Synthesis and electrical properties of poly[2-(2-(4-trifluoromethyl)phenyl)ethenyl-1,4-phenylenevinylene] and PPV copolymers

Summary Poly[2-(2-(4-(trifluoromethyl)phenyl)ethenyl)-5-methoxy-1,4-phenylenevinylene] (PFEMPV) and a series of PPV copolymers containing 1,4-phenylenevinylene (PV) units were synthesized through a water-soluble precursor route, and their electrical and third-order nonlinear optical properties were studied. The PFEMPV films could not be doped with I₂, but FeCl₃-doped films showed an electrical conductivity of 5.0x10^-4 S/cm. The conductivities of FeCl₃-doped copolymer films ranged from 2.0x10^-3 to 2.0 S/cm depending on their copolymer compositions. The third-order nonlinear optical susceptibility, ⁽³⁾(–;,,–), was also investigated by the degenerate four wave mixing technique at 602 nm. The ⁽³⁾ value of PFEMPV was 6.9x10^-11 esu. The photoluminescence spectrum of PFEMPV shows its emission maximum at 550 nm.     

Tribological Performance of Oil-Based Lubricants with Carbon-Fe Nanocapsules Additive

The present study investigates the tribological properties of carbon-Fe nanocapsules (CFNCs) under high contact loads. Block-on-ring wear tests are performed using mineral oil lubricants containing CFNC particles with concentrations ranging from 0.01 to 0.1 wt%. In addition, high-resolution electron transmission microscopy (HR-TEM) and scanning electron microscopy (SEM) analysis were conducted on the test samples. The results show that for a contact load of 650 N, a CFNC concentration of 0.07 wt% and a sliding velocity of 1.65 m/s enhance the surface permeability, fill-up properties, and microbearing lubrication mechanism and promote effective reduction in the wear at the surface contact interface.     

Investigation of temperature and thermal stress in ventilated disc brake based on 3D thermo-mechanical coupling model

Ventilated disc brakes are widely used for reducing velocity due to their braking stability, controllability and ability to prove a wide-ranging brake torque. During braking, the kinetic energy and potential energies of a moving vehicle are converted into thermal energy through friction heating between the brake disc and the pads. The object of the present study is to investigate the temperature and thermal stress in the ventilated disc-pad brake during single brake. The brake disc is decelerated at the initial speed with constant acceleration, until the disc comes to a stop. The ventilated pad-disc brake assembly is built by a 3D model with a thermo-mechanical coupling boundary condition and multi-body model technique. To verify the simulation results, an experimental investigation is carried out.     

Plastic continuum models for truss lattice materials with cubic symmetry

Analytical and numerical studies on continuum models for the elastic-plastic behavior of uniformly periodic lattice materials under multi-axial loading are presented in this paper. This study firstly investigates the basic topology of unit cell structures for three different lattice materials with cubic symmetry. By homogenizing the mechanical properties of these materials within the unit volume space, the equivalent continuum models are obtained with the internal variables which result in the mechanical and geometrical characteristics of discrete truss members at the micro-scale such as structural packing, axial stiffness, and material density. Therefore, in this study, the strain hardening was applied to the material model of individual truss members in a valuable effort to explain the plastic behavior of the homogenized lattice material. The expansion of pressure-dependent stress surface at the macro-scale level is estimated by analytical predictions, which are derived from the equivalent continuum models. Analytical predictions show good agreements with existing results obtained by finite element (FE) analyses.     

Comparison of tribological characteristics between aluminum alloys and polytetrafluoroethylene composites journal bearings under mineral oil lubrication

This study examined the tribological behavior of journal bearings made from polytetrafluoroethylene (PTFE) composites and aluminum (Al) alloys. The PTFE composite journal bearings consisted of a steel backing with a thickness of 1.6 mm, a middle layer of sintered porous bronze with a thickness of 0.24～0.27 mm, and a surface layer of PTFE filled with fluorinated ethylene propylene (FEP) powder and carbon fibers with a thickness 0.06～0.14 mm. The other was an aluminum alloy journal bearing consisted of a steel backing with a thickness of 1.5 mm and a surface layer of an Al-6Sn-6Si alloy with a thickness 0.35～0.75 mm. A series of lubrication tests were performed using a journal bearing tester under various normal loads. The tribological properties for each journal bearing were evaluated by measuring the lubricant oil temperature and friction coefficient as a function of the applied normal load. In addition, the chemical compositions and microstructures of the journal bearing materials used in this study was analyzed by inductively coupled plasma (ICP), optical microscopy (OM), and scanning electron microscopy (SEM), respectively. The experimental results showed that the Al alloy journal bearings reduce the friction coefficient by 28 % compared to the PTFE composites bearings. In addition, the Al alloy journal bearing worked properly at the maximum load of ～ 8,000 N without adhesion. However, the PTFE composite journal bearings exhibited strong adhesion at the loads ranging from 6300 to 8000 N. This suggests that the Al alloy is a more promising material in journal bearings than PTFE composites.     

Development of an apparatus for removing magnetic sludge by permanent magnets setup in the condenser of the power plant

In this paper, permanent magnets are used to remove magnetic sludge in the condenser of the power plant. To obtain the flow characteristics and magnetic information that are needed for determining a proper design of the magnetic sludge removal apparatus, we performed numerical simulations through the use of two commercial codes, ANSYS Workbench-Emag and CFX. We also performed experiments on various kinds and sizes of magnets to obtain the magnetic information through a gauss meter. By analyzing the results of simulations and experiments, the minimum magnetic force that is able to remove the any size of the magnetic sludge in the condenser was calculated, and the design of the removal apparatus was confirmed. We made the test model which was confirmed by the simulations and experiments for the tests of efficiency of the removal apparatus. After testing, the test results were compared with those of numerical simulations and have good agreements.     

Analysis of total harmonic distortion in microspeakers considering coupling effect

With the advent of the mobile phone, Digital Multimedia Broadcasting (DMB) service for multimedia data communication will soon be realized. With regard to the acoustic aspects of this service, a smaller and lighter microspeaker also soon will be implemented in MP3 song players and speakerphones. The sound quality of such microspeakers, as evaluated with reference to total harmonic distortion (THD) is becoming more important. THD is the proportion of the higher-order frequency output response to a sinusoidal input signal. It is affected by uneven magnetic distribution and nonlinear responses of diaphragms. In this work, THD was analyzed in consideration of the coupling effects between mechanical vibration and electromagnetic exciting forces. Simulated THD results were compared with the experimental data. The THD in the lower frequency range increased due to the increased displacement of the voice coil and the elevated high-order component response of the sound pressure.     

Stress profiles at contact surface in ring compression test

A perfectly plastic material has been employed as a model material in simulation to analyze numerically the ring compression process, especially to examine the deformation patterns along the die/workpiece interface, which is strongly related to the frictional condition at the contact boundary. The main objective is to provide the deformation characteristics in detail in ring compression, especially at the tool/workpiece interface. The surface flow patterns at the contact boundary in ring compression are summarized and analyzed in terms of surface expansion, surface expansion velocity, pressure distributions exerted on the die surface, relative sliding velocity between die and workpiece, and sliding distance along the die surface. Movement of neutral positions and folding phenomenon are also investigated to see the effect on the deformation patterns at the interface, that is, geometrical change, which is important to measure the frictional condition at the interface using calibration curves. Finite element (FE) simulation using rigid-plastic finite element code has been performed for analysis. The results of this study reveal that surface expansion as well as other surface flow patterns, such as sliding velocity and so on, shows different and distinctive characteristics between low and high frictional conditions at the interface. This is directly related to the movement of neutral positions and folding, which affects the sensitivity of dimensional changes to tribological conditions at the interface.     

β-Si3N4Whiskers Embedded in Oxynitride Glasses: Interfacial Microstructure

Interfacial microstructures in βP-Si₃N₄( w )-Si-Al-Y-O-N-glass systems were investigated by systematically varying the nitrogen content and the Al:Y ratio of the glass matrix. High-resolution and analytical transmission electron microscopy (HREM and AEM) studies revealed that the interfacial microstructure is a function of the glass composition. No interfacial phases were formed in glasses with low Al:Y ratios and in glasses with high Al:Y ratios and low nitrogen content, whereas epitaxial growth of an interfacial layer (100–200 μm thick) on the βP-Si₃N₄( w ) occurred in a glass matrix with high Al:Y ratio and high nitrogen content. The interfacial layer was identified to be a β'-SiAION phase. Interfaces containing the SiAION layer exhibited high debonding energy compared to Si₃N₄( w )–glass interfaces. HREM studies indicated that the lattice-mismatch strain in the SiAION layer was relieved by dislocation formation at the SiAION–Si₃N₄( w ) interface. The difference in interfacial debonding energy was, hence, attributed to the local atomic structure and bonding between the glass-β-Si₃N₄ and the glass–β'-SiAION phases. This observation was clear evidence of the strong influence of glass chemistry on the interfacial debonding behavior by altering the interfacial microstructure.     

Dielectric and thermal properties of dicyclopentadiene containing bismaleimide and cyanate ester. Part IV

A novel bismaleimide (BMI), bis(4-maleimidophenoxy-3,5-dimethylphenyl)dicyclopentadiene (DCPDBMI), containing a large dicyclopentadiene (DCPD) and aryl ether linkage, was synthesized from bis(4-aminophenoxy-3,5-dimethylphenyl)dicyclopentadiene and maleic anhydride by the usual two-step procedure that included ring-opening addition to give bismaleamic acid, followed by cyclodehydration to bismaleimide. The monomers were characterized by Fourier transform infrared spectroscopy (FT-IR), proton nuclear magnetic resonance (NMR), elemental analyses (EA), and mass spectra (MS). A series of bismaleimide-triazine (BT) resins were prepared from synthesized bismaleimide (DCPDBMI) and then cured with 2,6-dimethyl phenol-dicyclopentadiene dicyanate ester (DCPDCY) at various molar ratios. Thermal properties of cured BT resins (DCPDBMI/DCPDCY) were studied using dielectric analyzer (DEA), dynamic mechanical analyzer (DMA) and thermalgravimetric analyzer (TGA). These data were compared with that of commercial bismaleimide (DDMBMI) cured with bisphenol A dicyanate ester (BADCY). The cured DCPDBMI/DCPDCY exhibits lower dielectric constant, dissipation factor and moisture absorption than those of DDMBMI/BADCY. The effects of blend composition on the glass transition temperatures and thermal stability are discussed.