Structural size effects of intermetallic compounds on the mechanical properties of Mo-Si-B alloy: An experimental investigation

In general, size, shape and dispersion of phases in alloys significantly affect mechanical properties. In this study, the mechanical properties of Mo-Si-B alloys were experimentally investigated with regards to the refinement of intermetallic compound. To confirm the size effect of the intermetallic compound phases on mechanical properties, two differently sized intermetallic compound powders consisting Mo₅SiB₂ and Mo₃Si were fabricated by mechano-chemical process and high-energy ball milling. A modified powder metallurgy method was used with core-shell intermetallic powders where the intermetallic compound particles were the core and nano-sized Mo particles which formed by the hydrogen reduction of Mo oxide were the shells, leading to the microstructures with uniformly distributed intermetallic compound phases within a continuous α-Mo matrix phase. Vickers hardness and fracture toughness were measured to examine the mechanical properties of sintered bodies. Vickers hardness was 472 Hv for the fine intermetallic compound powder and 415 Hv for the coarse intermetallic compound powder. The fracture toughness was 12.4 MPa·√m for the fine IMC powders and 13.5 MPa·√m for the coarse intermetallic compound powder.     

Sb-Se-based phase-change memory device with lower power and higher speed operations

A phase-change material of Sb/sub 65/Se/sub 35/ was newly proposed for the nonvolatile memory applications. The fabricated phase-change memory device using Sb/sub 65/Se/sub 35/ showed a good electrical threshold switching characteristic in the dc current-voltage (I-V) measurement. The programming time for set operation of the memory device decreased from 1 /spl mu/s to 250 ns when Sb/sub 65/Se/sub 35/ was introduced in place of the conventionally employed Ge/sub 2/Sb/sub 2/Te/sub 5/ (GST). The reset current of Sb/sub 65/Se/sub 35/ device also dramatically reduced from 15 mA to 1.6 mA, compared with that of GST device. These results are attributed to the low melting temperature and high crystallization speed of Sb/sub 65/Se/sub 35/ and will contribute to lower power and higher speed operations of a phase-change nonvolatile memory.     

High-frequency SPICE model of anisotropic conductive film flip-chipinterconnections based on a genetic algorithm

This paper firstly reports on the high-frequency SPICE model of the ACF flip-chip interconnections up to 13 GHz. The extraction process is based on an optimization procedure, called a genetic algorithm, which is known as a robust optimization tool. The proposed equivalent circuit model of the ACF interconnection can readily be used in SPICE circuit simulations for signal integrity analysis of high-frequency packages. Two different ACF interconnections were studied using the Au-coated polymer ball and Ni-filled ball. The extracted models of the two ACFs were found strongly dependent on not only size and rigidity of the conducting balls, but also on their magnetic permeability     

The Effects of Portland's Urban Growth Boundary on Housing Prices

Unlike previous studies, which used metropolitan level data, this study uses spatially disaggregated data (block group data from the U.S. Census) to statistically test the effects of Portland's urban growth boundary (UGB) on housing prices. This analysis shows no evidence of a significant difference between housing prices inside and outside the UGB, suggesting that both inside and outside the UGB are parts of a single housing market.     

The effect of random point excitation on the vibration level of plates

When a mechanical structure is driven by stationary wide band random point forces, the resulting vibration depends upon the number, location, and joint statistical properties of the exciting forces. In this study, under the assumption of light damping, an approximate procedure for analyzing plates is briefly outlined. The effects of number, location and correlation of the force field on the vibration level are then investigated for various cases in which random point forces with band limited white noise are applied, and the optimal spacing between input forces that produces a relative minimum in the vibration response is predicted.     

Constrained isogeometric design optimization of lattice structures on curved surfaces: computation of design velocity field

This paper presents an immersed boundary approach for level set topology optimization considering stress constraints. A constraint agglomeration technique is used to combine the local stress constraints into one global constraint. The structural response is predicted by the eXtended Finite Element Method. A Heaviside enrichment strategy is used to model strong and weak discontinuities with great ease of implementation. This work focuses on low-order finite elements, which given their simplicity are the most popular choice of interpolation for topology optimization problems. The predicted stresses strongly depend on the intersection configuration of the elements and are prone to significant errors. Robust computation of stresses, regardless of the interface position, is essential for reliable stress constraint prediction and sensitivities. This study adopts a recently proposed fictitious domain approach for penalization of displacement gradients across element faces surrounding the material interface. In addition, a novel XFEM informed stabilization scheme is proposed for robust computation of stresses. Through numerical studies the penalized spatial gradients combined with the stabilization scheme is shown to improve prediction of stresses along the material interface. The proposed approach is applied to the benchmark topology optimization problem of an L-shaped beam in two and three dimensions using material-void and material-material problem setups. Linear and hyperelastic materials are considered. The stress constraints are shown to be efficient in eliminating regions with high stress concentration in all scenarios considered.     

Effects of substrate and deposition method onto the mirror scattering

The effect of surface roughness onto the mirror scattering has been studied. Five kinds of substrates with different surface roughness were fabricated. On those substrates, dielectric multilayer coating for high reflectivity was deposited by ion-beam sputtering (IBS) and by electron-beam (EB) evaporation. Total integrated scattering (TIS) measurement setup was built for the evaluation of deposited samples. Most of the IBS mirrors showed lower scattering than the EB mirrors, which were deposited on the similar substrates in surface roughness. The ratio of substrate TIS to mirror TIS was defined for evaluation. It increased abruptly at approximately 2A in surface roughness, which indicated that to make low-loss mirrors, the substrate roughness should be less than 2A in rms.     

Fabrication of a porous material with a porosity gradient by a pulsed electric current sintering process

A porous structure with a porosity gradient can be applied to the preparation of continuous FGM, where liquid or chemical vapor of the second phase is infiltrated into the graded pores. It also has applications in skeletal implant materials and ultrafiltration media. An attempt was made to fabricate a porous material with a porosity gradient by means of a pulsed electric current sintering (PECS) process. The present work describes not only the measured value of the temperature difference between the upper and lower part of the specimen, which brings about a gradual change in pore distribution, but also the sintering characteristics of the porous structure obtained by the pressureless PECS process.