Decoration of disclinations by solidification-induced band texture and focal-conic texture for a low-molar-mass liquid crystal

Two decoration techniques, solidification-induced band texture decoration and focal-conic texture decoration, have been established to exhibit the director field of disclinations in a low-molar-mass methacrylate liquid crystal. The disclinations with strength s=1/2 and s=±1 are observed by the two decoration methods. For the solidification-induced band texture decoration, the molecular orientation is perpendicular to the direction of the band. While for focal-conic texture decoration, it has been proved by the results of IR dichroism that the direction of the director is parallel to the direction of the focal-conic. Therefore, the sketch map of the molecular director filed can be mapped according to the morphological pattern of the solidification-induced band texture or focal-conic texture.

BAND-LIKE TEXTURE OF ETHYLCYANOETHYL CELLULOSE MESOPHASE

In the ethyl-cyanoethylcellulose ((E-CE)C)/dichloroacetic acid (DCA) cholesteric liquid crystalline solution, the hand-like texture is formed when the mesophase aggregates with the disk-like texture grow to big enough and merge with each other with increasing concentration. The band-like texture is composed of parallel equidistant bright and dark alternative strips which are about 0.2-2.0 μm in width. In the band-like texture, the layers of ordered polymer chains are perpendicular to the solution film and the axes of helicoids are parallel to it. The width of the strips is different in different zones. Under the effect of an external magnetic field, the strips in the band-like texture first become wider and then narrower gradually.Moreover, the axes of helicoids in the (E-CE) C/DCA mesomorphic solution change from the direction normal to the magnetic field to the agreement with the magnetic field direction.

BANDED TEXTURE FORMATION IN NEMATIC SOLUTION OF POLY (1,4-BENZAMIDE) IN SULFURIC ACID

The banded texture in films prepared from nematic poly (1,4-benzamide) (PBA)/H_2SO_4 solution by shearing and without shearing has been studied by using microscopy techniques. The kinetic parameters of banded texture formation γ_c and τ_b were measured for nematic solution of PBA by using parallel-plate shearing apparatus. The banded texture was also observed in randomly packed domains for nematic solution of PBA on standing without shearing. The properties of banded texture show no difference between the two samples with or without shearing.

Monte Carlo Simulation of Band Texture Formation in Macroscopically Oriented Semirigid Polymer System

ＭｏｎｔｅＣａｒｌｏＳｉｍｕｌａｔｉｏｎｏｆＢａｎｄＴｅｘｔｕｒｅＦｏｒｍａｔｉｏｎｉｎＭａｃｒｏｓｃｏｐｉｃａｌｌｙＯｒｉｅｎｔｅｄＳｅｍｉｒｉｇｉｄＰｏｌｙｍｅｒＳｙｓｔｅｍＺｈａｎｇＨｏｎｇ－ｄｏｎｇ；ＹＡＮＤｏｎｇ；ａｎｄＹＡＮＧＹｕ－ｌｉａ...

Effect of hot-band annealing process on microstructure,texture,and r-value of final sheets of ferritic stainless steel

In this paper,the effect of different annealing processes on the microstructure,texture,and formability of ferritic stainless steel was studied in detail.The results showed that the grain size in the final sheet was larger and the recrystallization texture was more uniform after the final recrystallization annealing of hot-rolled steel with continuous annealing than that without annealing or with batch annealing.In addition,the final sheet had a higher average r-value and the lowest planar anisotropy.

Microstructure and texture evolution of AZ31 magnesium alloy during large strain hot rolling

Commercial AZ31 magnesium alloy sheets were rolled by nearly 70% thickness reduction in one rolling pass at 823 K. The results show that ultrafine grains are distributed in both shear bands and surfaces of the rolled sheets. The grain size of the refined grain in the shear bands is 0.4-1 μm. The outstanding grain refinement is attained by dynamic recrystallization due to flow localization. The texture in middle layer of the sheet is basal texture with little change in intensity throughout the rolling process, while the texture on surface becomes a double-peak texture with basal poles splitting in the transverse direction（TD）. The relative intensity of the double-peak texture is 26.6, which is quite higher than that of the texture in the middle layer. The inhomogeneous strain distribution is responsible for the exceptional grain refinement and texture evolution.

The modified temperature term on Johnson-Cook constitutive model of AZ31 magnesium alloy with {0002} texture

The dynamic compression experiments with Split-Hopkinson Pressure Bar(SHPB)were performed on AZ31 magnesium alloy rolled sheet specimens in the normal direction(AZ31-ND)with{0002}texture at the temperature of 293-523 K and the strain rate of 0.001-2200 s^−1.The temperature term in Johnson-Cook(JC)constitutive model had been reasonably modified.This advantage made constitutive model promising for decribing the dynamic deformation behavior of AZ31-ND with{0002}texture more accurately.The obtained true stress-true plastic strain curves agreed well with the measured results in a wide range of strain rates and temperatures.The thermal softeninging,strain and strain rate hardening effect on the AZ31-ND with{0002}texture were discussed.The adiabatic shear band(ASB)of AZ31-ND with{0002}texture hat shaped specimen was successfully predicted by combining modified JC constitutive model and numerical simulation,which was also validated by Electron Back-Scattered Diffraction(EBSD)map under the same boundary condition.

Texture and color enhancement imaging in magnifying endoscopic evaluation of colorectal adenomas

BACKGROUND Olympus Corporation has developed texture and color enhancement imaging(TXI)as a novel image-enhancing endoscopic technique.AIM To investigate the effectiveness of TXI in identifying colorectal adenomas using magnifying observation.METHODS Colorectal adenomas were observed by magnified endoscopy using white light imaging(WLI),TXI,narrow band imaging(NBI),and chromoendoscopy(CE).This study adopted mode 1 of TXI.Adenomas were confirmed by histological examination.TXI visibility was compared with the visibility of WLI,NBI,and CE for tumor margin,and vessel and surface patterns of the Japan NBI expert team(JNET)classification.Three expert endoscopists and three non-expert endoscopists evaluated the visibility scores,which were classified as 1,2,3,and 4.RESULTS Sixty-one consecutive adenomas were evaluated.The visibility score for tumor margin of TXI(3.47±0.79)was significantly higher than that of WLI(2.86±1.02,P<0.001),but lower than that of NBI(3.76±0.52,P<0.001),regardless of the endoscopist’s expertise.TXI(3.05±0.79)had a higher visibility score for the vessel pattern of JNET classification than WLI(2.17±0.90,P<0.001)and CE(2.47±0.87,P<0.001),but lower visibility score than NBI(3.79±0.47,P<0.001),regardless of the experience of endoscopists.For the visibility score for the surface pattern of JNET classification,TXI(2.89±0.85)was superior to WLI(1.95±0.79,P<0.01)and CE(2.75±0.90,P=0.002),but inferior to NBI(3.67±0.55,P<0.001).CONCLUSION TXI provided higher visibility than WLI,lower than NBI,and comparable to or higher than CE in the magnified observation of colorectal adenomas.

Texture and color enhancement imaging for detecting colorectal adenomas: Good, but not good enough

Texture and color enhancement imaging(TXI)has been developed as a novel image-enhancing endoscopy.However,the effectiveness of TXI detecting adenomas is inferior to narrow band imaging.Thus,future studies will need to focus on investigating the feasibility of such combination in clinical settings in order to provide patients with more accurate diagnoses.

Modelling Textural Anisotropy of Magnetic Susceptibility of Banded Iron Formations

Anisotropy of magnetic susceptibility (AMS) of banded iron formations (BIFs) is characterized by high anisotropy and well-developed bedding-parallel magnetic foliation. Since most previous studies were focused on palaeomagneism of BIFs and BIF-derived iron ores, little effort has been made to further understand this special type of AMS for BIFs. A detailed theoretical analysis, incorporating with the previous experimental data, is made to understand the formative mechanism of this special anisotropy for BIFs. The good consistence between the theoretical and experimental results demonstrates that this type of anisotropy is likely caused by the layered structure of BIFs, and thus verifies the term of textural anisotropy for BIFs. Theoretical analysis also shows that in the negligence of the inter-layer magnetic action BIF’s apparent anisotropy increases with an increase in intrinsic susceptibility of magnetic layers, but decreases with an increase in length-to- diameter ratio of the magnetic layer.

基于电压阻尼振荡的变压器故障绕组识别方法

变压器绕组振荡波能够有效地反映绕组状态变化,实际应用中发现振荡波末期存在不规律振荡行为,影响了基于振荡波的变压器绕组故障诊断准确性。该文针对此问题,首先,搭建变压器绕组故障模拟平台,获取轴向移位、局部翘曲、饼间短路和匝间短路四种故障下绕组振荡波数据;其次,通过定义的能量衰减因子,提出了一种基于电压阻尼振荡的变压器绕组振荡波有效波段动态选取方法;再次,基于确定的有效波段,提出了基于二值化的Tamura纹理特征的特征参数提取方法,并结合波形特征关联度(FCD),提出了用于故障类型(轴向移位、局部翘曲、饼间短路和匝间短路)、区域、程度诊断的特征参数组合并分析了其分布规律;最后,基于特征参数组合的分布规律通过实际变压器进行了应用分析。结果表明,动态选取出的波段干扰信息少、衰减振荡规律性明显且包含丰富的特征信息,可实现对故障类型、故障程度和故障区域的识别分类。

冷轧压下率对高强无取向电工钢变形组织和磁性能的影响

借助场发射扫描电镜(SEM+EBSD)、快速升温管式炉和交流磁性能测量仪研究高强无取向电工钢冷轧变形组织和磁性能随冷轧压下率的变化规律。结果表明:冷轧高强无取向电工钢中形成含有大量亚结构的粗糙条带和变形量较小的光滑条带。粗糙条带具有γ取向,主要为{111}〈110〉,光滑条带具有{112}〈110〉和{001}〈110〉取向。粗糙条带中存在大量宽度约为2~3μm的剪切带,与轧向呈20°~35°夹角,且随压下率增大,数量逐渐增多。剪切带与基体间具有一定取向差,随压下率增大,剪切带逐渐从{111}〈110〉取向转向{223}〈110〉取向,与基体间取向差逐渐增大。退火后Goss和{111}面织构增多,{001}面织构减少;轧向磁感应强度增大,横向磁感应强度减小,各向异性显著,铁损下降。

累积叠轧道次对AZ31镁合金板微观组织和力学性能的影响

开展400℃轧制温度下的累积叠轧试验,并利用光学显微镜、拉伸试验机、显微硬度计、X射线衍射仪、扫描电镜对不同累积叠轧道次板材的微观组织和力学性能进行表征,研究累积叠轧道次对AZ31镁合金板材晶粒尺寸、基面织构、力学性能的影响。结果表明:累积叠轧工艺的晶粒细化主要发生在前3道次,随后的循环道次中晶粒不再明显细化,甚至略微长大。第3道次的综合力学性能最佳。剪切带的存在虽缓解了应力集中,提高了塑性,弱化了基面织构,但该处也易形成裂纹,加速板材的断裂,使伸长率急剧下降。基面织构强度随着轧制道次的增加呈先减弱后增强的趋势。

两步升温热轧工艺对AZ31镁合金薄板各向异性及成形性能影响

采用两步梯度升温轧制工艺对AZ31镁合金板材进行轧制,探究轧制过程对镁合金板材显微组织织演化、各向异性及成形性能的影响。第I步轧制在300℃开展,其每道次压下量为15%;第II步轧制在550℃进行,其每道次压下量为40%。经过共4道次轧制后,最终获得厚度为1 mm的镁合金薄板。结果显示,第I步低温轧制过程不更换轧制方向时,试样中生成大量剪切带;而更换轧制方向时,组织内部主要为孪晶和再结晶晶粒。随着II步轧制温度的升高,由于动态再结晶急剧激发,剪切带数量及尺寸逐渐减小,晶粒明显细化。根据IGMA分析得出,非基面滑移,特别是棱柱面滑移活动增强。轧制退火后的AZ31镁合金薄板的力学性能得到提高,各向异性减小,冲压成形性能得到明显改善。

电弧增材制造不锈钢动态加载绝热剪切带内组织研究

绝热剪切失效是增材制造金属材料在高应变率载荷下的重要失效方式。使用电火花从冷金属过渡电弧增材技术制备的316L不锈钢单壁上沿着制造方向和扫描方向割出动态加载圆柱试样(尺寸为φ4 mm×4 mm)。采用分离式霍普金森杆对增材制造316L试样在应变率4 000到6 000 s^(-1)下加载至绝热剪切状态,研究了其动态剪切变形行为特别是剪切带内微观组织特征结构。不同应变率动态加载下,电弧增材制造316L不锈钢的动态应力首先由于应变硬化而增大,随后绝热剪切热软化与应变硬化的平衡导致了动态变形最后阶段的应力平台效应。绝热剪切带中亚晶经历了动态再结晶过程,具有与基体完全不同的等轴晶形貌,晶粒尺寸大约在200~300 nm。动态剪切复杂热力过程导致剪切带内的亚晶形成了双重织构,既有与基体一致的沿着压缩方向的<110>丝织构,也有与宏观剪切方向相关的晶体学织构,即(111)沿着宏观剪切面,<112>沿着宏观剪切方向。不同剪切带的等轴亚晶都有大量残余Σ3 60°晶界,同时存在与基体相同的孪生织构,可以证明孪生再结晶是绝热剪切带内亚晶主要的动态再结晶机制。宏观绝热剪切带发展路径沿着压缩面35°的对称路径发展,这除了符合动态加载下试样中最大应变和热场分布的外加物理条件,还符合剪切面(111)与基体(110)面交角为35.2°的晶体学条件。此外,基体中存在大量微观局部变形带来承载应变,微观局部变形带内亚晶也具有与基体孪晶组织不同的位向和形貌。

晶界角度对Al-Mg-Sc-Zr合金板材各向异性行为的影响

通过多向锻造和退火处理对Al-Mg-Sc-Zr合金进行晶界优化,对比研究混合晶界结构对合金板材力学性能各向异性行为的影响。结果表明:均匀化状态合金以高角度晶界为主,经过轧制变形后形成较多轧制剪切带和高强度的Brass,Copper和S织构,轧制板材力学性能各向异性行为较为明显,屈服强度IPA_(YS)和抗拉强度IPA_(UTS)指数分别为6.68%和5.85%;合金经过多向锻造和退火处理后,基体为高/低角度晶界结构并存的混晶组织,经过轧制变形后剪切带密度和织构强度明显降低,合金轧制板材性能各向异性行为得到明显改善。

Effect of Hot Band Annealing Processes on Microstructure,Texture and r-Value of Ferritic Stainless Steel

The effect of hot band annealing processes,namely simulating batch annealing and continuous annealing,on microstructure,texture,grain boundary character and r-value of ferritic stainless steel was investigated.The hot band displayed a highly elongated ribbon-like structure and a pronounced deformation texture.The fully recrystallized grains were observed after continuous annealing while the ＂typical＂ hot rolled structure was remained after batch annealing.Also,the α-fibre texture formed during hot rolling almost disappeared after continuous annealing and a weak γ-fibre texture was obtained.By contract,the α-fibre texture remained very stable after batch annealing.After cold rolling and recrystallization annealing,the favorable γ-fibre texture was achieved in the continuous annealed steel.Instead of forming the γ-fibre texture,the recrystallization texture was notably shifted toward {223}〈582〉 in the batch annealed steel.Finally,the improvement in drawability with high r-value and low Δr-value were also displayed in sheet through the initial continuous annealing process.

Influence of Shear Banding on the Formation of Brass-type Textures in Polycrystalline fcc Metals with Low Stacking Fault Energy

Texture evolution in nickel, copper and α-brass that are representative of face-centered-cubic （fcc） materials with different stacking fault energy （SFE） during cold rolling was systematically investigated. X-ray diffraction, scanning electron microscopy and electron backscatter diffraction techniques were employed to characterize microstructures and local orientation distributions of specimens at different thickness reductions. Besides, Taylor and Schmid factors of the {111} 〈110〉 slip systems and {111} 〈112〉 twin systems for some typical orientations were utilized to explore the relationship between texture evolution and deformation microstructures. It was found that in fcc metals with low SFE at large deformations, the copper-oriented grains rotated around the 〈110〉 crystallographic axis through the brass-R orientation to the Goss orientation, and finally toward the brass orientation. The initiation of shear banding was the dominant mechanism for the above-mentioned texture transition.

Texture coefficient and band gap tailoring of Fe-doped SnO_(2) nanoparticles via thermal spray pyrolysis

An investigation of Fe-doping effect on SnO_(2) thin films was performed in this study using thermal spray pyrolysis(TSP) method.The surface morphology and structural,optical and electrical properties were studied by field energy scanning electron microscope(FESEM),X-ray diffraction(XRD),ultraviolet-visible(UV-Vis) spectroscopy and four-point probe method.FES EM images demonstrate that the surface morphology of the as-deposited films varies when Fe-doping content varies.XRD studies reveal that crystallite size and preferential growth orientations of the films are dependent on Fe-doping concentrations.The grain size is found to decrease with the increase in Fe content.These studies also specify that the films have tetragonal rutile-type structure with mixed secondary phases.The texture coefficient value of(110) plane increases with the concomitant in-plane(220) decrease in higher doping concentrations.The resistivity and the optical absorbance are found to increase with Fe concentration.The direct optical band gap decreases from 3.94 to3.52 eV with increasing Fe content.

Effect of Lüders Bands by Strain Ageing on Strain Distribution,Microstructure and Texture Evolution of High-Strength Pipe Steel

In this study,the high-strength pipe steel,i.e.X80,was heated at 260℃for half an hour followed by air cooling for thermal simulation of pipe coating process.During the uniaxial loading of the specified tension samples,the migration behaviour of Lüders bands and the re-distribution of stress after strain ageing heat treatment were investigated using digital image correlation.Digital image correlation was adopted to characterise the local axial and shear strain fields of samples that were extracted from different locations across the wall thickness of the high-strength pipe steel,and electron backscatter diffraction was used to compare the evolution of crystallographic texture among these locations.Other characterisation methods regarding microstructure and mechanical properties were conducted meanwhile,including optical microscopy,scanning electron microscopy and X-ray diffraction to accurately define the detailed performances that strain ageing,i.e.being heated to 260℃for half an hour,has led to.The obtained results show that the Lüders band-related microstructure,dislocation density,lattice constant and texture vary at the different locations across the wall thickness and influence the fi nal mechanical properties of the selected high-strength pipe steel.