关键词： Polystyrenes  

摘要： The mathematical model developed by Reneker et al. [J. Appl. Phys. 87, 4531 (2000)] and Yarin et al. [J. Appl. Phys. 89(5), 3018-3026 (2001)] for modeling filament formation in electro-spinning is combined in this work with the structure generation algorithm of Venkateshan et al. [Mater. Des. 96, 27-35 (2016)] to simulate the effects of electrospinning parameters on micro structural properties (i.e., fiber diameter, thickness, and porosity) of the resulting electrospun materials. The model is calibrated using the experimental data obtained from electrospinning polystyrene (PS) fibers. The computational tool developed in this work allows one to study the effects of electrospinning parameters, such as voltage, needle-to-collector distance (NCD), or PS concentration, on the thickness and porosity of the resulting fibrous materials. For instance, it was shown that increasing the voltage or decreasing the NCD in electrospinning polystyrene results in mats with thicker fibers but smaller dimensionless thickness (or lower porosities), in agreement with experimental observations reported in the literature. In addition to serving as a characterization tool for the electrospun materials, the computational model developed in this work can be used to create accurate representations of the surface morphology or the internal geometry of fibrous materials used in a variety of applications, such as particle filtration or droplet separation. Published by AIP Publishing.

关键词： failure mode   finite element method   granular material   instability   micromechanics   second-order work  

摘要： This paper aims to develop a multiscale approach that has the ability to characterise the influence of microstructural instabilities on global failures in granular materials. For this purpose, the Chang-Hicher multiscale constitutive relation has been implemented into a finite element code, and the expression of the second-order work, as an indicator of the material instability, has been computed at the interparticle contact scale, at the representative element volume scale, and at the boundary value problem scale. At the global scale, the second-order work can be obtained through the integration of that obtained at interparticle contacts. Hence, it becomes possible to analyse the range of instability from the microstructure to the macrostructure. Drained and undrained triaxial tests were numerically simulated. With this method, it was demonstrated that the grain-scale origin of the specimen instability was well captured. Additionally, biaxial tests were conducted and the onsets of localised and diffuse failure in granular assemblies were successfully predicted. The transition from diffuse to localised failure was demonstrated at different scales, whereby the coincidence between the direction of local instabilities and the direction of the shear band became evident. The influence of the boundary conditions and of the heterogeneity of the initial porosity on the failure mode of granular materials was also analysed. All these examples demonstrate that the developed multiscale approach can characterise in a satisfactory manner the influence of instability at the inter-grain contacts upon the global failure of granular assemblies.

关键词： 石英砂   托辊   抗折强度   微观结构   烧结性能  

摘要： 本文采集了海南六个地区的石英砂样品,对这些样品进行了化学成分,白度和粒径的分析;并研究了不同石英砂原料对托辊用陶瓷材料显微结构、烧结性能和力学性能的影响。结果表明:石梅湾采集的石英砂具有较细的粒度D70=0.24μm和较低的烧失量1.88wt.%;采用此石英砂制得托辊用陶瓷材料具有最佳的抗折强度(126.02 MPa)和良好的烧结性能,显气孔率0.4%,体积密度2.84 g/cm^3。较好的性能归因于材料微观尺度上较小的气孔尺寸、颗粒拔出机制的作用以及贝壳状和多片状断裂机制的作用。最后采用这种配方成功做出了陶瓷托辊试样。

关键词： 高熵合金   纳米孪晶   形变   电化学行为   腐蚀机制  

摘要： 纳米孪晶强化CoCrFeNi高熵合金线材以其优异的力学性能被视为是传统线材面向苛刻工况应用的潜在替代品。采用电弧熔炼、冷热机械加工、剧烈冷变形技术制备纳米孪晶强化CoCrFeNi高熵合金线材,采用场发射扫描电镜(FE-SEM)、透射电镜(TEM)分析其微结构,利用电化学分析在3. 5%(质量分数) Na Cl,1 mol·L^(-1)H2SO4,1 mol·L^(-1)Na OH溶液中分别分析CoCrFeNi高熵合金线材的腐蚀行为,采用FESEM观察其在不同介质中的腐蚀形貌,分析CoCrFeNi高熵合金线材在不同介质中的腐蚀机制。结果表明,CoCrFeNi高熵合金线材经冷变形后呈纤维状组织,其在3种典型环境下的耐蚀性均较为理想。其在3. 5%Na Cl溶液中的腐蚀机制主要为点蚀,自腐蚀电流密度低至3. 85×10^-7A·cm^(-2),腐蚀后仅有极少量蚀坑存在。而在1 mol·L^(-1)H2SO4与1 mol·L^(-1)Na OH溶液为均匀腐蚀,自腐蚀电流密度分别可达1. 26×10^-6,7. 88×10^-6A·cm^(-2),腐蚀形貌呈均匀腐蚀特征。CoCrFeNi高熵合金线材在3. 5%Na Cl溶液、1 mol·L^(-1)H2SO4溶液与1 mol·L^(-1)Na OH溶液中均具有较好的耐蚀性,具备在这几种典型环境应用的潜力。

关键词： 仿生结构   复合陶瓷刀具材料   显微结构   力学性能  

摘要： 针对不同烧结条件及TiC/WC组分比,采用热压烧结工艺制备出三层仿生结构复合陶瓷刀具材料。测试了仿生结构复合陶瓷材料力学性能,并对材料断口形貌和裂纹扩展进行了观察分析。结果表明:仿生结构复合陶瓷刀具材料抗弯强度达870 MPa,维氏硬度达21.83 GPa,断裂韧性达7.56 MPa·m^(1/2),比SG4均质陶瓷刀具材料性能有所提高。断口形貌显示仿生结构复合陶瓷刀具材料较SG4均质刀具材料晶粒细密,晶粒尺寸呈现多尺度特征。材料断裂模式为穿晶断裂和沿晶断裂混合型。仿生结构复合陶瓷材料表面裂纹扩展呈现偏转和分叉。裂纹穿过材料界面扩展时有明显偏转现象。

关键词： silver nanowires   capacitive pressure sensor   flexible   transparent   wearable electronics   e-skin  

摘要： The development of pressure sensors with highly sensitivity, fast response and facile fabrication technique is desirable for wearable electronics. Here, we successfully fabricated a flexible transparent capacitive pressure sensor based on patterned microstructured silver nanowires(AgNWs)/polydimethylsiloxane(PDMS) composite dielectrics. Compared with the pure PDMS dielectric layer with planar structures, the patterned microstructured sensor exhibits a higher sensitivity(0.831 kPa^-1, <0.5 kPa), a lower detection limit,good stability and durability. The enhanced sensing mechanism about the conductive filler content and the patterned microstructures has also been discussed. A 5×5 sensor array was then fabricated to be used as flexible and transparent wearable touch keyboards systems. The fabricated pressure sensor has great potential in the future electronic skin area.

关键词： 陶瓷基复合材料   碳化硅粉体   聚碳硅烷   浆料注射   热压烧结   断裂功  

摘要： 采用新型浆料注射/真空浸渍工艺实现了超高温陶瓷组分与碳纤维的有效复合,并结合低温(1 450℃)热压烧结实现了Cf/ZrB2-SiC复合材料的制备。研究了不同SiC源(SiC粉体和聚碳硅烷PCS)对复合材料微结构和力学性能的影响,结果表明:基于聚碳硅烷优异的流动性实现了陶瓷组分在纤维束内和束间的有效填充,并经低温热压烧结后Cf/ZrB2-PCS复合材料的相对密度为91.3%,主要归结于聚碳硅烷裂解后残留的微量无定性碳起到了表面除氧的作用而促进致密化,但该无定性碳弱化了晶界强度而导致力学性能降低。同时Cf/ZrB2-PCS复合材料表现出非脆性断裂模式且断裂功高达539 J/m^2,较Cf/ZrB2-SiCp复合材料提升高达84.6%;该复合材料断裂功的提升主要归结于裂纹偏转、裂纹分叉和纤维桥联等多种增韧机制的协同效应,大幅度改善了ZrB2基超高温陶瓷材料的损伤容限和可靠性。

关键词： 铜锌锡硫   热注入法   纳米晶   太阳电池  

摘要： 采用热注入法制备Cu_2ZnSnS_4(CZTS)纳米晶,研究了金属前驱体摩尔比对所制备的CZTS纳米晶的晶体结构、化学组分、形貌及光学性能的影响。实验结果表明:当Cu∶(Zn+Sn)前驱体摩尔比在0.8∶1～1∶1范围变化时,所得到的产物为纯锌黄锡矿结构CZTS纳米晶。当Cu∶(Zn+Sn)≤0.7∶1时,产物的XRD图谱在(112)晶面衍射峰附近出现微弱的SnS杂峰。当Cu∶(Zn+Sn)前驱体摩尔比从0.9∶1变化为0.8∶1时,纳米晶的形貌主要为球形,少量为多边形;当Cu∶(Zn+Sn)前驱体摩尔比从0.7∶1减小到0.6∶1时,纳米晶的形貌主要有纺锤形及少量球形。所制备样品的光学带隙随着Cu∶(Zn+Sn)前驱体摩尔比的减小而增大,其带隙宽度在1.44～1.56eV之间变化。

关键词： 化学液相沉积   C/C复合材料   热解碳   致密化速率  

摘要： 化学液相沉积法(简称CLVD)是一种快速致密C/C复合材料的有效工艺.利用自行研制的沉积装置,以碳毡为预制体,研究了其在不同工艺下的致密化行为.并对复合材料的密度、孔隙率、致密化速率及显微形貌与结构进行了分析.结果表明:自行研制的沉积装置可实现C/C复合材料的快速制备,在1 050℃下经1h沉积后制备出密度近1.6g/cm^3的C/C复合材料,致密化效果显著.沉积的热解碳以碳纤维为轴形成同轴层状结构,沉积温度升高,致密化速率加快,热解碳由光滑层向粗糙层过渡,并向有序的石墨结构进行转化.

关键词： 复合材料   SPAN   钙基膨润土   电阻率  

摘要： 膨润土具有良好的物理性能和化学稳定性,具有广泛的用途,被誉为"万能石",一些学者尝试将其运用于电力行业,但因其电阻率较大而不适用。而制备出一种低电阻率的磺化聚苯胺(SPAN)改性钙基膨润土复合材料,使其在电力领域运用成为可能。采用插层聚合法制备导电SPAN-钙基膨润土复合材料,并通过正交法优化苯胺(An)加入量、反应时间、反应温度3个制备工艺参数。利用扫描电子显微镜(SEM)、红外光谱(FT-IR)、X射线衍射(XRD)、四点探针对钙基膨润土和SPAN-钙基膨润土复合材料进行微结构组织和性能表征。制备SPAN-钙基膨润土复合材料的最佳工艺方案为:An加入质量分数为50%,反应时间为16h,反应温度为0℃。反应时间对复合材料的性能影响较为显著。与钙基膨润土相比,SPAN-钙基膨润土复合材料的微观组织更均匀,晶面间距较大,电阻率下降了5个数量级,测得电阻率是1Ω·mm。