Abstract. 1. Introduction

Transcription

1 Factors Influencing the Coefficient of Friction between Sea Ice and Various Materials Takashi Terashima & Naoki Nakazawa Pacific Consultants, Co., Ltd., New Stage Sapporo Bldg., 2-6, Kita-7 Nishi-1, Kita-ku Sapporo 060 Japan Hideki Honda & Hiroshi Saeki Civil Engineering Dept., Hokkaido University, Kita-13 Nishi-8, Kitaku, Sapporo 001 Japan Abstract A coefficient of friction test between sea ice and various construction materials was conducted to clarify ice-material interaction. The properties of the ice and material are necessary to calculate the ice forces on sloping structures in cold coastal and offshore regions. From experimental studies through six years, the following conclusions were made. The coefficient of friction was found to be affected by: i) the relative velocity: ii) the sea ice temperature: and iii) the surface roughness of the construction materials. It was found to be relatively unaffected by: iv) the contact area: v) normal stress: vi) the growth direction of sea ice: and vii) the water at the sea ice-material interface. 1. Introduction The evaluation of the coefficient of friction between sea ice and construction materials is essential to calculate the ice forces on sloping structures and the frictional resistance of sea ice on ice-breakers. From our experimental studies through six years on the coefficient of friction between sea ice and various materials (Saeki et al. 1986), the following conclusions were made: the coefficient of friction is affected by i) the relative velocity (moving velocity) between sea ice and materials, ii) the sea ice temperature, and iii) the surface roughness of

2 34 Contact Mechanics HI the material, while it is relatively unaffected by iv) the contact area between the sea ice and the materials, v) the normal stress, vi) the growth direction of sea ice, and vii) the water between the sea ice and the materials. In this paper we will discuss the factors influencing the coefficient of friction of sea ice, compare our results with the results of other research and evaluate the coefficient of friction between sea ice and various materials. 2. Test Apparatus The effects of the following factors were examined to clarify the characteristics of coefficient of friction between sea ice and various construction materials. i) contact area between sea ice and materials ii) normal stress on the contact area iii) the growth direction of sea ice iv) relative velocity (moving velocity) v) water at the contact area vi) sea ice temperature vii) surface roughness of construction materials Figure 1 shows the test apparatus. First, a test specimen is fixed on the platform car, which can be moved horizontally by a hydraulic jack. Next, an ice sample is placed on the test specimen, with a steel cap on top, where the vertical load works. The moving velocity of the platform can be changed by the hydraulic jack. SFEEL CAP Figure 1: Diagram of experimental setup 3. Test Specimen and Ice Sample 1) Test specimen The following materials and surface treatment were selected as test specimens due to their frequent use for coastal and offshore structures.

3 Contact Mechanics HI 35 i) steel plate - uncoated and uncorroded ii) steel plate - uncoated, but corroded by sea water iii) steel plate - coated with marine paint: ZEBRON iv) steel plate - coated with marine paint: INERT A160 v) concrete - smoothed by trowel 2) Ice sample Three types of ice samples with a diameter 4.5 cm, 10.0 cm, 15.0 cm, respectively, and a 10.0 cm height were used. Whereas samples of 4.5 cm and 15.0 cm diameter were only used in the experiments on the effects of contact area, samples of 10 cm diameter were used in the other experiments. 4. Experimental Results 1) Effect of contact area Figure 2 shows the effect of contact area for uncoated steel (uncorroded). The coefficients of kinetic friction (M k) and static friction ( JJL s) were almost constant, indicating the coefficient of friction is relatively unaffected by contact area in the range of this experiment. The same results were obtained in the experiments with coated steel, corroded steel, and concrete. The grain size of sea ice (Dgr) was 8-12 mm. 2) Effect of normal stress Figure 3 shows the effect of normal stress on uncoated steel (uncorroded). The coefficient of kinetic friction was almost constant in the range of normal stress between MPa and 1.0 MPa. For the coefficient of static friction, with the increase in vertical load, the data dispersion was narrowed, and //, s showed a tendency to decline until becoming constant at c\^ 0.5 MPa. 3) Effect of relative velocity The effect of relative velocity on the coefficient of friction should be clarified to evaluate the frictional resistance of ice on ice-breakers. Figures 4 and 5 show the effects of relative velocity on uncoated steel (uncorroded) and concrete, respectively. In either case, the coefficients of static and kinetic friction decreased with increasing relative velocity, and showed a tendency to approach a constant value at V ^ 3 cm/s for uncoated steel and at V ^ 30 cm/s for concrete. With a relative velocity of 0.01 ^ V ^ 130 cm/s, the following results were obtained.

4 36 Contact Mechanics HI i) uncoated steel (uncorroded) M t (min) / UL ^ (max) = 0.4, M, (min) / UL, (max) = 0.4 ii) concrete M i (min) / IL,< (max) =, M (min) / UL (max) = 0.5 u.o P 0.3 UNCOATED STEEL (UNCORRODED) Vs : cm/sec T : 'C S tress : MPa ^ 0 ij «A 6 M u c""~ ^ k /C ^ Figun^ 2: Effects of cc>ntact area for uncoated steel (uncon oded) u.o UNCOATED STEEL (UNCORRODED) Vs: cm/sec 0 10 cm T : "C H 0.3 " *"^Li_. ** : *p* , (MPa) Figuret 3: Effects of normal stress for uncoated steel (uncorroded) P 0 3 UNCOATED STEEL (UNCORRODED) BS^f o» * ^v ~>-0 N. «^Q. 0 :10cm Stress : MPa * Ms M* " yt~ " <# >4# -co So g<gcj - 00 "10'2 10"' 10 V (err l/s) 10' 10^ 1C)» Figure 4: Effects of relative velocity for uncoated steel (uncorroded) 0.3 *~"""***«^ ^\ CONCRETE o^ ^ 7\ P, «xt \ * M* o^e * \^ * n X^o T 0 -.-arc :10cm r^o aa o o Stress : MPa o ]-= 10-' 10 10' 10* 10* V (cm/s) Figure 5: Effects of relative velocity for concrete 4) Effect of sea ice temperature Figures 6 and 7 show the effect of sea ice temperature on the coefficients of static friction (MS) and kinetic friction (Atk), respectively. While MS increased with decreasing ice temperature regardless of the material, //, k showed a constant value for concrete and corroded steel, but increased with decreasing ice temperature for uncoated steel (uncorroded) and coated steel (INERTA160).

5 Contact Mechanics HI 37 5) Effect of surface roughness of the material Figures 6 and 7 show that the coefficient of friction differs greatly with difference in surface treatment of the same material. This is why we measured the degree of surface roughness of the materials, used as a parameter to observe its effects on the coefficient of friction (Figure 8). Both MS and Mk increase with increasing Jil A (/z: average wave height of surface roughness, A:average wave length of surface roughness) Stress V :1.5cm/s : MPa 0 :locm ' 0.3 CORRODED STEEL UNCOATED STEEL (UNCORRODED) COATED STEEL (INERTA160) CC) Stress : MPa V :n5cm/s 0 :locn y CORRODED STEEL ^ UNCOATED STEEL (UNCORRODED) ^COATED STEEL (INERTA160) Figure 6: Relation between A^ and T Figure 7: Relation between M, and T for various materials (1978) for various materials (1978) Figure 8: Relation between M and steepness of irregularities (hi X) These results indicate that Amontons' First Law (coefficient of friction is unaffected by contact area) and Second Law (coefficient of friction is unaffected by normal stress) also apply to sea ice and that the surface roughness of the material at contact area greatly affects the coefficient of friction of sea ice.

6 38 Contact Mechanics III 5. Discussion In this section, comparisons should be made between this experiment and other research concerning 1) normal stress and 2) relative velocity, and a conclusion should be drawn from the results of this experiment about 3) the evaluation of coefficient of friction. 1) Normal stress Table 1 summarizes the five experiments on the effect of the vertical load on the coefficient of friction of ice. These experiments can be roughly divided into two depending on the range of normal stress: experiments with o\ ^S 0.02 MPa (Oksanen (1980), Forland and Tatinclaux (1984), Arnold (1937)), and experiments with a ^ 1.00 MPa (Tabata and Tsushima (1979, 1981), present study). These experiments show that the coefficient of kinetic friction (ju.k) decreases with increasing normal stress and approaches a constant value, which means Amontons' First Law applies where the normal stress is high. 2) Relative velocity Table 2 summarizes the effect of the relative velocity. In the majority of tests, the coefficient of friction decreases with increasing relative velocity (Tabata and Tsushima (1979, 1981), Forland and Tatinclaux (1984)), or decreases before approaching a constant value (present study, Oksanen (1980)). Table 1: Summary of normal stress effects Author Oksanen (1 980) Forfand and Tatinclaux (1984) Arnold (1937) Tabata and (1979, Tsushima 1981) Present study M M, M* M, M* M, M* a, (/! JPa) aoomor,, < aoo/i a i 0.04 aoo; i a\ $ 0.02 aoojio».< 3 a /o 5 a. Mafena/ Sfee/, concrete, coatings, plastics Stainless steel Painted steel Metals, plastics, coatings Uncoated steel, coated steel, concrete Comment M* decreases w/m increasing a. M* decreases and approaches coristant for a, % aoo7 MPa P, decreases with Increasing Oy /ndependentof o. : Independent ot a, (decreases and approaches coristant for o, % 0.50 MPa

7 Contact Mechanics III 39 Table 2: Summary of relative velocity effects Author n v, (cm/s) Material Tabata and (1979, Metals, plastics Tsushima 1981) ^ 3.5*10* * V, t *20 coatings Foriand and Stainless steel, Tatinclaux (1984) ^* 5.0 iv^i 25.0 alminum, INERT* 160 Present PS,fudy ^ aw;y,i,,o Oksanen (1980) p* jaosy, sjcw Uncoated steel, coated steel. concrete Uncoated steel, coated steel, concrete Comments Pi decreases with increasing v, In majority of tests, p, decreases with increasing y, or is independent Pjand PiC/flcreases and approach constant for Vj i 3 cm/s uncoated steel, Vj i 30 cm/s - concrete ra-j'c Pi decreases and approaches constant with increasing v^ 3) Evaluation of the coefficient of friction Figure 9 shows the range of the coefficient of kinetic friction in our experiment for (a) corroded steel, (b) uncoated steel (uncorroded) and (c) concrete. The coefficient of friction of sea ice is affected by various factors. However, several years of experiments on the coefficient of kinetic friction have shown a certain range of Mk value for each construction material (Figure 9). Although the values have a wide range, they offer a broad index for actual implementation. So-ess: MPa V :i.5cmfc 0 :locm CORRODED STEEL Stress: MPa V :iacm& 0 :locm Stress : MPa V :1.5cnVs 0 :10cm (a) corroded steel T CO) (c) concrete Q (b) uncoated steel Figure 9: Obtained values of coefficient of kinetic friction between sea ice and (a) corroded steel, (b) uncoated steel, and (c) concrete as a function of ice temperature

8 40 Contact Mechanics HI References (1) Saeki, H., Ono, T., Nakazawa, N., Sakai, M. and Tanaka, S. (1986), "The Coefficient of Friction between Sea Ice and Materials Used in Offshore Structures", Journal of Energy Resource Technology, Transaction of The American Society of Mechanical Engineers, Vol. 108, (2) Oksanen, P. (1980), "Coefficient of Friction between Ice and Some Construction Materials, Plastics and Coatings," Laboratory of Structural Engineering, Report 7, Technical Research of Finland, Espoo, April, (3) Forland, K. A. and Tatinclaux, J. C. (1984), "Laboratory Investigation of the Kinetic Friction Coefficient of Ice", Proceedings, IAHR Ice Symposium, Hamburg, W. Germany, (4) Arnold-Alabieff, V. I. (1937), "The External Friction of Ice", Journal of Technical Physics, Vol. 7, No. 8, (5) Tabata, T. and Tsushima, K. (1979), "Friction Measurements of Sea Ice on Flat Plates Metals, Plastics and Coatings", Proceedings, Vol. 1, The 5th International Conference on Port and Ocean Engineering under Arctic Conditions (POAC 79), Trondheim, Norway, August 13-18, (6) Tabata, T. and Tsushima, K. (1981), "Friction Measurements of Sea Ice on Some Plastics and Coatings", Proceedings, Vol. 1, The 6th International Conference on Port and Ocean Engineering under Arctic Conditions (POAC 81), Quebec, Canada, July, 1981.