# In Situ Experimental Study of the Friction of Sea Ice and Steel on Sea Ice
## 1 Introduction  
A sustained decline in sea ice extent and thickness has taken place in the Arctic Ocean in recent years [1; 2; 3; 4]. These changes suggest more attractive prospects for navigation as the Arctic Ocean becomes more accessible in the marginal seas [5; 6; 7; 8; 9]. Chinese container vessels have sailed through the Northeast Passage to Europe in recent summer seasons [10]. When sea ice interacts with a ship's hull during navigation in ice-infested waters, it may fracture, collide with, or slide along the hull. During these interactions, the friction between sea ice and a ship's hull severely affects the performance of the vessel [11; 12]; approximately 70% of the power of icebreakers is consumed to overcome friction [13]. Therefore, knowledge of the engineering mechanism of ice friction is important for ice navigation in the Arctic Ocean.  
Ice friction has received relatively less attention than studies on compression, bending, and other ice mechanics [14; 15; 16; 17; 18; 19; 20]. To understand the behavior of ice friction, laboratory experiments have been conducted on the friction of ice against ice [21; 22; 23; 24; 25], against metals [26; 27], against coatings [28; 29], against polymethyl methacrylate [30; 31], against glass [32], and against rubber [33]. Several impact factors have been investigated, such as sliding velocity, temperature, normal load, and grain structure. Based on these laboratory experiments some physical mechanisms were proposed and proved, e.g., a water layer would be formed at contact surface by frictional heat [21; 22; 23; 24; 25; 27; 30; 31; 32]. However, in most of these above laboratory experiments, small manufactured ice samples with well-prepared smoothsurfaces were performed to slide a very short distance along the substrate using modified uniaxial testing, rotational, or linear devices. Moreover, some of the laboratory experiments were performed under very low sliding velocities, which were several orders of magnitude slower than the real speed during ice navigation [34]. Therefore, although the results from these small-scale tests are helpful in understanding the physics of ice friction, they cannot be used uncritically for engineering applications.  
To the authors' knowledge, only a limited number of experiments have been performed at large scale, namely in a basin or in field. [PERSON] [11] measured the friction between ice and an icebreaker hull under authentic icebreaking circumstances. [PERSON] et al. [35] conducted a series of meter-scale ice friction tests in an ice basin. [PERSON] et al. [36] and [PERSON] and [PERSON] [37] pulled sea ice blocks over a natural ice cover in field. From an engineering perspective, more field data are needed to verify the results obtained from tests in basins and in laboratories.  
The ice friction occurred during ice navigation is different from the previous experiments conducted in laboratories. Because when a ship sails in the ice region, such as sailing in the marginal ice zone in Antarctic/Arctic in summer, the navigation velocity and the ambient temperature are higher than the test conditions of the previous studies. Therefore, the objective of the current work was to better model the conditions of ice friction occurred during ice navigation, including the ambient temperature, contact material, sliding velocity, through field experiment using nature ice cover. We intended to observe the ice friction phenomena at the conditions closer to the real situation and tried to explain it based on the existing theories. With the objective, this paper has been organized as follows. Section 2 gives a detailed description of the field measurements, Section 3 presents the experimental results, and Section 4 discusses the uncertainty analysis, comparisons with previous reports, quantification of velocity dependence, and an approximate comparison with model estimation. Finally, conclusions are drawn in Section 5.