| As the largest developoing country in the world, the sustainable and healthy development of national economy of China will depend on the extraction and utilization of mineral resources for a long time. As the primary energy of industrial construction in China, the exploitation and consumption of coal increase higher and higher, and the mining depth grows deeper and deeper. The mining depth of main coals in our country have entered into 1000 m currently, however, the nonlinear damage of surrounding rocks have also been encountered more and more in the process of tunneling and mining. Represented by rockburst, embrassing characteristics of non-indication, short process, huge destructive and so on, these phenomena pose serious threat and hidden trouble to the security of people and property. Because of complex and difficult to observe, therefore we need to take maximum preventive measures in the tunnels and working faces before the large deformation disaster happens.As an effective kind of supporting methods, bolts supporting have the advantages of lower costs, less manpower and simple to use which have been widely applied to support coals and non-ferrous metal mines all over the world. The availability of bolt supporting depends on the main mechanical parameters, such as resistance and deformation. Traditional bolt are often not well suited for deep defomation damage and failed in the supporting process because of own structural defects, and the bolt support technology based on traditional material faces on bottlenecks undergoes a long time development. Therefore it is appeared imminent by researching new supporting material or structure of unique property, establishing exclusively constitutive relation of complex rocks and developing specific theory of supporting system in deep large deformation of surrounding rocks.Prof. Manchao He proposed concepts and scientific problems of negative Possion’s ration structure and material and relevant mechanical behavior in the field of rock mechanics and the scale of 10-2~10m firstly, and developed constant resistance and large deformation(CRLD) bolt with unique negative Possion’ ratio(named NPR bolt in this thesis) based on anti-impacting control concept of CRLD in 2011. Currently, the NPR bolt has been already performed a big number of indoor and outdoor experiments and practical engineering application, not only proving its superiorities, but also achieveing favorable effects for investigating and practicing the stability control technology of surrounding rocks and relevant supporting measures. However, unlike the static and quasi-static environment, structure and inertia effect are always influenced by dynamic response characteristic of material under dynamic loading environment. It means that it is still unknown that NPR bolt render unique NPR effect by the structure deformation under dynamic impacting.Aiming at the critical issue of the impacting and elongation mechanical properties under dynamic impacting, this thesis emphasizes integration of theory and practice and unity of experiment and simulation by using principle analysis, theory derivation, inner experiment and finite element analysis methods. Each part of content and conclusion of this thesis are as follows:Introducing the anti-impacting control concept of CRLD which means that the CRLD material can resist the residual external loading relying on its own material or structure properties, avoid broken or fracture failure,absorb deformation energy of surrounding rocks and make supporting system achieveing new energy balance. Introducing the concept of the NPR bolt and NPR rock, and the constitutice relations and supporting principles. Then introducing the rheological mechanic model, analytical model and the ideal elastic-plastic constitutice relation which can make possibility of quantitative design of complex rockbody. Introducing the conclusion of “whatever the engineering geological structure looks like, the surrounding rock will have the same constitutive relation with the NPR material afer embedding the NPR supporting”.In order to analyze and study the dynamic mechanical properties of NPR bolt, Prof. He developed the impacting and elongation experiment system for NPR bolt based on traditional SHPB device. This thesis introduce the theoretical assumptions and noticeable problems of SHPB experiment system.Then expositing and discussing the system compositon, component parameters and rationality of the new NPR bolt system. Using this new system, conducting several dynamic experiments for single bolt and double bolts separately. After introducing the specimen parameters, experimental preparation and experimental method in detail, analysis the phenomenon in the experimental course scientificly.Analysis the changing situation of mechanic parameters of NPR bolt specimens, such as expansion, elongation and impacting force. The experimental results show that the the convex and concave of thread pipe become expansive and thick and the concave deformation is significantly higher than convex when the constant resistance device get extension under impacting process. The average exponsion is about 1.58 mm. The final elongation of NPR bolt is defined as the length of bar when it dashed out from the constant resistance sleeve pipe, and the average ultimate elongation of this batch of NPR bolts is up to 450 mm and the average equivalent negative Possion’ ratio value is about-0.15 after calculation. The impacting force of NPR bolt withstanded is directly propotional to the increasing of gas pressure, meanwhile, the energy absorbing value of NPR bolt is proportional to different gas pressure and external loading and the anti-transformation ability of per extension unit of NPR bolt is up to the energy absorbing value. By comparing and analysis the results of the expansion, elongation and impacting force, the experiment verify the favourable adaptability and unique NPR effect of NPR bolt under dynamic impacting.By conducting finite element method(FEM) analysis of the new NPR bolt experiment system, the FEM can verify the reliability of the experimental results, and provide visual guide for the material or structure amelioration of NPR bolt. The dissertation introduce the advantages and disadvantages of main softwares in finite element analysis, numerical simulate the indoor experiment according the sequence of geometrical model establishing, pre-processing and calculating by using CAD/CAE software interation method. Among them, the simplified modeling criterion and optimization solutions in the 3D solid model and the meshing method and relevant parameters desiganation in the pre-processing are described and explained in detail.The FEM results of 12m/s initial velocity of bullet show that it is an elastic-plastic transformation process by the squeezing process of the concave and its adjacent units of thread pipe in the expansion analysis, the axis elongation of the NPR bolt has the similar phenomenon of “elastic backing” with the experiment result in the elongation analysis and the force-time curve obtain the same trend and value by equivalent conversing of stress and force in the impacting force analysis. The FEM results of different initial velocities of bullet show that NPR bolt model can generate obvious axis elongation only if the bullet velocity make the pipe expansion achieve maximum value. The above conclusions show that the FEM results are matched with the experiment ones and verify the rationality and feasibility of combining both methods.To sum up, the thesis verify the favourable dynamic mechanic properties and unique NPR effect of NPR bolt under dynamic impacting by indoor experiment and numerial simulation. By combining and synthesizing the FEM and experiment method, we can perform comparable type-electing and parameters-ameliorating of NPR bolt under differenet demands and conditions reasonably and efficiently which has positive effects for sustainable exploitation and safe production in coals and significant social and economic effectiveness. |
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