Theoretical And Experimental Research On Rock Fragmentation Under Coupling Dynamic And Static Loads

Mechanical rock fragmentation is a continuous, efficient and safe technique exhibiting great superiority in mining, geotechnical engineering, etc. In order to enlarge application domain further, mechanical hard rock fragmentation is studied deeply all over the world with focus on fracture characteristics of rock and optimal loading forms in uni-static or uni-impact loads, but the questions on hard rock fragmentation under coupling static and dynamic loads and the corresponding experimental equipment with many fracturing patterns are still not solved. Thereby the theoretical analysis and experimental research on rock fragmentation under coupling static and dynamic loads are primarily set forward.Based on summing and analyzing the characteristics of rock fragmentation using uni-dynamic and uni-static loads, and applying the load-fracturing depth curve, the load-specific energy consumption curve and the mechanical analysis, the feasibility improving the rock fragmentation effects under coupling static and dynamic loads is discussed, and the idea for determining the reasonable dynamic/static is proposed. According to the damage-fracture characteristics of rock under coupled loading cutter, the relationship between crack initiation and propagation energies, accumulating damage and numbers of impact and the influence of different coupling loads on crack length and fragmented rock volume are explored, which founds the theoretical foundation on rock fragmentation under coupling dynamic and static loads.A multifunctional testing device for rock fragmentation under coupling static and dynamic loads is designed and developed, whose dynamic loading system can change the magnitude of impact energy, the impact frequency and the impact speed; whose static loading system can apply various vertical or horizontal loads. Different cutters can be set up on the cutter clamp separately or simultaneously. Advanced data-collecting system is used to measure and process experimental data. The successful design and manufacture of the system has important meaning for studying the characteristics and rules of rock fragmentation under various loading patterns.The testing parameters and schedules under coupling static and dynamic loads are determined, the fragmentation courses of rock experiencing vertical static pressure and horizontal cutting force, or vertical impacting and cutting force are analyzed, and the cutting models are established. Many kinds of tests on granite and concrete specimens are conducted by means of changing test parameters such asdynamic load, static load, and cutting parameters. The results show that fragmentation effects of rock under coupling dynamic and static loads have more obvious advantages than that of uni-impacting or uni-static pressure. The reasonable ratio of dynamic load to static load may make the specific energy consumption Es of rock fragmentation least and fracture effect optimal.While cutting fragmentation under coupled loading, the space between impacting points, cutting depth and the Es, etc mainly depend on the physical and mechanical properties of rock, and the magnitude of static stress and impacting energy. The ratio R of impacting space to cutting depth and the Es is shown in some form of distribution. The Es may reach minimum in a certain R range. The method to determine R^ at which Es reaches minimum is that firstly the peeled fragments are collected, then the ratio Rv of average length to average thickness of the fragments are calculated, and finally R^ =Rv/2 is taken.PDC cutters and YG15 cutters are designed and chosen for contrast tests. The results show that general failure modes of PDC cutters are brittle fracture and that of YG15 cutters are worn out. By applying the stress wave, bending wave and information entropy theories, the damage mechanism of cutters is analyzed. The amplitude and incidence angle of stress wave, clearance of interface between impacted rock and cutter and cyclic times of loading-unloading-loading resulted from stress waves transmission and reflection at the interfaces greatly affect the damage and fragmentation effects, the analyzing formulae of bending wave energy of cutter are established, and its calculation results are in accord with experimental results.During testing, the dynamic and static information concerning with the rock fragmentation are measured, it is found that the effects of rock fragmentation are closely relative to the information entropy and increasing information entropy can improve the effects of rock fragmentation, but damage greatly the cutter, thereby it is necessary to resolve the contradiction between improving fragmentation effects and reducing cutter s damage.In summary, rock fragmentation under coupling dynamic and static loads is a new fragmentation method with application foreground for hard and very hard rock. The study of this paper has theoretical significance of enriching rock fragmentation theory and engineering application values for developing a new drilling and mining machine.