In order to understand the dominant factors of the physical properties of ice in ice thermodynamics and mechanics,in-situ observations of ice growth and decay processes were carried out.Two samplings were conducted in the fast and steady ice growth stages.Ice pieces were used to observe ice crystals and gas bubbles in ice,and to measure the ice density.Vertical profiles of the type and size of ice crystals,shape and size of gas bubbles,and gas bubble content,as well as the ice density,were obtained.The results show that the upper layer of the ice pieces is granular ice and the lower layer is columnar ice;the average crystal size increases with the ice depth and remains steady in the fast and steady ice growth stages;the shape of gas bubbles in the upper layer of ice pieces is spherical with higher total content,and the shape in the middle and lower layers is cylinder with lower total content;the gas bubble size and content vary with the ice growth stage;and the ice density decreases with the increase of the gas bubble content.
In order to understand the sea ice types and its region of origin frozen in Weddell Sea,27 ice cores were taken from Weddell Sea,Antarctica during September and October,2006.Their crystals were analyzed,and their ice forming processes were evaluated based on the crystals.Photos of the thin sections from two whole ice cores,and from polygonal granular superimposed ice were taken as well as corresponding stratigraphy descriptions.Vertical profiles of salinity, density and grain size were also obtained.Based on ice core structural texture,the findings include that: 1) although large and smooth ice floes were selected as the investigation sites, the ice sheet at the sampling position may be formed by rafted ice,consolidated ice ridges and second-year ice which were affected by dynamic and thermodynamic processes together subsequently.Ice formed in pure thermal growth comprises minority.The polygonal granular superimposed ice from refrozen wetted dense snow is one type of the ice in Antarctica.2) Of the all 27 ice cores,the granular,mixed granular-columnar and columnar crystals in sea ice occupy 28.7%,14.4% and 55.2%,respectively.3) The pure thermal growth ice is predominant in marginal sea ice zone;the rafted ice and consolidated ice ridges,even second-year ice and polygonal granular superimposed ice from dynamic and thermal effects were found in front of Larsen A Ice Shelf;the thermal growth ice froze in the polynyas of Larsen A,and was transferred outwards.
Uniaxial compression experiments on horizontal and vertical samples of first-year freshwater ice in a res- ervoir were conducted at different temperatures and strain rates with an electronic universal machine equipped with low temperature cabinet. The results show that there is no difference between the strengths of two horizontal samples with grain sizes ranging from 1 to 4,mm and 4 to 14,mm, while the strength of the 1-4 mm vertical samples is 1.4 times higher than that of the 4-14 mm vertical samples because of the change of crystal structure. For different loading directions, the strengths of the horizontal samples do not differ from those of the vertical samples with the same grain sizes. The relation among the uniaxial compressive strength, strain rate and temperature was established through data analysis in both the ductile and brittle regions.
For the abnormal ice condition in 2009–2010 winter,sea ice samples were collected in a tide ditch outside a port in the east coast of Liaodong Bay,and ice specimens were prepared.Experimental study was carried out with a temperature-control precision of 0.1°C,and 117 columnar-grained ice specimens were loaded along the direction parallel to ice surface under different test temperatures(-4,-7,-10,-13,-16°C)and strain rates ranging from 10-6 to 10-2 s-1 within which the ductile region,ductile-brittle transition and brittle region are contained.The uniaxial compressive strengths,density and salinity of the ice specimens were measured.The results support the curved-surface relationship between the uniaxial compressive strength and porosity within a wide range of strain rate.The curved-surface relationship gives a quantitative description about the variations of the mechanical behavior transition point with ice porosity,and supplies a uniform mathematical representation of uniaxial compressive strength under different failure modes.Besides,it is deduced that abnormal ice condition in 2009–2010 winter will not result in a change of the uniaxial compressive strength of sea ice in Bohai Sea.
LI ZhiJunZHANG LiMinLU PengMatti LEPPARANTALI GuangWei
