Study On The Cracking Behavior Of Ice In Yellow River Based Upon Multi Scale Method

The ice disaster of the Yellow River is one of the most prominent and important natural disasters in China in winter and spring.Among them,the ice disaster of the Yellow River in Inner Mongolia reach has become the focus and difficulty of the flood control work.River ice is a kind of heterogeneous quasi-brittle material,which contains micro defects such as bubbles and impurities,and the physical and mechanical properties are complex and varied.The study on fracture properties and failure mechanism of river ice is of great important to grasp river ice.Therefore,The river ice in Inner Mongolia reach during the freezing period was taken as the research object.Considering the influence of mesoscopic components such as grain size and internal defects of the river ice,the fracture performance of the river ice was studied at multiple mesoscopic and macro scales to reveal the fracture mechanism of the Yellow River ice and provide scientific basis for break-up river forecast and ice flood disaster prevention and control.The main work contents and results are as follows:(1)Quantitative analysis of the microstructure characteristics of Yellow River ice.The river ice of the Yellow River in Inner Mongolia typical reach was chosen as research object.Combined with optical microscopy and image analysis technology,the microstructure experiments of the Yellow River ice of two years were carried out.The distribution law of the micro components of the river ice was analyzed,and the microstructure characteristics of Yellow River ice were clarified,the ice grain size,bubble impurity content and ice grain direction were extracted and quantified.(2)Experimental study on uniaxial compression mechanical properties and fracture properties of the Yellow River ice.The uniaxial compression strength test,Brazilian disc splitting test and three-point bending beam test of the Yellow River ice were carried out.The failure process and mechanical properties were studied in different crystal structures,temperatures,loading rates,loaded methods and sample size.The basic mechanical properties and change characteristics of the Yellow River ice were mastered.The relationship between different composition forms of river ice and its macro mechanical properties was analyzed.(3)Microscopic numerical analysis of the ice cracking process of the Yellow River.Based on the experimental results of the microstructure and basic mechanical properties of the Yellow River ice,the numerical calculation models of uniaxial compression,Brazilian disk splitting and three point bending fracture of the Yellow River were established with finite element method,which considering ice grains,ice boundaries and initial defects.The influenced factors of the ice fracture process were analyzed,and the cracked process of river ice was simulated under uniaxial compression,disc splitting and three-point bending beam.The fracture process of river ice was simulated and analyzed in different grain size,different ice sample size and different crack height ratio by Brazilian disk and three-point bending beam.The rationality and validity of the numerical model were verified.(4)The fracture performance study on the Yellow River ice based on multiple scales.The multi-scale numerical calculation model was established based on the regional decomposition method.The fracture performance of large-scale river ice was calculated and analyzed.Based on the theory of boundary effect,the size dependence of the fracture toughness of Yellow River ice material was analyzed,and the size independent material parameters of the fracture toughness of Yellow River ice were determined.