Effects of carbon content on microstructure and mechanical properties of SiC ceramics fabricated by SLS/RMI composite process

Selective Laser Sinering (SLS) and Reactive Melting Infiltration (RMI) were combined to fabricate complicated SiC ceramics with high performance in the research. The influence of carbon content on green parts’ mechanical properties was studied. Then, the effect of carbon density on the microstructure of SiC was studied. The results showed that the density of sintered body increased first and then decreased with the increase of carbon black content. Due to the increase of carbon density, the siliconizing property of carbonated preforms is also improved by impregnating asphalt. When the carbon density was 0.6612 g/cm³, sintered density reached 2.899 g/cm³. But the flexural strength reached peak value of 190.19 ± 1.89 MPa as the carbon density decreased to 0.5542 g/cm³. Therefore, this research lays a foundation for laser sintering to fabricate high performance and complex structure SiC ceramics by regulating carbon content.     

On the use of cellulose nanowhisker as reinforcement in all-cellulose composite membrane from corn stalk

All-cellulose composite (ACC) membranes were prepared with cellulose and cellulose nano whisker (CNW) extracted from corn stalk by using NaOH/thiourea as solvent. CNW was isolated via acid hydrolysis method and the yield, size distribution and morphology of CNW were investigated. ACC Membranes were characterized via SEM, XRD, TGA as well as water flux and were further plasticized with glycerol aqueous solution. The mechanical property and transparency of ACC membranes before and after plasticization were compared. CNW prepared with 63% sulfuric acid for 60 min of hydrolysis time had the biggest ratio of length to diameter and moderate yield. ACC membrane with 5% CNW content had the highest tensile strength and the structure of ACC membranes was observed clearly in SEM images. TGA testing indicated that the initial degradation temperature tended to lower after CNW was introduced into membrane. ACC membrane had good optical transmittance and good flexibility after plasticization.     

Flexible and sensitive piezoresistive electronic skin based on TOCN/PPy hydrogel films

In recent years, the wearable electronic skin (E-skin) has attracted more and more attention due to high sensitivity, good portability and flexibility. In this work, we used the 2,2,6,6-tetramethylpiperidinyl-1-oxyl (TEMPO)-oxidized cellulose nanofibril (TOCN) as the substrate, and used the in-situ polymerization method to introduce polypyrrole (PPy) into the TOCN substrate. Then, the nylon gauze was used as microstructure template to prepare a TOCN/PPy E-skin with a surface microstructure. This E-skin possessed excellent sensing and mechanical properties. In the pressure range of 0–600 Pa, the sensitivity of E-skin was 3.13 kPa⁻¹. In addition, the E-skin exhibited ultrafast response/recovery time (≤10 ms), ultralow detection limit of 0.3 Pa, good stability (>9000 cycles) and mechanical strength of up to 117 MPa. Therefore, the TOCN/PPy E-skin has broad development prospects in the fields of artificial intelligence and health monitoring.     

Forcespinning technique for the production of poly(d,l-lactic acid) submicrometer fibers: Process–morphology–properties relationship

This work addresses a systematic study for the process development and optimization of poly(d ,l -lactic acid) (PDLLA) submicrometer fibers utilizing the centrifugal spinning technique known as Forcespinning. This study analyzes the effect of polymer concentration (8, 10, and 12 wt %) and angular speed on the fiber morphology, diameter distribution, and fiber yield. The increase in polymer concentration and angular speed favored the formation of continuous and homogeneous submicrometer fibers with an absence of bead formation and higher output. The optimal conditions were established considering the morphological characteristics that exhibit a greater surface area (homogeneous and submicrometer fibers); and they were achieved at a polymer concentration of 10 wt % at an angular speed ranging from 8000 to 10 000 rpm. Optimization of PDLLA submicrometer fiber fabrication lays the groundwork for scaling up the process and serves as a platform to further develop promising applications of PDLLA nonwoven mats, particularly in the biomedical area such as in scaffolds for tissue engineering. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47643.     

木体系墙体混凝土质量问题分析及预防措施

介绍了墙体木模施工时，墙体混凝土常出现的表面平整度差、截面尺寸偏差大等质量问题，并针对这些质量问题逐一进行了原因分析，在原因分析的基础上制定了行之有效的预防措施。     

Damage Mechanisms in Composite/Composite Bonded Joints Under Static Tensile Loading

This paper presents an experimental study of the initiation and development of damage in composite/composite joints. The materials studied are glass fibre reinforced polyester laminates and these are bonded together using an epoxy adhesive. Two types of joint interface are examined, assemblies between woven roving layers and between mat layers. The experimental techniques employed are dye impregnation, extensometry, visual observation and photoelasticimetry. It is shown that the nature of the surface layer does not influence the damage initiation load but does affect subsequent crack propagation. This revised version was published online in June 2006 with corrections to the Cover Date.     

Solvent effects on liquefaction: Solubilization profiles of a canadian prototype wood,populus deltoides,in the presence of different solvents

Populus deltoides was treated with straight chain alcohols from methanol to n-hexanol, mono and triethanolamine, water, ethyleneglycol, acetone, cyclohexane and lactic acid. A batch reactor was used in all the runs and the temperature range used was from 100 to 320°C. A reaction ordinate concept was used to evaluate the treatment severities. The results of these experiments showed a significant influence of the solvent on the extent of liquefaction of wood as well as on the holocellulose and lignin contents of the residues. An attempt to relate the liquefaction profiles to the solubility parameters of the solvents is discussed.     

Behavior and survival ofReticulitermes hesperus banks (Isoptera: Rhinotermitidae) on selected sawdusts and wood extracts

Survival ofReticulitermes hesperus workers was assessed inPseudotsuga menziesii, Lysiloma seemanii, andTabebuia ochracea sawdusts; and on heartwood solvent extracts ofP. menziesii, L. seemanii, T. ochracea, Pinus ponderosa, Tabebuia guayacan, and aCentrolobium species. Survival inP. menziesii sawdust was 100% at 5 days and 81–87% at 15 days. Survival inL. seemanii andT. ochracea sawdusts was significantly less over both 5 and 15 days than in the starvation control, indicating toxicity. Survival on filter papers treated with solvent extracts ofT. ochracea andP. ponderosa was significantly less than that on control papers, but onlyP. ponderosa differed significantly from the starvation control. In behavioral assays with groups and with individualR. hesperus workers, extracts ofP. menziesii andP. ponderosa were preferred. In the individual behavioral assays, extracts ofT. guayacan andT. ochracea were repellent. Results of toxicity assays were not predictable from preference assays.     

Finite Element Assisted Modelling of the Microscopic Impregnation Process in Thermoplastic Preforms

Fibre reinforced composite materials incorporating thermoplastic matrices are gaining increasing popularity in many industrial applications. One of the potential preforms for the manufacture of technical components is commingled yarn composed of reinforcement and matrix in fibre form. These are often employed in the pultrusion process. Another innovative preform consists of polymer powder preimpregnated sheath surrounding fibre bundles. To achieve adequate mechanical properties of the final product it is essential, when producing laminates by a process such as pultrusion with both types of preform, that sufficient matrix impregnation is achieved. The prevention of voids and dry-spots in the laminate requires a theoretical understanding of the mechanisms involved. On a microscopic scale, several finite element (FE) models can be used to simulate the progress of the matrix flow into the interstitial spaces between the single reinforcement fibres. In the present simulations, a hexagonal and a square arrangement account for two of the various fibre packings occurring in a laminate. It permits an estimation of the impregnation performance of commingled and powder impregnated yarns. For each preform the shear rate, to which the polymer matrix is subjected during the impregnation and consolidation process, can be predicted.     

PC机在沥青自动浸渍工艺中的应用

介绍了我国第一条自行设计、制造的密闭型高压沥青浸渍自动化生产线。生产线由加热入口室、加热室、加热出口室、浸渍室和冷却室组成，整个系统由ＰＣ机按输入指令来完成。详细介绍了该生产线工艺过程、控制方法选择及ＰＣ机控制原理。生产线经一年的试生产证明，其工作性能不亚于国外同类型引进设备。