【作者】 张丽敏；

【导师】 李志军；

【作者基本信息】 大连理工大学 ， 港口、海岸及近海工程， 2012， 博士

【摘要】 冰荷载是寒冷区域水工和海洋结构物设计的控制荷载之一,也是冰管理中不可或缺的冰参数之一,其中冰的单轴压缩强度则是冰荷载计算的关键参数。但由于冰是一种受水文、气象等地理和环境条件所控制的性质较复杂的天然复合材料,所以其物理和力学性质也各有差异,并且科学工作者们试验所选取的冰样存在地域差异和试验研究方法的不同致使获得的结果也各不相同,所以采用人工冻结的方法来模拟天然冰是获取不同冰试样的有效手段；进一步开展冰单轴压缩强度以及不同因素对压缩强度的影响实验研究来充实已有的试验研究和理论研究是非常有必要的；研究不同类型冰的单轴压缩强度及其与影响因素之间的关系也是非常有意义的。利用低温环境实验室和动态水体冰生消模拟水槽,通过逐步控制降温幅度的冻结方法进行人工制备淡水冰。使用配置了高精度低温恒温试验箱的冰压力试验机,分别对人工冻结冰、现场取样的水库冰和海冰进行了单轴压缩强度试验研究。通过制备水平和垂直晶体薄片分析确定三种冰的晶体结构。同时采用等效圆直径的方法计算出相应的平均粒径尺寸,并得到了冰内气泡分布情况和随深度变化的气泡含量变化曲线,以及海冰盐度随深度呈现“C”型的变化趋势。利用试验数据,分别得到人工冻结冰、水库冰和海冰的应力-应变曲线,对应冰试样不同的变形形态,并给出冰破坏应力与破坏时间的关系曲线。通过试验观测发现冰试样主要存在鼓胀、剪切和劈裂的破坏形式,且对应的冰试样破坏现象各有差异。选取不同的温度和大范围内的应变速率作为条件进行试验,重点分析了应变速率、温度、平均粒径尺寸等不同因素对冰单轴压缩强度的影响。试验结果表明：人工冻结冰、水库冰和海冰均表现了明显的应变速率敏感性,存在着韧性区、韧脆过渡区和脆性区；冰单轴压缩强度与温度有着密切的关系,在相同的应变速率下,冰单轴压缩强度值随着冰温的降低而一直增大,且随着温度的降低,韧脆过渡区向低应变速率方向偏移。同时采用非线性方法拟合峰值压缩强度和温度的关系式,使其更符合冰温度接近冰点时,其强度接近零的物理事实。探讨了在试样尺寸相同的条件下,平均粒径尺寸变化对冰单轴压缩强度的影响,引入参数平均粒径尺寸/试样尺寸比(D/A),相同试样尺寸不同平均粒径尺寸下冰单轴压缩强度变化表明,在D/A<1.5的情况下,随着比值的减小,冰的单轴压缩强度增大。针对水库冰,在水平和垂直两种加载方向条件下,上层冰单轴压缩强度相同,体现了粒状冰各向同性的特性；下层冰由于同时存在粒状冰和柱状冰结构,加载方向对冰单轴压缩强度的影响表现不明显。将试验结果进行拟合,对于淡水冰,建立了单轴压缩强度与大范围应变速率和温度三者之间的统计关系式；对于海冰,建立了单轴压缩强度和大范围应变速率及与孔隙率之间的定量关系表达式。探讨了冰单轴压缩强度在工程中的应用。水库冰和海冰的峰值压缩强度结果分别与同区域的历史研究结果在同一范围内,因而在工程设计中,仍可取实测冰强度的峰值作为设计强度参考依据。在海冰管理中,利用已定型的渤海气象预报、海冰厚度预报和海冰漂移预报模式,在获得气温、水温、冰厚以及冰速等参数值的基础上,将单轴压缩强度的应用范围扩展到冰工程管理中,基于获得的冰单轴压缩强度与大范围应变速率和孔隙率之间的定量关系,建立了海冰荷载计算流程,并采用冰荷载预警指标反映出结构物所受的实时冰力的状态,为结构物的安全状态、正常生产作业及人员感受提供警示,为冰区结构物的安全运营的预警系统提供科学指导。更多还原

【Abstract】 In cold region, ice load is regarded as a control load in the design of hydraulic and offshore structures, and the compressive strength is a key parameter of ice load calculation. As a natural composite material, the properties of ice are very complicated by the influence of hydrological and meteorological conditions and environmental factor, so physical and mechanical properties of ice are also different. At the same time, due to regional differences of the tested objects and different testing methods, different research results, have acquired by scientists Therefore, artificial freezing method is an effective experimental means to simulate natural ice; it is essential that experiment studies of the uniaxial compressive strength and the effect of many factors on uniaxial compressive strength were conduced to enrich result and theory study; it is very significant to further study the relationship of compressive strength and influence factors for different type ice.In the low temperature laboratory, freshwater ice was prepared through the freezing method of decreasing temperature step by step in a dynamic water tank of ice growth and decay. A series of tests was conducted on artificial freshwater ice, reservoir ice and sea ice under uniaxial compression by an electronic universal machine equipped with a low temperature cabinet with high precision. Reservoir ice and sea ice were collected from the Hongqipao reservoir in the Heilongjiang Province and the Liaodong Bay respectively. The crystal structures for the artificial freshwater ice, reservoir ice and sea ice were analyzed through horizontal and vertical crystal thin sections of the ice. The corresponding average grain size was calculated by the method of the equivalent circle diameter; the bubble distribution in ice and bubble content curves with depth change were given; salinity of sea ice with different depth presented nearly "C" type change tendency.The stress-strain curves of the artificial freezing ice, reservoir ice and sea ice were respectively described through analysis of test data, and the different curves showed that the ice samples had the different deformation pattern. The corresponding damage stress and damage time relationship curve was presented, and the ice samples had mainly bulge failure, shear failure and split failure through the test observation. The corresponding failure phenomenon of the ice samples was different.Choosing different temperatures and wide range of strain rates as test conditions, and the effect of some factors such as temperature, strain rate, loading direction and average grain size of ice on the uniaxial compressive strength were analyzed. The test results show that:the artificial ice, reservoir ice and sea ice have significant strain rate sensitivity; there are ductile region, ductile to the brittle transition region and brittle region. Ice uniaxial compression strength and temperature have close relations, the uniaxial compression strength value of the ice decreases with increasing temperature under the same strain rate, and ductile to brittle transition region change with decreasing temperature. The relationship between the method peak compression strength and temperature was fitted using the nonlinear method, which meets more physical fact that ice strength is almost zero when the temperature of ice closes to freezing. The effect of average grain size on the uniaxial compressive strength is discussed under the same sample size condition, and ratio of average grain size and sample size (D/A) is introduced, the uniaxial compressive strength of ice increases with the decrease of (D/A) when D/A is less than1.5. For the reservoir ice, the uniaxial compressive of the upper layer ice is not influenced by the loading direction, which shows the isotropy property of granular ice; the effect of loading direction on the uniaxial compressive strength of the lower layer ice is not obvious due to existing simultaneously of granular ice and columnar ice. For freshwater ice, the statistical relationship between the uniaxial compressive, strain rate and temperature is established by fitted test data; for sea ice, the curved-surface relationship between the uniaxial compressive strength and porosity within a wide range of strain rate is described quantitatively.The application of the compressive strength of ice in engineering design is discussed, and the peak compressive strength of reservoir ice and sea ice and historical research results in the same areas is being within the same limit respectively. Therefore, the peak compressive strength is regarded as the design strength in engineering design. In ice management, uniaxial compressive strength of ice is introduced on the basis of acquired ice parameters including atmospheric temperature, water temperature, ice depth, ice speed and so on through established meteorological forecast, numerical study modes on sea ice depth and drift in Bohai Sea. Forecasting process of ice load for sea ice is established through the quantitative relationship among the uniaxial compressive strength, strain rate in wide range and porosity, and the alarming index of ice load is set to reflect the structure state under the action of ice load and to provide the alert for worked feeling, normal operation and safe operation of structures, and scientific guidance is provided for alariming system for safety operation of structures in ice region.更多还原