Laboratory Experiments And Distinct Element Method Research On Quasi-Static And Dynamic Mechanical Properties Of Ice

Engineering projects in cold regions inevitably face various forms of ice-induced threat,among which those involving static and dynamic ice mechanics are particularly prominent.Owning to the increasingly serious global ecological and environmental problems,the gradual transformation of the energy resource structure is in progress and marine development and utilization is into the new journey.As a result,more and more operations are being or going to be conducted in ice-covered waters and polar region,ice-related issues are becoming more and more common.As a basis for the study of ice mechanics,a comprehensive understanding of ice mechanical properties and their relationships with ice internal structure and external environmental conditions is of great significance,as it can help to improve the accuracy of ice force prediction,to prevent and alleviate damages of cold engineering projects from ice-related disasters,then to improve safety and reliability of cold-region engineering projects on the perspective of design and operation.Though a large number of experiments on ice mechanical properties have been carried out,they mainly focused in the quasi-static strain-rate range,systematic investigations on ice mechanical properties in the moderate and high strain-rate rage are rarely conducted.Customarily,we used to study ice dynamics issues with mechanical properties in the quasi-static strain-rate range,dynamic effects of material properties themselves were ignored.While,in fact,strain rates in some dynamic ice mechanics issues such as the interaction between floes and structure,breaking ice cover with icebreakers,blasting ice blocks for discharge,and hail ice attack,may go beyond the quasi-static strain rate.In addition,in the dynamic ice mechanics issues involving crack initiation and propagation,and ice fragmentation,relatively traditional numerical methods such as the finite element method are with limited abilities for these problems,new numerical methods are required.In view of the shortcomings in the study of ice mechanics,in present study,a series of physical experiments on ice mechanics,including ice quasi-static flexural test,uniaxial compression test and dynamic uniaxial compression test are carried out.Ice mechanical properties in the quasi-static and moderate strain-rate range were obtained,and their relationships with both internal and external influencing factors were investigated,as well as the corresponding failure modes and mechanisms.Numerical experiments of uniaxial compression test of ice under quasi-static and dynamic strain rates were conducted by using distinct particle-element method(DEM).The microscopic constitutive parameters of ice for DEM model were obtained at temperature of –5 °C and –10 °C,and a series of strain rates.Finally,simulation of a typical ice mechanics problem—ice-pier collision—was carried out by using DEM.The main innovations are summarized as follows:(1)For the first time,flexural experiments on river ice in freeze-up period was carried out,and ice flexural mechanical properties were obtained.It is of great importance to predict bearing capacity of ice cover in freeze-up period and to study the variation law of ice mechanics in the whole cycle.(2)Innovative measurement method for dynamic compression deformation and stress uniformity detection.Through making artificial speckles on the surface of ice specimen,the measurement of dynamic compression deformation of ice specimen is realized by digital speckles correlation method.By using upper and lower dynamic force sensors at the same time,detection and judgment of stress uniformity in loading direction under dynamic compression test are realized.Optimization methods on deformation measurement and load measurement effectively overcome difficulties encountered in ice compression test under middle strain-rate range;(3)Quasi-static and dynamic uniaxial compression mechanical properties of lake ice,and their dependences on temperature,strain rate,porosity and loading direction,are obtained,as well as the corresponding failure modes and mechanisms.This contributes to developing constitutive parameters of dynamic ice mechanics.(4)Numerical experiments on quasi-static and dynamic uniaxial compression of ice are carried out by using the flat-joint contact model.A series of microscopic parameters of ice in DEM model are obtained.(5)Carrying out discrete element method simulation on actual ice dynamics related issues,the applicability and effectiveness of DEM in modelling small and medium scale ice mechanics problem are commented.