Interfacial reaction and shear strength of SnAgCu-xNi/Ni solder joints during aging at 150 °C

The interfacial microstructure and shear strength of Sn3.8Ag0.7Cu-xNi (SAC-xNi, x = 0.5, 1, and 2) composite solders on Ni/Au finished Cu pads were investigated in detail after aging at 150 °C for up to 1000 h. The interfacial characteristics of composite solder joints were affected significantly by the weight percentages of added Ni micro-particles and aging time. After aging for 200 h, the solder joints of SAC, SAC-0.5Ni and -1Ni presented duplex intermetallic compound (IMC) layers regardless of the initial interfacial structure on as-reflowed joints, whose upper and lower IMC layers were comprised of (CuNi)₆Sn₅ and (NiCu)₃Sn₄, respectively. Only a single (NiCu)₃Sn₄ IMC layer was ever observed at the SAC-2Ni/Ni interface on whole aging process. Based on the compositional analysis, the amount of Ni within the IMC regions increased as the proportion of Ni addition increased. The IMC (NiCu)₃Sn₄ layer thickness on the interface of SAC and SAC-0.5Ni grew more slowly when compared to that of SAC-1Ni and -2Ni, while for the (CuNi)₆Sn₅ layer the reverse is true. Except the IMCs sizes are increased with increased aging time, the interfacial IMCs tended to transfer their morphologies to polyhedra. In all composite joints testing, the shear strengths were approximately equal to non-composite joints. The fracturing observed during shear testing of composite joints occurred in the bulk solder, indicating that the SAC-xNi/Ni solder joints had a desirable joint reliability.     

强光辐照下白宝石高反镜尺寸对热变形的影响

为了进一步减小白宝石（Al2O3）高反镜在强光辐照下的热变形,提高光束质量,研究了白宝石高反镜厚度、直径尺寸对热变形的影响。采用以极坐标表示的热传导方程和热变形公式来描述白宝石高反镜的温度场分布和位移场分布;在有限元分析软件中建立数值计算模型,并计算了不同厚度、直径尺寸下的温度场和位移场,得到了热变形随厚度尺寸和直径尺寸变化的规律。结果表明,影响白宝石高反镜反射面峰谷值变化的主要因素是温度,而尺寸变化对温度和刚度均有影响;选择合适的高反镜直径和厚度尺寸,可以有效降低镜面温升,同时得到合适的轴向结构刚度,从而减小反射镜镜面热变形。该研究结果对强光辐照下白宝石高反镜尺寸设计和选择具有一定的参考价值。     

静电拉伸薄膜反射镜成形机理研究

静电拉伸薄膜反射镜是利用静电场库仑力作用使薄膜产生面形变化,生成所需的光学曲面.由于薄膜反射镜成形过程中力场与静电场的相互耦合作用非常复杂,使其到目前为止在面形控制的理论分析上仍未有定量的结果.首先以平板电容理论为基础,对薄膜成形静电力场进行了近似分析,然后根据半球模型求解了薄膜结构变形,最终得到了薄膜反射镜面形尺寸与静电压参数的函数关系.所得结论对静电拉伸薄膜的研究工作具有一定的指导意义.     

光电经纬仪车载平台变形测量技术研究

采用一种高精度非接触测量系统对光电经纬仪车载平台变形进行实时测量,利用视频 判读技术对CCD视频信号进行接收和处理,采用图像采集和图像处理同时进行的工作方式,对图像进行实时处理和判读,得出动态脱靶量,进而计算出车载平台的变形量,这为进一步研究车载平台技术打下理论和实践基础。     

Application of an asymmetrical four point bend shear test to solder joints

The asymmetrical four-point bend shear (AFPB) test method was used to measure the shear strength and creep properties through the stress relaxation experiments using three different Pb-free solder joint compositions in an assolidified condition. Since it was difficult to shear the uniform specimens and the local bending usually occurs at the inner loading points, the notches were introduced at the joint line to preferentially weaken this region. The stress analysis by finite element modeling showed that the straight notches transform the parabolic shear stress distribution in the uniform specimen into a relatively uniform shear distribution along the bond line in the notched specimens. Therefore, the shear strength results from the notched specimens are expected to be much more accurate. Experiments showed that both the Sn-3.6Ag-1Cu (wt.%) and Sn-3.6Ag-1Cu-0.45Co joints have superior strength and creep properties as compared to the Sn-3.5Ag joint. However, there was no statistical difference between the shear strength of the Sn-3.6Ag-1Cu and Sn-3.6Ag-1Cu-0.45 Co joints. Moreover, the difference between the creep resistance of these two types of joints was small.     

Learning shape and texture progression for young child face aging

Face aging (FA) for young faces refers to rendering the aging faces at target age for an individual, generally under 20s, which is an important topic of facial age analysis. Unlike traditional FA for adults, it is challenging to age children with one deep learning-based FA network, since there are deformations of facial shapes and variations of textural details. To alleviate the deficiency, a unified FA framework for young faces is proposed, which consists of two decoupled networks to apply aging image translation. It explicitly models transformations of geometry and appearance using two components: GD-GAN, which simulates the Geometric Deformation using Generative Adversarial Network; TV-GAN, which simulates the Textural Variations guided by the age-related saliency map. Extensive experiments demonstrate that our method has advantages over the state-of-the-art methods in terms of synthesizing visually plausible images for young faces, as well as preserving the personalized features.     

Towards a Better Prediction of Cell Settling on Nanostructure Arrays—Simple Means to Complicated Ends

Vertical arrays of nanostructures (NSs) are emerging as promising platforms for probing and manipulating live mammalian cells. The broad range of applications requires different types of interfaces, but cell settling on NS arrays is not yet fully controlled and understood. Cells are both seen to deform completely into NS arrays and to stay suspended like tiny fakirs, which have hitherto been explained with differences in NS spacing or density. Here, a better understanding of this phenomenon is provided by using a model that takes into account the extreme membrane deformation needed for a cell to settle into a NS array. It is shown that, in addition to the NS density, cell settling depends strongly on the dimensions of the single NS, and that the settling can be predicted for a given NS array geometry. The predictive power of the model is confirmed by experiments and good agreement with cases from the literature. Furthermore, the influence of cell‐related parameters is evaluated theoretically and a generic method of tuning cell settling through surface coating is demonstrated experimentally. These findings allow a more rational design of NS arrays for the numerous exciting biological applications where the mode of cell settling is crucial.     

Failure Deformation and Stress Relaxation of Heated Egg White Gels

Stress-strain relationships were determined for heated egg white gels. Compressive strain at failure was independent of protein concentration, while stress at failure increased with protein concentration. Between the length ratios of 1.6 and 2.4 before and after compression, the heated egg white gels followed the Mooney Rivlin model. In stress relaxation, the asymptotic hypothetical equilibrium modulus increased with protein concentration.     

纵向变形协调时纤维增强复合材料的横向模量分析

近些年来,复合材料横向模量的分析受到了普遍的重视,并获得一定进展.本文采用Phillips提出的串联/并联模型,考虑到沿纵向纤维与基体的变形协调,利用材料力学方法,求得具有正方形截面的纤维增强复合材料的横向模量,进而讨论了其它形状纤维截面的应用.     

钢薄壁圆筒体的吊装

介绍了钢薄壁圆筒体吊装方法的选择及吊点位置的确定 ,对于钢薄圆筒体局部失稳进行了分析 ,提出了相应的加固措施