密度对各向同性冰雪应变率的影响

Effects of Ice and Snow Density on Minimum Isotropic Strain Rate

为了考察冰密度对最小应变率的影响,应用实验室制备冰和南极LawDome冰帽顶端附近的BHD冰芯进行了单轴压缩实验。当密度由0.66Mg/m^3增至0.80Mg/m^3时,最小应变率降低约一个数量级。密度超过0.83Mg/m^3时,最小应变率接近一恒定数值,该值与实验室制备冰(0.912Mg/m^3)的实验结果相吻合。当密度<0.912Mg/m^3时,为获得最小应变率所需要的总应变有所增加。当密度为0.66Mg/m^3时,为获得最小应变率所需要的总应变为6—8％。为得到最小应变率而付出的额外应变的一部分被用于试样的密实化。

Uniaxial compression tests were performed on laboratory prepared ice samples and core ice samples. The temperature for all tests was - 3.3C and the octahedral shear stress was 0.2 MPa. 23 samples were tested, 4 of them were of laboratory prepared isotropic ice, the remaining isotropic samples were cut from BHD core, drilled near the summit of Law Dome, Antarctica. The depths of the core samples ranged from 30 to 122 m, and the densities of them ranged from 0.66 to 0.89 Mg / m3.It was found that, minimum strain rate decreases with increase of density. In the density range 0.66 to 0.80 Mg/m3, the minimum strain rate decreased by about an order of magnitude. At densities higher than 0.80 Mg/m3 however, the rate of minimum strain rate decrease was lower. The minimum strain rate at the close-off density was within a factor of two of that for dense (0.912 Mg/m3) ice. Therefore the minimum strain rates approach a constant value at densities greater than 0.83 Mg / m3.A comparison was made with the previous studies and similarities were found at the same density ranges.Total axial strain at minimum strain rate is unaffected by sample density at values above the close-off density. This parameter for sample with lower density is density dependent, increasing to 6% to 8% for a sample with density of 0.66 Mg/m3. Some of this extra strain expended in attaining minimum strain rate is due to densification of the sample. The amount of densificaiton can be measured by the volume change in the sample.