Microstructure of External Stress Whiskers and Mechanical Indentation Test Method

Lead-free commercial products have been dramatically increasing in the world markets as the restriction of certain hazardous substances (RoHS) directive in the European Union has been enacted. At the same time, the problem of “tin whiskers” has become one of the most serious problems in the industry. Growth of tin whiskers is believed to be related to residual stress inside the tin plating film and external compressive stress. Whiskers in fine-pitch connectors have affected the practical production of advanced digital equipment. The Japan Electronics and Information Technology Industries Association (JEITA) has proposed a new testing method to evaluate tin whiskers, especially for the fine-pitch connectors. This paper describes the microstructures of external stress whiskers and the mechanical indentation test method.     

A fast first-order optimization approach to elastoplastic analysis of skeletal structures

It is classical that, when the small deformation is assumed, the incremental analysis problem of an elastoplastic structure with a piecewise-linear yield condition and a linear strain hardening model can be formulated as a convex quadratic programming problem. Alternatively, this paper presents a different formulation, an unconstrained nonsmooth convex optimization problem, and proposes to solve it with an accelerated gradient-like method. Specifically, we adopt an accelerated proximal gradient method, that has been developed for a regularized least squares problem. Numerical experiments show that the presented algorithm is effective for large-scale elastoplastic analysis. Also, a simple warm-start strategy can speed up the algorithm when the path-dependent incremental analysis is carried out.     

Canadian Field Soils I. Mineral Composition by XRD/XRF Measurements

Forty Canadian soils were laboratory tested for the presence of quartz and other minerals using X-ray diffraction/X-ray fluorescence techniques. On average, the highest quartz content was observed in soil samples from sites in Nova Scotia followed by Prince Edward Island sites, whereas soil sample from British Columbia sites had the lowest quartz content. The second most abundant mineral was albite that mainly occurred in soil samples from Ontario and Quebec sites. Illite was the third most abundant and prevailed in soils mainly from British Columbia and New Brunswick sites. Soil samples from British Columbia sites had the highest combined clay and silt content and were composed of illite, albite, kaolinite, and chlorite. The lowest clay content was found in the samples from the Quebec sites. The highest microcline (a potassium feldspar) content was observed in Quebec, Ontario, and Prince Edward Island sites. In contrast to other provinces, samples from Quebec and Ontario sites also included amphibole. Soil samples from Saskatchewan and Manitoba sites also comprised carbonates, i.e., calcite and dolomite. Iron oxides (e.g., goethite) were present in all soils, except the Quebec sites, but their occurrence was rather insignificant.     

Hydrolytic degradation of poly(L-lactic acid): Combined effects of UV treatment and crystallization

Amorphous and crystallized poly(L -lactic acid) (PLLA) films were prepared and the hydrolytic degradation of the ultraviolet (UV)-treated and UV-nontreated films was investigated. This study reveals that the combination of UV and thermal treatments can produce the PLLA materials having different hydrolytic degradation profiles and that the UV-irradiation in the environment will affect the design of recycling process for PLLA articles. In an early stage, the degrees of hydrolytic degradation monitored by weight loss (W_loss), number-average molecular weight (M _n), and melting temperature (T _m) were higher for the UV-treated films than for the UV-nontreated films. In a late stage, the trend traced by W_loss was reversed, and the difference in the degrees of hydrolytic degradation between the UV-treated and UV-nontreated films monitored by M _n and T _m became smaller, with the exception of the degrees of hydrolytic degradation of the amorphous films traced by T _m. Also, in the early stage, the degrees of hydrolytic degradation monitored by W_loss and M _n were higher for the crystallized films than for the amorphous films. In the late stage, this trend was reversed, with the exception of the degrees of hydrolytic degradation of the UV-treated films monitored by M _n. The main factors that determined the W_loss and T _m were the molecular weight and initial crystallinty but not the molecular structures such as terminal CC double bonds and crosslinks. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Starting method of a superconducting generator in a combined‐cycle power plant

In the combined‐cycle power plant generators are started by using the igniting arrangement up to the ignition rotational speed of the gas turbine. On the other hand, in the case of using the superconducting generator, it is difficult to apply the igniting arrangement used to generate electricity on the combined cycle for the structure as is. We examined the induction motor starting method for the superconducting generator by using the 70‐MW‐class quick‐response excitation superconducting model generator and the VVVF power supply. From the examination, we confirmed the ability to raise the rotational speed from 6 to 360 rpm. Moreover, it was found to be able to start 200‐MW‐class superconducting generators by the induction motor starting method with the analysis. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 160(2): 30– 38, 2007; Published online in Wiley InterScience ( www.interscience. wiley.com ). DOI 10.1002/eej.20283     

A new detection method for the primary cosmic heavy nuclei by the plastic track detector CR-39

A new multiple scanning method is developed and applied to detect cosmic heavy nuclei. The plastic track detectors CR-39 exposed to cosmic heavy nuclei are over-etched in 8.0N NaOH for 94 h at 80°C. We found that the etched cones can easily be scanned on the plastic plates without using an optical microscope. The trajectories of heavy nuclei can be reconstructed with the naked eyes by superposing four or more over-etched plates. The charge detection threshold is obtained by this method, and appears to be 10. The charge resolution is estimated to be 1.0 charge units for iron nuclei. By adopting this method, the scanning time is much shortened and CR-39 plastic chamber size can easily be scaled up. The method is very useful for detecting particles with low flux intensity, like for searching magnetic monopoles or for measuring the high energy spectra of cosmic heavy nuclei.     

Non-uniqueness and symmetry of optimal topology of a shell for minimum compliance

Uniqueness and symmetry of solution are investigated for topology optimization of a symmetric continuum structure subjected to symmetrically distributed loads. The structure is discretized into finite elements, and the compliance is minimized under constraint on the structural volume. The design variables are the densities of materials of elements, and intermediate densities are penalized to prevent convergence to a gray solution. A path of solution satisfying conditions for local optimality is traced using the continuation method with respect to the penalization parameter. It is shown that the rate form of the solution path can be formulated from the optimality conditions, and the uniqueness and bifurcation of the path are related to eigenvalues and eigenvectors of the Jacobian of the governing equations. This way, local uniqueness and symmetry breaking process of the solution are rigorously investigated through the bifurcation of a solution path.     

Role of adsorbed iodine into poly(vinyl alcohol) films drawn in KI/I2 solution

We have investigated the microstructure of the poly(vinyl alcohol) (PVA) films using small- and wide-angle X-ray scattering (SAXS and WAXS, respectively) techniques. The samples were uniaxially drawn in water or KI/I₂ aqueous solution and then dried in an air-oven at 333 K for 1 h prior to SAXS and WAXS measurements. It was found that for the films drawn in KI/I₂ solution PVA chains in the microfibrillar structure are more extended upon the film drawing compared to the case of the films drawn in pure water, which is resulted from the correlation function analysis on the SAXS data. Adsorbed iodines into the film were anticipated to act as junction points between the microfibrils via the formation of the PVA-iodine complexes.