Fracture control for composite structures

A fracture control technique for composite structures is presented which takes advantage of the unique capability of composite materials to be tailored in stiffness and fracture toughness. Crack arrestment is achieved through the use of integral ‘buffer’ strips in the primary load-carrying laminate. Experimental uniaxial tension data obtained from damaged laminates containing such buffer strips indicate residual strength capacity in excess of the limit design stress for the selected laminate.     

质子交换膜燃料电池复合材料双极板的研究

以高分子预聚物为粘合剂，天然或人造石墨为导电骨料，通过模压一次成型制备质子交换膜燃料电池双极板。研究了导电骨料的组分、树脂的种类及其含量，成型温度、成型压力对双极板性能的影响。结果表明：1)导电骨料的组分、树脂的种类及其含量对制品的性能影响较大；成型温度、成型压力对制品的性能影响较小。2)人造和天然两种石墨混合组分为导电骨料的制品，其导电性能明显高于单一石墨组分的制品；乙烯基树脂为粘合剂的性能优于以邻苯基树脂为粘合剂的双极板的性能。3)使用质量分数为16％～18％的乙烯基树脂作粘结剂，在成型压力为10MPa～20MPa，成型温度为150℃～200℃时制备的复合材料双极板的电导率＞300S／cm，抗折强度＞30MPa，空气透气率为10^-7cm^2／S。     

A study of the differential scheme for composite materials

The overall moduli of a 2-phase linearly elastic composite are estimated by the differential scheme. The phases may be arbitrarily anisotropic and 1 phase is regarded as similar ellipsoidal inclusions at any concentration embedded homogeneously in a matrix. For an isotropic dispersion of spheres and for a fibre reinforced material it is shown that the estimates of the overall moduli lie between their Hashin-Shtrikman bounds. Also some known exact results are reproduced using this scheme.     

A study on the composite screw rotors for superchargers

In this work, the screw rotors for superchargers were manufactured with chopped carbon fiber epoxy composite materials by resin transfer molding process. The manufactured composite screw rotors were tested in different combinations such as the male composite and female composite rotors, the male composite and female aluminium rotors, and the male aluminium and female composite rotors. The temperature and pressure increases of the air at the outlet and the required torque of the supercharger were measured with respect to the angular velocities.     

Feasibility study to control fiber distribution for enhancement of composite properties via three-dimensional printing

The distribution of fibers in the composite (which takes into account both their locations and orientations) is one of the important factors that affect the mechanical properties of FRCs. However, this parameter depends on various factors during composite fabrication, and controlling the distribution of fibers in the produced material represents a significant challenge. In this study, the applicability of three-dimensional (3D) printing technique for controlling fiber distributions was evaluated. The fibers fabricated using a 3D printer were placed inside a mold to produce cementitious composites. Three-point bending tests were conducted and the results of the experiment were discussed.     

化学复合镀Ni-P-PTFE-SiC的研究

在化学镀Ni-P-PTFE与Ni-P-SiC的基础上,成功获得了Ni-P-PTFE-SiC复合镀层。同时对镀层进行了X射线衍射和SEM分析,并着重研究了镀层的耐磨－减摩性能。发现Ni-P-PTFE-SiC的加入使镀层硬度显著降低,但其耐磨性远优于NiP,Ni-P-PTFE和Ni-P-SiC镀层。     

A study of the tribological properties of cobalt-titania composite

The frictional and wear behaviour and hardness of cobalt and cobalt-titania (anatase) particulate composites, developed by sediment electro-codeposition method, were studied. Frictional and wear studies, performed on a disc-on-disc type machine, show that the microhardness of the composite increases as the titania content in the composite increases. A decrease in both the coefficient of friction and specific wear rate was observed for the composites with increasing titania content in the cobalt matrix. The effect of sliding velocity and load on the coefficient of friction and specific wear rate of cobalt and cobalt titania composites was also investigated. The optical microphotographs and X-ray diffractogram reveals that the tribo-deformation is oxidation dominated for cobalt. A probable mechanism is discussed.     

A study on the low-velocity impact response of laminates for composite railway bodyshells

This paper presents a study on the low-velocity impact response of woven fabric laminates for the composite bodyshell of a tilting railway vehicle. In this study, low-velocity impact tests for the three laminates with size of 100 mm × 100 mm were conducted at three impact energy levels of 2.4 J, 2.7 J and 4.2 J. Based on these tests, the impact force, the absorbed energy and the damaged area were investigated according to different energy levels and stacking sequences. The damage area was evaluated by visual inspection and C-scan measurement. The test results showed that the absorbed energy of [fill]₈ laminate was highest whereas [fill₂/warp₂]_s laminate was lowest. The [fill]₈ laminate had the largest delamination area because of the highest impact energy absorption.     

A numerical study of adhesively bonded composite panel-flange joints

A geometrical non-linear numerical analysis for two-dimensional models of adhesively bonded composite panel-flange joints is presented to investigate the peel and shear stress redistribution in the joints when the panels buckle. The maximum stress failure criterion is used to predict failure loads and the associated failure modes induced by the buckled panels. Parametric studies for a variety of geometric configurations are carried out to show the effect of the relative stiffness and length ratios of the panel and flange on the redistribution of the peel and shear stresses as well as the failure loads and the associated modes. It is also shown that flexible joints provide higher joint efficiency.     

A composite model for superplasticity

A composite model for superplasticity, based on the joint influences of both the behaviour of a composite boundary and creep, is proposed. In this model, superplasticity is considered as a combination of two mechanisms: grain-boundary sliding and dislocation creep, which occur either together or sequentially. Applied to experimental data, it can describe the logarithmic stress versus strain rate curves observed for superplastic materials showing regions I, II and III.     

基于参数化模型的高高空浮空器飞行机理研究

建立了高高空浮空器的参数化非线性模型和参数化线性模型.采用牛顿-欧拉方法建立了系统非线性动力学模型,并考虑了风对飞行器的作用.基于非线性模型分析了风和飞行高度对浮空器动力学的影响.通过小扰动方法进行了模型线性化;考虑到浮空器的飞行速度较低、易受风的影响,对动压进行了线性化;基于线性化模型进行了系统的耦合特性分析和稳定性...     

锂二次电池SnO2-MCMB复合负极材料的研究

用直接沉淀法将氧化锡颗粒沉积在中间相碳微球(MCMB)核心上,制备了一种锂离子电池用的新型复合负极材料.用X射线衍射(XRD)和扫描电镜(SEM)对材料的结构及形貌进行了表征.通过恒流充放电、交流阻抗等测试手段对该材料的嵌脱锂特性进行了研究,循环20周后其比容量仍然保持在420mAh/g以上.电化学测试表明,此种复合物可以作为一种锂离子电池新型负极材料.     

基于组合非线性反馈技术的机器人控制方法

为解决机器人跟踪控制中响应速度和超调量之间的矛盾,实现快速的响应和较小的超调,研究了机器人非线性动力学与组合非线性反馈技术相结合的控制策略,提出了一种基于组合非线性反馈的机器人控制器.该控制器由两部分组成,一部分由完全的机器人非线性动力学补偿来实现反馈线性化,另一部分由组合非线性反馈技术实现镇定.通过反馈线性化技术与Lyapunov理论,证明了闭环系统的渐近稳定性.同时,把组合非线性反馈理论拓展到多输入多输出(MIMO)饱和线性系统的时变轨迹跟踪控制,利用非线性项的变阻尼特性,使得系统的动态响应快速且没有超调.仿真结果证实了此方法的有效性.     

化学复合镀梯度镀层工艺研究

研究了梯度复合镀层Ni-P／Ni-P-PTFE／Ni-Cu-P-PTFE的形成工艺,探讨了镀液的温度、pH值、阳离子表面活性剂浓度、PTFE浓度以及镀层中的铜含量对Ni-Cu-P-PTFE镀层的沉积速度、组成和耐蚀性的影响,分别用数字测微计和能量分散X射线光谱测量了涂层厚度和组成,Ni-Cu-P-PTFE镀层在HCl和NaCl溶液中的抗蚀性研究表明,Ni-Cu-P-PTFE镀层的耐蚀性优于Ni-P-PTFE镀层和铜．     

A scanning electron microscopic study of hybrid composite impact response

Scanning electron micrographs of fracture surfaces of various hybrid composite materials subjected to Charpy impact tests are presented. Macrophotographs of the failed specimens which indicate the gross failure modes, and actual impact load-time traces obtained using an instrumented tup impact test technique are also included. These data permit a direct comparison between observed microfailure modes and the gross response of each composite to failure. An all-graphite/epoxy control configuration and three hybrid configurations are considered. The third-phase fibre additions in these hybrids include glass, Kevlar 49, and Nomex nylon. Longitudinal and transverse impact tests of both notched and unnotched standard Charpy specimens are included, for both a basic unidirectional graphite/epoxy composite and a quasi-isotropic laminate orientation.     

A study on dose control for Tokaimura criticality accident termination

Verification of the dose control method for Tokaimura criticality accident was performed. Personal dose estimation for accident termination was performed based on measurements of dose rate taken before the work commenced, but the personal dose to workers as a result of the termination work was found to be approximately 50 times higher than the previous estimation. For this report, the doses are reevaluated based on the results of close range measurements from 40 to 100 m, and the results were found to agree with the actual personal doses within the uncertainty of its determination 60-80 %. Therefore, the work can likely be done safely by taking into account factors such as annual dose limits and the guideline dose constraints for works in high-level neutron radiation fields.     

羧基化氧化石墨烯-镧复合物抗凝血性能的研究

将稀土La(3+)离子接枝到羧基化的氧化石墨烯片层上,制备了一种功能化的氧化石墨烯(GeneO-La).利用红外光谱和透射电镜等手段对所合成的GeneO-La复合物进行了表征;将功能化的氧化石墨烯应用到抗凝血体系中,研究其抗凝血性能.结果表明,La(3+)已经通过配位作用吸附在羧基化的氧化石墨烯片层上.通过溶血实验和血...