Effects of Joining Sequence on the Interfacial Reactions and Substrate Dissolution Behaviors in Ni/Solder/Cu Joints

The effects of the joining sequence on the interfacial reactions and substrate dissolution behaviors in Ni/solder/Cu joints were studied by using 500-μm (diameter) Sn-3.5Ag solder balls and substrates with a 375-μm (diameter) opening. Three distinct paths for the joining sequence were studied. In path I, a solder ball was first joined to the Cu substrate and then to the Ni substrate. In path II, a solder ball was joined to both the Cu and Ni substrates simultaneously. Path III had the opposite joining sequence to path I. The results of this study indicated that (Cu,Ni)₆Sn₅ was the predominant reaction product at both the Ni/solder and solder/Cu interfaces regardless of the joining sequence. However, the composition, morphology, and thickness of the (Cu,Ni)₆Sn₅ varied considerably with the different paths. The dissolution behaviors of Cu and Ni were also different. Dybkov’s dissolution kinetics and Cu-Ni-Sn isotherm data were utilized to rationalize these differences.     

单导线覆冰舞动的非线性数值模拟

提出了一种单导线覆冰舞动的教值模拟方法,基于更新拉格朗日列式推导了可考虑轴向扭转和大变形效应的两节点索单元,建立了连续多档导线舞动的有限元模型,采用四阶荣格—库塔法对覆冰导线的舞动进行了数值求解,并研究了初始张力对舞动的影响.算例结果表明,该方法可行、有效,且具有较高的计算效率.     

An approximation analysis for safety messages transmission in vehicle-to-vehicle WAVE networks

Wireless Access in the Vehicular Environment (WAVE) specification defines the WAVE Short Message Protocol (WSMP) for delivering WAVE Short Messages (WSMs). In the multihop transmission, WSMs are first received and stored in queues and then forwarded to the next hop. Unfortunately, WSMP does not specify any mechanism to avoid the messages loss resulted from queueing overflow. In this paper, a dual threshold-based queueing management which adjusts the message accepting rate upon the current queue length is proposed. The multihop transmission can be modeled as a tandem queueing network, and a discrete time Markov chain (DTMC) can be applied to evaluate the proposed queueing management. Since the computational complexity increases with the number of hops, an approximation approach to resolve DTMC model is also presented. Simulation results demonstrate the accuracy of approximation and the effectiveness of the proposed queueing management.     

Highly conductive and electrochemically stable plasticized blend polymer electrolytes based on PVdF-HFP and triblock copolymer PPG-PEG-PPG diamine for Li-ion batteries

A new plasticized poly(vinylidene fluoride-co-hexafluoropropylene (PVdF-HFP)/PPG-PEG-PPG diamine/organosilane blend-based polymer electrolyte system has been synthesized and characterized. The structural and electrochemical properties of the electrolytes thus obtained were systematically investigated by a variety of techniques including differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), tensile test, Fourier transform infrared spectroscopy (FTIR), ¹³C and ²⁹Si solid-state NMR, AC impedance, linear sweep voltammetry (LSV) and charge-discharge measurements. The FTIR and NMR results provided the information about the interaction among the constituents in the blend polymer membrane. The present blend polymer electrolyte exhibits several advantageous electrochemical properties such as ionic conductivity up to 1.3 × 10⁻² S cm⁻¹ at room temperature, high value of Li⁺ transference number (t₊ = 0.82), electrochemical stability up to 6.4 V vs. Li/Li⁺ with the platinum electrode, and stable charge-discharge cycles for lithium-ion batteries.     

Nanoscale elemental sensitivity study of Nd2Fe14B using absorption correlation tomography

Transmission X‐ray microscopy (TXM) is a rapidly developing technique with the capability of nanoscale three dimensional (3D) real‐space imaging. Combined with the wide range in energy tunability from synchrotron sources, TXM enables the retrieval of 3D microstructural information with elemental/chemical sensitivity that would otherwise be inaccessible. The differential absorption contrast above and below absorption edges has been used to reconstruct the distributions of different elements, assuming the absorption edges of the interested elements are fairly well separated. Here we present an “Absorption Correlation Tomography” (ACT) method based on the correlation of the material absorption across multiple edges. ACT overcomes the significant limitation caused by overlapping absorption edges, significantly expands the capabilities of TXM, and makes it possible for fully quantitative nano‐scale 3D structural investigation with chemical/elemental sensitivity. The capability and robustness of this new methodology is demonstrated in a case study of an important type of rare earth magnet (Nd₂Fe₁₄B). Microsc. Res. Tech. 76:1112–1117, 2013. © 2013 Wiley Periodicals, Inc.     

Physical properties of fish gelatin-based bio-nanocomposite films incorporated with ZnO nanorods

Well-dispersed fish gelatin-based nanocomposites were prepared by adding ZnO nanorods (NRs) as fillers to aqueous gelatin. The effects of ZnO NR fillers on the mechanical, optical, and electrical properties of fish gelatin bio-nanocomposite films were investigated. Results showed an increase in Young''s modulus and tensile strength of 42% and 25% for nanocomposites incorporated with 5% ZnO NRs, respectively, compared with unfilled gelatin-based films. UV transmission decreased to zero with the addition of a small amount of ZnO NRs in the biopolymer matrix. X-ray diffraction showed an increase in the intensity of the crystal facets of (10^ī1) and (0002) with the addition of ZnO NRs in the biocomposite matrix. The surface topography of the fish gelatin films indicated an increase in surface roughness with increasing ZnO NR concentrations. The conductivity of the films also significantly increased with the addition of ZnO NRs. These results indicated that bio-nanocomposites based on ZnO NRs had great potentials for applications in packaging technology, food preservation, and UV-shielding systems.     

The influence of surface roughness on the starved lubrication of ball bearings

Abstract

A theoretical analysis is made for starved lubrication of a rigid point contact under the influence of surface roughness. The results show that both the directional property and the standard deviation of the combined surface roughness can affect the load carrying capacity of the lubricant film as well as the friction on the solid surfaces. The combined effects of speed ratio of the contiguous surfaces and the roughness on starved lubrication are also obtained. The results show that the effects of surface roughness may improve the starvation a little, but that they are not remarkable. A regression equation is found for determining the critically starved lubricant inlet level. Such an inlet level can indicate the minimum limit of lubricant supplied quantity, and, beyond this limit, the load carrying capacity of the lubricant film will decrease sharply. In addition, experiments have been carried out to observe the starved lubrication of a ball rolling on a flat glass disc. It is shown that higher surface speeds may make the starved condition much worse.