitting failure mode and crushing failure mode. Since the employed aspect ratio of ice specimen is not large enough, friction at interfaces may affect the fracture mode to some degree; a deeper understanding of the fracture mode in moderate strain-rate range and its intrinsic micromechanical mechanisms still needs more studies.