Yb:Y3Al5O12/Y3Al5O12复合晶体的制作和光谱性能

采用热键合技术,制作中运用不同的工艺参量制作出12片Yb:Y3Al5O12/Y3Al5O12(Yb:YAG/YAG)复合.晶体.利用偏光显微镜对其键合界面进行了观察,研究了样品的透射光谱,从而确定出复合晶体合适的制作工艺.通过透射光谱的形状和透射率来表征复合晶体键合界面的质量.研究表明Yb:YAG/YAG复合晶体键合质量较好,可实现一体化.     

碳纳米管增强镍磷基复合镀层研究

对CVD方法制备的碳纳米管进行表面改性处理，然后在液相中分散，利用化学共沉积方法形成碳纳米管镍磷基复合镀层，研究了碳纳米管表面改性后的红外谱、碳纳米管复合镀层的表面形貌、硬度及摩擦学行为.结果表明：碳纳米管的加入明显地提高镍磷复合镀层的硬度和改善了镍磷复合镀层的摩擦性能.硬度达到946HV，20N载荷时摩擦系数为0.7，增至80N时降为0.6；相同条件下与传统耐磨材料SiC增强的镍磷基复合镀层相比，具有更低的摩擦系数和磨损量. 关键词： 碳纳米管 表面改性 复合镀层 摩擦行为     

Free vibration of composite membranes with arbitrary shape

This paper is concerned with a method for solving problems of a composite membrane with an arbitrarily shaped outer boundary and an arbitrarily shaped inner boundary. The boundary conditions and the conditions of continuity are satisfied directly by using a Fourier expansion collocation method which has been given by Nagaya. The general equation for finding the natural frequencies of the composite membranes has been presented. As examples, numerical calculations have been carried out for composite polygonal membranes, composite elliptical membranes and composite circular membranes with eccentric circular boundaries.     

Diffuse field transmission into infinite sandwich composite and laminate composite cylinders

This paper is concerned with the modelling of diffuse field transmission into composite laminate and sandwich composite infinite cylinders. Two models are presented and compared: Symmetrical Laminate composite and discrete thick laminate composite. The latter is shown to handle accurately, as a particular case, the first model, and the important case of sandwich composite shells. In both models, membrane, bending, transverse shearing as well as rotational inertia effects and orthotropic ply angle of the layers are considered. Starting from the dynamic equilibrium relations and stress–strain–displacement relations, a dispersion system is given in a wave approach context. Next, expressions for the matrix systems governing the structural impedance, critical frequencies and ring frequency are given. The developed equations are applied to the calculation of the diffuse field transmission of an infinite cylinder. Predictions with the presented models are compared to results presented in the literature for both laminate composite and sandwich composite configurations. They confirm the accuracy of both models and the general nature of the presented discrete thick laminate composite model.     

旋转超声磨削平行砂轮复合变幅器设计与试验

为了获得大负载平行砂轮复合变幅器的设计方法,将复合变幅器简化为复合变幅杆与多阶环盘组成.利用Mindlin中厚板理论,求解了各振动环盘的位移、转角、弯矩和剪力解析表达式,通过复合变幅杆各振动单元间的力、位移的边界条件和连续条件,以及复合变幅杆和环盘两者结构间力与位移的耦合条件,建立了复合变幅器的数学模型和频率方程.针对...     

超高速碰撞下C-SiC复合材料双层防护结构的力学特性

 C-SiC复合材料是一种随着航空航天技术发展而研制开发的新型材料,具有优异的力学性能,可以很好地满足航天器防护系统的使用要求,因此其超高速碰撞力学性能研究具有重要意义。基于现有的有关C-SiC复合材料力学性能的实验数据和模拟结果,推导得到模拟C-SiC复合材料超高速碰撞时所需的一系列参数。利用AUTODYN进行数值模拟,获得了C-SiC复合材料双层防护结构在超高速碰撞下的特性及弹道极限曲线,总结得出预测C-SiC复合材料双层防护结构的弹道极限方程。     

The renormalization of several composite operator insertions,Wilson expansions of composite operators,and the applications to short-distance behaviour

We examine the renormalization of composite operator insertions within a normal product framework, and prove various identities between composite operator insertions. In particular a proof of the Wilson expansion of composite operators in the presence of other composite operators is given. The analysis necessitates a re-examination of several physical processes, and it is shown in particular why the results for deep inelastic scattering still hold.     

Superposition rule for light scattering by a composite particle

A superposition rule for light scattering by composite particles is presented that expresses the scattering amplitude of a composite particle as a superposition of that of the host particle and those of the shadowed inclusions. The superposition rule is derived for a soft composite particle but also provides insight into light scattering by a general composite scatterer. Favorable comparison with an exact numerical method demonstrates the usefulness of the rule in analyzing light scattering by composite particles such as biological cells.     

Wear Performance and Mechanisms of Polyphenylene Sulfide/Polytetrafluoroethylene Wax Composite Coatings Reinforced by Graphene

Polyphenylene sulfide (PPS) composite coatings reinforced by graphene were prepared through a spraying method. Wear performance of the composite coatings were evaluated using a block-on-ring test rig, and the results showed that the wear life of the composite coatings were over seven times higher than that of a pure PPS coating. Wear mechanisms of PPS composite coatings reinforced by graphene are discussed. It was concluded that adhesive wear was the major wear mechanism of the pure PPS coating but the wear form of the composite coatings was dominated by abrasive wear due to the graphene filler that has high mechanical strength. In addition, fatigue wear appeared for composite coatings with higher content of graphene. The formation of a uniform thin transfer film on the counterpart ring and fine wear debris for the composites coatings during abrasion were consistent with the improvement of wear performance. The 3D morphology of the surface of the counterpart ring was also used to discuss the wear mechanism of PPS composite coatings.     

Effect of multi-walled carbon nanotubes on dielectric and electro-optic properties of a high tilt antiferroelectric liquid crystal

By dispersing a small amount of multi-walled carbon nanotubes in a high tilt antiferroelectric liquid crystal, a nano composite is prepared. Though the phase sequence remains the same, the transition temperatures of the composite get changed, the stability of SmA* and SmC* phases increases whereas that of SmC_A* phase decreases. Pitch of the helicoidal structure shows a discontinuous change at SmC*–SmC_A* transition. Absorption strength and critical frequency of the anti-phase antiferroelectric mode are reduced in the composite. The dielectric increment of the Goldstone mode (GM) decreases and the critical frequency increases due to increased elasticity of the composite. A two-fold increase in the critical field for suppression of the GM is observed which signifies more stable helical structure in the composite. The switching time is reduced by 56% in the nano composite as a result of decrease in rotational viscosity but the high tilt remains intact. An observed lower value of conductivity indicates ion trapping in the composite.     

Interfacial p-n heterojunction of polyaniline-nickel ferrite nanocomposite as room temperature liquefied petroleum gas sensor

In this work, we introduce polyaniline–nickel ferrite (PANI-NF) nanostructured composite to detect liquefied petroleum gas (LPG) at room temperature. The composite synthesized by relatively simple method of in-situ chemical polymerization was structurally characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques. The presence of characteristic absorption bands of both PANI and NF in the FTIR spectrum of the composite with small shifts confirmed interfacial interaction of PANI with NF. The XRD studies also confirmed interfacial interaction between PANI and NF in the composite and its crystalline nature with an average crystallite size of 20 nm. Highly agglomerated granular porous morphology favourable for LPG adsorption was revealed by SEM image of the composite. The TEM image of the composite clearly showed nanosized NF particles embedded in PANI matrix. The LPG sensing performance of the composite at room temperature was tested using a film prepared by depositing the composite on an ordinary glass substrate by cost-effective spin coating technique. The maximum sensing response of the composite was found to be 57% at 700 ppm of LPG, with a response time of 50 s and a recovery time of 200 s. The composite was found to be stable for a period of one month. The sensing mechanism has been discussed on the basis of formation of interfacial p–n heterojunction barrier.     

Investigation of the microstructure and tribological behavior of cold-sprayed tin-bronze-based composite coatings

In this paper, tin-bronze/TiN and tin-bronze/quasicrystal (AlCuFeB) composite coatings were fabricated by cold spray process. Microstructure and microhardness of the prepared coatings were investigated. Ball-on-disc dry sliding wear tests were conducted in an ambient condition to examine the tribological behavior of the composite coatings. The results show that the microhardness and the density of composite coatings increase significantly compared to the pure tin-bronze coating. The friction coefficient of composite coating decreases when reinforcing particles were introduced. Furthermore, the bronze/quasicrystal composite coating has a lower friction coefficient and wear rate than the bronze/TiN coating. Tribological mechanisms of the composite coatings were discussed.     

A microstructure model for finite-element simulation of 3D rectangular braided composite under ballistic penetration

The non-delamination feature of 3D braided composites under transverse impact leads to their potential application in the field of ballistic impact protection. One of the effective ways to investigate the ballistic impact damage of the 3D braided composite is to simulate the penetration process by numerical method, such as finite element method. However the numerical simulations of ballistic impact damage are seldom conducted based on the microstructure level. This paper presents a microstructure model for simulating ballistic impact damage of 4-step 3D braided rectangular composite penetrated by a rigid steel projectile. The microstructure model is based on the same yarn spatial configuration with that of the braided composite and also on the assumptions of the braided yarns appear straight inside the braided preform, bending and then change to other directions only at the surface. The ballistic perforation of the braided composite specimen by a cylindrical-conically steel projectile has been simulated with finite element method. The comparisons between FEA and experimental results show the validity of the microstructure model, especially for the penetration resistance and impact damage of the composite. Compared with the other continuum models of the braided composite, the microstructure model can simulate impact damage more precisely. The velocity history and acceleration history of projectile, and impact damage development of the composite in FEM simulation indicate the different damage and energy absorption mechanisms of the braided composite compared with those of laminated composite.     

THE COMPOSITE PARTICLE REPRESEPITATION THEORY

Based on the composite particle representation presented in the last paper(I),a method of solving the many-body problem knpwn as the compqsite particle approximation is proposed.It is shown that a many-body system can be simplified to a composite particle system (plus one or more uncorrelated basic particles if any existed) if the following conditions are satisfied:1) the binding energies of the composite particles are much larger than the excitation energies of the system; 2)there is domination of the collective mode for the composite particles.The interac-tions between the composite particles,,as well as the interactions between composite particles and the basic particles can be evaluated from the original particle-particle interactions. Applications of this theory are indicated.     

Study on the Compatibility of SMA and Composite Materials by Holographic Interferometry

With the help of holographic interferometry a study is conducted on the compatibility of SMA (shape memory alloy) and epoxy resin composite material. The paper gives experiment results and analysis which show that after coupling SMA with the composite material, the flexural rigidity of composite material is somewhat reinforced. Under certain conditions, SMA and the epoxy resin composite material are compatible.     

Study on the Compatibility of SMA and Composite Materials by Holographic Interferometry

With the help of holographic interferometry a study is conducted on the compatibility of SMA (shape memory alloy) and epoxy resin composite material. The paper gives experiment results and analysis which show that after coupling SMA with the composite material, the flexural rigidity of composite material is somewhat reinforced. Under certain conditions, SMA and the epoxy resin composite material are compatible.     

Optical characterisation and modelling for oblique near-infrared laser heating of carbon fibre reinforced thermoplastic composites

The optical behaviour of a carbon fibre reinforced thermoplastic composite material is investigated for a near infrared laser heating process applied to automated composite tape placement. A nip point heating strategy in laser tape placement results in a shadow before the nip point on both the incoming tape and substrate. The moderate laser angle relative to the surface of the composite leads to reflections in the cavity formed by the tape and the substrate, reducing the shadow. An optical ray tracing model can provide valuable insight to the interaction of the laser with the composite, as well as detailed estimation of the irradiance distributions. This paper provides the foundations for such a model, describing an optical characterisation process and formulation of appropriate models to capture the composite surface and laser source behaviour. A micro-half-cylinder surface treatment was shown to give a good approximation of the anisotropic scattering behaviour of the composite. Angular dependent reflectance was described well by Fresnel equations. An approximation of the laser beam profile and propagation is also presented.     

Comparative study on the high frequency performances of the easy-plane FeNi@SiO2 powder soft magnetic composite

In this work, an easy-plane FeNi@SiO₂ powder soft magnetic composite (SMC) was imitated and fabricated and its high frequency magnetic properties were comparatively investigated with a non-easy-plane composite. Due to the planar distribution of easy magnetization axes, the easy-plane composite exhibits a constant permeability of 38 up to 100 MHz. Moreover, the easy-plane SMC exhibits a lower core loss at higher frequencies. Loss separated results show that the hysteresis loss plays a dominant loss component in the composite, rather than dominant excess loss in the non-easy-plane powder composite. These results indicate that, compared with non-easy-plane powder composite, the easy-plane powder composites exhibit comprehensive advantages of higher permeability, wider effective operating frequencies and lower loss, which suggest that the use of easy-plane ferromagnetic powder is a promising and efficient measure to develop a new generation of soft magnetic composites for higher frequency application.     

Electrochemical characteristics of sulfur composite cathode for reversible lithium storage

The electrochemical characteristics of the sulfur composite cathode for reversible lithium storage were investigated. The sulfur composites showed novel electrochemical characteristics as well as high specific capacity and good cycleability. The sulfur composite presented the average discharge voltage of 1.9 V, which was just the half of conventional LiCoO₂ cathode materials, indicating that the double cells in series presented the same working voltage as conventional LiCoO₂ cells and meaning that the sulfur composite cells will have good interchangeability with conventional LiCoO₂ cells. The overcharge test showed that the sulfur composite cell cannot be charged over 5.0 V, indicating that the sulfur composite cell presented the intrinsic safety for overcharge. Overcharge can cause serious problems for the conventional Li ion cells. The overcharge test also showed that the sulfur composite cell was destroyed when the cell was charged over 4.0 V, resulting in that the cell cannot normally be discharged again. It is found, however, that the sulfur composite cell can be discharged again at very low current density of a 0.002-C rate after the cell was overcharged. Being much safer than lithium metal anode, the graphite anode was used to fabricate sulfur composite/graphite lithium ion cells with a prelithiated sulfur composite cathode, which was produced by electrochemical lithiation. The charge/discharge and cycling characteristics of the sulfur composite/graphite cell was investigated. The result showed that the sulfur composite/graphite cells can be normally cycled and showed the different voltages from that of the cell with the lithium metal anode. This paves the effective way to fabricate safer sulfur composite/graphite lithium ion cells.     

非局域颗粒复合介质的相干完美吸收效应

研究了两束相干光以相同的入射角从左、右两侧分别入射到Au-SiO_2复合介质板时,在不同的体系参数下该复合材料体系发生相干完美吸收的情形.运用有效媒质理论推导出了复合介质的有效介电常数以及有效磁导率;在得到有效电磁参数的基础上进一步推导得到平面波入射复合介质板时的反/透射系数.通过比较分析非局域和局域情况下颗粒复合介质的相干完美吸收现象,发现当颗粒尺寸很小时非局域效应的影响会导致复合介质产生相干完美吸收的入射光的频率范围显著变宽.在进一步的解析计算中,通过调节复合介质板的厚度、入射光波长、金属颗粒体积分数等参数得到了不同情况下产生的相干完美吸收现象,并由此分析非局域情形下对于相干完美吸收现象的调控.