Applied Mechanics and Materials Vols. 249-250

Abstract: The fundamental frequency of a plate can be raised by placing appropriate number of rigid supports at various optimal locations along the nodal lines of vibration modes, as previously shown by other researchers. Unlike previous works, however, the present study aims to determine the optimal locations and the corresponding minimum stiffness of elastic spring supports using a direct search optimization method, presuming that the nodal lines of vibration modes can be identified a priori. As examples of applications, the optimal locations and stiffness are determined for isotropic plates and laminated composite plates with various lamination schemes, results of the latter are presented for the first time in open literature. Although only plates with regular geometry are treated in this preliminary study, further extension to plates with irregular geometry and other boundary conditions is being carried out.

Abstract: Adhesive-bonded composite integrated structures (ACIS) are widely used in civil and military aircrafts now. The failure laws of such structures should be studied obligatorily to design them reasonably. In a composite wing-box test debonding damage was found at the connection between the skin and the wall in mechanical-joint region while the load was added up to certain magnitude. However the shear stress of the adhesive layer in plane was not high. The real reason of the damage is that there is significant out-plane normal tensile stress at the local place. The main factors, which induced out-of-plane normal tensile stress, include out-of-plane force resulting from changing of force transfer path and sudden change stiffness. In this paper an integrated composite I-beam is investigated to expound the existing objectively of out-of-plane force, and analyze the relationships between out-of-plane force, sudden change stiffness and out-plane normal tensile stress or peeling stress. Research indicates that the out-of-plane force and debonding damage resulted from it should be highly valued for ACIS in mechanical-joint region.

Abstract: The paper presents the results of transient plasma ignition for delay reduction of quiescent ethane-air mixture. The transient plasma was produced by repetitive pulses nanosecond discharge, 30 kV peak voltage, 70 ns pulse width and 2 kHz repetition rate. The effects initial conditions including equivalence ratio (RE=1), temperature of 300K, and pressure range of 50 to 200 kPa were evaluated. The ignition delays were reduced by up to 50% when compared to conventional capacitive discharge systems.

Abstract: At hot working condition, forming tools must be durable at operating temperatures during continuous forming process and especially dimensional stability and corrosion resistant property are required. In this paper, oxidation behavior of several hot work die steels was studied at elevated temperature forming condition. It is shown that test specimens begin to form oxides at the surface during the initial heating period. Transient oxidation is observed during the initial stage of oxidation, in which the initial fast reaction rates may be related to local thermal instabilities such as fast nucleation of oxide grains due to microstructural variation or chemical potential differences through the thin initial oxide layer. When initial mass gain does not contribute to steady state parabolic law, the Pieraggi model is successfully applied to the high temperature oxidation of tool steels. Based on this information, suitable forming die material was selected for reheating application above 850°C.

Abstract: It is well known that alloy 718 shows excellent mechanical strength and corrosion resistance and this alloy is now successfully utilized for aerospace and oil industry application. In order to design and manufacture components to satisfy the design requirements of the applied system, it is necessary to consider formability and weldability of the material. This paper provides experimental results of lap shear strength of welded specimens of alloy 718 with EBW(Electron Beam Welding) and LBW(Laser Beam Welding) and Brazing. The purpose is to determine the optimum welding method for overlap welding of alloy 718 for blow forming.

Abstract: In this paper a theoretical relationship for the effective thermal conductivity of a multiphase transversely isotropic composite system is obtained. The Generalized Self-Consistent Method and simple energy balance principle is employed to derive a more appropriate model. In the derivation, it is assumed that the orientation of fiber within the transversely isotropic composite system is unidirectional and surrounded by two different phases of porous and matrix phase. A combined effect of these three different phases on the effective thermal conductivity of the composite system in transverse direction is studied. The effect of the interfacial contact conductance between the fibers and porous medium is also considered. Results of effective thermal conductivity are plotted against volume fraction and conductance which shows extremely good agreement.

Abstract: This paper introduces several models for different piezoelectric composites with the modeling process and mechanism. In order to characterize the uniformity and stability, the volume density of particles and fibers changed with volume is studied. The models generated by ANSYS finite analysis are showed, which the codes are produced by the models.

Abstract: Several E4303 type welding electrodes with different coating compositions were designed and manufactured using TL-25 welding electrode extrusion press. Welding slags of these electrodes were collected after welding on the low carbon steel, then the microstructure and the phase constitutes of the slags were investigated by optical microscope,scan electron microscope (SEM), electron probe microanalyzer (EPMA), Transmission electron microscope (TEM) and X-ray diffraction (XRD). It was indicated that the slags were mainly composed of amorphous matrix and Fe2MnTi3O10 crystal phase. Fe, Mn and Ti were the main elements to form the crystal phase, while Si, Al and Ca were mostly distributed in the amorphous matrix. The formation of the crystal phase in the slag could be controlled by adjusting the amount and the proportion of Fe, Mn and Ti in the welding rod coating.

Abstract: The presence of heavy metals in municipal solid waste incineration (MSWI) fly ash is of environmental concern due to their leaching potential in landfill environments. Acid extraction is a conventional method of safe treatment of fly ash. In this work, nitric acid was used as the extraction acid to leach Ni, Zn, Pb and Cu out from the ash. In addition, influence of nitric acid concentration and liquid to solid ratio on removal ratio of the four heavy metals was studied. It was found that removal ratio followed the decreasing sequence of Pb > Cd > Cu > Zn for acid extraction using nitric acid. The optimal extraction condition was 5.3 mol/L of nitric concentration at 20 liquid to solid ratio, which resulted in a removal ratio of 98% for Pb, 86% for Cd, around 73% for Cu and around 42% for Zn.

Abstract: Municipal solid waste incineration (MSWI) fly ash, a must by-product in incineration of municipal solid waste (MSW) combustion is of environmental concern due to its enrichment in heavy metals (Ni, Cd, Cu and Pb). Extraction using sulfuric acid is a conventional method of safe treatment of fly ash. In this work, influence of sulfuric acid concentration and liquid to solid ratio on removal efficiency of the four heavy metals was investigated. It was found that Removal ratio followed the decreasing sequence of Cd > Cu > Pb >Zn for acid extraction using sulfuric acid, quite different with that sequence of Pb > Cd > Cu > Zn for extraction using nitric acid. Sulfuric acid was efficient in removing Cd and Cu, but less efficient in removing Ni and Zn. Compared with nitric acid, sulfuric acid was less effective in removing Pb, Cu and Ni.