Anh Dung Ngô

Dielectric properties of PE/clay nanocomposites

Polyethylene/nanoclay specimens containing from 0 to 5% nanoclays were prepared from a commercially available premixed PE/nanoclay masterbatch containing 50% wt of nanoclay. The masterbatch was diluted to the desired concentration by adding PE along with various amounts of compatibilizer in order to achieve the best possible dispersion of the nanoclay platelets. The dielectric response of the compounded samples was investigated using a combination of time and frequency-domain spectroscopy in order to cover a wide frequency window. Both techniques were in good agreement when the time-domain data was transformed into frequency-domain data. Despite their low concentration, the addition of the dispersed nanoclays led to a significant alteration of the material dielectric response in the form of the appearance of various interfacial relaxation processes and an increase of charge carrier transport within the insulation material. Moreover, an onset of nonlinear charge transport process was observed at moderate fields for specimens containing a relatively low level of nanoclays. The high-field breakdown strength was shown to have been improved by the incorporation of the nanoparticles, particularly when the exfoliation was enhanced by the use of a maleic anhydride grafted polyethylene compatibilizer.

LDPE/HDPE/clay nanocomposites: Effects of compatibilizer on the structure and dielectric response

PE/clay nanocomposites were prepared by mixing a commercially available premixed polyethylene/O-MMT masterbatch into a polyethylene blend matrix containing 80 wt% low-density polyethylene and 20 wt% high-density polyethylene with and without anhydride modified polyethylene (PE-MA) as the compatibilizer using a corotating twin-screw extruder. In this study, the effect of nanoclay and compatibilizer on the structure and dielectric response of PE/clay nanocomposites has been investigated. The microstructure of PE/clay nanocomposites was characterized using wide-angle X-ray diffraction (WAXD) and a scanning electron microscope (SEM). Thermal properties were examined using differential scanning calorimetry (DSC). The dielectric response of neat PE was compared with that of PE/clay nanocomposite with and without the compatibilizer. The XRD and SEM results showed that the PE/O-MMT nanocomposite with the PE-MA compatibilizer was better dispersed. In the nanocomposite materials, two relaxation modes are detected in the dielectric losses. The first relaxation is due to a Maxwell-Wagner-Sillars interfacial polarization, and the second relaxation can be related to dipolar polarization. A relationship between the degree of dispersion and the relaxation rate of Maxwell-Wagner-Sillars was found and discussed.

Correlation between Structure and Dielectric Breakdown in LDPE/HDPE/Clay Nanocomposites

Cross-linked polyethylene (XLPE) is commonly used in medium/high voltage insulation due to its excellent dielectric properties and acceptable thermomechanical properties. To improve both electrical and thermal properties to a point that would possibly avoid the need for crosslinking, nanoclay fillers can be added to polymer matrix to form nanocomposites materials. In this paper, PE/clay nanocomposites were processed by mixing a commercially available premixed polyethylene/O-MMT masterbatch into a polyethylene blend matrix containing 80 wt% low density polyethylene LDPE and 20 wt% high density polyethylene HDPE with and without compatibilizer using a corotating twin-screw extruder. Various characterization techniques were employed in this paper, including optical microscopy, AFM, TEM, TGA, DMTA, and dielectric breakdown measurements in order to understand the correlation between structure and short-term dielectric breakdown strength.

Dielectric response of LLDPE/Clay nanocomposite melt compounded from a masterbatch

In this paper, linear low density polyethylene (LLDPE) specimens containing from 0 to 5% of nanoclays were prepared from a commercially available premixed LLDPE/nanoclay masterbatch containing 50% wt of nanoclay. The masterbatch was diluted to the desire concentration by the addition of LLDPE pellets along with various amount of compatiblizer in order to achieve the best possible dispersion of the nanoclay platelets. The dielectric response of the compounded samples was investigated using a combination of time and frequency domain spectroscopy in order to cover a wide frequency window. Both techniques were in good agreement when the time domain data was transformed into the frequency domain. Despite the low concentration, the addition of the dispersed nanoclays lead to a significant alteration of the material dielectric response in the form of the appearance of various interfacial relaxation processes and an increase of charge carrier transport within the insulation material. Moreover, the onset of nonlinear charge transport process was observed at moderate fields for specimen containing a relatively low level of nanoclays.

Structural and Dielectric Studies of LLDPE/O-MMT Nanocomposites

Nanocomposites made of linear low density polyethylene (LLDPE) and organo-modified montmorillonite (O-MMT) were processed by melt compounding from a commercially available premixed LLDPE/nanoclay masterbatch, at different nanoclay loadings, by co-rotating twin-screw extruder. The morphological and dielectric properties of LLDPE/O-MMT nanocomposites were investigated to understand the structure-dielectric properties relationship in the nanocomposites. The microstructures of the materials were characterized by wide angle X-ray diffraction (WAXD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and atomic force microscopy (AFM). Initial findings by FTIR spectroscopy characterization indicated the absence of any chemical interaction between LLDPE and nanoclay during the extrusion process, while DSC showed that a 1% wt loading of nanoclay particles increased the degree of crystallinity of the nanocomposites samples. On the other hand, XRD, SEM, TEM and AFM indicated that nanoclay layers were intercalated or exfoliated in the LLDPE matrix. A correlation between the structure and dielectric properties of LLDPE/O-MMT nanocomposites was found and discussed.

Experimental investigation of speed control of hydraulic motor using proportional valve

In this paper, experimental results about the speed stability of one shaft operating by using the hydraulic motor with proportional valve are presented. Exclude the elastic deformation of the transmission belt. Besides, the mathematical model and fuzzy self-tuning PID controller is introduced. In the model, the V-belt is assumed as an elastic module and the friction coefficient and mass inertia moment of the hydraulic motor can be considered as constant. The Matlab is used to simulate the speed response of the hydraulic motor to the working shaft. The main parameters for the experimental investigation are setting time, overshoot and error of rotation at the steady state. So, speed stability of the working shaft operating by the hydraulic motor which is controlled by the proportional valve with the fuzzy self-tuning PID controller. Based on our findings, we propose the applicability on the main shaft of the metal cutter.

Simulation and Modeling of Polyethylene/Clay Nanocomposite for Dielectric Application

Copyright ©2014 KIEEME. All rights reserved. This is an open-access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted noncommercial use, distribution, and reproduction in any medium, provided the original work is properly cited. pISSN: 1229-7607 eISSN: 2092-7592 DOI: http://dx.doi.org/10.4313/TEEM.2014.15.4.175 TRANSACTIONS ON ELECTRICAL AND ELECTRONIC MATERIALS Vol. 15, No. 4, pp. 175-181, August 25, 2014

Experimental investigation and phenomenological modeling of hygrothermal effect on tensile fatigue behavior of carbon/epoxy plain weave laminates

The purpose of this paper is to study the hygrothermal effect on fatigue behavior of quasi-isotropic carbon/epoxy plain weave aerospace laminates containing artificial flaw under axial tension–tension loading. Dry and wet specimens were tested at tensile load-controlled cyclic loading with a stress ratio R = 0.1 and a load frequency of 7 Hz at room temperature (RT) and at 82℃ under different stress levels. Allowable stiffness change as a failure criterion was used to determine the delamination propagation onset threshold under cyclic tensile loading at each environmental condition. The delamination propagation onset was verified using the ultrasonic imaging (C-Scan) technique. The experimental results show that (1) fatigue life of CFRP specimens was more individually affected by moisture than by temperature and (2) combined moisture and temperature cause a drastic decrease in fatigue life. Finally, an investigation of the effect of hygrothermal conditions on stiffness degradation and damage of composite laminates subjected to tensile fatigue loading has been also carried. On the basis of the residual stiffness degradation, a damage variable was presented and phenomenological damage models were proposed by employing fatigue modulus and secant modulus concepts as measure of material damage.

Expert Elicitation Methodology in the Risk Analysis of an Industrial Machine

Calculation of the probability of occurrence of an accident involving an industrial machine such as a metal bending press requires knowledge of the failure rates. Specifically, what is needed are the failure rate of the protective device and, the failure rate associated with the human action consisting in having one’s hands between the press dies while the operator is bending a part. The first data could, in principle be obtained from the manufacturer of the device. However, in reality, this data involves knowledge of the reliability of not only the protective device but also of the associated command circuitry. In reality, such data may be difficult to obtain. Also, many important statistics relating to human performance are not collected by workplaces. So, another way to obtain the data is through expert elicitation, that is consulting people knowledgeable with the problem at hand and asking them to estimate, based on their judgement, the probabilities or failure rates that are sought. This process is often used in the literature but is seldom described in detail. In this paper, expert elicitation is used and described in order to gather relevant data for the purpose of probability estimation. Thus, eight bending press operators in a large manufacturing plant, the health and safety coordinator as well as the workers’ supervisor were solicited.

Design for manufacture: Cost-estimating model for randomly oriented strand advanced composite aerospace parts:

This work aimed at developing a parametric cost-estimating model based on physical laws for making three categories of thermoplastic composites structural aerospace parts from discontinuous prepreg randomly oriented strands. The proposed cost model will use Microsoft Excel spreadsheet developed in house which imputes all industrial and academic data for calculating costs elements such as material, labour, energy, machinery, building costs and costs of working capital, overheads and then the total cost per part. This research study focused, on one hand, at estimating the heating costs for experimental and virtual parts by changing the volume and keeping the same process cycle times. The heating power was determined by simulating the process thermal diagram numerically using finite elements COMSOL software and validated by experimental data. On the other hand, the tooling costs were estimated by DFMA software for experimental and virtual moulds by changing the projected area. Then, the heating energy and tooling costs sizing scaling laws were established under linear equation forms limited to the size of platens areas. These linear equations were inputted in an Excel spreadsheet to calculate the cost of new parts, which have not been made yet. The variation of the total cost with the size and the complexity of the part were investigated. The results showed that the calculated heating energy costs of the three experimental randomly oriented strand parts were different due to different geometries of the heating platens and the moulds. For the mould cost, the more complex the form was the higher the cost. For total cost, it was also demonstrated that the manufacturing cost of L-bracket part was higher than that of flat plate and T-shape part due to higher process cycle time.