Effects of Heating Temperature on Interfacial Microstructure and Compressive Strength of Brazed CBN-AlN Composite Abrasive Grits

CBN-AlN composite abrasive grits and AISI 1045 steel were brazed using Ag-Cu-Ti active filler alloy by heating up to the temperature of 890,900 and 920 ℃,respectively,and then held at the temperature for 8 min.Optical microscope,scanning electron microscope and X-ray diffraction equipment were utilized to study the effects of heating temperature on the microstructure of the joining interface.The compressive strength of the brazed composite grits was also measured.The experimental results show that the atoms of Ti,Al,B and N have preferentially penetrated towards the joining interface of composite grits and filler alloy.The compounds of Ti-nitride,Ti-borides and Ti3AlN were formed in the reaction layer.Degradation effect was not made on the compressive strength of the CBN-AlN composite grits when the brazing process was carried out in the temperature range of 890-920 ℃.

Blade Segment with a 3D Lattice of Diamond Grits Fabricated via an Additive Manufacturing Process

Diamond tools with orderly arrangements of diamond grits have drawn considerable attention in the machining field owing to their outstanding advantages of high sharpness and long service life.This diamond super tool,as well as the manufacturing equipment,has been unavailable to Chinese enterprises for a long time due to patents.In this paper,a diamond blade segment with a 3D lattice of diamond grits was additively manufactured using a new type of cold pressing equipment(AME100).The equipment,designed with a rotary working platform and 16 molding stations,can be used to additively manufacture segments with diamond grits arranged in an orderly fashion,layer by layer;under this additive manufacturing process,at least 216000 pcs of diamond green segments with five orderly arranged grit layers can be produced per month.The microstructure of the segment was observed via SEM and the diamond blade fabricated using these segments was compared to other commercial cutting tools.The experimental results showed that the 3D lattice of diamond grits was formed in the green segment.The filling rate of diamond grits in the lattice could be guaranteed to be above 95%;this is much higher than the 90%filling rate of the automatic array system(ARIX).When used to cut stone,the cutting amount of the blade with segments made by AME100 is two times that of ordinary tools,with the same diamond concentration.When used to dry cut reinforced concrete,its cutting speed is 10%faster than that of ARIX.Under wet cutting conditions,its service life is twice that of ARIX.By applying the machine vision online inspection system and a special needle jig with a negative pressure system,this study developed a piece of additive manufacturing equipment for efficiently fabricating blade segments with a 3D lattice of diamond grits.

Simulation and Experiment of Double Grits Interacting Scratch for Optical Glass BK7

The elastic-plastic transition regime and brittle-ductile transition regime in scratch process for optical glass BK7 were analyzed based on the Hertzian equation and the stress ratio theory which was proposed by Wei. The interacting scratch process for optical glass BK7 with the grit interval distance as the variable was simulated by the ABAQUS software of finite element simulation based on the energy fracture theory. Double grits interacting scratch test for optical glass BK7 was carried out on the DMG ULTRASONIC 70-5 linear, by which the reliability of finite element simulation was verified. The surface morphology of the workpiece was analyzed by scanning electron microscopy（SEM）, which showed that the width of groove increased obviously with the increase of scratch depth and the grit interval distance. Results of the width of groove were consistent with the simulation results. The subsurface damage layer was analyzed by the method of HF acid etching, which showed that there was an area of cracks intersecting. The scratching force was measured by the threedimensional dynamometer of KISTLER, which showed that the second scratching force increased with the increase of scratching depth and the grit interval distance. The force in the second scratch was smaller than that in the first time, which was consistent with the Griffith fracture theory.

活动理论视角下TPACK发展过程的动态分析——以美国GRITS教育实习生研究项目为例

TPACK理论作为一项革新性教育技术理论,已经获得了广泛的认可,但在实践中缺点也很明显,即对真实的复杂教育现场而言,还缺乏较为实用和动态的解释框架。很多学者已经对此问题进行了大量有益的探索,这其中的努力主要包括TPACK实践框架和TPACK活动分析法等。TPACK活动分析法是基于活动理论视角,对TPACK发展过程的动态分析。

Usability of Waste Steel Grits in Concrete Pavement

The usability of waste steel grits and limestone sand in the construction of concrete pavement was investigated.Four different types of pavement concretes were produced,including coarse limestone concrete not containing waste steel grit,coarse limestone concrete containing waste steel grit,limestone sand concrete not containing waste steel grit,and limestone sand concrete containing waste steel grit.In this study,water/binder ratio in concrete production was taken as 0.44.In the production of limestone sand concrete containing waste steel grit,limestone sand with a grain diameter of 0.1-1.0 mm was used as aggregate.Waste steel grits with a grain diameter of 0.2-0.7 mm were added to the concrete mixture.Standard water curing and combined curing were applied to concrete samples.After standard water curing and combined curing,compression and bending tests of the same types of cube and beam concrete samples were carried out.As a result of the study,the maximum compressive and bending strengths were found to be 50.21 MPa and 5.07 MPa for limestone sand concrete containing waste steel grit.The study results show that waste steel grits increase the compressive and bending strength of concrete pavement.

Thermal residual stress analysis of coated diamond grits

Residual stresses of coated diamond grits were analyzed by a finite element unit cell model. Diamond grits coated with four types of metals, W, Mo, Ti, and Cr, were considered. The numerical results show that compressive stress occurs in the diamond particles and tensile stress occurs in the metal matrix; compressive stress is concentrated in the diamond sharp comer; interface stresses decrease by more than 1000 MPa with a metal interlayer; plastic deformation of the matrix begins near the sharp corner of diamond grits and extends toward the peripheral zone. Stress concentration dramatically decreases due to plastic deformation of the matrix. The deposition of transition metals on a diamond surface can dramatically promote the adhesion between diamond grits and the metal bond.

Farmer Grits Teeth for Record Train Tug

斯里兰卡的一条好汉正在策划一项新的吉尼斯世界记录:用他的牙齿拉动重达40吨的铁路的车厢,并前进25米。先前的记录是在29分钟内用牙齿将车厢拉动24米。此君已有两项记录被载入吉尼斯世界记录。本文用得最精彩的一个表达含“双关”:but has good reason to be confident he has not bittenoff more than he can chew。】

Residual stresses of polycrystalline CBN abrasive grits brazed with a high-frequency induction heating technique

Residual stresses produced in polycrystalline CBN abrasive grits during a high-frequency induction brazing process are calculated by using ?nite element analysis, with a consideration of the nonuniform temperature distribution in the induction brazing model. The in?uences of induction brazing parameters on the residual stresses of polycrystalline CBN abrasive grits have been analyzed, including the embedding depth, grit side length, etc. Results obtained show that the tensile stress with a 40% embedding depth is 292 MPa, which is the minimum on the bonding interface compared with other embedding depths. Meanwhile, the maximum tensile stress is 575 MPa, with an increase of 59% compared with that of a grit side length of 50 mm. Finally, the simulation results of the brazing residual stress of polycrystalline CBN abrasive grits have been con?rmed valid based on the residual stress measurement of the brazed monocrystalline CBN grit.

Polycrystalline diamond mini-cubes for sawing applications

Diamond grits are indispensable for sawing granite or concrete.Each year about 1 000 tons of diamond grits are consumed for such purposes.In all cases,mono crystalline diamond is used.However, polycrystalline grits(polygrits) are generally better performed than mono grits as abrasives.For example,poly grits of cubic boron nitride(e.g.Borazon(?) CBN-550 of Diamond Innovations) can cut faster and they last longer than mono grits(e.g.Borazon(?) CBN-500). Polygrits of alumina(e.g.Cubitron(?) of 3M) also out perform by far glassy grits(e.g.white alumina).For diamond superabrasives,micron polygrits formed by shock waves may polish as fast as mono grits of the same size,but without causing as much scratches due to the presence of smaller sintered grains.The improved performance of poly grits is attributed to their ability to micro chipping that renews the sharp cutting corners from time to time.By contrast,mono grits tend to round off at low cutting force or macro fracture at high cutting force,so they may lose the cutting ability rapidly. For sawing granite with mesh sizes 40/50 or coarser,poly grits of diamond have not been available until recently.In this research,we have made polygrits in mini cube with sizes of 18/20,20/25,and 30/40.Turbo grinders and wire saws were made by brazing both mono grits and polygrits on steel substrates.Cutting performance on granite demonstrated that grinding speed was faster with turbo grinder,and the surface finish was smoother with wire saw for poly grits than mono ones. Polygrits and mono grits of diamond were mixed for comparison(upper left).Polygrits of mini cubes were brazed on the pearl of a wire saw(upper right).Mono diamond grits were brazed on a turbo grinder(bottom diagrams ).

Micro/nano Indentation and Single Grit Diamond Grinding Mechanism on Ultra Pure Fused Silica

The existing research about ductile grinding of fused silica glass was mainly focused on how to carry out ductile regime material removal for generating very ＂smoothed＂ surface and investigate the machining-induced damage in the grinding in order to reduce or eliminate the subsurface damage.The brittle/ductile transition behavior of optical glass materials and the wear of diamond wheel are the most important factors for ductile grinding of optical glass.In this paper,the critical brittle/ductile depth,the influence factors on brittle/ductile transition behavior,the wear of diamond grits in diamond grinding of ultra pure fused silica（UPFS） are investigated by means of micro/nano indentation technique,as well as single grit diamond grinding on an ultra-stiff machine tool,Tetraform ＂C＂.The single grit grinding processes are in-process monitored using acoustic emission（AE） and force dynamometer simultaneously.The wear of diamond grits,morphology and subsurface integrity of the machined groves are examined with atomic force microscope（AFM） and scanning electron microscope（SEM）.The critical brittle/ductile depth of more than 0.5 μm is achieved.When compared to the using roof-like grits,by using pyramidal diamonds leads to higher critical depths of scratch with identical grinding parameters.However,the influence of grit shapes on the critical depth is not significant as supposed.The grinding force increased linearly with depth of cut in the ductile removal regime,but in brittle removal regime,there are large fluctuations instead of forces increase.The SEM photographs of the cross-section profile show that the median cracks dominate the crack patterns beneath the single grooves.Furthermore,The SEM photographs show multi worn patterns of diamond grits,indicating an inhomogeneous wear mechanism of diamond grits in grinding of fused silica with diamond grinding wheels.The proposed research provides the basal technical theory for improving the ultra-precision grinding of UPFS.

“Grit”教育理念在临床病理医师培养中的应用

随着临床分子时代的来临,如何培养身心健康且优秀的病理医师是教育者所关注的问题,传统教育注重培养学生对基础知识的掌握,"Grit"教育理念注重学生性格的培养,在传统教育的基础上引入"Grit"教育理念值得探讨和应用。

“Grit(坚毅)”教育理念对中国民办高等教育的启示

该文通过分析"Grit(坚毅)"教育理念的概念与内涵,结合中国民办高等教育的实际情况,尝试提出提高中国民办高等教育质量的几点建议。

Ultrahigh pressure sintering of polycrystalline diamond cubes

Polycrystalline grits(polygrits) have been used widely in industry as abrasives.Due to their higher impact strength and the friable nature,polygrits are more endurable and more efficient than monocrystal grits (monogrits) in material removal applications.For example,polygrits of alumina may last longer and cut faster than monogrits.Similarly,polygrits of cubic boron nitride is a superior superabrasive than monogrits of the same. Although diamond superabrasives have been indispensable for constructional sawing applications and industrial grinding applications,there has no polygrits of diamond that are commercially available.In this research,we used a novel technology to sinter micron diamond fines to form polygrits of diamond.The characterization demonstrated that polygrits of diamond can be tough to withstand impact.But due to the presence of micro grains,the grit can sharpen itself without dulling by shedding the worn grains.This paper revealed many examples of using diamond polygrits.

Assessment of Microbial Changes and Nutritional Qualities of Extruded White Yam (<i>Dioscorea rotundata</i>) and Bambara Groundnut (<i>Vigna subterranean</i>) Blends

Two flavoured extruded products were developed by co-extruding yam grits (750 μm) obtained from white yam (Dioscorea rotundata) and bambara groundnut flour (250 μm) in 160:40 respectively obtained from white bambara groundnut with added flavouring agents of salt (1% - 3%) and sugar (4% - 6%) in the feed blends at screw speed of 70 rpm, 17.5%, feed moisture and at the barrel temperature of 145℃. The extruded products were packaged in low density polyethylene bag (0.02 μm gauge size) and stored at room temperature (28℃ ± 2℃) and at refrigeration temperature (9℃ ± 2℃) for a period of twenty weeks. The microbiological changes in the extruded products as determined by the total plate under both storage conditions showed that maximum total plate counts were 0.5 × 104 and 5.4 × 104 cfu/g at 9℃ ± 2℃ and 28℃ ± 2℃ respectively. Nutritional evaluation studies of extrudates were comparable (p ≥ 0.05) with standard casein diet with minimum crude protein content of 13.51% providing 1707.2 KJ energy per 100gof diet and supported weight gain and growth of laboratory animals.

缺失与呼唤:Grit(坚毅)理念下的中职教育

近年来,美国教育学界被新教育理念Grit（坚毅）所席卷。美国宾夕法尼亚大学教授安吉拉·李·达克沃斯将Grit（坚毅）定义为＂向着长期的目标,坚持自己的激情,即便历经失败,依然能够坚持不懈地努力下去,这种品质就叫做Grit（坚毅）＂。她通过十多年研究发现：无论在何种情况下,比起智力、学习成绩或者长相,Grit（坚毅）是最为可靠的预示成功的指标。

Effect of Seed Size, Suspension Recycling and Substrate Pre-Treatment on the CVD Growth of Diamond Coatings

CVD growth of uniform conformal polycrystalline diamond (PCD) coatings over complex three dimensional structures is very important material processing technique. It has been found that the nucleation and subsequent growth period is very critical for successful development of CVD diamond based technologies. There are many methods of enhancing diamond nucleation on foreign substrates-ultrasonic treatment with diamond seed suspension being the best among them. A combination of ultrasonic seeding (US) technique with prior treatment (PT) of the substrate under CVD diamond growth conditions for brief period of time, has found to be very effective in enhancing the diamond nucleation during CVD growth—together they are known as NNP. But successive usage of the same seeding suspension up to ten cycles deteriorates the seeding efficiency. 6th seeding cycle onwards the silicon substrates are barely get covered by diamond crystallites. Five different diamond micron grits were used for seeding the silicon substrates and it is observed that US with the sub-micron particles (0.25 μm) is very effective in efficient nucleation of PCD on Si substrates. PT of the substrate somewhat negates the effect of successive use of the same seeding slurry but it is best to avoid recycling of the same seeding suspension using micron size diamond grits.

大学生的意志力发展及其对职业的影响

近年来,学生能力当中的非智力因素,尤其是以意志力为代表的可迁移能力受到了学术界的广泛关注。以五大人格量表和Grit量表为代表的心理学手段已经能对个人的意志力水平进行科学的主观评价。本文以简化的Grit量表为工具,对首都高校学生的意志力水平进行了测量和研究。研究发现,(1)大学生意志力在其大学期间的各个阶段都发挥了非常重要的作用。意志力发展对大一新生的适应,大二学生的转折以及大三学生的职业成熟都具有显著的影响;(2)以院校类型、专业类型和人际互动为代表的院校因素对大学生意志力的发展具有显著的影响;(3)意志力作为一种可迁移能力,不仅会影响学生的学业成就,还会影响学生毕业后的职业发展。

河畔随想

他的浑厚而音域高昂的喉音在蓝调乐坛是最好的标志,他那极富表现力的吉他演奏让人毫不怀疑他成长于密西西比河三角洲,他是仅次于B.B.King的蓝调演唱大师,他就是Little Milton.和所有蓝调演唱大师一样,Little Milton的演艺生涯已经跨越了近半个世纪.在他所演唱的专辑中,许多作品已经成了他的代表性作品,如<The Blues Is All Right>、<Grits Ain't Groceries>、<Annie Mae's Cafe>,同时在舞台表演上他也是个实力雄厚的大师.年过七旬的他在2005年再度震撼乐坛,推出了这张<Think of Me>.

Grit教育视域下辩论式主题课堂翻转教学的思考

为培养高校大学生面对问题学习的表达能力和主观能动性,从角色分析、情景组织、教学元素等方面探索以Grit理念为主导的辩论式主题课堂翻转的教学方法。该方法尝试训练学生在面对困难时坚毅的学习研究性格,引入辩论式主题讨论的方法,以教师的启发引导为总指挥,融合引导式教学、辩论式教学与解析式教学模式为一体,建立教师与学生之间、学生与学生之间的教学互动活动的多层次立体学习过程,以提升教学效果。

Grit理念辩论式主题翻转课堂联合情景式教学在妇产科护理临床带教中应用效果研究

临床实习在护理教学中占据重要地位,是理论向实践过度的重要环节,故对带教质量要求较高[1]。传统护理临床带教主要为讲授式教学模式,但是该教学方法已逐渐不能满足护理教学要求,教学中涉及学生尚未接触的各种临床问题,大部分学生认为其比较抽象、难于理解、枯燥难学、容易遗忘[2,3]。