纯锡的速率相关性变形行为

考察了纯锡在拉伸载荷下的力学性能及形变,探讨了应变速率对纯锡的变形机制的影响。采用扫描电镜形貌观察,对比不同应变速率(0.001~0.1 s–1)下样品表面的晶粒形貌、形变特征、断口信息。发现在较低的应变速率(0.001 s–1)下,纯锡的形变机制以蠕变为主要模式;在较高的应变速率(0.1 s–1)下,形变机制以位错滑移为主要特征。     

气瓶瓶口螺母裂纹分析

飞机试飞后进行检查时发现5A06铝合金制氧气瓶瓶口螺母开裂。对裂纹形貌进行检查,裂纹断口宏、微观检查表明,断口呈沿晶开裂特征。能谱分析结果表明,断口含有腐蚀性元素Cl和S。通过对气瓶材质进行分析,结合气瓶瓶口螺母加工工艺及使用状态,确定瓶口螺母裂纹开裂性质为应力腐蚀开裂,并提出了相应的预防措施和改进建议。     

一种新型钛合金半固态锻造后的断裂行为研究

以新型钛合金Ti14为对象,对比研究常规和半固态锻造合金经不同时间热暴露后的室温拉伸性能,探讨热暴露后的断裂行为及其断裂机制。结果表明,半固态锻造试样热暴露后的强度均明显高于常规锻造试样,而塑性略低于常规锻造试样。常规锻造试样宏观断口三要素清晰可见,断口由细小的韧窝组成,韧窝密度较大;半固态锻造试样纤维区模糊,剪切唇区较大,断口为韧窝和解理的混合型断口,并伴随少量二次裂纹的出现。析出相的尺寸、形态、分布的差异是导致两种锻造态合金热暴露后断裂机制改变的主要原因。     

Adhesion strength of leadframe/EMC interfaces

Cu-based leadframe sheets were oxidized in alkaline solutions to produce brown and/or black oxide on the surfaces, and molded with epoxy molding compound (EMC). The adhesion strength of leadframe/EMC interface was measured using sandwiched double-cantilever beam (SDCB) specimens and pull-out specimens. Results showed that the adhesion strength of leadframe/EMC interface was inherently very poor but could be increased drastically with the nucleation of acicular CuO precipitates. The presence of smooth-faceted Cu₂O on the surface of the leadframe gave close to zero fracture toughness (G_C) and suitable pull strength (PS). A direct correlation between G_C and PS showed that PS can be a measure of G_C only in a limited range.     

Indirect Control of Donor/Acceptor Interactions for Highly Efficient Space-Confined Thermally Activated Delayed Fluorescence Emitters

Conformational engineering is essential to further reinforce the luminescent properties of thermally activated delayed fluorescence (TADF) materials featuring through-space charge transfer (TSCT) characteristics. Herein, two TSCT-TADF emitters (8MeDM-B and 8FDM-B) with the methyl and fluorine moieties substituted at the C8 site of the rigid spiro-fluorene bridge is reported. Derivation of the C8 site is first proposed to control the molecular configuration with the ability to indirectly tune the intramolecular interaction between donor and acceptor groups. As a result, 8MeDM-B and 8FDM-B both present small singlet-triplet energy gaps, fast reverse intersystem crossing rates, and high photoluminescence quantum yields. Interestingly, the smaller fluorine atom not the bigger methyl group exhibits more evident electrostatic repulsive force onto the central donor and thus rectifies the central spiro structure. Consequently, the high external quantum efficiency values of 28.8% and 31.7% for 8MeDM-B and 8FDM-B-based electroluminescence devices are achieved, respectively. This study offers a measure for enhancing TSCT-TADF emitters without directly modifying the donor or acceptor.     

龙滩碾压混凝土重力坝试验研究

碾压混凝土重力坝采用大仓面薄层连续浇筑，其层面是一个薄弱环节，这是与常规混凝土坝的主要区别之一。为此结合仿真模型试验和非线性有限元法计算，论述碾压混凝土重力坝层面破裂面的形状、位置、发生条件及其影响因素，为设计碾压混凝土重力坝提供了科学依据     

超高强度钢疲劳塑性区内的应变诱发马氏体相变

对一种低碳马氏体型超高强度钢疲劳断口薄膜试样的电子衍射分析表明,疲劳塑性区内的残余奥氏体在交变应力的作用下转变为马氏体.本文就这种应变诱发相变对疲劳性能的作用机理进行了分析讨论.     

采用环状裂纹圆棒试样测定中低强度钢的断裂韧度

本文应用环状裂纹受拉圆棒试样的尺寸效应于测定中低强度钢的平面应变断裂韧度K_(IC)。所用试样的尺寸比标准试样小很多。用J积分分析了尺寸效应,并通过有限元计算和断口分析探讨了允许用较小尺寸的圆棒试样测定K_(IC)的原因。     

高动态GPS接收机中伪码捕获问题研究

设计在高动态环境下工作的GPS接收机，其难点之一便在于对卫星伪码的快速捕获。针对缩短GPS接收机捕获伪随机码时问的问题，在对GPS信号结构作出分析的前提下，解释了时域滑动相关的常规捕获方法；提出了基于FFT的快速捕获技术，并在Marlab环境下做了系统仿真，仿真结果显示捕获速度可以得到显著提高。     

改善块体金属玻璃室温脆性的研究进展

块体金属玻璃有许多优良的性能,如高强度、高硬度、高比强度、好的耐腐蚀抗力以及优良的软磁性能等。然而,近乎于零的室温塑性应变严重限制了其作为结构材料的实际应用。总结了近年来改善块体金属玻璃室温脆性的最新研究进展,并对这些方法的优缺点进行了分析。