Chengying Xu

Fully Printed Halide Perovskite Light-Emitting Diodes with Silver Nanowire Electrodes

Printed organometal halide perovskite light-emitting diodes (LEDs) are reported that have indium tin oxide (ITO) or carbon nanotubes (CNTs) as the transparent anode, a printed composite film consisting of methylammonium lead tribromide (Br-Pero) and poly(ethylene oxide) (PEO) as the emissive layer, and printed silver nanowires as the cathode. The fabrication can be carried out in ambient air without humidity control. The devices on ITO/glass have a low turn-on voltage of 2.6 V, a maximum luminance intensity of 21014 cd m(-2), and a maximum external quantum efficiency (EQE) of 1.1%, surpassing previous reported perovskite LEDs. The devices on CNTs/polymer were able to be strained to 5 mm radius of curvature without affecting device properties.

Polymer-Derived Ceramic Composite Fibers with Aligned Pristine Multiwalled Carbon Nanotubes

Polymer-derived ceramic fibers with aligned multiwalled carbon nanotubes (MWCNTs) are fabricated through the electrospinning of polyaluminasilazane solutions with well-dispersed MWCNTs followed by pyrolysis. Poly(3-hexylthiophene)-b-poly (poly (ethylene glycol) methyl ether acrylate) (P3HT-b-PPEGA), a conjugated block copolymer compatible with polyaluminasilazane, is used to functionalize MWCNT surfaces with PPEGA, providing a noninvasive approach to disperse carbon nanotubes in polyaluminasilazane chloroform solutions. The electrospinning of the MWCNT/polyaluminasilazane solutions generates polymer fibers with aligned MWCNTs where MWCNTs are oriented along the electrospun jet by a sink flow. The subsequent pyrolysis of the obtained composite fibers produces ceramic fibers with aligned MWCNTs. The study of the effect of polymer and CNT concentration on the fiber structures shows that the fiber size increases with the increment of polymer concentration, whereas higher CNT content in the polymer solutions leads to thinner fibers attributable to the increased conductivity. Both the SEM and TEM characterization of the polymer and ceramic fibers demonstrates the uniform orientation of CNTs along the fibers, suggesting excellent dispersion of CNTs and efficient CNT alignment via the electrospinning. The electrical conductivity of a ceramic fibers with 1.2% aligned MWCNTs is measured to be 1.58 x 10(-6) S/cm, which is more than 500 times higher than that of bulk ceramic (3.43 x 10(-9) S/cm). Such an approach provides a versatile method to disperse CNTs in preceramic polymer solutions and offers a new approach to integrate aligned CNTs in ceramics.

Control of Cutting Force for Creep-Feed Grinding Processes Using a Multi-Level Fuzzy Controller

In this paper, a multi-level fuzzy control (MLFC) technique is developed and implemented for a creep-feed grinding process. The grinding force is maintained at the maximum allowable level under varying depth of cut, so that the highest metal removal rate is achieved with a good workpiece surface quality. The control rules are generated heuristically without any analytical model of the grinding process. Based on the real-time force measurement, the control parameters are adapted automatically within a stable range. A National Instrument real-time control computer is implemented in an open architecture control system for the grinding machine. Experimental results show that the cycle time has been reduced by up to 25% over those without force control and by 10-20% compared with the conventional fuzzy logic controller, which indicates its effectiveness in improving the productivity of actual manufacturing processes. The effect of grinding wheel wear is also considered in the creep-feed grinding process, where the grinding force/power can be maintained around the specified value by the proposed MLFC controller as the wheel dulls gradually.

Design, Fabrication, and Characterization of Linear Multiplexed Electrospray Atomizers Micro-Machined from Metal and Polymers

Multiplexed electrospray is a promising aerosol generation technique to produce high throughput quasi-monodisperse droplets in the nanometer and micron size range. Here we report the design, fabrication, analysis, and performance of a linear electrospray (LINES) system. The fabrication of the nozzle array is based on a precision computer numerical control (CNC) micromachining platform with 1-micron resolution. This rapid prototyping approach offers the flexibility of creating devices from a wide range of materials including metals and polymers with packing densities on par with silicon microfabrication at 20 sources/cm for LINES devices and 460 sources/cm2 for the two-dimensional array. The LINES device uses a slot extractor design to simplify alignment and enhance operation robustness. We also used dummy nozzles (posts without fluidic channels) to offset edge effect on electric field and improved droplet size uniformity. We derived the approximate spray expansion model from charge conservation and Gauss’ law. We applied the line-of-charge approximation to establish scaling laws for prescribing operating conditions. The devices show excellent droplet size uniformity from source to source, with relative standard deviation (RSD) of primary droplets <3%. Copyright 2013 American Association for Aerosol Research

An Adaptive Fuzzy Controller for Constant Cutting Force in End-Milling Processes

A novel multilevel fuzzy control system is introduced and implemented for online force control of end-milling processes to increase machining productivity and improve workpiece quality, where the cutting force is maintained at its maximum allowable level in the presence of different variations inherent in milling processes, such as tool wear, workpiece geometry, and material properties. In the controller design, the fuzzy rules are generated heuristically without any mathematical model of the milling processes. An adaptation mechanism is embedded to tune the control parameters online, and the resultant closed-loop system is guaranteed to be stable based on the input-output passivity analysis. In the experiment, the control algorithm is implemented using a National Instrument real-time control computer in an open architecture control environment, where high metal removal rates are achieved and the cycle time is reduced by up to 34% over the case without any force controller and by 22% compared with the regular fuzzy logic controller, thereby indicating its effectiveness in improving productivity for actual machining processes.

Experimental investigation on the machinability of SiC nano-particles reinforced magnesium nanocomposites during micro-milling processes

This paper experimentally investigates the machinability of magnesium metal matrix composites (Mg-MMCs) with high volume fractions of SiC nano-particles using micro-milling process. The nanocomposites containing 5 vol.%, 10 vol.% and 15 vol.% reinforcements of SiC nano-particles were studied and compared with pure magnesium. The milling was carried out at different feedrates and spindle speeds chosen according to design of experiment (DOE) method. Cutting forces, surface morphology and surface roughness were measured to understand the machinability of the four different materials. Based on response surface methodology (RSM) design, experimental models and related contour plots were developed to build a connection between material properties and cutting parameters. Those models can be used to predict the cutting force, the surface roughness, and then optimise the machining conditions with the required cutting forces and surface roughness.

Wireless passive sensor development for harsh environment applications

Three researchers at University of Central Florida from electrical engineering, materials science, and mechanical engineering teamed together to develop high-temperature (>; 1000°C) sensors for various harsh environment applications such as combustion turbines. In this paper, we will provide an overview of the recent progress in the development of sensing materials, sensor fabrication methods, and wireless sensing techniques.

Cutting Force Prediction on Micromilling Magnesium Metal Matrix Composites With Nanoreinforcements

Due to its light weight, high creep, and wear resistance, magnesium metal matrix composites (Mg-MMCs) with nanosized reinforcements are promising for various industrial applications, especially those with high volume fractions of reinforcements. The machinability of Mg-MMCs and related cutting process modeling are important to study. In this paper, an analytical cutting force model is developed to predict cutting forces of Mg-MMC reinforced with SiC nanoparticles in micromilling process. This model is different from previous ones by encompassing the behaviors of nanoparticle reinforcements in three cutting scenarios, i.e., shearing, ploughing, and elastic recovery. By using the enhanced yield strength in the cutting force model, three major strengthening factors are incorporated, including load-bearing effect, enhanced dislocation density strengthening effect, and Orowan strengthening effect. In this way, material properties, such as the particle size and volume fraction as significant factors affecting the cutting forces, are explicitly considered. To validate the model, experiments based on various cutting conditions using two types of end mills (diameters as 100 μm and 1 mm) were conducted on pure Mg, Mg-MMCs with volume fractions of 5 vol. %, 10 vol. %, and 15 vol. %. The experimental results show a good agreement with the predicted cutting force value.

Synthesis of nanostructured silicon carbide at ultralow temperature using self-assembled polymer micelles as a precursor

Nanostructured SiC ceramics exhibit unusual and superior properties compared to their microstructured counterparts, thus hold promise for widespread applications. We report a novel technique for synthesizing dense nanostructured SiC at an ultralow-temperature without pressure. In this technique, polyvinylsilazane-block-polystyrene (PVSZ-b-PS) block copolymers were synthesized and then self-assembled into nano-scaled micelles with the precursor PVSZ as the core and the sacrificial PS as the shell. The subsequent pyrolysis converted the aggregation of the micelles into dense nanostructured SiC with a grain size of ∼20–30 nm at 800 °C.

Characterization and Alignment of Carbon Nanofibers under Shear Force in Microchannel

This work presents a novel method to align CNFs by using shear forces in microchannels. Effect of two different microchannel sizes 1 mm × 0.1 mm and 1 mm × 0.2 mm on CNFs alignment is investigated. SEM images of CNFs preform display significant alignment by both microchannels, which can be interpreted using a second-order alignment tensor and a manual angle meter. In the second-order alignment tensor description, an elongated ellipse can signify high degree of alignment in the direction of the major axis. When the microchannel size is 1 mm × 0.2 mm, the lengths of major and minor axes of the ellipse are 0.982 to 0.018. An angle meter manually shows that 85% of the CNFs are aligned in the direction between 60° and 90° when the microchannel is 1 mm × 0.2 mm. Both methods can demonstrate that better alignment of CNFs can be obtained using the 1 mm × 0.2 mm microchannel.