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Advances in molecular dynamics simulation of ultra-precision machining of hard and brittle materials

Xiaoguang GUO,Qiang LI,Tao LIU,Renke KANG,Zhuji JIN,Dongming GUO

《机械工程前沿（英文）》 2017年第12卷第1期页码 89-98 doi: 10.1007/s11465-017-0412-7

摘要：

Hard and brittle materials, such as silicon, SiC, and optical glasses, are widely used in aerospace, military, integrated circuit, and other fields because of their excellent physical and chemical properties. However, these materials display poor machinability because of their hard and brittle properties. Damages such as surface micro-crack and subsurface damage often occur during machining of hard and brittle materials. Ultra-precision machining is widely used in processing hard and brittle materials to obtain nanoscale machining quality. However, the theoretical mechanism underlying this method remains unclear. This paper provides a review of present research on the molecular dynamics simulation of ultra-precision machining of hard and brittle materials. The future trends in this field are also discussed.

关键词： MD simulation ultra-precision machining hard and brittle materials machining mechanism review

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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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Crystalline mesoporous transition metal oxides: hard-templating synthesis and application in environmental

Zhen MA, Bei ZHOU, Yu REN

《环境科学与工程前沿（英文）》 2013年第7卷第3期页码 341-355 doi: 10.1007/s11783-012-0472-1

摘要： Mesoporous silicas such as MCM-41 and SBA-15 possess high surface areas, ordered nanopores, and excellent thermal stability, and have been often used as catalyst supports. Although mesoporous metal oxides have lower surface areas compared to mesoporous silicas, they generally have more diversified functionalities. Mesoporous metal oxides can be synthesized via a soft-templating or hard-templating approach, and these materials have recently found some applications in environmental catalysis, such as CO oxidation, N O decomposition, and elimination of organic pollutants. In this review, we summarize the synthesis of mesoporous transition metal oxides using mesoporous silicas as hard templates, highlight the application of these materials in environmental catalysis, and furnish some prospects for future development.

关键词： mesoporous materials silica metal oxide hard-templating environmental catalysis

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A concise review about fracture assessments of brittle solids with V-notches

Hsien-Yang YEH, Bin YANG

《结构与土木工程前沿（英文）》 2019年第13卷第2期页码 478-485 doi: 10.1007/s11709-019-0520-z

摘要：

A concise review of recent studies about the fracture assessments of elastic brittle solid materials containing V-notches is presented. In this preliminary and brief survey, elastic stress distributions in V-notched solids are discussed first. The concept of notch stress intensity factor is introduced. Combine the digital image correlation method with numerical computation techniques to analyze the stress distribution near the notches. Fracture criteria such as strain energy density, J-integral, theory of critical distance are used.

关键词： fracture assessment brittle solids V-notches review

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A FEniCS implementation of the phase field method for quasi-static brittle fracture

HIRSHIKESH, Sundararajan NATARAJAN, Ratna Kumar ANNABATTULA

《结构与土木工程前沿（英文）》 2019年第13卷第2期页码 380-396 doi: 10.1007/s11709-018-0471-9

摘要： In the recent years, the phase field method for simulating fracture problems has received considerable attention. This is due to the salient features of the method: 1) it can be incorporated into any conventional finite element software; 2) has a scalar damage variable is used to represent the discontinuous surface implicitly and 3) the crack initiation and subsequent propagation and branching are treated with less complexity. Within this framework, the linear momentum equations are coupled with the diffusion type equation, which describes the evolution of the damage variable. The coupled nonlinear system of partial differential equations are solved in a ‘staggered’ approach. The present work discusses the implementation of the phase field method for brittle fracture within the open-source finite element software, FEniCS. The FEniCS provides a framework for the automated solutions of the partial differential equations. The details of the implementation which forms the core of the analysis are presented. The implementation is validated by solving a few benchmark problems and comparing the results with the open literature.

关键词： phase field method FEniCS brittle fracture crack propagation variational theory of fracture

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Research progress on ultra-precision machining technologies for soft-brittle crystal materials

Hang GAO,Xu WANG,Dongming GUO,Yuchuan CHEN

《机械工程前沿（英文）》 2017年第12卷第1期页码 77-88 doi: 10.1007/s11465-017-0411-8

摘要：

Soft-brittle crystal materials are widely used in many fields, especially optics and microelectronics. However, these materials are difficult to machine through traditional machining methods because of their brittle, soft, and anisotropic nature. In this article, the characteristics and machining difficulties of soft-brittle and crystals are presented. Moreover, the latest research progress of novel machining technologies and their applications for soft-brittle crystals are introduced by using some representative materials (e.g., potassium dihydrogen phosphate (KDP), cadmium zinc telluride (CZT)) as examples. This article reviews the research progress of soft-brittle crystals processing.

关键词： brittle soft functional crystal ultra-precision machining

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Analysis of load and adaptability of disc cutters during shield tunneling in soft–hard varied strata

《结构与土木工程前沿（英文）》 2023年第17卷第4期页码 533-545 doi: 10.1007/s11709-023-0946-1

摘要： The disc cutters of shield machines exhibit unsatisfactory adaptability and performance during the soft–hard varied strata tunneling process. To analyze the rotation state, cutting performance, and adaptability of disc cutters during shield tunneling in soft–hard varied strata, the Holmquist Johnson Cook and Federal Highway Administration constitutive models are introduced to numerically simulate the failure process of materials on the excavation face and to calculate the load of disc cutters. Additionally, the parameters of the models are modified based on laboratory disc cutter excavation test results. The results of numerical calculation can reflect the load level and the behavior of the disc cutters during operation. The tangential loads of the disc cutters during the cutting of four typical soft-strata excavation face models are numerically calculated, thus providing reference values for the starting torque of the disc cutters. A greater penetration is suggested for soft-strata tunneling to allow the disc cutters to rotate smoothly and continuously as well as to guarantee a better cutting effect. The disc cutters in the center of the cutterhead should be specified with a lower starting torque to prevent uneven wear, rotation stagnation, cutterhead clogging, and other adverse phenomena.

关键词： shield tunneling disc cutter load laboratory excavation test numerical calculation soft–hard varied strata

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浅埋深两硬条件下特厚煤层综放开采技术

张忠温,吴吉南

《中国工程科学》 2011年第13卷第11期页码 107-112

摘要：

针对平朔矿区4号煤层条件，采用理论分析方法研究了浅埋深两硬条件下4号煤层顶煤的冒放性及合理采煤方法。以提高顶煤冒放性为目标，采用数值模拟的方法进行了综放工作面参数及设备选型配套研究。实践表明，浅埋深两硬煤层条件下通过加大综放工作面长度与割煤高度，可以实现安全、高效、高回收率开采。

关键词：浅埋深两硬煤层顶煤冒放性大采高综放

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Primary cilia in hard tissue development and diseases

《医学前沿（英文）》 2021年第15卷第5期页码 657-678 doi: 10.1007/s11684-021-0829-6

摘要： Bone and teeth are hard tissues. Hard tissue diseases have a serious effect on human survival and quality of life. Primary cilia are protrusions on the surfaces of cells. As antennas, they are distributed on the membrane surfaces of almost all mammalian cell types and participate in the development of organs and the maintenance of homeostasis. Mutations in cilium-related genes result in a variety of developmental and even lethal diseases. Patients with multiple ciliary gene mutations present overt changes in the skeletal system, suggesting that primary cilia are involved in hard tissue development and reconstruction. Furthermore, primary cilia act as sensors of external stimuli and regulate bone homeostasis. Specifically, substances are trafficked through primary cilia by intraflagellar transport, which affects key signaling pathways during hard tissue development. In this review, we summarize the roles of primary cilia in long bone development and remodeling from two perspectives: primary cilia signaling and sensory mechanisms. In addition, the cilium-related diseases of hard tissue and the manifestations of mutant cilia in the skeleton and teeth are described. We believe that all the findings will help with the intervention and treatment of related hard tissue genetic diseases.

关键词： primary cilia bone mechanical sensing hard tissue cilium-related bone disease tooth

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Field and laboratory experimental studies on hard-rock tunnel excavation based on disc cutter coupled

《结构与土木工程前沿（英文）》页码 1370-1386 doi: 10.1007/s11709-023-0947-0

摘要： The tunnel boring machine (TBM) is typically used in hard-rock tunnel excavation. Owing to the unsatisfactory adaptability of TBM to the surrounding rock, when crossing high-strength and high-wear strata, the TBM can easily cause defects, such as abnormal wear on cutters and overload damage to bearings, thus affecting the construction efficiency and cost. Therefore, high-pressure waterjet technology should be applied to assist in rock breaking for efficient TBM tunneling. In this study, the effects of water pressure, nozzle diameter, and nozzle speed on cutting are investigated via laboratory experiments of cutting hard rock using high-pressure waterjets. The penetration performance of the TBM under different water pressures is investigated via a field industrial penetration test. The results show that high-pressure waterjets are highly efficient for rock breaking and are suitable for industrial applications, as they can accommodate the advancing speed of the TBM and achieve high-efficiency rock breaking. However, during the operation of high-pressure waterjets, the ambient temperature and waterjet temperature in the tunnel increase significantly, which weakens the cooling effect of the cutterhead and decreases the construction efficiency of the TBM. Therefore, temperature control and cooling measures for high-pressure waterjets during their long-term operation must be identified. This study provides a useful reference for the design and construction of high-pressure water-jet-assisted cutterheads for breaking road headers.

关键词： tunnel boring machine hard-rock cutting free face disc cutter rock-cutting efficiency

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Improved CO

Mahboube Ghahramaninezhad, Fatemeh Mohajer, Mahdi Niknam Shahrak

《化学科学与工程前沿（英文）》 2020年第14卷第3期页码 425-435 doi: 10.1007/s11705-019-1873-5

摘要： Post-synthetic functionalization or modification has been regarded as a promising strategy to treat surfaces of adsorbents for their applications in targeted adsorption and separation processes. In this work, a novel microporous adsorbent for carbon capturing was developed via functionalization of zeolitic imidazolate framework-91 (ZIF-91) to generate a hard/hard (metal-oxygen) structure named as lithium-modified ZIF-91 (ZIF-91-OLi compound). To this purpose, the ZIF-91 compound as an intermediate product was achieved by reduction of ZIF-90 in the presence of NaBH as a good reducing agent. Afterwards, acidic hydrogen atoms in the hydroxyl groups of ZIF-91 were exchanged with lithium cations via reaction of -BuLi compound as an organo lithium agent through an appropriate procedure. In particular, the as-synthesized ZIF-91-OLi operated as an excellent electron-rich center for CO adsorption through trapping the positive carbon centers in the CO molecule. DFT calculations revealed that the presence of lithium over the surface of ZIF-91-OLi adsorbent plays an effective role in double enhancement of CO storage via creating a strong negative charge center at the oxygen atoms of the imidazolate linker as a result of the lithium/hydrogen exchange system. Finally, the selectivity of CO /N was investigated at different temperatures, revealing the ZIF-91-OLi as a selective adsorbent for industrial application.

关键词： hard/hard structure acidic hydrogen ZIF-91 carbon capture ZIF-91-OLi

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Implementation aspects of a phase-field approach for brittle fracture

G. D. HUYNH, X. ZHUANG, H. NGUYEN-XUAN

《结构与土木工程前沿（英文）》 2019年第13卷第2期页码 417-428 doi: 10.1007/s11709-018-0477-3

摘要： This paper provides a comprehensive overview of a phase-field model of fracture in solid mechanics setting. We start reviewing the potential energy governing the whole process of fracture including crack initiation, branching or merging. Then, a discretization of system of equation is derived, in which the key aspect is that for the correctness of fracture phenomena, a split into tensile and compressive terms of the strain energy is performed, which allows crack to occur in tension, not in compression. For numerical analysis, standard finite element shape functions are used for both primary fields including displacements and phase field. A staggered scheme which solves the two fields of the problem separately is utilized for solution step and illustrated with a segment of Python code.

关键词： phase-field modeling FEM staggered scheme fracture

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Microstructure investigation of dynamic recrystallization in hard machining: From thermodynamic irreversibility

Binxun LI, Xinzhi ZHANG, Song ZHANG

《机械工程前沿（英文）》 2021年第16卷第2期页码 315-330 doi: 10.1007/s11465-020-0612-4

摘要： The drastically changed thermal, mechanical, and chemical energies within the machined surface layer during hard machining tend to initiate microstructural alteration. In this paper, attention is paid to the introduction of thermodynamic potential to unravel the mechanism of microstructure evolution. First, the thermodynamic potential-based model expressed by the Helmholtz free energy was proposed for predicting the microstructure changes of serrated chip and the machined surface layer. Second, the proposed model was implemented into a validated finite element simulation model for cutting operation as a user-defined subroutine. In addition, the predicted irreversible thermodynamic state change in the deformation zones associated with grain size, which was reduced to less than 1 m from the initial size of 1.5 m on the machined surface, was provided for an in-depth explanation. The good consistency between the simulated results and experimental data validated the efficacy of the developed model. This research helps to provide further insight into the microstructure alteration during metal cutting.

关键词： thermodynamic irreversibility Helmholtz free energy microstructure evolution dynamic recrystallization hard milling

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Effect of magneto rheological damper on tool vibration during hard turning

P. Sam PAUL, A. S. VARADARAJAN

《机械工程前沿（英文）》 2012年第7卷第4期页码 410-416 doi: 10.1007/s11465-012-0341-4

摘要：

Recently, the concept of hard turning has gained considerable attention in metal cutting as it can apparently replace the traditional process cycle of turning, heat treating, and finish grinding for assembly of hard wear resistant steel parts. The present investigation aims at developing a magneto rheological (MR) fluid damper for suppressing tool vibration and promoting better cutting performance during hard turning. The magneto rheological Fluid acts as a viscoelastic spring with non-linear vibration characteristics that are controlled by the composition of the magneto rheological fluid, the shape of the plunger and the electric parameters of the magnetizing field. Cutting experiments were conducted to arrive at a set of electrical, compositional and shape parameters that can suppress tool vibration and promote better cutting performance during turning of AISI 4340 steel of 46 HRC with minimal fluid application using hard metal insert with sculptured rake face. It was observed that the use of MR fluid damper reduces tool vibration and improves the cutting performance effectively. Also commercialization of this idea holds promise to the metal cutting industry.

关键词： tool vibration magneto rheological damper hard turning surface finish tool wear

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Crack evolution of soft–hard composite layered rock-like specimens with two fissures under uniaxial compression

《结构与土木工程前沿（英文）》 2021年第15卷第6期页码 1372-1389 doi: 10.1007/s11709-021-0772-2

摘要： Acoustic emission and digital image correlation were used to study the spatiotemporal evolution characteristics of crack extension of soft and hard composite laminated rock masses (SHCLRM) containing double fissures under uniaxial compression. The effects of different rock combination methods and prefabricated fissures with different orientations on mechanical properties and crack coalescence patterns were analyzed. The characteristics of the acoustic emission source location distribution, and frequency changes of the crack evolution process were also investigated. The test results show that the damage mode of SHCLRM is related to the combination mode of rock layers and the orientation of fractures. Hard layers predominantly produce tensile cracks; soft layers produce shear cracks. The first crack always sprouts at the tip or middle of prefabricated fractures in hard layers. The acoustic emission signal of SHCLRM with double fractures has clear stage characteristics, and the state of crack development can be inferred from this signal to provide early warning for rock fracture instability. This study can provide a reference for the assessment of the fracture development status between adjacent roadways in SHCLRM in underground mines, as well as in roadway layout and support.

关键词： soft−hard composite layered rock mass double cracks crack evolution acoustic emission digital image correlation