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On subsurface box-shaped lined tunnel under incident SH-wave propagation

《结构与土木工程前沿（英文）》 2021年第15卷第4期页码 948-960 doi: 10.1007/s11709-021-0740-x

摘要： In this paper, a half-plane time-domain boundary element method is applied to obtain the seismic ground response, including a subsurface box-shaped lined tunnel deployed in a linear homogenous elastic medium exposed to obliquely incident SH-waves. Only the boundary around the tunnel is required to be discretized. To prepare an appropriate model by quadratic elements, a double-node procedure is used to receive dual boundary fields at corners as well as change the direction of the normal vector. After encoding the method in a previously confirmed computer program, a numerical study is carried out to sensitize some effective parameters, including frequency content and incident wave angle for obtaining a surface response. The depth and impedance ratio of the lining are assumed to be unvaried. The responses are illustrated in the time and frequency domains as two/three-dimensional graphs. The results showed that subsurface openings with sharp corners distorted the propagation path of the anti-plane waves to achieve the critical states on the ground surface. The present approach can be proposed to civil engineers for preparing simple underground box-shaped models with angular boundaries.

关键词： box-lined tunnel half-plane BEM surface response SH-wave time-domain

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Subsurface damage pattern and formation mechanism of monocrystalline -GaO in grinding process

《机械工程前沿（英文）》 2022年第17卷第2期 doi: 10.1007/s11465-022-0677-3

摘要： Monocrystalline beta-phase gallium oxide (β-Ga₂O₃) is a promising ultrawide bandgap semiconductor material. However, the deformation mechanism in ultraprecision machining has not yet been revealed. The aim of this study is to investigate the damage pattern and formation mechanism of monocrystalline β-Ga₂O₃ in different grinding processes. Transmission electron microscopy was used to observe the subsurface damage in rough, fine, and ultrafine grinding processes. Nanocrystals and stacking faults existed in all three processes, dislocations and twins were observed in the rough and fine grinding processes, cracks were also observed in the rough grinding process, and amorphous phase were only present in the ultrafine grinding process. The subsurface damage thickness of the samples decreased with the reduction in the grit radius and the grit depth of cut. Subsurface damage models for grinding process were established on the basis of the grinding principle, revealing the mechanism of the mechanical effect of grits on the damage pattern. The formation of nanocrystals and amorphous phase was related to the grinding conditions and material characteristics. It is important to investigate the ultraprecision grinding process of monocrystalline β-Ga₂O₃. The results in this work are supposed to provide guidance for the damage control of monocrystalline β-Ga₂O₃ grinding process.

关键词： monocrystalline beta-phase gallium oxide grinding process subsurface damage nanocrystals amorphous phase

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Relationships between loading rates and nitrogen removal effectiveness in subsurface flow constructed

ZHANG Rongshe, LI Guanghe, ZHANG Xu, ZHOU Qi

《环境科学与工程前沿（英文）》 2008年第2卷第1期页码 89-93 doi: 10.1007/s11783-008-0002-3

摘要： Nitrogen removal of wetlands under 40 different inflow loadings were studied in the field during 15 months. The removal efficiency of four different sets of beds, namely the reed bed, the Zizania caduciflor bed, the mixing planting bed, and the control bed were studied. The outflow loading and total nitrogen (TN) removal rate of these beds under different inflow loadings and pollution loadings were investigated. The inflow loadings of 4 sub-surface flow systems (SFS) ranged from 400 to 8000 mg·(m·d), while outflow loadings were less than 7000 mg·(m·d). The results showed that the inflow and outflow loading of TN removal rate in SFS presented an obvious linear relationship. The optical inflow loading to run the system was between 2000 to 4000 mg·(m·d). Average removal rate was between 1062 and 2007 mg·(m·d). SFS with plant had a better removal rate than the control. TN removal rates of the reed and Zizania caduciflora bed were 63% and 27% higher than the control bed, respectively. The results regarding the TN absorption of plants indicated that the absorption amount was very limited, less than 5% of the total removal. It proved that plants clearly increase TN removal rates by improving the water flow, and increasing the biomass, as well as activities of microorganisms around the roots. The research provided a perspective for understanding the TN removal mechanism and design for SFS.

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Theoretical and experimental analysis on super precision grinding of monocrystal silicon

GUO Xiaoguang, GUO Dongming, KANG Renke, JIN Zhuji

《机械工程前沿（英文）》 2007年第2卷第2期页码 137-143 doi: 10.1007/s11465-007-0023-9

摘要： Through investigating the diamond-silicon grinding system, the grinding mechanism, including chip removal and subsurface damage, is discussed with the aid of the molecular dynamics (MD) approach and grinding experiments. Based on MD simulation, nanometric-grinding mechanism is analyzed from the viewpoint of instantaneous distribution of atoms, grinding force, and the potential energy between atoms and the profile of the groove. The simulation results show that some silicon atoms are deformed and piled up in front and on two sides of the abrasive surface because of the extrusion and cutting. When the energy in silicon lattice reaches its maximum value, the bonds of silicon atoms are broken and the material is removed. With the advancement of the abrasive, the silicon lattice under the abrasive surface is fractured, and then the amorphous layers are formed and propagated, which causes the subsurface damage. At the same time, some amorphous atoms are reconstructed and the degenerating layer of the machined surface is formed. Besides, the recovery of elatstic deformation occurs in the machined surface of the workpiece. In addition, the grinding experiment and profile detection with the aid of the measurment for 3D profiling are performed to verify the simulation results. The good agreement in the profile of the groove between the experimental value and the simulating value shows that MD simulation is very effective and reliable, and successful to fulfill the investigation on nanometric machining mechanism.

关键词： machining mechanism recovery advancement mechanism subsurface

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A review on ductile mode cutting of brittle materials

Elijah Kwabena ANTWI, Kui LIU, Hao WANG

《机械工程前沿（英文）》 2018年第13卷第2期页码 251-263 doi: 10.1007/s11465-018-0504-z

摘要：

Brittle materials have been widely employed for industrial applications due to their excellent mecha-nical, optical, physical and chemical properties. But obtaining smooth and damage-free surface on brittle materials by traditional machining methods like grinding, lapping and polishing is very costly and extremely time consuming. Ductile mode cutting is a very promising way to achieve high quality and crack-free surfaces of brittle materials. Thus the study of ductile mode cutting of brittle materials has been attracting more and more efforts. This paper provides an overview of ductile mode cutting of brittle materials including ductile nature and plasticity of brittle materials, cutting mechanism, cutting characteristics, molecular dynamic simulation, critical undeformed chip thickness, brittle-ductile transition, subsurface damage, as well as a detailed discussion of ductile mode cutting enhancement. It is believed that ductile mode cutting of brittle materials could be achieved when both crack-free and no subsurface damage are obtained simultaneously.

关键词： ductile mode cutting brittle materials critical undeformed chip thickness brittle-ductile transition subsurface damage molecular dynamic simulation

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Effects of taping on grinding quality of silicon wafers in backgrinding

Zhigang DONG, Qian ZHANG, Haijun LIU, Renke KANG, Shang GAO

《机械工程前沿（英文）》 2021年第16卷第3期页码 559-569 doi: 10.1007/s11465-020-0624-0

摘要： Taping is often used to protect patterned wafers and reduce fragmentation during backgrinding of silicon wafers. Grinding experiments using coarse and fine resin-bond diamond grinding wheels were performed on silicon wafers with tapes of different thicknesses to investigate the effects of taping on peak-to-valley (PV), surface roughness, and subsurface damage of silicon wafers after grinding. Results showed that taping in backgrinding could provide effective protection for ground wafers from breakage. However, the PV value, surface roughness, and subsurface damage of silicon wafers with taping deteriorated compared with those without taping although the deterioration extents were very limited. The PV value of silicon wafers with taping decreased with increasing mesh size of the grinding wheel and the final thickness. The surface roughness and subsurface damage of silicon wafers with taping decreased with increasing mesh size of grinding wheel but was not affected by removal thickness. We hope the experimental finding could help fully understand the role of taping in backgrinding.

关键词： taping silicon wafer backgrinding subsurface damage surface roughness