| It has been proved that high pressure puled water jet (PWJ) is a kinds of powerfultool for hard-rock fragmentation due to its special loading styles of water hammerpressure，ultra-speed lateral jetting and pulse dynamic load etc., which can create shear,tensile and fatigue deformation of hard-rock. In mining industry, its good performanceon hard-rock fragmentation makes this technique become a potential method forsecond-breakage of large blocks created during mining and excavating process inhard-rock stratum. Among all types of PWJ generated by different method, interruptionand percussion PWJ have been considered as two of most potential ways to breakhard-rock due to its controllability on slug length and pulse frequency to enhance theerosion efficiency by reducing the effects of water cushion in the erosion hole. Theperformance of PWJ on hard-rock fragmentation is determined by the flow-fieldstructure of jets. So the essential information on flow-field structure should be obtainedbefore conducting the study on corresponding rock breaking mechanism. However,currently, it is hard to detect detailed flow-field information through pure theoretical andexperimental ways because of its high speed transient characteristic. As the complicatedconditions on mechanisms of coupling between impact water jet and rock, existingstudy achievements can’t more detailed analyze the effect of impact stress waves andpulsed stagnation pressure and so on. Consequently, by investigating the jet flow-fieldstructure and related rock breaking mechanism, important reference foundations can beachieved for developing PWJ technique on hard-rock fragmentation.In this thesis, first, the generation process and mechanism of percussion PWJ andinterruption PWJ were detailed investigated by experimental, theoretical and numericalmethods respectively. Secondly, the experiments on granite cube breaking under pulsedwater jet (PWJ) with different jet parameters settings were conducted to obtain therelationship between jet parameters and its performance on hard rock fragmentation. Atlast, based on the archived results, the analysis work on rock fragmentation mechanismunder PWJ also was carried out. The main achievements of this thesis are briefly listedbelow:①A differential model of percussion PWJ was established. The jet pressure and velocity can be expressed by geometry of generation device and operating parametersbased a multi-collision model of pistons. The computing results revealed the multi-pulsephenomenon. And the relationships between jet pressure and mass of pistons, diameterof chamber and length of accumulated water were achieved.②The main parameters of jet structure of the interrupted slug were derived. A2Dcoordinate of jet cut cross-sectional face was built. The relationships between thecutting area of jet, jet flow rate, energy of one slug and geometry of the slug and jetoperating parameters were obtained. By ideal assumption, the normal structure of theslug was predicted.③The multi-pulse phenomenon of percussion pulsed water jet and the deflectionof the sharp tail structure of interruption puled water jet were captured by using highspeed photography technique.④2D simulation model was built by defining the transient pressure inlet. Thismodel simulated the generation process of the mushroom shape nose of percussionpulsed jet.⑤3D dynamic modeling for disc interruption pulsed water jet generation processwas carried out. The simulated jet structure has a good agreement with the high speedimages taken with same operating settings. The flow filed study was focused on thesharp front tail which directly affects the impact pressure amplitude peak and duration.⑥The effects of jet diameter, slug length, frequency, power to erosion ability forhard rock were experimentally investigated. The results indicated: The larger jetdiameter, the larger erosion hole and higher the specific energy. The rate of slug lengthand gap length has apparent effect on erosion ability and an optimized value shouldexist.⑦The damage inside of granite cube and its distribution were obtained. Bydetecting ultrasonic speed change, the damage condition changes of the granite cube at4pair of measuring points were achieved and the trend of concentrating to diagonal lineof impacting surface was found.⑧The theoretical analysis was put on the mechanism of main contributions forhard-rock fragmentation under PWJ. The new concept of compound pulse stress fieldon the external part of the fracture was put forward. Two threshold value of compoundpulse stress for fracture propagating was achieved, name (?) and (?). |
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