The theoretical study of the efficiency of diffusion deposition of nanoaerosols in the extended range of the Peclet numbers

The efficiencies of the diffusion deposition of nanoaerosols for a single fiber for the models of aerosol filter and wire mesh screen are studied numerically in the extended range of the Peclet number Pe. The rectangular periodic cell model for fluid flow and convective-diffusive transport of small aerosol particles is used. Most of the previous theoretical and experimental studies of single fiber diffusion deposition efficiency were for the case of Pe > 1. The array with uniform square or chess grid of fibers and of a row of circular cylindrical fibers are considered as the filter and wire mesh screen models. The flow and particles transport equations are solved numerically using the Boundary Element Method.The obtained numerical data are used to derive the approximate formulas for the deposition efficiency in the entire range of the Peclet number for the various porosities of the filter medium or distances between fibers in a wire mesh screen. The derived dependencies take into account nonlinearity of the deposition efficiency at the low Peclet numbers. The obtained analytical dependencies compare well with the numerical and experimental data.     

一种三芯液晶光子晶体光纤的特性

针对三轴光纤陀螺共用光源问题,提出了一种新型的多芯液晶光子晶体光纤,该光纤具有三个呈等边三角形几何形状排列的液晶纤芯.利用有限元法对其功率分布、模场、有效折射率和色散特性进行了数值分析,结果表明,这种三芯液晶光子晶体光纤可将传输光完全等分为三束光,且具有平坦色散特性,在波长为1.45μm～1.75μm之间的色散变化小于2 ps·km-1·nm-1.此外,该光纤在大约150 nm的波长范围内显示出超平坦的色散,并且可以通过改变中心空气孔的直径来调整超平坦色散的波长范围.研究成果对液晶光子晶体光纤、三轴光纤陀螺和三相光纤电流互感器的等光分束器、1×3多芯光子晶体耦合器和平坦色散光纤的进一步发展具有重要意义.     

Short-term microdamageability of a fibrous composite with physically nonlinear matrix and microdamaged reinforcement

A structural theory of short-term microdamage is proposed for a fibrous composite with physically nonlinear matrix and microdamaged reinforcement. The theory is based on the stochastic elasticity equations of a fibrous composite with porous fibers. Microvolumes of the fiber material are damaged in accordance with the Huber-Mises failure criterion. A balance equation for damaged microvolumes in the reinforcement is derived. This equation together with the equations relating macrostresses and macrostrains of a fibrous composite with porous reinforcement and physically nonlinear matrix constitute a closed-form system. This system describes the coupled processes of physically nonlinear deformation and microdamage that occur in different components of the composite. Algorithms are proposed for computing the dependences of microdamage on macrostrains and macrostresses on macrostrains. Uniaxial tension curves are plotted for a fibrous composite with a linearly hardening matrix __________ Translated from Prikladnaya Mekhanika, Vol. 42, No. 2, pp. 3–13, February 2006.     

纤维排列方式对单向纤维加强复合材料弹性常数的影响

本文应用GMC方法计算了纤维在规则排列和随机排列时单向纤维加强复合材料的总体弹性系数，结果表明，在一定纤维体积比范围内，虽然纵向弹性模量不受纤维排列方式的影响，但是复合材料的横向弹性模量和横向剪切模量受纤维排列方式的影响较大，所以，在考察复合材料的横向弹性常数时，应该考虑纤维排列方式的影响，在相同纤维比的情况下，正方形排列和正方形对角排列所得的弹性常数是上下界，而六角形排列和随机排列的结果位于以上两者之间，当纤维比较小时（小于20％），纤维的排列方式对各弹性常数均无明显影响，本文的结果在工程应用中有指导意义。     

End-shaped copper fibers in an epoxy matrix—predicted versus actual fracture toughening

End-shaped copper fibers are placed in a brittle thermoset epoxy matrix at 10 vol% and tested in four-point bending to determine the fracture toughness of the composite. Results from four-point bend tests agree well with the theoretical predictions of the fracture toughness increment ‘ΔG’ of a metal fiber/brittle thermoset matrix composite based on single fiber pullout (SFP) tests. This close agreement demonstrates that SFP testing, along with the theoretical model, can be used as an effective end-shape screening tool for ductile fibers before full scale composite testing. The model predicts that the composite’s fracture toughness will be 46% higher with flat end-impacted fibers and 4% lower with rippled fibers compared to straight fibers at a 0° orientation. Four-point bend results show the actual composite’s fracture toughness is 49% higher with flat end-impacted fibers and 5% lower with rippled fibers compared to straight fibers. Further, four-point bend results show that end-shaped copper fibers improve both the flexural strength and modulus of the composite, demonstrating that end-shaped ductile fibers provide a good stress transfer to the fibers by anchoring the fibers into the matrix. Lastly, experimental validation of the model also indicates that at low fiber volume fractions, fiber–fiber interaction has only a minor influence on the fracture toughness for the tested ductile fiber/brittle matrix composite.     

化纤切割过程中切断刀的磨损性能研究

利用自制小型短纤维切断试验装置模拟涤纶短纤维的切割加工过程,采用台式投影仪测量切断刀刃口的线磨损量,采用扫描电子显微镜观察刃口和刃面的磨损表面形貌,采用傅立叶变换红外-拉曼光谱仪分析刃口磨损表面转移膜的性质,并采用顺磁共振仪分析了纤维切断前后自由基的含量.结果表明:切割涤纶半消光纤维时,高速钢刀片的磨损很快,主要磨损机制为纤维中TiO2粒子的磨粒磨损;硬质合金刀片的磨损缓慢,其磨损主要是由于刃口上高分子转移膜脱落引起的.     

A new method for measuring damping in flexural vibration of thin fibers

In this paper we describe a new method for measuring damping in flexural vibration of filamentous matter, such as polymeric or metallic fibers. This method enables us to measure the damping characteristics of very thin fibers (down to lateral dimensions of a few micrometers). The fiber sample is clamped at one extremity and excited in the flexural vibration mode of a cantilever beam configuration, using a piezoelectric actuator. While the fiber sample vibrates around a flexural eigenfrequency, structural damping is determined from the measurement of the curve of phase difference between excitation and motion. This technique does not require the amplitude of the fiber motion to be determined. The phase curve is inferred from the periodic disturbance occurring when the fiber acts as a shutter for a light beam. This method can be applied to fibers of arbitrary shape and material. Examples are shown of measurements with polymer and metallic fibers. Flexural damping is evaluated at atmospheric pressure and in vacuum. The technique is validated by a comparison with polypropylene damping measurements from standard dynamic mechanical thermal analysis techniques.     

Z-pin复合材料细观模型固化残余应力研究

针对植入Z-pin后碳纤维增强复合材料的微观结构，通过施加Z-pin周期性边界约束条件，建立了Z-pin复合材料单层板单胞细观模型．考虑固化过程中树脂体积收缩、弹性模量随固化度变化和纤维因Z-pin进入偏转因素，运用有限单元法计算了单胞结构在固化成型工艺过程中树脂和纤维应力发展和分布，并研究了Z-pin直径和分布密度对单层板面内残余应力的影响．结果表明：凝胶点之前，树脂模量和残余应力很小，凝胶点之后，树脂模量和残余应力增加较快；残余应力分布与纤维偏转有关；Z-pin直径和分布密度增加会使固化残余应力增大．     

An Isoperimetric Inequality for the Torsional Rigidity of Imperfectly Bonded Fiber Reinforced Cylinders

An isoperimetric inequality for the torsional rigidity of imperfectly bonded, fiber reinforced cylinders is found. The fiber cross sections can be simply or multiply connected. The imperfect bonding conditions are given in terms of a flexible interface model. This revised version was published online in August 2006 with corrections to the Cover Date.     

光纤传感器对机敏复合材料结构性能的影响

本文通过实验研究了光纤传感器对埋光纤机敏复合材料机械性能的影响，详细分析了埋光纤机敏复合材料层板在外载作用下的应力分布，针对三种不同铺层方式，研究了六种树脂填充区对机敏复合材料层板应力集中的影响，得出了减小应力集中的有效方案。