Advanced Materials Research Vol. 629

Abstract: For conductive-carbon-fiber-filled polymer composites, the residual stresses developed during injection molding process may affect not only the molding’s conductive property, but its dimensional stability as well. In order to improve the conductivity of the molding fabricated with this kind of composites, we investigated, using layer removal method, the distribution of the residual stresses of injection-molded conductive-carbon-fiber-filled polypropylene in this paper. The residual stresses were obtained under the actions of different processing conditions. Our results indicate that processing pressures have more significant effects on the residual stresses at the skin areas than the core areas of the sample because of fiber orientation. The tensile stresses of the molding at the core areas drop under the action of packing pressure, but the compressive stresses at the skin areas increase. The results reveal that the action of packing pressure may decrease the anisotropy of the residual stresses in the molding.

Abstract: In the active field of vascular graft research, in situ vascular tissue engineering is a novel concept. This approach aims to use biodegradable synthetic materials. After implantation, the synthetic material progressively degrades and should be replaced by autologous cells. Poly (ε-caprolactone) (PCL) is often used for vascular graft because of its good mechanical strength and its biocompatibility. It is easily processed into micro and nano-fibers by electrospinning to form a porous, cell-friendly scaffold. However, the degradation time of polycaprolactone is too long to match the tissue regeneration time. In this study, poly (ε-caprolactone) /poly (trimethylene carbonate) (PTMC) blend scaffold materials have been prepared for biodegradable vascular graft using an electrospinning process. Because the degradation time of PTMC is shorter than PCL in vivo. The morphological characters of PCL/PTMC blend scaffold materials were investigated by scanning electron microscope (SEM). The molecular components and some physical characteristics of the blend scaffold materials were tested by FT-IR and DSC analysis.

Abstract: The effects of Na and Mg doped Li site for Li_1-xM_xFePO₄ have been studied using first-principles within GGA+U. Elastic band method has been used to calculate the activation energy for Li diffusion. The calculated results mean that, the band gaps of the Na and Mg doped Li_1-xM_xFePO₄ are both narrow than that of the un-doped. Especially Mg dopant gives rise to much narrow gap, which is attributed to the appearance of impurity level in the forbidden band of un-doped LiFePO4. The calculated activation energies for LiFePO₄, Li_0.875Na_{0.125Subscript text}FePO₄, and Li_0.875Mg_0.125FePO₄ are 0.33eV, 0.31 eV, and 0.15 eV, respectively. From the calculated results of band gap and activation energy, we can find that Mg dopant will benefit for the hopping of electrons and the improvement of the electronic conductivity for LiFePO₄.

Abstract: This paper presented a novel synthesis method for yttria-stabilized zirconia (YSZ) by using the flame spray pyrolysis (FSP) method. Spherical and dense YSZ particles for thermal barrier coating were successfully synthesized by FSP from the nebulized precursor solution. XRD results revealed that the YSZ powder is only composed of tetragonal phase particles. Most particles are a few hundred nanometers in diameter and their sizes are mainly dependent on the concentration of the precursor solution, while flame condition has little effect. Particle size and morphology are greatly affected by the precursor composition. Particles synthesized from ethanol precursor solution are more uniform and better-defined than those from aqueous solution.

Abstract: The research background and the generation of friction are introduced. The importance of the coefficient of friction test in sheet metal forming field is indicated. Standards of coefficient of friction of metallic sheet and other related materials testing method are described. The experimental principle, the size and preparation of testing sample, testing equipment and procedure, result data processing method are presented.

Abstract: An analytical model based on the displacement function of the opening of crack applied by Lundmark and Varna [26] in the internal layers to study the evolution of the decrease of stiffness in a laminate is investigated. The results of axial rigidity versus the crack density are presented for three composite materials. The influences of the temperature and moisture on the mechanical properties of composite material are highlighted. The micromechanical model of the laminates used in present study describes the degradation of the mechanical properties of composite material by the variation in the temperature and moisture. The hygrothermal effect is observed to be harmful for composite materials.

Abstract: The current study seeks to further understand the precipitation sequence in a WE54 Mg alloy using in situ X-ray diffraction, micro-hardness and electrical resistivity during ageing at 250 and 300 °C. We show that the mean hardening effect is due to the precipitation of β' and β₁ metastable phases. The analysis of the kinetics of the precipitation shows that both phases nucleate at grain boundaries and within grains in the form of plates.

Abstract: This paper presents an investigation of the creep behavior of an industrial aluminum drawn wire, where uni-axial tension creep testing was used to characterize the general creep behaviour. This material was crept at different stress with constant temperature. The scanning electronic microscopy and X-ray diffraction were used at different steps of creep test in order to identify the creep mechanism. From this investigation, the effects of applied stress and temperature on thelife time of drawn wires were observed during many tests.

Abstract: In this study, a buckling analysis is performed on rectangular composite plates with single and double circular notch using the finite element method. Laminated plates of carbon/bismaleimde (IM7/5250-4) are ordered symmetrically as follows [(θ/-θ)2]S. The buckling strength of symmetric laminated plates subjected to uniaxial compression is highlighted as a function of the fibers orientations. The results show that whatever the notch radius, the buckling load is almost stable. Increasing the degree of anisotropy significantly improves critical buckling load.

Abstract: Metal injection molding(MIM) is a high efficient and near net shape manufacturing technology, which is appropriate for parts of small size and complex shape. MIM provides a viable method to fabricate metal and metal matrix composites with discontinuous reinforcements, and micro metal injection molding (μMIM) is applied to manufacturing products at micro scale. The status of the research and development of MIM and μMIM are reviewed. Processes including mixing, injection molding and subsequent debinding and sintering are summarized. And technical characteristic, injection processing and application of μMIM are introduced. The disadvantages in mixing, injection molding and debinding processes limit MIM to fabricating components with small size, low precision and mechanical properties, and it is necessary to prevent the powder from reuniting and avoid any oxidation and impurity during μMIM process. Further investigations in these areas will give rise to being explored of full potential of MIM technology.