Applied Mechanics and Materials Vols. 130-134

Abstract: This paper presents the effects of clearance on reactive violence to RDX-based energetic material at the temperature rate of 2 ± 0.2°C / min. The experimental effort is to introduce the safe use of energetic materials in ammunitions and to reduce the vulnerability of energetic materials in practice. The results indicated that reactions were violent when charge clearance occurred. These phenomena are explained in relation to detonation theory. So clearance should be restricted for the safe use energetic materials in practice.

Abstract: Glutaraldehyde cross-linked Poly (vinyl alcohol)/Polyvinylamine (PVA/PVAm) membranes for removal of metal ions from aqueous solution were prepared by solution casting and solvent evaporation techniques. The membranes were characterized using XRD, Swelling studies and metal ions adsorption experiments. The results show that PVA/PVAm membranes exhibit semi-crystalline natures as PVA macromolecular, however, the degree of crystallinity of membranes decrease as PVAm increased. The membranes were pH-sensitive and the swelling ability of membranes was significantly enhanced. It was found that the change of swelling behavior versus pH was consistent with the change of degree of ionization versus pH. The amount of Cu²⁺ ions adsorbed increased as PVAm increased as well as increasing pH of solution in the range of 2.5~6.0.

Abstract: In this paper, the effect of modified-silicon rubber (MSR) on thermal degradation and anti-droplet properties of melamine cyanurate (MCA) flame retardant polyamide 6 (PA6) composites was studied by using thermogravimetric analysis (TG) and vertical burning test. TG analyses indicated that modified-silicon rubber could markedly promote the condensation process of PA6/MCA/MSR composites compared with PA6/MCA composites, and the char residue of PA6/MCA/MSR composites at 600¡æwas much higher than that of PA6/MCA composites. DTGcurves showed that MSR could slow down the rate of degradation of PA6/MCA composites. More importantly, there was no melt-drip produced when PA6/MCA/MSR composites was burning. It was concluded that MSR increase the thermal stability of composites and could effectively prevent the formation of melt drip.

Abstract: The effects of silicon dioxide addition on the sintering, microstructure and microwave dielectric properties of Ca-Al-B-Si-O glass/Al₂O₃ composites were investigated. Results show that: Increasing the silicon dioxide content in the glass leads to the corresponding rise of bulk density, dielectric constant of the LTCC materials and the decrease of its dielectric loss and porosity. A bulk density of 2.92 g·cm^-3, a porosity of 0.2%, aε_r value of 7.11 and a tan δ value of 0.00096(measured at 10 MHz) are obtained for 68 wt% silicon dioxide of the samples sintered at 875°C for 30 min.

Abstract: A new kind of liquid crystalline material with an azo group in the molecular core was synthesized successfully. The chemical structures of the compounds were confirmed by mass spectrometry and 1H NMR. Their phase structures and transitions were investigated by differential scanning calorimetry. And the liquid crystalline behaviors were researched with polarized light microscopy experiments. The experimental results suggested that the compounds with a azo group in the molecular core can develop into a well-defined nematic phase.

Abstract: Ternary composites of Polyamide 6 (PA6), the mixture of Maleated and Unmaleated Ethylene Propylene Diene terpolymer rubber (named EPDM-M), and nanoCalcium Carbonate (nanoCaCO₃) were prepared by one-step and two-step compounding routes. The toughness of the composites was tested by impact test. The microstructure morphology of impact surface and etched impact surface was investigated through scanning electron microscope (SEM). The result shows that toughness of the ternary composites with sandbag microstructure was 270 % higher than neat PA6. The SEM morphology shows that strongly elongated microfibrils and deformation are formed in ternary composite with sandbag microstructure, which cause larger shear yielding and crazes in the surrounding matrix to dissipate more impact energy. Additionally, strong ligaments are observed at the crack tip, which could promote plastic deformation and consumption of fracture energy.

Abstract: Gelator (G₂-C₁₂-G₂) was synthesized successfully, the structure of which was confirmed by ¹H-NMR and Mass spectra (MS). And G₂-C₁₂-G₂ was used to modify PMMA by “in-situ” polymerization. The results of gel permeation chromatography (GPC) showed that Mn and M_w/M_n of the PMMA composite were barely influenced by the incorporation of gel. The results of dynamic mechanical analysis (DMA) showed that the modified PMMA had higher modulus, toughness and glass transition temperature (T_g) than pure PMMA. Furthermore the results of spectrophotometer showed that the transparency of modified PMMA was nearly the same as pure PMMA .

Abstract: The FeMnCrNi/Cr₃C₂ inter metallic composite coatings are prepared by high velocity arc spraying (HVAS) technology on 20G steel. The properties, such as the microstructure, micro hardness, binding strength, high temperature oxidation, thermal shock resistance, and erosion in high temperature, are studied based on methods such as analysis of optical microscope, micro hardness, field emission scanning electron microscope (FESEM), and spectrum analysis. The result shows that FeMnCrNiAl/Cr₃ C₂ coatings, compared with 20G steel substrate, present higher micro hardness, binding strength and more excellent high temperature properties, which will be improved if added with rare-earth Alloy.

Abstract: TiO₂/CNTs nanocomposites with different Ti/C molar ratios were prepared by a sol-hydrolysis method at 368 K, using titanium tetrachloride as a precursor and nitrified carbon nanotubes as a support. The crystal phase, morphology and microstructure of the sample were characterized by X-ray Diffraction (XRD) and High-Resolution Transmission Electron Microscope (HRTEM). The photocatalytic activity of the samples was performed by methyl orange in aqueous solutions under UV light.The supernatant liquid of methyl orange during degradation was determined by using an UV-vis spectrophotometer (UV-vis). XRD results show that the crystal phases of the sample are composed of carbon nanotubes, anatase and rutile. HRTEM results show that the average diameter of oval titania is about 4.2 nm, and it decorates on the surface of carbon nanotubes uniformly. UV-vis results show that the photocatalytic activity of the TiO₂/CNTs nanocomposite with the optimum Ti/C molar ratio is much higher than that of P25. These results indicate that a synergistic effect exists between titania and carbon nanotubes in the nanocomposite.

Abstract: A three species system with time delays was considered. Firstly, we got the system’s three population equilibrium point and shifted it to zero point through transformation. Secondly, we analyzed the stability of the system at the equilibrium point. We support our analytical findings with numerical simulation.