One of the functionally graded material (FGM) fabrication methods is a centrifugal method, which is an application of the centrifugal casting technique. The centrifugal force applied to a homogeneous molten composite assists the formation of the desired gradation. In this paper, the wear properties of two kinds of Al base FGMs, namely Al-Al₃Ti FGM and Al-Al₃Ni FGM, are reported. The former and the latter hold the oriented intermetallic compound platelets and the particle size gradient, respectively. Here, volume fraction, size, shape and orientation of the reinforcements in the composite play an important role in improving the mechanical properties of the materials, whereby FGMs with oriented platelets or particle size gradient may have special mechanical properties such as increased wear resistance. Based on the experimental results, the origin of anisotropic wear resistance and the effect of particle size on the wear properties are discussed.

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Effect of MCrAlY bond coat alloy systems on thermal fatigue failure of thermal barrier coatings (TBCs) was investigated, where the TBC specimen consisted of Ni-based superalloy IN738LC substrate, bond coat, and 8 wt.% Y₂O₃-stabilized ZrO₂ (YSZ) top coat. The top coat was fabricated by EB-PVD method with 250 μm in thickness. Three kinds of MCrAlY alloys were studied as the bond coat material. Employing the originally developed test equipment, thermal fatigue tests were carried out, by applying thermal cycles between 400 and 950°C in air. Special attention was paid not only to the failure life of the TBC specimen, but also the underlying failure mechanisms. The experimental results clearly demonstrated that the effect of MCrAlY bond coat alloys on the thermal fatigue life was very significant. Some discussions were made on the experimental results based on the measurements of mechanical and metallurgical properties of the bond coat alloys: i.e., elastic stiffness, thermal expansion coefficient and high temperature oxidation resistance.

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A computational modeling is established for the electrochemical-poroelastic behavior of conducting polymers (CPs) such as polypyrrole. The three-dimensional continuum modeling given by Della Santa et al. for the passive, poroelastic behavior of CPs is extended to the formulation for the active, electrochemical-poroelastic formulation according to Onsager-like laws, which is combined with the one-dimensional equation for ionic transportation. The validity of the finite element formulation for these governing equations has been illustrated by numerical studies for the passive and active responses of polypyrrole films.

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PZT ceramics can emit a high electric field externally if surface charges are removed. For this study, the PZT surface charges were removed by heating. Then the electret microphones laminated with electrodes, insulation films, and a PZT element (disk) were prepared. Several contact conditions between laminated layers were examined to elucidate their influence on the microphones' sensitivity. The fabricated samples showed the same level of output (ΔV_out) as a commercial electret microphone (sensitivity: 5.6 mV·Pa^-1 [-45dB]), although the vibration amplitude of the fabricated samples was much smaller than that of the commercial microphone. The output measurement of laminating films under several conditions revealed that the interface gap between the layers had an important role in increasing the output. That of the fabricated samples, however, was degraded because of insufficient removal of surface charges and/or poor insulation properties. Furthermore, the output was temporarily decreased during heating between 50 and 180°C, but recovered after cooling to room temperature. Such behavior is explainable according to the pyroelectricity of PZT.

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Pipe inspection with guided waves is expected to provide an efficient screening technique that will enable the inspection of lengths of pipe of up to a few dozen meters. In contrast with conventional inspection equipment widely used in practical inspection that employ easy-to-use axisymmetric modes, the present authors have developed a defect imaging technique that uses non-axisymmetric modes. In a previous paper, defect images were only available over a short range of 1.2 meters from the transducers. Therefore, in the present study, the effects of long propagation on defect images are discussed. Long-range imaging was performed experimentally using source signals and their multiple reflections between both edges of a four-meter-long pipe, rather than the reflected waves from defects. In the experimental investigation, large degradation of images was found in the far field. A computer simulation of the guided wave propagation reveals that a major reason for the degradation is the difference between dispersion curves for an actual pipe and the theoretical dispersion curves. In order to reduce the degradation, images were obtained by neglecting higher modes with larger differences in phase velocity. As a result, images were obtained at correct locations at distances of up to approximately 20 meters from the transducers.

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This paper presents an analytical solution for an infinite strip having a circular inclusion when the strip is subjected to tension. In this analysis, two types of inclusions, i.e., a perfectly bonded inclusion (displacements and tractions are continuous) and a slipping inclusion (tractions and normal displacements are continuous and shear traction vanishes) are discussed. The solution is based on the Papcovich-Neuber displacement potentials approach and is deduced through making use of simple forms of Cartesian and cylindrical harmonics. The boundary conditions on the strip at infinity and around the inclusion are fully satisfied with the aid of the relationships between the Cartesian and cylindrical harmonics. The solution is represented in the form of graphs and the effects of the inclusions on the stress distribution are clarified.

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The development of materials to suppress electromagnetic noise is in demand. In this paper, we present a method for the material design of functionally graded material (FGM) plates with the function of electromagnetic noise suppression. The FGM plates are considered to be multilayered plates in which the material properties are homogeneous inside each layer. Therefore, the approximate analytical solutions of electromagnetic fields in the FGM plates subject to electromagnetic noise are derived. The expressions for electromagnetic noise suppression are then obtained based on the above analytical solutions. Numerical calculations are carried out for epoxy resin/titanium oxide FGM plates with graded composition distribution expressed in the form of a power function. The effects of graded composition and plate thickness on the electromagnetic noise suppression are quantitatively evaluated, and the material design suitable for the suppression of electromagnetic noise is discussed.

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In this paper, an attempt is made to investigate the relationships between the material ductility and the characteristic size of casting porosities correlated by two different sources. The first source is the metallographic analysis on the cross section before testing. The second one is the fractographic analysis on the fracture surface after testing. Three types of cast round bars are manufactured with various levels of porosity. An image processing code is developed within Matlab to quantify the size and number of the porosities. It is found that the three types of aluminum cast components have similar microstructure and the same true stress-strain curve is able to predict well the load-displacement response of the three types of castings. A large variation in the size of the largest pore and the area fraction of pores is observed among the cast components. Three distinct fracture loci are predicted using a combined experimental-numerical approach. The material ductility tends to decrease with the increasing size of the pores based on the correlations of two sources. A linear relationship is used to correlate the ductility with the size and number of this type of pores. The correlated trend between the material ductility and the pore size is similar qualitatively on the specimens before/after testing. It is also shown that the effect of the porosity on the material ductility can be preferably correlated by the area fraction of pores measured before testing and after testing in a linear way, respectively.

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To reduce tensile residual stress in a welded region, we developed a new welding method that applies a water-shower behind the welding torch. When this method is applied to welding of austenitic stainless-steel plates, the water-shower cooling conditions mainly determine how much the residual stress can be reduced. To determine the conditions for reducing tensile residual stress, we first used FEM to evaluate the effects of interpass temperature on residual stress. To verify the validity of the FEM-obtained conditions, specimens welded in the case of with or without water-shower cooling were manufactured. Residual stresses in the specimens were then experimentally measured. These measurements showed that tensile residual stresses were generated on the surface of the welds and could be reduced by applying the water-shower cooling. These measurement results agree well with the results of FEM analyses. It can therefore be concluded from these analytical and experimental results that applying water-shower cooling during welding effectively reduces tensile residual stress generated by welding of austenitic stainless steel.

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Slurry erosion with sand particles is a serious problem for pumps operating at the Yellow River pumping station. Therefore, a technique to predict erosion volume loss is required for selecting erosion resistant material and determining specification of the maintenance period. This paper reports a method to predict the volume loss of SCS6 specimen using slurry jet apparatus. An equation for prediction is derived from combining an analysis of sand particle behavior in the slurry jet apparatus with measurement of surface profile on specimens obtained by slurry jet test by silica sand of approximate 60μm in mean diameter. There is a critical value for kinetic energy of particle above which erosion occurs being about 1.0x10^-6N•m for SCS6. It was found that the loss was a maximum at an impact angle of about 40 degrees. The equation can predict the wear depth on the slurry jet test with the Yellow River sand of approximate 30μm in mean diameter.

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In this study, a linearization method is used to develop an implicit integration scheme for a class of high-temperature inelastic constitutive models based on non-linear kinematic hardening. A non-unified model is first considered in which the inelastic strain rate is divided into transient and steady parts driven, respectively, by effective stress and applied stress. By discretizing the constitutive relations using the backward Euler method, and by linearizing the resulting discretized relations, a tensor equation is derived to iteratively achieve the implicit integration of constitutive variables. The implicit integration scheme developed is shown to be applicable to a unified constitutive model in which back stress evolves due to static and dynamic recoveries in addition to strain hardening. The integration scheme is then programmed for a subroutine in a finite element code and applied to a lead-free solder joint analysis. It is demonstrated that the integration scheme affords quadratic convergence in the iterations even for considerably large increments, and that the non-unified and unified models give almost the same results in the solder joint analysis.

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