Study on Higher Efficiency Thermal Cycling Profile for HALT

HALT (highly accelerated life test) is a new reliability test technique. This paper uses nonlinear finite element method to analyze the stress strain characteristic of solder joints of PQFP (plastic quad flat packaging) and BGA (ball grid array) under thermal cycle test, and studies influences of profile parameters of the thermal cycle, such as hot and cold soak temperature, hot and cold soak time and temperature change rate, on elastic strain range, accumulated plastic strain, fatigue life and test efficiency of two types of solder joints. Based on the above research and experimental verification, this paper presents the method to build an optimal thermal cycling profile for HALT of electronic components.     

The effect of employed loading mode on the mechanical cyclic stabilization of NiTi shape memory alloys

One of the effective parameters on the characteristic response of the nickel-titanium (NiTi) shape memory alloy (SMA) is the employed loading mode during the uniaxial cycling. In this study, the uniaxial tensile tests are conducted under an extended number of mechanical cycles in order to investigate the effect of force control on the pseudoelastic response of the NiTi SMA. The results which are obtained under the force control are compared with the mixed (force/displacement) control counterpart. An evolutionary stress-strain pattern is observed during the 100 cycles of mechanical loading. Additionally, it is noticed that the residual strain and mechanical hysteresis area also show an evolutionary pattern. The observed evolutionary patterns are delineated in three regimes: (i) early evolution; (ii) approach to a nearly stable stage (transient); and (iii) stabilization stage. Furthermore, the in-situ digital image correlation (DIC) is applied to receive the meso-/micro-scale full-field strain measurements. Severe strain localization is observed under force-controlled tensile test during meso-,/micro-scale DIC analysis.     

Influence of preparation temperature on the oxidation resistance and mechanical properties of C/SiC coated C/C composites

A C/SiC oxidation resistance coating was prepared on carbon/carbon (C/C) composites by slurry and pack cementation. The microstructure, oxidation resistance and mechanical properties of C/SiC coating prepared from 1773 to 2573 K were investigated. With the increase of the preparation temperature, the oxidation resistance of C/SiC coating increases, however, the flexure strength decreases gradually. The preparation of C/SiC coating on C/C composites results in the fracture behavior of C/C composites changing from pseudo-plastic to brittle failure model. The decrease of flexure strength is mainly attributed to the decrease of C/C matrix’ flexure strength at high temperature.     

A Cyclic Internal Pressure Characteristics Analysis of Long Distance Transmission Pipelines

The objective of this work is to present the cyclic internal pressure behaviors and generated reasons of different long distance transmission pipelines, considering transported fluid, in-service period, and pressure data sampling methods. Rainflow counting method is adopted to obtain pressure cycles, and the analysis results indicate that pipelines pressure show variously in respects of cycle number and amplitude value, and pressure cycling reasons and suggestions are specially discussed. The authors argue that suitable operation scheme should be carried out to avoid unnecessary pipeline damage according to the oil or gas pipelines’ special pressure fluctuation characteristics and generated reasons.     

铅酸蓄电池正极活性物质的研究

采用有效添加剂,提高了铅酸蓄电池正极活性物质利用率,延长了使用寿命.软化脱粉现象明显改善.通过X射线衍射分析、电子扫描显微镜分析和比表面的测定,解释了不同添加剂对PbO_2电极的组成、结构和性能的影响原因,确定了添加剂的最佳合量,从而得到较好的配方.     

Cyclic voltammetric behaviour of polyfuran perchlorate doped films

Electroactivity with continuous cycling and the electrochemical behaviour of polyfuran perchlorate films (PFu/ClO₄) were investigated to determine the reversibility of doping/dedoping processes and the electrochemical mechanism of these processes as a function of the electropolymerization potential. A surface capacitive oxidation mechanism and a diffusion controlled mechanism in the dedoping process were detected when the potential scan rate was varied in D films (_p = 2.3 V). Moreover, D films (_p = 2.1 V ) showed a mixture of mechanism in the reduction processes. The polymeric material was found to deteriorate with continuous charge–discharge over successive days.     

Correction to Dittmar, Halliwell, and Ive (2006).

Reports an error in "Does Barbie make girls want to be thin? The effect of experimental exposure to images of dolls on the body image of 5- to 8-year-old girls" by Helga Dittmar, Emma Halliwell and Suzanne Ive (Developmental Psychology, 2006 Mar, Vol 42[2], 283-292). A substantive error occurs in the Body shape dissatisfaction section on page 287. The sentence describing the calculation of body shape dissatisfaction scores from girls' responses to the Child Figure Rating Scale should instead read as follows: "A body shape dissatisfaction score was computed by subtracting the girl's actual from her ideal body size." (The following abstract of the original article appeared in record 2006-03514-007.) The ubiquitous Barbie doll was examined in the present study as a possible cause for young girls' body dissatisfaction. A total of 162 girls, from age 5 to age 8, were exposed to images of either Barbie dolls, Emme dolls (U.S. size 16), or no dolls (baseline control) and then completed assessments of body image. Girls exposed to Barbie reported lower body esteem and greater desire for a thinner body shape than girls in the other exposure conditions. However, this immediate negative impact of Barbie doll was no longer evident in the oldest girls. These findings imply that, even if dolls cease to function as aspirational role models for older girls, early exposure to dolls epitomizing an unrealistically thin body ideal may damage girls' body image, which would contribute to an increased risk of disordered eating and weight cycling. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effect of thermal cycling on the growth of intermetallic compounds at the Sn-Zn-Bi-In-P lead-free solder/Cu interface

The low-temperature Sn-9Zn-1.5Bi-0.5In-0.01P lead-free solder alloy is used to investigate the intermetallic compounds (IMCs) formed between solder and Cu substrates during thermal cycling. Metallographic observation, scanning electron microscopy, transmission electron microscopy, and electron diffraction analysis are used to study the IMCs. The γ-Cu₅Zn₈ IMC is found at the Sn-9Zn-1.5Bi-0.5In-0.01P/Cu interface. The IMC grows slowly during thermal cycling. The fatigue life of the Sn-9Zn-1.5Bi-0.5In-0.01P solder joint is longer than that of Pb-Sn eutectic solder joint because the IMC thickness of the latter is much greater than that of the former. Thermodynamic and diffusivity calculations can explain the formation of γ-Cu₅Zn₈ instead of Cu-Sn IMCs. The growth of IMC layer is caused by the diffusion of Cu and Zn elements. The diffusion coefficient of Zn in the Cu₅Zn₈ layer is determined to be 1.10×10⁻¹² cm²/sec. A Zn-rich layer is found at the interface, which can prevent the formation of the more brittle Cu-Sn IMCs, slow down the growth of the IMC layer, and consequently enhance the fatigue life of the solder joint.     

估算低温下金属材料应变疲劳寿命和疲劳极限的新方法

本文建立了估算低温下金属材料应变疲劳寿命的新方法,并首次提出了金属疲劳极限的热激活模型。该模型可定量地解释温度和频率对疲劳极限的影响。研究结果表明,提出的应变疲劳公式可很好地拟合低温下金属材料应变疲劳寿命的实验结果;疲劳极限可表示成非热激活分量σ_(ai)(ε_(apc))和热激活分量σ_a~*(T,ε_p)之和;σ_(ai)(ε_(apc))是与温度和频率(或应变速率)无关的材料常数;σ_a~*(T,ε_p)与流变应力的热激活分量近似相等。最后用文献中的实验数据对本文提出的低温下就应变疲劳寿命和疲劳极限的估算方法进行了验证。     

Electrochemical supercapacitors based on industrial carbon blacks in aqueous H2SO4

It is shown that industrial carbon blacks (CBs) are interesting materials for electrochemical supercapacitors (ECSCs). The specific areas A _s ranged from 28 to 1690 m² g^–1. The highest values were realized through activation in CO₂ at 1100 °C. Precompacted carbon black electrodes with 5–10 wt% PTFE as a binder in the pellet in 10–12 M H₂SO₄ were characterized by constant current cycling, CCC, j = 20–50 mA cm^–2. Voltage–time curves showed nearly pure capacitive behaviour. Specific capacitance of single electrodes, C _s,1, could be derived therefrom. A plot of C _s,1 against A _s shows a linear behavior according to C _s,1 = C _A,DL A _s, where C _A,DL is the Helmholtz double layer capacitance per atomic surface area. Best fit was obtained with C _A,DL = 16 F cm^–2. The highest experimental values, C _s,1 = 250 F g^–1, are due to 60% of the theoretical maximum, which corresponds to an A _s calculated from both faces of isolated graphene layers. Only marginal pseudocapacitances are observed. Model cells for ECSCs (with microporous Celgard^TM separators) could be extensively cycled (CCC). A monopolar cell endured Z > 2000 cycles. Bipolar cells (5 units) allowed 700 cycles. Practical problems such as the development of electrode holders and of carbon black filled polypropylene composites for current collectors are discussed. It is concluded that entirely metal-free ECSCs with low cost can be produced.