基于能量等效的2.5维机织复合材料刚度预测

提出了用能量等效原理预测2.5维机织复合材料经向拉伸的弹性模量的方法。以2.5维机织复合材料受经向拉伸载荷时经纱的变形为基础,分析了受经向拉伸载荷时2.5维机织复合材料中经纱、纬纱和填充树脂的变形能,利用各组分材料的变形能之和与整体复合材料的变形能相等的原理,推导出2.5维机织复合材料的经向拉伸弹性模量的计算方法。与试验数据对比发现,本文方法对经纬向拉伸弹性模量的预测结果比采用组分材料力学性能体积平均加权的方法更加精确。结果验证了本文方法的合理性,表明本文的计算公式对纬向拉伸时同样适用,并且本文方法所需要的基础参数更容易获得。     

纤维增强树脂基复合材料的吸湿性和湿变形

阐述了纤维增强树脂基复合材料的吸湿与湿变形机理及其影响因素,从环境、材料和工艺3个方面,总结了环境温度、相对湿度、纤维、树脂基体、纤维-基体界面以及铺层方式对复合材料吸湿性与湿变形的影响,并提出了降低纤维增强树脂基复合材料吸湿率与湿变形的途径。     

A New Scheme and Microstructural Model for 3D Full 5-directional Braided Composites

Three-dimensional(3D) braided composites are a kind of advanced ones and are used in the aeronautical and astronautical fields more widely. The advantages, usages, shortages and disadvantages of 3D braided composites are analyzed, and the possible approach of improving the properties of the materials is presented, that is, a new type of 3D full 5-directional braided composites is developed. The methods of making this type of preform are proposed. It is pointed out that the four-step braiding which is the most possible to realize industrialized production almost has no effect on the composites'properties. By analyzing the simulation model, the advantages of the material compared with the 3D 4-di- rectional and 5-directional materials are presented. Finally, a microstructural model is analyzed to lay the foundation for the future theoretical analysis of these composites.     

压电纤维复合材料铺层用于翼面设计的驱动特性与刚度影响

压电纤维复合材料驱动器在形状控制、振动控制、颤振抑制与抖振控制等方面有广泛的应用前景。首先简单介绍了压电应变驱动的比拟载荷方法,并采用该方法讨论了压电陶瓷片状驱动器与压电纤维复合材料驱动器在驱动特性上的主要差异。在此基础上,对压电纤维复合材料在不同铺设方式、铺设角度与铺设层数下的驱动特性进行了分析,在刚度影响方面展示了不同铺设角度下模型刚轴的移动。分析结果表明:对称铺设反向电场可以同时获得弯曲与扭转变形,而反对称铺设同向电场主要获得扭转变形;两种铺设方式下45°铺设角均获得最大弦向转角,而0°铺设角将获得最大挠度;多铺层可以增加驱动载荷,但总体变形效果还取决于结构系统的刚度比例;对称铺设方式下铺设角对结构刚轴移动的影响非常明显,在气动弹性控制中应着重关注。     

凝固过程对颗粒增强Al—4%Mg复合材料中颗粒分布的影响

研究了凝固过程ＳｉＣ、Ａｌ＿２Ｏ＿３、ＳｉＯ＿２颗粒增强Ａｌ－４％Ｍｇ复合材料中颗粒分布的影响。通过分析，建立了描述等轴晶凝固条件下，颗粒推移强烈程度的晶粒与颗粒质量比模型，模型预测与试验结果吻合良好。     

Damage characteristics and constitutive modeling of the 2D C/Si C composite: Part I – Experiment and analysis

This paper reports an experimental investigation on the macroscopic mechanical behaviors and damage mechanisms of the plain-woven(2D) C/Si C composite under in-plane on- and offaxis loading conditions. Specimens with 15, 30, and 45 off-axis angles were prepared and tested under monotonic and incremental cyclic tension and compression loads. The obtained results were compared with those of uniaxial tension, compression, and shear specimens. The relationships between the damage modes and the stress state were analyzed based on scanning electronic microscopy(SEM) observations and acoustic emission(AE) data. The test results reveal the remarkable axial anisotropy and unilateral behavior of the material. The off-axis tension test results show that the material is fiber-dominant and the evolution rate of damage and inelastic strain is accelerated under the corresponding combined biaxial tension and shear loads. Due to the damage impediment effect of compression stress, compression specimens show higher mechanical properties and lower damage evolution rates than tension specimens with the same off-axis angle. Under cyclic tension–compression loadings, both on-axis and off-axis specimens exhibit progressive damage deactivation behaviors in the compression range, but with different deactivation rates.     

Grinding behavior and surface appearance of（TiC_p＋ TiB_w）/Ti-6Al-4V titanium matrix composites

（TiCp＋ TiBw）/Ti-6Al-4V titanium matrix composites（PTMCs） have broad application prospects in the aviation and nuclear field. However, it is a typical difficult-to-cut material due to high hardness of the reinforcements, high strength and low thermal conductivity of Ti-6Al-4V alloy matrix. Grinding experiments with vitrified CBN wheels were conducted to analyze comparatively the grinding performance of PTMCs and Ti-6Al-4V alloy. Grinding force and force ratios, specific grinding energy, grinding temperature, surface roughness, ground surface appearance were discussed. The results show that the normal grinding force and the force ratios of PTMCs are much larger than that of Ti-6Al-4V alloy. Low depth of cut and high workpiece speed are generally beneficial to achieve the precision ground surface for PTMCs. The hard reinforcements of PTMCs are mainly removed in the ductile mode during grinding. However, the removal phenomenon of the reinforcements due to brittle fracture still exists, which contributes to the lower specific grinding energy and grinding temperature of PTMCs than Ti-6Al-4V alloy.     

考虑复合材料层合板就地效应的强度理论

为了能准确预测复合材料层合板的失效起始和破坏过程,发展了一种考虑层合板就地效应(In-situ Effect)的强度理论,方法包括就地强度的确定、失效起始判定和材料性能退化。介绍并推导了基于断裂力学假设的就地强度计算方法,将层合板内的铺层分为内嵌厚层、内嵌薄层和外表面层3种类型,不同类型的层分别对应不同的计算方法。建立了一种考虑就地强度的面内失效起始准则,提出了相应的强度分析方法流程。对单向和多向层合板的失效包线进行了预测,计算结果表明发展的强度理论能很好地预测结构的失效起始,充分反映材料从失效起始到最终破坏的试验现象和规律,与传统Hashin准则相比预测精度明显提高。通过对准各向同性层合板失效包线预测发现,在进行层合板强度分析时考虑就地强度能明显提高预测失效起始的准确性和精度,在复合材料结构强度分析过程中考虑层合板的就地效应十分必要。     

纳米SiC增强碳纤维层合板摩擦磨损性能

为了探寻一种简便的制备纳米SiC增强碳纤维层合板的方法,本文将纳米SiC颗粒均匀分散在无水乙醇中,制备成不同质量分数的SiC试剂,然后均匀喷涂在碳纤维预浸料表面,固化成型。对不同试件进行摩擦磨损实验,得到不同含量的纳米SiC颗粒对碳纤维层合板摩擦因数、磨损量的影响规律,并且对磨损形貌和复合材料的硬度进行分析。实验结果表明：在碳纤维预浸料表面喷涂纳米SiC颗粒能够有效改善碳纤维层合板的摩擦磨损性能;当纳米SiC浓度为1%时,层合板的摩擦因数、磨损量、磨痕的宽度及深度较于不含纳米SiC的层合板分别降低52%,63%,32.3%,54.8%,摩擦磨损性能最好。