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。

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。

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]。

Effects of Dietary Fiber and Grit on Performance, Gastrointestinal Tract Development, Lipometabolism, and Grit Retention of Goslings

This study investigated effects of dietary ifbre and grit on growth performance, gastrointestinal tract （GIT） development, serum indexes and grit retention of Sichuan white goslings in China. The experiment was a 3×2 factorial design consisting of dietary crude ifbre （CF） at 2.0, 4.0 and 6.0%levels by adding grass meal and with or without grit supplementation. A total of 720 1-d-old male goslings were randomly allocated into 36 pens of 20 goslings/pen （n=6 pens/treatment）. At 21 d of age, GIT, blood samples and grit in gizzards were collected. Body weight （BW）, empty BW （without GIT）, average daily gain （ADG） and average daily feed intake （ADFI） were affected by CF levels and the medium （4.0%） had the highest value. Adding grit improved BW, empty BW, ADG and ADFI. CF affected relative weight or length of proventriculus, gizzard and duodenum. Increasing CF levels decreased jejunum villus height and affected caecal crypt depth and villus height to crypt depth ratio. Higher CF levels decreased serum triglyceride. Adding grit increased relative weight of abdominal fat. Grit addition increased grit weight in gizzard and the ratio of grit in 0.45-1 and 1-2 mm while decreasing the ratio of grit〈0.45 and 2-3 mm. In conclusion, moderate CF level and grit addition increased performance of goslings without interaction. Dietary CF levels affected the development of upper GIT and serum triglyceride. Grit needed by goslings should be less than 2 mm. Goslings’ gizzard would accumulate grit from feed when other grit could not be acquired.

Investigation of modeling on single grit grinding for martensitic stainless steel

Single grit grinding is the simplified model to abstract the macro scale grinding.Finite element analysis is a strong tool to study the physical fields during a single grit grinding process,compared to experimental research.Based on the dynamic mechanical behavior of 2Cr12Ni4Mo3VNbN steel and the mathematical statistics of abrasive grit,modeling of the single grit grinding process was conducted by using commercial software AdvantEdge.The validation experiment was designed to validate the correctness of the FEA model by contrast with grinding force.The validation result shows that the FEA model can well describe the single grit grinding process.Then the grinding force and multi-physics fields were studied by experimental and simulation results.It was found that both the normal and tangential grinding forces were linearly related to the cutting speed and cutting depth.The maximum temperature is located in the subsurface of the workpiece in front of the grit,while the maximum stress and strain are located under the grit tip.The strain rate can reach as high as about 106 s–1 during the single grit grinding,which is larger than other traditional machining operations.

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 ℃.

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.

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.

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。

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.

如何让我们的孩子离成功更近一些——Grit

美国心理学教授安吉拉·李·德克沃斯等人通过研究发现,坚毅比其他因子能更有效地预测成功,是各个领域取得成功的本质性特征。面对孩子学习缺乏内在动机、未能发掘有意义的人生和易敏感脆弱三重问题,可以通过如下四种策略让孩子变得更加坚毅,从而离成功更近一些：培养成长型思维模式;有技巧地表扬;营造＂不便利＂的园所环境,鼓励发现和探索;提供充足的社会资源和情感支持。

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.

12项坚毅量表(12-Item Grit Scale)的中文修订

目的:对12项坚毅量表(12-Item Grit Scale)在中国成年人群中进行中文版的初步修订。方法:按量表翻译程序将12项目坚毅量表翻译成中文版,然后采用验证性因素分析对其结构效度进行分析,以心理弹性量表(RS-14)作为校标工具。在北京市随机选取360名成年人进行测验,两周后随机选取其中80名成年人进行重测,分析中文版信效度。结果:坚毅量表中文版所有题目的决断值(CR)均达到0.001的显著性水平,每个题目与对应量表的相关系数较高。因素分析结果表明,坚毅量表符合Duckworth两因素模型结构,量表的结构效度良好(RMR=0.037,NFI=0.927,GFI=0.957,RMSEA=0.049)。用心理弹性量表(RS-14)作为效标,坚毅量表得分与心理弹性量表的得分呈现正相关(r=0.671,P<0.001)。量表的Cronbach`sα系数为0.729,折半信度为0.784,两周后的重测信度为0.804(P<0.001)。结论:12项坚毅量表在成年人中试用具有较高信度和效度,可以作为测量成年人坚毅品质的有效工具。

Grit教育在中国初中教育的践行

目前，中小学的课堂不在单单注重课本知识的教学，更加注重学生品格的学习。因此，Grit教育进入了社会大众的视野，文章就是通过对Grit教育进行一系列的研究，进而是指能够在中小学课堂更好的运用。

FEM Simulation of Single-Grit Grinding on a 2.5D Woven Composite

Single-grit grinding of a 2.5D woven composite was investigated by the finite-element method (FEM) using a unit-cell model. According to our hypotheses, the axis of the warp yarn was a sinusoidal curve and the cross section of the weft yarn was shaped like a biconvex lens. AVUMAT subroutine was used to construct the constitutive model of the 2.5D woven composite. The grinding process of the composite was analyzed using an FEM simulation with the ABAQUS/Explicit software. A validation experiment was also carried out. The simulation results showed that a grinding crack was well simulated. Furthermore, the junctions between the warp yarn and weft yarn were found to be seriously damaged and cracks were observed to extend outward along the warp fiber during grinding, in good agreement with the experimental results. In addition, the strain of weft yarns was obviously greater than that of warp yarns when the grinding direction was perpendicular to the weft yarns and parallel to the axis of the warp yarns. These results demonstrate that the mesostructure strongly influences the grinding damage inflicted on woven composites. © 2017 Tianjin University and Springer-Verlag GmbH Germany

Effects of the extrusion and enzymatic extrusion treatment on the apparent viscosity of degerminated maize grits

Apparent viscosity is an important parameter for glucose syrup production.which is greatly affected by particle size and concentration of samples.In order to analyze the factors influencing the apparent viscosity,the particle size distribution,steady shear flow behavior,temperature,and time sweep test of native degerminated maize grits(NDMG),extruded degerminated maize grits(EDMG),and enzymatically extruded degerminated maize grits(EEDMG)with different particle sizes(passed through 20,40,60,80,and 100 mesh sieves)and concentrations(water-sample ratios:2:1,3:1,5:1,10:1,and 20:1)were investigated.All samples passed through different mesh sieves showed a gradient and a relatively concentrated distribution,and slurries had typical shear-thinning properties.Apparent viscosity increased with increasing particle size and concentration.The lowest apparent viscosity was attained from the samples obtained at 100+mesh and 20:1 water-sample ratio.Moreover,the sample with a 20:1 water-sample ratio showed the most stable apparent viscosity in the temperature sweep test.In the time sweep test,the power law equation with high determination coefficients(R^(2)=0.9446,0.9382)and low root mean square error(RMSE=0.0002)had the best fit to the experimental data of the EDMG and EEDMG samples passed through 100+mesh.Overall,the lower apparent viscosities of the EDMG and EEDMG samples obtained at 100+mesh and 20:1 water-sample ratio can improve the activity and accessibility of enzymes for glucose syrup production.This study provides critical insight into decreased apparent viscosity and expands the uses of EDMG and EEDMG in the glucose syrup sector.

弹性磨抛轮加工硅片面形预测模型及试验验证

目的为分析弹性磨抛轮磨削硅片面形精度变化的影响因素,优化加工参数以获得良好的磨削面形。方法通过建立考虑弹性磨抛轮转速、硅片转速、偏心距等参数的弹性磨抛轮磨粒运动轨迹模型,结合单颗磨粒切削深度,提出了弹性磨抛轮加工硅片的材料去除非均匀性预测方法,建立了基于弹性磨抛轮磨削硅片的面形预测模型,并通过不同转速比下的磨削试验验证了预测模型的准确性。结果面形预测模型仿真出的面形与弹性磨抛轮加工试验后的硅片面形一致,均呈“凸”形,且PV值随转速比的增大而增大。转速比为1时,磨削后硅片面形PV值为0.54μm,仿真模型计算出的PV值为0.49μm,转速比为5时,磨削后硅片面形PV值为2.12μm,仿真模型计算出的PV值为2.38μm。结论磨削试验面形PV值与模型计算面形PV值的预测误差小于13%,建立的面形预测模型能够成功预测硅片的面形规律,可以分析加工参数对硅片面形的影响规律。由面形预测模型分析可知,转速比对硅片面形精度有影响,且随着转速比的增加,硅片面形不断恶化,因此在实际加工中,应选择较小的转速比进行加工,以获得更优的硅片面形精度。