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Rock cutting methods for disc cutters with coupled static--dynamic loads and static loads are explored and compared through rock breaking experiments to improve the TBM excavation efficiency. Results indicate that the rock breaking characteristics, including rock debris, cutting force, and rock breaking efficiency, significantly varies with different cutting methods. The average size of rock fragmentation produced under coupled static--dynamic loads is 1.6 times larger than that under static loads. The cutting forces of disc cutter under the coupled static--dynamic loads are larger than those under static loads when the cutting depth (h) is lower than 4 mm, whereas is contrary when h exceeds 4 mm. The specific energy of disc cutter under the coupled static--dynamic load is approximately 1.5 times smaller than that under the static load, indicating the cutting method with the coupled static--dynamic load can significantly improve the cutting performance. There is an optimal cutter spacing (S) for the cutter under each cutting method. The optimal S under the coupled static--dynamic loads is larger than that with static loads. This study provides new insights into improving the tunneling efficiency in high-strength rock conditions. [ABSTRACT FROM AUTHOR]

The Tunnel Boring Machine (TBM) tunneling process always contains a certain degree of vibrations due to the step broken phenomenon of the cutting tools. Undoubtedly, there is a quite difference in the fragment characteristics which are related to the construction efficiency of TBM under the static load and the combination of static and impact load. In this study, a series of rock breaking tests with a 216 mm diameter disc cutter and marble samples were conducted under different load cases. Based on the Rosin-Rammler distribution curve, the fragments from the cutting tests were also sieved to calculate the absolute size constant (x') and coarseness index (CI). The relationship between coarseness index, absolute size parameter and the cutting parameters, specific energy, production rate was evaluated. The results show that there is an increasing trend of x' and CI with the increase of cut spacing and penetration as well as adding impact load component. An overall downtrend in specific energy and upward trend in production rate which are associated with the high efficiency can be observed with the increasing CI and x'. It is believed that the conclusions are of great significance for improving TBM construction efficiency and cutterhead design. [ABSTRACT FROM AUTHOR]

Interactive erosion and cavitation wear widely exist in engineering. Based on the principle of orthogonal experiment, flow pressure, erosion angle, and rotational speed are selected for the interactive erosion and cavitation wear experiment on plastic material 40Cr, 45 steel, and brittle material HT200 using the L9 (3x4) orthogonal experiment table. The wear loss and the SEM (scanning electron microscope) photo of the specimen are also analysed. The result shows that the main factors that influence interactive erosion and cavitation wear loss are flow pressure, erosion angle, and rotational speed from primary to secondary. For 40Cr and 45 steel, the difference in the R value between the three factors is small. For HT200, the R value of pressure on interactive wear is the highest, which is signifi- cantly different from the R value of rotational speed. Under the same rotational speed, erosion angle, flow pressure, and other environmental factors, cavitation caused by pressure is the major wear form for brittle materials with smaller elongation. The impact strength of micro-bubble collapse can easily reach its fatigue strength. Materials peel off in patches under repeated impacts of micro-bubble collapse and sand grains, which aggravates the degree of interactive wear. The anti-cavitation capacity of the plastic materials with large elongation is strong, with erosion wear, to a lesser degree. [ABSTRACT FROM AUTHOR]

The pre-cutting machine is becoming valued due to its ability to effectively prevent surface settlement and reduce vibration in tunnel construction. To obtain the cutting characteristics and layout of pre-cutting machine cutter, the cutting tests by the pre-cutting machine cutter are conducted and the cutting laws are also studied. The research results show that the cutting force rather than normal force and side force is responsible for the rock breaking. With the increase of the cutting depth and cutting spacing, the cutting forces increase generally. But for the little value of cutting spacing, the cutting force can not increase continuously when the cutting depth increase to a relatively large value. Furthermore, for a given cutting depth, the cutting force will keep at an approximate constant rather than continuous increase with the increase of the cutting spacing when the cutting spacing increases to a relatively large value. The specific energy decreases nonlinearly with the increase of cutting depth and the decrease of specific energy is not significant when the cutting depth is more than 12 mm. Moreover, there exists an optimal cutting spacing for a given cutting depth. To maintain a desirable cutting efficiency, the ratio of cutting spacing to cutting depth should be controlled between 1 and 2. Finally, the layout plan of the pre-cutting machine cutter is proposed based on the research results and is applied in the actual manufacturing of the pre-cutting machine. [ABSTRACT FROM AUTHOR]

One of the key points in numerical simulation of coal-rock cutting by conical picks is to select a proper coal-rock constitutive model. In order to find a reasonable coal-rock constitutive model, a uniaxial compression test was conducted to obtain the constitutive model. The several stages for linear elastic deformation and creep, plastic yielding, hardening, and finally brittle cracking of the constitutive units were studied, and the coal-rock constitutive model was established. As a result, the coal-rock cutting by one conical pick or two conical picks was simulated and the results were compared with coal-rock cutting experiment on a Coal-rock Cutting Machine. According to the simulation and experimental results, it is believed that the numerical simulation can reveal coal-rock crushing process. And the total error rate of coal-rock cutting by one conical pick between the simulation and experiment is 8.5%. The maximum deviation of coal-rock cutting by two conical picks between the simulation and experiment is 9.8%. All simulation values are within a reasonable range. The comparison indicates that the coal-rock constitutive model should better be defined considering the coal-rock crushing process by conical picks. [ABSTRACT FROM AUTHOR]

• Wear experiments of the scaling cutter ring and the rock were carried out on a self-developed experimental platform. • Comparison of wear behavior of commonly used TBM cutter ring materials under granite conditions. • Under the condition that the hardness of the cutter ring is the same, analyze the effect of microstructure composition on the wear resistance of the cutter ring. The wear failure of disc cutter rings is a crucial factor affecting the efficiency of TBM construction. At present, many tool manufacturers improve the content of the elements of the cutter ring material to improve its wear resistance and reduce the number of cutter changes. However, the enhancement of wear resistance by adjusting the elemental content in the cutter ring material relies mainly on experience, and the results can only be verified by improvements in macroscopic properties such as hardness and toughness. In contrast, the reason for the wear resistance improvement is unclear. Therefore, this study carried out scaled-down cutter ring and rock wear experiments, compares the wear behavior of the modified cutter ring material based on H13 steel, and analyzes the reasons for the improved wear resistance of the modified material by metallography and XRD. The result is obtained as follows: (1) Ni-H13 and H418E have better wear resistance than Modified H13, H418E has better abrasion resistance with a 34.9 % reduction in wear rate. (2) The wear mechanisms of Ni-H13 and H418E cutter ring samples were both micro-cutting and furrow wear. A few microscopic fracture wear mechanisms appeared in the Ni-H13 cutter ring. (3) The increased carbide content in H418E and its more refined and uniform tissue distribution are the main reasons for its excellent wear resistance. At the same time, the powder smelting material did not significantly improve the wear resistance of the cutter ring. [ABSTRACT FROM AUTHOR]

To explore the rock-breaking characteristics of cutting hard rock under free-face condition by tunnel boring machine (TBM) hob and obtain the optimum free-face condition, the rock-breaking processes such as crack propagation, amount of micro crack and reaction force with penetration depth are first investigated based on discrete element simulation method. Then, the crack length, rock chip area, specific energy consumption etc. with different free-face spacing (S) and free-face height (H) are studied combined with rockcutting simulation and experiment. The research results show that the formation of the rock chip under free-face condition by TBM hob is driven by tensile failure, and it exists an optimum free-face condition with the S of 80 mm and the H of 200 mm to promote main crack propagation and enhance the rock-cutting efficiency, which can provide a reference for the application of rock-breaking technology under the free-face. [ABSTRACT FROM AUTHOR]