The polarization changes caused by applying mechanical stresses to a lead zirconate titanate (PZT) thin film were investigated. Both the remnant and spontaneous polarizations decreased when the PZT film was loaded with tensile stress. For compressive stresses, the remnant polarization increased, but spontaneous polarization did not change. In fatigue with tensile stress state, the polarization decreased earlier than when there was no stress, which depend on whether or not the initial polarization value was high. Conversely, in fatigue with compressive stress, the initial higher remnant polarization value was maintained compared with the polarization in the unstress condition.
A new unified visco-plastic constitutive model for the 60 Sn-40 Pb alloy used in solder joints of surface-mount IC packages and semiconductor devices is proposed. The model accounts for the measured stress-dependence of the activation energy and for the strong Bauschinger effect exhibited by the solder. The latter is represented by a back stress state variable which, in turn, evolves according to a hardening-recovery equation. Based on the observed hardening behavior, it is assumed that the isotropic resistance to plastic flow does not evolve within the deformation range covered in this study (ε< 3 percent). The deformation phenomena associated with the solder’s monotonic and steady-state cyclic responses are accurately predicted for −55°C≦T≦150°C and 8 x 10−2 s−1 ≦ ε ≦ 8 x 10−5 s−1. The model also predicts well the overall trend of steady-state creep behavior. The constitutive model is formulated within a continuum mechanics framework and is therefore well suited for implementation into finite element or other structural codes.
The extent to which the intramolecular heterophotodimerization of the photochromic molecule 9-(hydroxymethyl)-10-[(naphthylmethoxy)methyl]anthracene (HNMA), incorporated into a poly-(methyl methacrylate) (PMMA) matrix, is induced by irradiation with linearly polarized light was investigated. The degree of photodimerization was evaluated by using the polarization-induced efficiency parameter, 7, which is defined as the normalized difference between the two components of dichroic absorbance. It was found that 7 is affected by both the @-relaxation process and the glass transition temperature, Tg (T, = 103 "C) of the PMMA matrix. As irradiation time increases, 7 increases and reaches a limiting value, qmar, of ca. 6% at temperatures of around 40 "C. These results indicate that, by utilizing the selective induction of the intramolecular heterophotodimerization of HNMA, which occurs upon excitation with polarized light, it is possible to generate and control the spatial distribution of the refractive index of glassy polymer films, thereby making them potentially useful as optoelectronic materials for wave guiding or light modulation.
Large scale three-dimensional finite element analyses of 68 and 44 pin types Quad Flat I-Leaded packages subjected to −55°C to 150°C temperature cycling are performed to predict the way in which inelastic strains and microstructure evolve in the solder joints. A new set of unified constitutive equations, which correctly accounts for the inelastic strain rate dependency on stress, temperature, and microstructure (internal stresses) and the evolution of the latter with deformation, was used to model the solder joints’ thermo-mechanical behavior. Estimates of the critical inelastic strain ranges in the solder joints were obtained from the calculated inelastic deformation histories. The range of inelastic strain associated with each thermal cycle is small and practically unaffected by the observed ratcheting of the cycles toward positive strains due to the non-zero mean cycle stresses. By combining the numerical results with fatigue life data obtained from leads subjected to the same thermal loading, a fatigue life relation for mean failure probability of the IC packages’ solder joints has been proposed. The analysis correctly predicts the critical locations for crack initiation.
Radio frequency (RF) direct sampling is a technique used to sample RF signals that are higher than the sampling rate, without the use of a frequency converter and an anti-aliasing filter. In the case of geodetic VLBI, the RF frequency is at most 9 GHz. Recently, a digital sampler with high sensitivity at RF frequencies greater than 10 GHz was developed. The sampler enables us to evaluate the use of the RF direct sampling technique in geodetic VLBI. RF direct sampling has the potential to make the system simple and stable because, unlike a conventional system, analog frequency converters are not used. We have developed two sets of RF direct sampling systems and operated them on Kashima and Tsukuba baseline (about 50 km length) in Japan. At first, we carried out the VLBI experiment only for X band (8 GHz) signals and successfully got the first fringes. Aliased signals could be discriminated through correlation processing. Then, we adopted RF direct sampling for mixed signals, i.e., S band (2 GHz) and X band signals are combined with each other to make a geodetic VLBI observation. We carried out a 24 hr geodetic VLBI session on 2011 October 19 and succeeded in fringe detection for both S and X bands. After correlation processing, baseline analysis was carried out and we got results consistent with those obtained by conventional VLBI.
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