scholarly journals The Influence of Confining Stresses on Rock Fragmentation, Thrust Force, and Penetration Energy in Sandstone Indentation Tests Using Disc Cutters

2021 ◽  
Vol 2021 ◽  
pp. 1-13
Author(s):  
Gaofeng Wang ◽  
Ting Ren ◽  
Gaolei Zhu
Keyword(s):  
Thrust Force ◽  
Coal Mines ◽  
Rock Fragmentation ◽  
Disc Cutter ◽  
Confining Stress ◽  
Disc Cutters ◽  
Underground Coal Mines ◽  
Indentation Tests ◽  
Boring Machines ◽  
Maximum Thrust

Hard rock Tunnel Boring Machines (TBMs) engaging disc cutters as cutting tools have been employed in considerable underground coal mines to accommodate the requirement of more stone drivage as operations are going deeper. This study conducted a set of disc cutter indentation tests to explore the influence of confining stresses on rock fragmentation, thrust force, and penetration energy on sandstone, which is commonly encountered in underground coal mines. The test results show that there exists a critical confining stress, under which the maximum thrust force and penetration energy keep increasing with confining stress mounting while the maximum thrust force and penetration energy will decrease or flatten if it is surpassed. By combining with previous studies and comparing the critical confining stress values to the rock mechanical properties’ values, the critical value is most likely to be of cohesion. For subsurface rock fragmentation, the Constant Cross Section (CCS) disc cutter indentation has denser cracks and their orientations are more lateral than those under the V shape one; the V shape disc cutter indentation is less sensitive to confining stresses, with no notable increase of crack number and crack reorientation with increasing confinement. Thus, the CCS disc cutter is more favorable than the V shape one from the perspective of rock fragmentation under confining stresses.

scholarly journals The Effects of Confining Stress on Rock Fragmentation by TBM Disc Cutters

2019 ◽  
Vol 2019 ◽  
pp. 1-13
Author(s):  
S. F. Zhai ◽  
S. H. Cao ◽  
M. Gao ◽  
Y. Feng
Keyword(s):  
Confining Pressure ◽  
Numerical Results ◽  
Rock Fragmentation ◽  
Disc Cutter ◽  
Confining Stress ◽  
Disc Cutters ◽  
Initiation And Propagation ◽  
Maximum Angle ◽  
Indentation Tests ◽  
Crushed Zone

In this paper, General Particle Dynamics (GPD3D) is developed to simulate rock fragmentation by TBM disc cutters under different confining stress. The processes of rock fragmentation without confining pressure by one disc cutter and two disc cutters are investigated using GPD3D. The crushed zone, initiation and propagation of cracks, and the chipping of rocks obtained from the proposed method are in good agreement with those obtained from the previous experimental and numerical results. The effects of different confining pressure on rock fragmentation are investigated using GPD3D. It is found that the crack initiation forces significantly increase as the confining stress increases, while the maximum angle of cracks decreases as the confining stress increases. The numerical results obtained from the proposed method agree well with those in previous indentation tests. Moreover, the effects of equivalent confining stress on rock fragmentation are studied using GPD3D, and it is found that rock fragmentation becomes easier when the equivalent confining stress is equal to 15MPa.

scholarly journals Mechanical and Acoustic Emission Responses of Rock Fragmentation under Disc Cutter Penetration

2021 ◽  
Vol 2021 ◽  
pp. 1-17
Author(s):  
Qi Liu ◽  
Yucong Pan ◽  
Penghai Deng
Keyword(s):  
Acoustic Emission ◽  
Damage Zone ◽  
Three Dimensional ◽  
Rock Fragmentation ◽  
Disc Cutter ◽  
Rock Damage ◽  
Rock Types ◽  
Penetration Ability ◽  
Indentation Tests ◽  
Spatio Temporal

To better understand the rock fragmentation mechanism and optimize cutter design and selection for rock excavation by TBM, a set of three-dimensional indentation tests was conducted with different rock and cutter types. Acoustic emission (AE) monitoring technique was employed to capture the information of the rock damage evolution real-timely. It is found that the penetration by using the constant cross section (CCS) cutter tends to induce inconspicuous rock chips formation before the sudden occurrence of the macrocrack, but that by using the V-type cutter tends to induce gradual rock fragmentation accompanied by the multiple local rock chips formation and the sawtooth force-penetration curve. Meanwhile, rock fragmentation models for CCS and V-type cutters were compared, and the spatio-temporal evolution of AE events was quantitatively analyzed to reflect the rock damage zone development process. Results indicate that the V-type cutter has greater penetration ability and the CCS cutter can cause larger unit damage zone radius. Microscopic observation by using the scanning electron microscope (SEM) reveals that the fracture mechanism for the crushed zone of rock is mainly shear type and that for the major crack is tensile type. It does not matter with rock types or cutter types.

Research on the Optimal Disc Cutter Spacing for Rock-Breaking Based on ANSYS

2014 ◽  
Vol 664 ◽  
pp. 143-147
Author(s):  
Yan Li ◽  
Ke Zhang ◽  
Jian Sun ◽  
Hong Sun ◽  
Zi Nan Wang
Keyword(s):  
Finite Element ◽  
Rock Breaking ◽  
Rock Fragmentation ◽  
Cutting Process ◽  
Disc Cutter ◽  
Rock Stress ◽  
Fragmentation Efficiency ◽  
Finite Element Software ◽  
Disc Cutters ◽  
Cutter Spacing

Objective: To study the influence of disc cutter spacing on rock fragmentation efficiency and optimize cutter layout and improve the efficiency of disc cutter. Method: ANSYS, a finite element software was used to simulate double disc cutter cutting process. Result: Find a good corresponding relationship between penetration and cutter spacing. At the process of sandstone, if disc cutter spacing as 54 ~ 55 mm, rock crushing as the largest and rock fragmentation efficiency is the highest; with the penetration of 10 mm. If disc cutter spacing as 66~68.5mm, rock crushing as the largest and rock fragmentation efficiency is the highest with the penetration of 15 mm. Changing the cutter spacing and penetration, rock stress and broken degree will also change. Conclusion: Double disc cutters change within the range of best cutter spacing, cutter spacing is proportional to the rock crushing. If the cutter distance is greater than the best cutter spacing, the ledge will be appeared. For one type of rocks, the penetration would have some effects on the optimal cutter spacing. If the penetration increases, the optimal cutter spacing increases gradually, at the time of other construction parameters unchanged.

scholarly journals Evaluating the Efficiency of a New Cutterhead Design to Counteract the Drawbacks of Excavation through Very Hard Rocks

2021 ◽  
Author(s):  
Roohollah Narimani Dehnavi ◽  
Masoud Sadeghi ◽  
Nikolaus August Sifferlinger ◽  
Rohola Hasanpour
Keyword(s):  
Disc Cutter ◽  
Geological Condition ◽  
Cutting Efficiency ◽  
Main Bearing ◽  
Disc Cutters ◽  
Water Conveyance ◽  
Boring Machines ◽  
Kerman Water ◽  
Main Components ◽  
Rock Tunnel

AbstractThe application of appropriate excavation equipment in difficult grounds is of crucial importance and consequently improves the performance of hard rock Tunnel Boring Machines (TBMs). The cutterhead is one of the main components of TBMs which is directly involved in the excavation process, and its design can highly affect the cutting efficiency, the overall balance of the head, the performance of main bearing in long term, and the wear of the whole cutting face and muck buckets. This paper mainly focuses on the significant role of a proper design on the cutting efficiency with reference to a TBM tunneling project. Due to existence of very hard and abrasive rocks on the path of Kerman water conveyance tunnel, a new cutterhead was designed to be applied on a second hand TBM. The new cutterhead contains larger 19-inch disc cutters with a new disc cutter layout. Since the new cutterhead was launched following the excavation of the old one in a specific chainage of the tunnel, the performance of the two cutterheads in pyroclastic rocks could be compared with respect to the cutting efficiency, and lower specific energy values were observed for the new cutterhead which is the indicator of a better cutting efficiency in this geological condition.

scholarly journals Effect of Twist Drill Geometry and Drilling Parameters on Hole Quality in Single-Shot Drilling of CFRP/Al7075-T6 Composite Stack

2021 ◽  
Vol 5 (7) ◽  
pp. 189
Author(s):  
Muhammad Hafiz Hassan ◽  
Jamaluddin Abdullah ◽  
Gérald Franz ◽  
Chim Yi Shen ◽  
Reza Mahmoodian
Keyword(s):  
Feed Rate ◽  
Thrust Force ◽  
Critical Dimension ◽  
Helix Angle ◽  
Single Shot ◽  
Twist Drill ◽  
Hole Quality ◽  
Drilling Parameters ◽  
Industry Practice ◽  
Maximum Thrust

Drilling two different materials in a layer, or stack-up, is being practiced widely in the aerospace industry to minimize critical dimension mismatch and error in the subsequent assembly process, but the compatibility of the drill to compensate the widely differing properties of composite is still a major challenge to the industry. In this paper, the effect of customized twist drill geometry and drilling parameters are being investigated based on the thrust force signature generated during the drilling of CFRP/Al7075-T6. Based on ANOVA, it is found that the maximum thrust force for both CFRP and Al7075-T6 are highly dependent on the feed rate. Through the analysis of maximum thrust force, supported by hole diameter error, hole surface roughness, and chip formation, it is found that the optimum tool parameters selection includes a helix angle of 30°, primary clearance angle of 6°, point angle of 130°, chisel edge angle of 30°, speed of 2600 rev/min and feed rate of 0.05 mm/rev. The optimum parameters obtained in this study are benchmarked against existing industry practice of the capability to produce higher hole quality and efficiency, which is set at 2600 rev/min for speed and 0.1 mm/rev for feed rate.

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