Effect of Stress State on Growth of Interfacial Intermetallic Compounds Between Sn-Ag-Cu Solder and Cu Substrates Coated with Electroless Ni Immersion Au

Excessive intermetallic compound (IMC) growth in solder joints will significantly decrease the reliability of the joints. IMC growth is known to be influenced by numerous factors during the component fabrication process and in service. It is reported that, other than temperature and holding time, stress can also influence the IMC growth behavior. However, no existing method can be used to study the effect of stress state on IMC growth in a controlled manner. This paper presents a novel method to study the effect of stress on interfacial IMC growth between Sn-Ag-Cu solder and a Cu substrate coated with electroless Ni immersion Au (ENIG). A C-ring was used and in-plane bending induced tensile and compressive stresses were applied by tightening the C-ring. Results revealed that in-plane compressive stress led to faster IMC growth as compared with in-plane tensile stress.     

An efficient return algorithm for non-associated plasticity with linear yield criteria in principal stress space

An efficient return algorithm for stress update in numerical plasticity computations is presented. The yield criterion must be linear in principal stress space and can be composed of any number of yield planes. Each of these yield planes may have an associated or non-associated flow rule. The stress return and the formation of the constitutive matrix is carried out in principal stress space. Here the manipulations simplify and rely on geometrical arguments. The singularities arising at the intersection of yield planes are dealt with in a straightforward way also based on geometrical considerations. The method is exemplified on non-associated Mohr–Coulomb plasticity throughout the paper.     

On the microhardness testing of electrically stressed poly(phenylene oxide): Polystyrene blends

Microhardness measurements have been performed on untreated (virgin) and electrically stressed, solvent‐cast laboratory‐prepared samples of pure poly(phenylene oxide) (PPO), pure polystyrene (PS), and PPO : PS polyblends with different weight proportions. Results of such measurement on untreated polyblend sample show that microhardness (H_v) increases with increase in the content of PS up to 10 wt %, which attributed to the existence of homogeneous phase morphology. However, this feature is not observable in samples containing higher content of PS. Electrical stress is found to modify considerably the mechanical property of polymer. The effect of electric field on the microhardness of such samples (PPO : PS :: 90 : 10) has been characterized by the existence of a peak. Trapping of charge carriers in electrically stressed samples imparts hardening to the polyblend up to an applied step field of 190 kV/cm. However, the excessive charging beyond this step field value destroys this characteristic. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Numerical Study of Scale Effects of Ultra-Thin Nickel Beams

Recent experiments have shown that metallic materials display significant size effects when the characteristic length scale of non-uniform plastic deformation is close to a micron. Couple stress plasticity has been developed to explain such phenomena by Fleck and Hutchinson. The mechanical behaviors of ultra-thin nickel beams in different boundary conditions were studied with the hybrid element developed for couple stress plasticity before. Strong scale effects are found when the beam's thickness is close to the material characteristic length scale. Such phenomena will disappear if the beam' s thickness is greatly larger than the material characteristic length scale. The scale effect is the beams inherent property and it does not change with the change of support conditions.     

Stress in Dairy Farming and the Adoption of New Technology.

Previous studies have identified a number of different farm stressors and have reported gender and age differences in levels of stress. This study aimed to determine stress experienced by New Zealand dairy farmers, particularly in relation to adoption of new technology and its relationship to age and gender. Measures of farm stress and adoption of technology were completed by 985 dairy farmers. The highest levels of stress were reported for time pressures, machinery breakdown, weather, and government policies. Stress related to new technologies occurred rarely. Women reported more stress and higher levels of stress for understanding new technologies. There was also an increase in severity of stress with age related to new technologies. Overall, stress levels were moderate and may reflect favorable economic conditions. The findings suggest a need to tailor stress interventions to meet specific needs. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

锅炉未焊透椭圆接管结构应力数值分析

应用有限元法对未焊透的椭圆接管结构进行了应力数值分析,并应用压力容器分析设计法,对该结构进行了疲劳分析,得出结构因未焊透缺陷导致疲劳破坏。     

石油套管的壁厚公差对承载能力的影响

石油套管的强度计算是按API标准进行的，它未能反映高强度套管和尺寸公差对抗压溃能力的影响。利用弹塑性力学理论建立理想的石油套管的抗压溃能力计算公式，并考虑套管的壁厚公差对计算公式进行修正。用该方法对受均匀载荷及非均匀载荷作用的套管进行分析，并同有限元计算结果相比，两者十分吻合，说明该方法的有效性。     

200m3液氨球罐裂纹成因分析

通过检验,从球罐的应力状态、球罐的金属材料和腐蚀介质等方面对200m3液氨球罐表面裂纹的形貌及产生裂纹的原因进行了分析,确定了球罐的裂纹是应力腐蚀裂纹,并对球罐进行了强度计算及安全评估。     

Longitudinal analysis of the relationship between symptoms and quality of life in veterans treated for posttraumatic stress disorder.

This study examined how change in posttraumatic stress disorder (PTSD) symptoms relates to change in quality of life. The sample consisted of 325 male Vietnam veterans with chronic PTSD who participated in a randomized trial of group psychotherapy. Latent growth modeling was used to test for synchronous effects of PTSD symptom change on psychosocial and physical health-related quality of life within the same time period and lagged effects of initial PTSD symptom change on later change in quality of life. PTSD symptoms were associated with reduced quality of life before treatment. There were synchronous effects of symptom change on change in quality of life but no significant lagged effects. Results indicate the importance of measuring quality of life in future investigations of PTSD treatment. (PsycINFO Database Record (c) 2010 APA, all rights reserved)