芯子宽厚比对铝蜂窝夹层结构平压强度的影响

用正六边形代替实际蜂芯,推导了夹层结构的平压强度与芯子宽厚比的关系,并对八种规格的芯子平压强度进行统计,统计结果虽然与推导的结果有偏差,但规律却是一致的,即蜂窝夹层结构的平压强度随着芯子宽厚比d/t_s增大呈负指数减小。     

Modified micro-mechanics based multiscale model for progressive failure prediction of 2D twill woven composites

To consider fiber random distribution at the microscale for the multiscale model based on the micro-mechanics failure (MMF) theory, clustering method is used for the extraction of amplification factors. As the clustering method is a kind of unsupervised machine learning method, the elements with similar mechanical behavior under external loading can be included in a cluster automatically at the microscale. With this modification, the fiber random distribution model can be used for multiscale damage analysis in the framework of MMF theory. To validate the modified multiscale analysis method, progressive damage analysis of a kind of 2D twill woven composites is conducted based on different microscale models. The stress values for microscale models with fiber hexagonal and random distribution patterns are compared first. Much higher stress concentration is generated in the fiber random distribution model due to the smaller inter-fiber distance especially under longitudinal shear loading. The obtained cluster distribution results exhibit the characters of the stress distribution in the two microscale models. Thereafter, tensile and compressive responses of the 2D twill woven composite are predicted with the modified multiscale analysis method and accuracy of the method is verified through comparison with published experimental results. From the simulation results, it can be found that the matrix damage initiation from the model based on the fiber random distribution model is premature compared with that from the model based on the fiber hexagonal distribution model. Besides, under tensile loading, the damage all initiates from the fill tows and propagates to the wrap tows. However, under compressive loading, the matrix damage initiates from the wrap tows in the model based on the fiber random distribution model.     

基于模型重构的变形叶片配准定位技术

叶片毛坯的精确定位是叶片数控加工的核心问题,为了提高叶片数控加工质量,保证叶片各处余量分配均匀,本文以叶片进排气边的自适应数控加工中的检测定位为研究对象,提出了一种基于模型重构的配准定位方法.该方法利用偏置模型的叶片测量方式提高了测量精度,对基于重构的测量模型进行变形与定位分析,得出较优的定位参数.通过仿真试验和对比分析,论证了本文方法的正确性.     

基于Nastran/Patran对飞机蒙皮损伤修理技术的研究

针对民用飞机蒙皮常见的凹坑损伤,利用Nastran/Patran软件总结归纳了修理时补片厚度、大小、形状等主要修理工艺参数的变化对修理质量的影响,进而优化修理方案。     

氦气涡轮转子系统整体数值仿真研究

针对氦气涡轮转子系统中各构件复杂的非线性接触关系及结构强度问题,采用Pro/E建模软件对氦气轮机转子系统进行了3维实体造型,并利用ANSYS软件进行了数值仿真强度分析。真实模拟了涡轮转子在4种工况下的应力分布以及变形趋势。结果表明:除接触应力和开孔处应力较大外,在转子轴系整体强度计算中,各级轮盘盘心处应力较大。根据各工况下的计算结果比较分析得出,离心力对盘心处的应力影响最大,对温度场的影响次之。     

Experimental investigation of laser peening on TiAl alloy microstructure and properties

In order to study the effect of laser peening on microstructures and properties of Ti Al alloy, Ti Al alloy samples were treated by Nd:YAG laser system with the wavelength of 1064 nm,pulse-width of 18 ns, and pulse-energy of 0–10 J. Surface micro-hardness, roughness, and microstructural characteristics were tested with micro-hardness tester, roughness tester and scanning electron microscope. Residual stress and pole figures were tested with X-ray diffraction and its high-temperature stability was analyzed. The experimental results show that surface micro-hardness increases by up to 30%, roughness increases to 0.37 lm, compressive residual stress increases to 337 MPa, and local texture and typical lamellar microstructure are generated. Residual stress, micro-hardness, and(002) pole figures tests are conducted, compressive residual stress value drops from 337 MPa to 260 MPa, hardness value drops from 377 HV_(0.2) to 343 HV_(0.2), and the(002)poles shift back to the center slightly. Laser peening improves microstructure and properties of Ti Al alloy significantly.     

热处理对AZ80镁合金疲劳性能的影响

通过对AZ80镁合金进行总应变幅控制下的室温低周疲劳实验,研究其在热锻、时效态(T5)、固溶时效态(T6)三种不同热处理状态下的循环应力响应、疲劳寿命和循环应力-应变行为。结果表明:在三种不同的热处理制度下,AZ80镁合金大体上都表现为循环应变硬化现象;此外,AZ80镁合金的应变疲劳寿命与塑性应变幅、弹性应变幅之间的关系分别服从Coffin-Manson和Basquin关系式。随着外加总应变幅的不断增大,其疲劳寿命减少。在0.3%的最小外加总应变幅下,AZ80热锻态的疲劳寿命最长;在0.9%的最大外加总应变幅下,AZ80-T5的疲劳寿命最长,而热锻态最短。此外,对疲劳断口形貌的观察结果表明,疲劳裂纹萌生于疲劳试样表面,并以穿晶方式扩展。     

基于北斗的灾害预警信息发布应用层FEC性能分析

根据北斗卫星系统特有的信息传输特征,本文研究了在北斗灾害预警信息发布系统中采用应用层前向纠错（FEC）技术能够成功提高预警信息传输的准确性。仿真结果表明预警信息的成功传输率可到达99.99%以上。所得到的结论对于北斗灾害预警信息发布系统中的参数选择及性能优化具有指导意义。     

基于虚位移原理的宏细观统一本构模型

结合虚位移原理和宏细观统一本构模型的基本理论提出了一种宏细观统一本构模型.该模型将宏观位移表示为宏观应变与细观位移的线性组合,然后应用虚位移原理建立基本方程,采用有限元法进行求解,得到宏观应变增量和应力增量的关系式.通过算例分析对比了模型与FVDAM(finite volume directe average meth...     

聚集状态下燃烧室凝相粒子粒度特性实验

设计了具有收敛段的粒子发生装置,采用密闭收集水罐,针对HTPB推进剂开展实验,有效完整地收集到了聚集状态下的凝相粒子。采用扫描电镜和粒度分析仪对收集的粒子进行了分析。结果表明,聚集状态下颗粒间碰撞聚合非常严重,大颗粒一般由多个颗粒聚合而成。碰撞聚合条件下凝相粒子的粒度分布范围比较宽,颗粒分布峰值粒度在9～13μm之间,比非聚集状态下的主峰粒度大很多。研究结果可为两相流数值计算、发动机工作过程分析提供基础数据。