Longsheng Lu

Fabrication and Characterization of Aluminum Fibers by Peripheral Milling

A novel peripheral milling process with an end milling cutter for manufacturing aluminum fibers is proposed. Most of the cutting is done by the peripheral teeth of the cutter and the chips removed by the teeth form aluminum fibers, while the cutter end has little effect on aluminum fibers. The machining principle and the formation mechanism of aluminum fiber cross-section are presented. The feasibility of this new fabrication process is experimentally investigated under different machining conditions. In addition, influences of cutting parameters on the equivalent diameter, the length, and surface morphology of aluminum fibers are analyzed. Experimental results indicate that aluminum fibers can be successfully manufactured by peripheral milling and the productivity can be improved by increasing the rotational speed n. Smaller radial depth of cut a e , larger rotational speed n, and smaller feed speedv f are in favor of obtaining slim aluminum fibers. The length of aluminum fibers is theoretically determined by the axial depth of cut a p and also actually affected by other cutting parameters. Of all the cutting parameters considered in these experiments, the optimum parameters of a e , n, and v f are 0.3 mm, 118 r/min, and 60 mm/min, respectively.

The Electrochemical Behavior of Carbon Fiber Microelectrodes Modified with Carbon Nanotubes Using a Two-Step Electroless Plating/Chemical Vapor Deposition Process

Carbon fiber microelectrode (CFME) has been extensively applied in the biosensor and chemical sensor domains. In order to improve the electrochemical activity and sensitivity of the CFME, a new CFME modified with carbon nanotubes (CNTs), denoted as CNTs/CFME, was fabricated and investigated. First, carbon fiber (CF) monofilaments grafted with CNTs (simplified as CNTs/CFs) were fabricated in two key steps: (i) nickel electroless plating, followed by (ii) chemical vapor deposition (CVD). Second, a single CNTs/CF monofilament was selected and encapsulated into a CNTs/CFME with a simple packaging method. The morphologies of as-prepared CNTs/CFs were characterized by scanning electron microscopy. The electrochemical properties of CNTs/CFMEs were measured in potassium ferrocyanide solution (K4Fe(CN)6), by using a cyclic voltammetry (CV) and a chronoamperometry method. Compared with a bare CFME, a CNTs/CFME showed better CV curves with a higher distinguishable redox peak and response current; the higher the CNT content was, the better the CV curves were. Because the as-grown CNTs significantly enhanced the effective electrode area of CNTs/CFME, the contact area between the electrode and reactant was enlarged, further increasing the electrocatalytic active site density. Furthermore, the modified microelectrode displayed almost the same electrochemical behavior after 104 days, exhibiting remarkable stability and outstanding reproducibility.

Effect of a sizing agent on short carbon fiber production with radial chopping technology

Short carbon fiber (short-CF) has been extensively used as enforcement in composites or conductors in fibrous network materials, owing to its good subsequent processing compatibility with routine manufacturing technologies. Conventionally, short-CFs were made by cutting continuous CF-tows from thousands of meters into several millimeters length scale using a radial chopping technology, mainly through sizing, drying and chopping processes in sequence. In this work, four kinds of CF-tows with different physical properties were chopped to study the effect of a sizing agent on the production of short-CFs, including product morphology and yield ratio. All experiments were conducted on polyacrylonitrile-based CFs sized by polyurethane (PU)-acetone solution. Results show that the uniformity (an important index of short-CF appearance) of short-CFs is closely related to the unit sizing weight. The yield ratio is affected by the relative sizing amount of PU coated on CF-tows. In addition, a raw CF-tow with little fiber hairiness is beneficial to increase the yield ratio of short-CFs.

Fracture analysis of a single polyacrylonitrile-based carbon fiber in rigid-fixing and flexible-fixing chopping processes

Chopping is an efficient way to produce short carbon fiber (CF). Generally, there are two types of fixing constraints available in the chopping process: rigid-fixing and flexible-fixing. Simplified experiments were performed using glass and rubber as the fixing constraints in cutting a single polyacrylonitrile-based CF to reveal the influence of the fixing constraints in CF chopping. The cutting forces and the bending angles with different fixing constraints were analyzed. Furthermore, the failure surface of the CF was observed. Due to an additional bending effect in the flexible-fixing cutting, the failure surface of the CF was rough, and the cutting-off force was approximately 5% of the force in rigid-fixing cutting. Therefore, flexible-fixing cutting is a suitable way to decrease the cutting-off force in CF chopping. Moreover, it was concluded that the fiber fracture in rigid-fixing cutting is caused by compression, whereas in flexible-fixing cutting, it results from bending. We hope our work is beneficial to the design of the chopping procedure for short CF.

Manufacture of high-quality chopped carbon fibers based on fuzzy comprehensive evaluation

Chopped carbon fiber, as a commercially available category of carbon fiber, is an important intermediate material to fabricate carbon fiber–reinforced composites or nonwoven fabrics. Due to lack of direct quality assessment method, the quality of chopped carbon fibers is always indirectly evaluated by its composites or fabrics. Here, we employed an entropy-weighted fuzzy comprehensive evaluation method to directly assess the quality of chopped carbon fibers in mass production. Considering chopped carbon fibers with good quality should appear in the forms of good length uniformity, well bundling appearance, good surface properties, and identical fracture, four evaluation indexes were selected, including length standard deviation, width dispersion standard deviation, average scores of fracture morphology, and bundling morphology. Among which, both the fracture morphology and bundling morphology were scored by an expert scoring method. Furthermore, we established an orthogonal test consisting of four factors and three levels with the aim of reducing experiment frequency. The results indicated that the optimal processing parameters were obtained through the calculation of fuzzy comprehensive evaluation, thus fabricating high-quality chopped carbon fibers. This work can have a certain guidance value for the mass production of chopped carbon fibers in the industry.

Experimental Study on Tensile Properties of a Novel Porous Metal Fiber/Powder Sintered Composite Sheet

A novel porous metal fiber/powder sintered composite sheet (PMFPSCS) is developed by sintering a mixture of a porous metal fiber sintered sheet (PMFSS) and copper powders with particles of a spherical shape. The characteristics of the PMFPSCS including its microstructure, sintering density and porosity are investigated. A uniaxial tensile test is carried out to study the tensile behaviors of the PMFPSCS. The deformation and failure mechanisms of the PMFSCS are discussed. Experimental results show that the PMFPSCS successively experiences an elastic stage, hardening stage, and fracture stage under tension. The tensile strength of the PMFPSCS is determined by a reticulated skeleton of fibers and reinforcement of copper powders. With the porosity of the PMFSS increasing, the tensile strength of the PMFPSCS decreases, whereas the reinforcement of copper powders increases. At the elastic stage, the structural elastic deformation is dominant, and at the hardening stage, the plastic deformation is composed of the structural deformation and the copper fibers’ plastic deformation. The fracture of the PMFPSCS is mainly caused by the breaking of sintering joints.

Effect of Drawing Parameters on Elongation of Micro Copper Tube with Straight Grooves

Using high-speed oil-filled spinning and multi-pass drawing composite machining methods, a micro straight groove of copper tube(MSGCT) with an outer diameter about 3 mm~6 mm was obtained, and the forming mechanism of micro straight grooves was investigated. The key factors of process parameters influence the drawing were analyzed. The experimental results show that the values of drawing elongation increases with reduction and die angle increasing. However, drawing elongation increases firstly and then becomes smooth with drawing speed increasing. Stable-quality MSGCT can be achieved by controlling the drawing process parameters and the configurations of micro straight grooves were observed by scanning electron microscope(SEM). In addition, the high-speed oil-filled spinning and multi-pass drawing composite manufacturing can further improve the capillary force of the micro straight grooves of copper heat pipe.

A Thermoplastic Multilayered Carbon-Fabric/Polycarbonate Laminate Prepared by a Two-Step Hot-Press Technique

Carbon fiber (CF) reinforced thermoplastic composites have gradually become increasingly popular in composite production owing to their lower hazard level, good structural flexibility and recyclability. In this work, a multilayered carbon–fabric/polycarbonate laminate (multi-CFPL) was fabricated by a two-step hot-press process, mainly based on the thermoplastic properties of its polycarbonate (PC) matrix. Different from the conventional one-step method, the two-step hot-press process was composed of two separate procedures. First, a unit-hot-press operation was introduced to prepare a single-layered carbon–fabric/PC laminate (simplified as unit-CFPL). Subsequently, a laminating-hot-press was employed to compress several as-prepared unit-CFPLs bonded together. This combined process aims to reduce the hot-press temperature and pressure, as well as facilitate the structure designability of this new composite. Several mechanical investigations were conducted to analyze the effect of the hot-press parameters and unit-CFPL numbers on the performance of this multi-CFPL material, including flexural, uniaxial tensile and impact tests. The results reveal that the multi-CFPL exhibits a good stability of flexural and tensile properties in terms of strength and modulus. Furthermore, during impact tests, the multi-CFPL presents an accelerated growth of peak force and energy absorption capability with increasing unit-CFPL layers.

Three-Dimensional Copper Foil-Powder Sintering Current Collector for a Silicon-Based Anode Lithium-Ion Battery

In this work, we propose a facile method for manufacturing a three-dimensional copper foil-powder sintering current collector (CFSCC) for a silicon-based anode lithium-ion battery. We found that the CFSCC is suitable as a silicon-based paste electrode, and the paste-like electrodes are commonly used in industrial production. Compared with flat current collectors, the CFSCC better constrained the silicon volume change during the charging-discharging process. The capacitance of electrodes with CFSCC remained as high as 92.2% of its second cycle after 40 cycles, whereas that of electrodes with a flat current collector only remained at 50%.

Rake Angle Effect on a Machined Surface in Orthogonal Cutting of Graphite/Polymer Composites

Graphite and its composites have been widely used in various industrial fields. It has been generally accepted that, for positive rake angles, there is a significant increase in tension stress at the cutting zone during the machining of brittle materials, and cracks occur and spread easily, degrading the quality of the machined surface quality. However, it is found in this study that positive rake angles can improve the machined surface finish during the orthogonal cutting of graphite/polymer composites. Better machined surface finish is obtained for a larger rake angle. A finite element model is developed to reveal the mechanism of influence of the positive rake angle on the machined surface. Based on the effective stress field obtained from finite element analysis, it can be predicted that the crack initiates at the tool tip, subsequently propagates downward and forward, and later spreads gradually toward the free surface of the workpiece. A larger rake angle can promote crack propagation far from the machined surface. The crack initiation and propagation laws are validated by the edge-indentation experiments. In addition, the cutting force at various rake angles is investigated.