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Is Mg_(17)Al_(12) ductile or Brittle?A theoretical insight

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Journal of Magnesium and Alloys 2023年第3期11卷 936-944页

作者： Jiajia Wang Lei Niu Yanglin Zhang Jianqing Chen Jinghua Jiang Dan Song Baosong Li Guobing Ying Jiangbo Cheng Aibin Ma College of Mechanics and Materials Hohai UniversityNanjing 210098P.R.of China

The Mg_(17)Al_(12)-phase,which is common and important in Mg-Al alloy,has long been regarded as a Brittle phase in experiments but theoretical calculations report controversial results.To unravel why theoretical calculations report controversial results and determine whether Mg_(17)Al_(12)is Brittle or ductile,density functional theory calculations on atomic level are performed to investigate mechanic properties of Mg_(17)Al_(12)without containing alloying elements and without taking the size effect.The results showed that the parameter k-point played critical role in the DFT-based elastic calculations.The convergent G/B ratio of Mg_(17)Al_(12)was about 0.52,suggesting that the Mg_(17)Al_(12)-phase was theoretically ductile although its ductility was poor.The chemical bonding in Mg_(17)Al_(12)was the mixture of metallic Mg-Mg bond and covalent Al-Al bond.The advantage of metallic bonding over covalent bonding provided a possible explanation for the ductility of Mg_(17)Al_(12).Possible reasons for the Brittleness of Mg_(17)Al_(12)in experiments are also discussed.

关键词： Mg_(17)Al_(12) Ductile Brittle DFT Elastic properties

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

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Frontiers of Mechanical Engineering 2017年第1期12卷 77-88页

作者： Hang GAO Xu WANG Dongming GUO Yuchuan CHEN Key Laboratory for Precision and Non-traditional Machining Technol-ogy of Ministry of Education Dalian University of Technology Dalian116024 China

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 diff^culties 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-precisionmachining

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

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Frontiers of Structural and Civil Engineering 2019年第2期13卷 478-485页

作者： Hsien-Yang YEH Bin YANG Department of Mechanical and Aerospace Engineering California State UniversityLong BeachCA 90801USA Department of Chemical Engineering Shanghai Jiao Tong UniversityShanghai 200240China

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. However, various new materials are developed in different engineering fields, thus, the establishment of reliable and accurate material strength theory or failure criterion is imperative. Therefore, predicting fracture for various modem materials would require more experiments to infer material dependent parameters in the local fracture model.

关键词： fracture assessment Brittle solids V-notches review

Rockburst characteristics of several hard Brittle rocks:A true triaxial experimental study

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Journal of Rock Mechanics and Geotechnical Engineering 2020年第2期12卷 279-296页

作者： Shaobin Zhai Guoshao Su Shunde Yin Bin Zhao Liubin Yan Key Laboratory of Disaster Prevention and Structural Safety of Ministry of Education School of Civil and Architecture EngineeringGuangxi UniversityNanning530004China Department of Civil and Environmental Engineering University of WaterlooWaterlooON N2L 3G1Canada State Key Laboratory of Geohazard Prevention and Geoenvironment Protection Chengdu University of TechnologyChengdu610059China

Rockburst is a typical rock failure which frequently threatens both human life and construction equipment during highly stressed underground excavation.Rock lithology is a control factor of rockburst.In this paper,rockburst tests were conducted on rectangular prismatic specimens of six types of intact hard Brittle rocks,i.***.granodiorite,granite,marble,basalt,sandstone and limestone,under one-free-face true triaxial loading conditions.With the use of high-speed cameras,an acoustic emission(AE)system and a scanning electron microscope(SEM),rockburst of different rocks was investigated.The results show that the strainbursts of granodiorite,granite and marble were accompanied by tensile splitting near the free face,and consequently were relatively strong with a large amount of fragment ejection and kinetic energy release.For basalt,sandstone and limestone,failure was primarily dominated by shear rupture.The strainbursts of basalt and sandstone were relatively small with minor fragment ejection and kinetic energy release;while no burst failure occurred on limestone due to its relatively low peak strength.Rock strength,fracturing and fragmentation characteristics,and failure modes of different rocks can significantly affect rockburst proneness and magnitude.The AE evolution coupled with SEM analysis reveals that the differences in the inhe rent microstructures and fracture evolution under loading are the primary factors accounting for different rockbursts in various rock types.

关键词： Rockburst Strainburst Hard Brittle rocks True triaxial test Acoustic emission(AE)

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

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Frontiers of Structural and Civil Engineering 2019年第2期13卷 380-396页

作者： HIRSHIKESH Sundararajan NATARAJAN Ratna Kumar ANNABATTULA Integrated Modeling and Simulation Lab Department of Mechanical EngineeringIndian Institute of Technology MadrasChennai- 600036India

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

Crack propagation simulation in Brittle elastic materials by a phase field method

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Theoretical & Applied Mechanics Letters 2019年第6期9卷 339-352页

作者： Xingxue Lu Cheng Li Ying Tie Yuliang Hou Chuanzeng Zhang School of Mechanical Engineering Zhengzhou UniversityZhengzhou 450001China Department of Civil Engineering University of SiegenD-57076 SiegenGermany

To overcome the difficulties of re-meshing and tracking the crack-tip in other computational methods for crack propagation simulations,the phase field method based on the minimum energy principle is introduced by defining a continuous phase field variable(x)∈[0,1]to characterize discontinuous cracks in Brittle materials.This method can well describe the crack initiation and propagation without assuming the shape,size and orientation of the initial crack in advance.In this paper,a phase field method based on Miehe's approach[Miehe et al.,Comp.Meth.App.Mech.Eng.(2010)]is applied to simulate different crack propagation problems in twodimensional(2D),isotropic and linear elastic materials.The numerical implementation of the phase field method is realized within the framework of the finite element method(FEM).The validity,accuracy and efficiency of the present method are verified by comparing the numerical results with other reference results in literature.Several numerical examples are presented to show the effects of the loading type(tension and shear),boundary conditions,and initial crack location and orientation on the crack propagation path and force-displacement curve.Furthermore,for a single edge-cracked bi-material specimen,the influences of the loading type and the crack location on the crack propagation trajectory and force-displacement curve are also investigated and discussed.It is demonstrated that the phase field method is an efficient tool for the numerical simulation of the crack propagation problems in Brittle elastic materials,and the corresponding results may have an important relevance for predicting and preventing possible crack propagations in engineering applications.

关键词： Brittle fracture Phase field method Crack propagation Finite element method

Rotary ultrasonic-assisted milling of Brittle materials

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中国有色金属学会会刊：英文版 2012年第S3期22卷 793-800页

作者： KUO Kei-lin TSAO Chung-chen Department of Vehicle Engineering National Taipei University of Technology Department of Automation Engineering Tahua Institute of Technology

In order to improve the machining efficiency of ultrasonic milling,the easiest and most effective approach was started with the improvement of tool design.The main objective of this research was to utilize rotary ultrasonic machining (RUM's) effectiveness in removing Brittle materials to extend the applications of this independent,innovative manufacturing method (self-driving rotary ultrasonic machining),and to experimentally investigate its milling application on Brittle materials.The designed tool was used in the conjunction with previously established RUM machine tools,and glass was selected as workpiece for experiments.The interrelationship between feed rate and depth of cut was discussed.By measuring the surface roughness of workpiece,the overall efficacy of utilizing RUM for milling was evaluated and presented.Ultrasonic assisted milling results in the reduction of milling resistance,which leads to a greater process rate.

关键词： rotary ultrasonic ultrasonic assisted milling Brittle material

Characterization and cloning of a Brittle culm mutant (bc88) in rice (Oryza sativa L.)

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Chinese Science Bulletin 2013年第24期58卷 3000-3006,2914页

作者： RAO YuChun YANG YaoLong XIN DeDong LI XiaoJing ZHAI KaiEn MA BoJun PAN JianWei QIAN Qian ZENG DaLi College of Chemistry and Life Sciences Zhejiang Normal University State Key Laboratory of Rice Biology China National Rice Research Institute

This study characterizes a Brittle culm (bc88) mutant of rice (Oryza sativa L.) obtained by ethylene methylsulfonate (EMS)-induced mutagenesis of Wuyunjing 7. The bc88 mutant exhibits a diversity of pleiotropic phenotypes, including Brittle culm at the whole-plant growth stages, withered leaf tips at the seedling stage, and 18-d delay in heading date at the mature stage. Genetic analysis indicates that the bc88 mutant is controlled by a single recessive nuclear gene. The mutated bc88 gene isolated by map-based cloning contains only one point mutation in the 5th exon relative to its wild-type BC88 (LOC_Os09g25490 and Os09g0422500), leading to an amino acid change from P to L in bc88 plants. Alignment of the putative protein sequence with its homologs indicates that the mutation is located in the conserved region of the sequence. Detection of the transcription level of BC88 in rice plants shows that the expression level of BC88 is higher in spikes and culms than in leaves, roots, and leaf sheaths. These contribute to understanding of the molecular mechanism of cellulose synthesis. The target gene BC88 can be a useful tool in molecular marker-assisted selection for rice culm trait breeding.

关键词： rice (Oryza sativa L.) Brittle culm Wuyunjing 7 clone mutation

Laser machining of transparent Brittle materials: from machining strategies to applications

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Opto-Electronic Advances 2019年第1期2卷 11-23页

作者： Xiaozhu Xie Caixia Zhou Xin Wei Wei Hu Qinglei Ren Laser Micro/Nano Processing Lab School of Electromechanical Engineering Guangdong University of Technology Guangzhou 510006 China Department of Experimental Teaching Guangdong University of Technology Guangzhou 510006 China

Transparent Brittle materials such as glass and sapphire are widely concerned and applied in consumer electronics, optoelectronic devices, etc. due to their excellent physical and chemical stability and good transparency. Growing research attention has been paid to developing novel methods for high-precision and high-quality machining of transparent Brittle materials in the past few decades. Among the various techniques, laser machining has been proved to be an effective and flexible way to process all kinds of transparent Brittle materials. In this review, a series of laser machining methods, e.g. laser full cutting, laser scribing, laser stealth dicing, laser filament, laser induced backside dry etching (LIBDE), and laser induced backside wet etching (LIBWE) are summarized. Additionally, applications of these techniques in micromachining, drilling and cutting, and patterning are introduced in detail. Current challenges and future prospects in this field are also discussed.

关键词： transparent Brittle materials glass sapphire laser machining