咖啡纤维结构与性能研究

介绍了咖啡纤维的生产过程和物理性能,通过红外光谱仪、X射线粉末衍射仪和扫描电子显微镜研究了咖啡纤维的亲水基团、吸湿性、结晶度和形态结构等,并与棉纤维和麻纤维进行了对比,证明了咖啡纤维的可纺性,有利于咖啡纤维的进一步开发和利用.     

Studies regarding simulation process to static loading of the structures obtained from polylactic acid, 3D printed

Being a relatively new process, additive manufacturing needs many studies to be able to produce parts with the required properties. The aim of the paper is to establish whether, based on the physical and mechanical properties determined by tensile testing and by applying finite element analysis (FEA), viable results can be obtained regarding the behavior of the 3D printed structures at the different, static loading. The application of FEA for the tensile testing of 3D specimens led to the results close to those obtained by the tests. The values of the results obtained by simulation are higher by up to 7.2% compared with those recorded by tests. The simulation was applied both for the printed specimens from a single material and from two materials (multi-material). Regardless of the materials used in printing and the simulation method, the results of applying FEA are close to those recorded by testing.     

Impact of processing conditions and sizing on the thermomechanical and morphological properties of polypropylene/carbon fiber composites fabricated by material extrusion additive manufacturing

For the 3D printed composites, fiber alignment is affected by the direction of melt-flow during extrusion of filaments and subsequently through the printing nozzle. The resulting fibers orientation and the fiber-matrix compatibility have a direct correlation with mechanical properties. This study investigates the impact of processing conditions on the state of the carbon fiber types and their orientation on the mechanical properties of 3D-printed composites. Short and long carbon fibers were used as starting reinforcing materials, and the state of fibers at the beginning and on the printed parts were evaluated. Strong anisotropy in terms of mechanical properties (flexural and impact properties) was observed for the samples printed with different printing orientations. Interestingly, the number of voids in the printed composites was found to be correlated with the fiber types. The present work provides a step towards the optimization of tailored composite properties by additive manufacturing.     

Polymer matrices on the basis of polyacrylamide and β-cyclodextrin-containing pseudorotaxane for prolonged drug release: Synthesis and properties

Polymer cross-linked matrices based on polyacrylamide (PAA) and β-cyclodextrin-pseudorotaxane have been designed. The structure and properties of the objects synthesized were confirmed and studied by a series of methods, involving ultraviolet-, Fourier transform infrared-spectroscopy, thermal mass spectrometry, DSC, X-ray diffraction analysis (WAXS and SAXS). Desorption kinetics (especially significant slowing of desorption process) of some drugs, like metoprolol succinate and loratadine from obtained polymer matrices is shown to be optimal with 10 wt% β-CD-pseudorotaxane in their structure.     

Characterization of PA-12 specimens fabricated by projection sintering at various sintering parameters

Large area projection sintering (LAPS) promises to be a new method in the field of additive manufacturing. Developed in the Mechanical Engineering Department, University of South Florida, LAPS uses long exposure times over a broad area of powder to fuse into dense, reproducible materials. In contrast, LS, a common powder-based additive manufacturing, uses a focused beam of light scanned quickly over the material. Local regions of concentrated high-energy bursts of light lead to higher peak temperatures and differing cooling dynamics and overall crystallinity. The mechanical properties of laser sintered specimens suffer because of uneven particle fusion. LAPS offers the capacity to fine-tune fusion properties through enhanced thermodynamic control of the heating and cooling profiles for sintering. Further research is required to identify the relationship between LAPS build settings and part properties to enable the fabrication of custom parts with desired properties. This study examines the influence of LAPS sintering parameters on chemical structures, crystallinity, mechanical, and thermal properties of polyamide-12 specimens using powder X-ray diffraction, Fourier transform infrared spectroscopy, differential scanning calorimetry, small-angle X-ray scattering, scanning electron microscopy, and microhardness testing. It was observed that higher crystallinity was imparted to specimens that were sintered for a shorter time and vice versa.     

Effect of MgO sintering additive on mullite structures manufactured by fused deposition modeling (FDM) technology

An optimized recipe for 3D printing of Mullite-based structures was used to investigate the effect of MgO sintering additive on the processing stages and final ceramic properties. To achieve dense 3:2 mullite, ceramic filaments were prepared based on an alumina powder, a methyl silicone resin, EVA elastomeric binder and MgO powder. Using 1 wt% MgO and a dwell time of 5 h at 1600 °C, a dense mullite structure could be obtained from filaments with a diameter of 1.75 mm. Ceramic structures with and without sintering additive were printed in vertical and horizontal direction, to investigate the effect of printing direction on mechanical strength after sintering. Using four-point bending test, it was demonstrated that by using MgO, the printing orientation did not affect the mechanical strength significantly anymore. The low Weibull modulus could be explained by the closed porosity that emerge during the degassing of the preceramic polymer due to cross-linking.     

Effect of amide type modified rapeseed oil as lubricating additive on friction and wear behavior of steel-steel and steel-aluminum alloy systems

A new type of environmentally friendly lube additive-amide type modified rapeseed oil was synthesized and characterized by infrared spectrum. Its effect on the friction and wear behavior of steel-steel and steel-aluminum alloy systems were investigated with a four-ball machine and an Optimol SRV friction and wear tester respectively.The morphographies of the worn surfaces were analyzed by means of scanning electron microscopy(SEM). The worn surfaces of the 2024Al alloy block were analyzed by means of X-ray photoelectron spectroscopy(XPS). The results show that the modified rapeseed oil as additives can obviously decrease the wear rate and friction coefficient of steel pair and steel-aluminum frictional pair. Its lubrication mechanism is inferred that a high strength complex protection films form on the worn surface of the Al alloy due to the adsorption or tribochemistry reaction of a long chain additive molecule and high reaction activity of N element.     

浇注法制备表面复合材料用复合剂的强度表征及测试

用改进后的强度测试仪，检测分析了三种自制复合剂不同温度下的抗弯强度，探讨了复合剂强度的测试方法，结果表明：抗弯强度可用来表征用于浇注法制备金属基复合材料的复合剂强度，抗弯强度越高，铸件浇铸成型率越高。     

纳米复合自修复添加剂的制备及其在发动机上的应用

利用合成和复配等技术研制了一种含纳米铜和稀土化合物的复合自修复添加剂,在发动机上考察了该添加剂的使用性能,分析了不同工作时期发动机机油的衰变情况,测量了该添加剂对发动机外特性的影响。结果表明:含纳米自修复添加剂的润滑油对发动机中不同材料的摩擦副均有较好的抗磨效果,在发动机运行300 h后,连杆轴、铜套等部位达到了“零磨损”,实现了摩擦副表面的动态自修复;使用该自修复添加剂还能够有效地改善发动机的外特性、降低油耗和延长发动机的服役寿命。     

砂型铸造WC颗粒增强灰铸铁基轧钢导位板的研制

针对轧钢导位板的工况特点, 应用复合材料设计原理和铸造技术相结合,运用自行研制的复合剂,在普通砂型无负压条件下,制备出WC颗粒增强灰铸铁基强力抗磨局部复合材料的轧钢导位板.铸件表面平整光洁,尺寸精度高,复合层厚度均匀,可达7～9 mm,与基体之间呈冶金结合.实际运行表明使用寿命比以往使用的灰铸铁高5倍以上.