Preparation and Characterization of Silicon-containing Polyarylacetylene/montmorilloite Nanocomposites

Dimethylphenylpropargyl ammonium bromide (DMPPAB) was synthesized and used to modify pristine montmorillonite (MMT) by a cation exchange process. The organically modified montmorillonite (OMMT) was verified and used to mix with a silicon-containing polyarylacetylene (PSA) as well as MMT. The PSA/MMT and PSA/OMMT nanocomposites were prepared by solution under sonication and melting intercalation processes, respectively, and then cured by a step heating process. The thermal and flexural properties of the cured PSA and nanocomposites were studied by thermogravimetric and dynamic mechanical analysis. The results showed that the intercalation of DMPPAB into the MMT galleries made the d-spacing enlarge. During PSA curing, the cure heat of PSA caused the MMT and OMMT to delaminate and exfoliate in the PSA matrix. The glass transition temperature of the cured PSA and nanocomposites were higher than 500?°C. The inner acetylenic groups in the PSA resin could further crosslink above 300?°C. The temperature at 5% mass loss of the cured PSA decreased by 4.6% with 3% mass fraction of OMMT loading, and the char yield of the cured PSA changed only slightly. The flexural strength of the cured PSA was augmented with addition of MMT or OMMT, but the flexural modulus of the cured PSA decreased slightly. The flexural strength of the cured nanocomposite increased from 20.1?MPa to 30.1?MPa when 3% mass fraction of OMMT was added into the PSA matrix.     

STUDY ON AMPLIFICATION FACTOR OF FLEXURAL BUCKLING CRITICAL LOAD OF AXIAL COMPRESSION BARS1)

为了建立一般条件下轴压构件屈曲临界载荷的计算理论,首先对轴心受压构件发生屈曲时的总势能方程进行了推导,然后采用Rayleigh-Ritz法并基于势能驻值原理得到了4种不同端部约束条件下轴压构件的屈曲临界载荷,对比欧拉临界载荷,给出了临界载荷放大系数 的计算式,全面考虑了构件长细比、压缩变形、剪切变形以及截面形状系数对临界载荷的影响,推导的计算式可用于较小长细比轴压构件发生屈曲时临界载荷的计算.圆截面和双轴对称工字形截面轴压构件屈曲临界载荷的分析表明构件长细比是影响放大系数的主导因素。     

基于导波技术的螺柱轴力无损检测

根据弹性动力学理论,采用纵向导波与弯曲导波相结合的方法对螺柱所受轴向应力进行无损检测。计算了M22螺柱中纵向导波和弯曲导波的群速度频散曲线。根据频散曲线,确定了采用导波对螺柱轴向应力进行无损检测的最优检测信号频率范围(50~80 kHz),此频率范围的纵向导波与弯曲导波模态单一,并且频散性较低。分别计算了不同轴向应力σ作用下,多种频率的纵向导波和和弯曲导波在螺柱中传播的群速度值cgσrL和cgσrF。结果表明,随着轴向应力的增大,同频率纵向导波和弯曲导波的群速度皆呈线性递减趋势。利用纵向导波和弯曲导波群速度与轴向应力的线性关系及纵向导波和弯曲导波在轴向应力作用螺柱端面的反射时间tLσ和tσF,可以迅速确定螺柱所受轴向应力值。     

Efficient Use of Carbon Fibers as Heating Elements for Curing of Epoxy Matrix Composites

The aim of this study is to achieve a fully cured thermoset matrix that is heated by a direct electric current passing through the reinforcement fibers i.e., the Joule heating effect. Two types of fibers were used as heating elements for curing the epoxy resins. Kanthal resistance fibers were used as reference heating elements and subsequently, they were replaced by a Torayca Carbon Tow of the same radius. The specimens were cured by the heat produced by a direct electric current passing through the fibers and achieving temperatures of 50 °C and 70 °C. Specimens cured in a conventional oven were also manufactured, to compare the resistance heating method to the conventional one. Next, all specimens were mechanically characterized in a quasi-static three-point bending mode of loading and experimental results were compared to derive useful conclusions concerning the applicability of the technique to polymer/composite materials mass production. Finally, a preliminary economical study concerning power consumption needed for the application of both the traditional oven curing and the carbon fibers heating elements use for the manufacturing of the same amounts of materials is presented, showing a maximum financial benefit that can be achieved, on the order of 68%.     

变刚度复杂梁结构损伤检测方法研究

提出了适用于复杂梁结构损伤检测的子段模态应变能法SSEM(subsectionstrainenergymethod),并分析了该方法的适用性条件．通过对变截面梁的有限元计算,以及对纤维增强复合材料风机叶片缩比模型的试验分析,验证了SSEM方法确定的结构损伤指标对损伤准确定位的可靠性．该基于振动的变刚度复杂梁结构的损伤检测方法,可应用于工程实际中梁和类梁整体结构的损伤检测．     

用电子散斑法对纯镍薄片弯曲变形的测量

由于建立的电子散斑法有位移测量精度高、量程大的特点,且自制的力传感器灵敏度高、量程相对较大,从而保证了本实验中镍片在三点弯中的反应被全程、精确地记录下来．基于时间序列的电子散斑法,测出了10—100μm不同厚度的纯镍薄片在三点弯下的载荷-位移曲线,其中包括弹性部分以及进入塑性屈服两个阶段,据此可以推出不同厚度镍片的三点弯刚度．实验表明镍片的抗弯刚度受其厚度的影响很大,尤其在薄片厚度较小时表现得更为明显,即表现出明显的尺度效应．     

圆截面弹性细杆的平面振动

基于Kirchhoff理论讨论圆截面弹性细杆的平面振动．以杆中心线的Frenet坐标系为参考系建立动力学方程．杆作平面运动时,其扭转振动与弯曲振动解耦．讨论任意形状杆的扭转振动和轴向受压直杆在无扭转条件下的弯曲振动,证明直杆平衡的静态Lyapunov稳定性与欧拉稳定性条件为动态稳定性的必要条件．考虑轴向力和截面转动惯性效应的影响,导出弯曲振动的固有频率．     

EEPROM耐久和数据保持试验方法标准分析

介绍了存储器分类,论述非易失性存储器编程机理以及编程/擦除耐久和数据保持试验方法,分析了MIL-STD-883B中的《耐久寿命试验》和JESD22-A117《电可擦除可编程只读存储器(EEPROM)编程/擦除耐久和数据保持应力试验》等试验方法标准.     

Reliability impacts of high-speed 3-bit/cell Schottky barrier nanowire charge-trapping memories

This study experimentally examines the reliability impacts of high-speed 3-bit/cell Schottky barrier nanowire charge-trapping memories. Unique Schottky barrier junctions strongly enhance hot-carrier generation, ensuring high-speed multi-level programming at low gate voltages. However, strong injected gate currents might cause potential retention and endurance concerns when the programming voltage is beyond 9 V. The effective number of deep-level traps is insufficient for capturing injected electrons, such that some electrons occupy shallower states, producing retention degradation after thermal stress. The charge-trapping layers are susceptible to additional trap generation under strong gate currents, leading to considerable threshold-voltage shifts after cycling stress. A compromise of cell characteristics exists between excellent reliability and high-speed programming in 3-bit/cell Schottky barrier nanowire cells. The application of sub-8-V multi-level programming can alleviate the potential reliability generated by strong injected currents, preserving a favorable cycling endurance and thermal retention in 3-bit/cell Schottky barrier nanowire charge-trapping cells.     

多频谱光电综合系统高精度稳定技术研究

本文提出了并采用一种组／精组合二级稳定的新方案，用于对多频谱，大负载，多传感器光电综合系统瞄准线或图像进行高精度稳定与跟踪。本技术的重要特征是采用挠性支承精稳反射镜组件以及粗／精多回路复合控制技术以获得高回路带宽和扰动大幅度衰减。