预环化处理方式对腈纶预氧化纤维性能的影响

研究了预环化处理方式对预氧化纤维阻燃性能和力学性能的影响。实验结果表明,先用羟胺处理,再用水合肼处理,所得预氧化纤维的阻燃性能和力学性能相对较好,在预氧化温度260℃时,可得到极限氧指数36.5%的预氧化阻燃纤维。扫描电镜观察表明,表面处理后纤维外表面裂纹明显减少,预氧化处理后纤维裂纹有所恢复。红外光谱分析表明,表面处理后纤维有少量吡啶环状结构生成,而预氧化后纤维中有大量吡啶环化结构产生。X射线衍射分析显示,经表面处理和预氧化之后纤维的形态结构没有发生大的变化,仍为高有序区和非晶区组成的准晶有序结构。     

高温后上海软黏土的物理性能试验研究

土的温度效应是岩土工程领域的热点问题,但对于100℃以上高温环境下土的物理性能的研究并不多。详细介绍了自行研制的高温加热试验装置,并利用该设备测定了上海软黏土样在105℃,120℃,150℃和200℃等高温加热2.5h和4.0 h后的体积变化、干密度和饱和度的变化,测定了105℃,150℃和200℃下恒温4.0 h土的导热情况。试验结果表明土样的体积和饱和度均随温度增加而减小,土样的干密度随温度的增加而增加,且随加热时间增加变化趋缓;湿土和干土的导热系数均随温度升高而增大,且干土的导热系数小于湿土的导热系数。说明软黏性土在100℃以上高温环境作用下会出现塑性变形和加热硬化现象,高温对土的导热系数影响显著。     

Compressive behavior of C/SiC composite sandwich structure with stitched lattice core

C/SiC composite sandwich structure with stitched lattice core was fabricated by a technique that involved polymer impregnation and interweaving. The mechanical behaviors of C/SiC composite sandwich structure were investigated at room temperature. The out-of-plane compressive strength was 20.97 MPa while modulus was 1473.55 MPa. The microstructural evolution on compression fracture surfaces of the stitching yarns was investigated by scanning electron microscopy, and the damage pattern of fibers on compression fracture surface was presented and discussed. Under an in-plane compression loading, the C/SiC composite sandwich structure displayed a linear-elastic behavior until failure. The peak strength and average modulus are 165.61 MPa and 19.74 GPa, respectively. The failure of the specimen was dominated by the fracture of the facesheet.     

单个非球面扩束透镜的设计

为设计单个非球面扩束(缩束)透镜,由光线折射定律矢量形式和对非球面折射特性的理论分析,提出了一种设计单个非球面扩束(缩束)透镜的新方法全面学习策略的粒子群算法,并用此方法设计出了线度小于170 mm缩束14.16倍的单个非球面缩束透镜,用光线追迹方法模拟了缩束或扩束过程。模拟结果表明,单个非球面透镜可以起到缩束或者扩束作用,全面学习策略的粒子群算法可用于非球面缩束透镜的设计。单个非球面透镜作为扩束镜使扩束系统结构大大简化,大大提高了出射光斑的均匀性。     

基于Morris方法的纤维复合材料结构件固化均匀性的全局灵敏度分析

纤维增强树脂基复合材料结构件的残余应力问题是制约其在航空航天、汽车和建筑领域大规模应用的关键问题。复合材料固化过程中温度场和固化度场的非均匀性是引起残余热应力和固化收缩应力的重要因素。为了探讨纤维复合材料结构件在固化成型过程中固化工艺温度、热传导系数、对流换热系数及结构件厚度对固化均匀性的敏感程度,采用数值模拟分析了这4个关键参数对温度场和固化度场均匀性的影响规律。模拟结果表明:升高固化工艺温度,复合材料温度场的非均匀性增大,固化度场的非均匀性减小;增大对流换热系数和热传导系数,复合材料温度场和固化度场的非均匀性减小;增加复合材料结构件的厚度,复合材料温度场和固化度场的非均匀性增大。在此基础上,应用Morris全局灵敏度分析方法对4个关键参数对复合材料固化均匀性的影响程度进行定量分析,得到固化均匀性的影响因素按灵敏程度由大到小的顺序为:结构件厚度、热传导系数、固化工艺温度、对流换热系数。     

移动加热器法晶体生长的研究

介绍了移动加热器法晶体生长的基本原理及其优缺点,报道了国内外最新研究进展,讨论了不同工艺参数,如磁场、加速坩埚旋转、重力、生长速度、温度等对THM生长晶体的影响,提出了提高THM生长晶体速度的设想,并就未来THM生长晶体的研究方法和发展趋势提出了自己的看法。     

薄膜厚度对TGZO透明导电薄膜光电性能的影响

利用直流磁控溅射法,在室温水冷玻璃衬底上成功制备出了可见光透过率高、电阻率低的钛镓共掺杂氧化锌(TG-ZO)透明导电薄膜。X射线衍射和扫描电子显微镜研究结果表明,TGZO薄膜为六角纤锌矿结构的多晶薄膜,且具有c轴择优取向。研究了厚度对TGZO透明导电薄膜电学和光学性能的影响,结果表明厚度对薄膜的光电性能有重要影响。当薄膜厚度为628 nm时,薄膜具有最小电阻率2.01×10-4Ω.cm。所制备薄膜在波长为400~760 nm的可见光中平均透过率都超过了91%,TGZO薄膜可以用作薄膜太阳能电池和液晶显示器的透明电极。     

A robust condition monitoring methodology for grinding wheel wear identification using Hilbert Huang transform

Grinding is a finishing operation performed to obtain the desired finish on the component. Wheel wear is one of the primary constraints in achieving the desired productivity in grinding. A new methodology is proposed for accurate and timely identification of wheel wear in cylindrical grinding using Hilbert Huang transform and support vector machine. During the grinding of EN31 carbon steel, the condition of the wheel and its wear was monitored with an accelerometer and power cell. Both vibration and power signals captured were used to identify the condition of the wheel and its wear. An exhaustive feature set is generated in the frequency and the time-frequency domain. Hilbert Huang transform, an adaptive time-frequency analysis technique, was used to extract the features of tool wear in the time-frequency domain. The first three IMF constituents were further chosen for feature extraction of statistical parameters based on their mean energy. Random forests algorithm was used to identify the relevant features. The methodology was validated with several grinding experiments and, is found to give an accuracy of 100% with both low and high cutting depths. The results indicated the robust and reliable wheel wear detection in cylindrical grinding with the use of relatively cheap sensors like accelerometers. The proposed method can be widely used in many applications in the industry where grinding is predominantly used as the finishing operation.