天然纤维增强复合材料力学性能及其应用

本文介绍了天然纤维的化学成分、结构以及力学性能;综述了天然纤维的表面处理方式,分析了其作用机理,并讨论了表面处理对其复合材料力学性能的影响;从增强体形式出发,介绍了短纤维、纤维毡、纤维织物以及单向纤维增强复合材料,并研究了成型工艺、纤维含量和表面处理等对其拉伸、弯曲、界面性能和冲击强度以及断裂韧性的影响;最后总结了天然纤维增强复合材料在汽车、建筑土木等领域的应用现状,并展望了其发展和应用前景。     

无风条件下马蹄波波面演化特征的实验研究

在实验室无风条件下对马蹄波进行了实验研究. 得到了L2型的马蹄波,也发现了两种新的类似马蹄波的波型,给出了马蹄波的横向波长和波高参数的几何特征,分析了马蹄波演化的过程中波面时间历程和振幅谱特征,讨论了马蹄波产生的机理和条件.      

一种车载自主定位模式及考核方法研究

论述了自主定位模式，对其模式中系统组成、功能展开了讨论，提出了对该系统的考核方式。对200km不停车自主定位进行了分析，着重强调了航向修正点设置及作用，同时对GIS标准点设置及维护进行了讨论。通过实际考核验证了此种模式和考核方式的有效性和实用性。     

金属表面改性中界面力学性能的实验研究

提出了适用于微区测量的两步数字图像相关法,采用二阶泰勒多项式子区位移模式有效地降低了截断误差;采用B-样条插值函数提高了亚像素重建的精度;采用拟牛顿迭代法提高了计算速度等,使微区内应变测量精度控制在100~150με。在残余应变测量中通过数字标记点相关技术实现了试件的精确复位,提高了其测量精度。文中利用上述方法测量了镀层改性试件跨界面的位移场和应变场,分析了裂纹对镀层的影响以及测出了基材中引起的残余应变;同时对镀层改性界面结合性能作了定量比较。     

基于H∞控制方法的AMD Benchmark主动控制结构的试验研究

针对结构主动控制系统中存在的模型不确定性问题,进行了H∞主动控制策略及实验研究,目的是使控制系统具有良好的鲁棒性.文中首先建立了AMD (active mass damper) Benchmark主动控制结构的试验系统,然后介绍了主动控制试验系统的工作原理,随后提出了基于H∞控制理论的主动控制方法,详细阐述了控制器中有关H∞控制权函数选取的过程以及控制器设计过程,最后通过试验验证了H∞控制器的有效性和鲁棒性.     

GPS／SINS组合导航系统的动基座快速初始对准方法

—本文首先建立了ＳＩＮＳ的误差模型，并对系统模型进行了可观测性分析，然后基于ＳＩＮＳ误差模型的特点，通过对所采用卡尔曼滤波器仿真结果的分析，提出了一种快速估计方位失准角Ｄ的方法，从而大大缩短了初始对准时间，提高了对准速度。最后计算机仿真结果表明了该方法的有效性。     

强爆轰驱动飞片的数值模拟研究

在一维流体动力学程序中,使用了JWLT状态方程,对强爆轰驱动飞片的实验模型进行了数值模拟研究,得到了炸药爆轰产物的压力和密度分布,验证了强爆轰的存在,同时得到了二级飞片自由面的速度曲线,与实验测量结果符合较好,为解释实验结果和设计新的强爆轰实验提供了计算依据,同时验证了程序的正确性。     

基于虚拟仪器的惯性敏感器自动测试系统

介绍了基于虚拟仪器技术的惯性敏感器自动测试系统的实现方法.系统可用于对多种敏感器进行测试,具有X-Y和V-T两种测试方式.系统除了能完成测试任务之外,还添加了仿真模块,可根据用户设定的敏感器指标模拟输出测试曲线,用于与实际测试情况进行比较.在数据处理与分析中建立了各种敏感器参数的解算模型,用户可根据实际测试需要进行动态选取.对测试需求进行了分析,提出了系统的总体方案与组成结构,对硬件配置作了说明,介绍了软件的模块化设计方案,列出了软件运行流程图,最后给出了测试实例.应用证明,该系统在功能、操作性、通用性及可靠性等方面达到了预期效果.     

基于GPRS的GPS实时差分系统研究与实现

介绍了GPS实时差分系统基本原理及实现过程，提出了基于GPRS的GPS实时差分系统的总体结构；完成了基于GR47的GPRS数据传输模块的硬件和软件设计；实现了服务器软件数据监控及处理功能；采用无缝技术实现GPRS与Internet链接，建立了GPS差分数据传输通道；提出了通讯链路时间延迟的测试方法，分析了过大时间延迟的原因并给出了解决方案。实际测试结果表明：基于GPRS的GPS实时差分系统达到了厘米级定位精度。     

混凝土断裂能

本文从能量的观点分析了混凝土Ⅰ型和Ⅱ型断裂能表达式,探讨了梁自重对Ⅰ型断裂能的影响;介绍了Ⅰ型断裂能的测试方法,给出了拉应变软化曲线.     

Viscoelastic properties of polymerlike reverse micelles

A dramatic increase in the viscosity of reverse micellar solutions of lecithin in a variety of organic solvents of up to a factor of 10⁶ upon the addition of a small amount of water can be observed. The formation of viscoelastic solutions can be explained by a water-induced aggregation of lecithin molecules into flexible cylindrical reverse micelles and the subsequent formation of a transient network of entangled micelles. The viscoelastic properties of these solutions are characterized as a function of water content and temperature for different organic solvents by means of dynamic shear viscosity measurements. The results are interpreted by making analogies to the behavior of semidilute polymer solutions and living polymers.Dedicated to Prof. Dr. J. Meissner on the occasion of his 60th birthday.     

Flow birefringence and rheological measurements on shear induced micellar structures

Aqueous solutions of cationic surfactant systems with strongly binding counterions show the striking phenomenon of shear induced phase transitions. At low shear rates or angular frequencies, the solutions exhibit Newtonian flow. At high rates of shear, however, the rheological properties change dramatically. Above a well defined threshold value of the velocity gradient, a supermolecular structure can be formed from micellar aggregates. This shear induced structure (SIS) behaves like a gel and exhibits strong flow birefringence. The formation of the shear induced structure is very complicated and depends on the specific conditions of the surfactant system. In this paper we discuss new results which have been obtained from rheological measurements and from flow birefringence data. We examine the stability of the shear induced state as a function of temperature, surfactant concentration and salt concentration and we analyse the effect of solubilisation of alcohols and hydrocarbons. The results are interpreted in terms of a kinetic model which accounts for the observed behavior.Dedicated to the 60. birthday of Prof. H. Harnisch, Hoechst AGPartly presented at the 2nd Conference of European Rheologists, Prague, June 17–20, 1986     

Evolution of viscoelastic properties of polyurethane in the course of curing

Simultaneous measurements of the components of dynamic modulus at the set of frequencies were made by Fourier-Transform Mechanical Spectroscopy (FTMS) to investigate the curing process of a segmented polyurethane.The whole process of curing is treated as consisting of three stages. In the first stage, the material can flow and this stage is complete at the gel-point. In the second stage, the curing proceeds in the network and ends with phase separation of aggregating segments (blocks) of polymeric chains. In the third stage, the curing continues in the two-phase system. The object of investigation was the transition from the second to the third stage. It was shown that the position of the maximum of loss tangent depends on frequency and does not coincide with different characteristic points marking the time dependencies of G and G. This is due to the formation of micro-particles of the newly formed phase. The FTMS method is used for separation of the modulus changes into parts related to formation of chemical and physical networks.Special means of treating calorimetric measurements identified a weak maximum heat output at the moment corresponding to the transition point.     

Viscoplasticity of agglomerated suspensions

This work is a theoretical study on the effects of agglomeration on the fluidity and plasticity of a suspension of neutrally buoyant particles in a Newtonian fluid. The dynamics of a cluster of permanently attached spherical particles in a simple shear field is analyzed. The viscous and plastic components of the drag force acting on each of the agglomerated particles is then calculated and found to depend on the size of the individual particle unit, its location being relative to the center of the cluster and the material properties of the engulfing fluid. This information in conjunction with the knowledge of the interparticle cohesive forces is used to establish criteria for the agglomerate size reduction during dispersive mixing. From the kinematics of the cluster movement and the forces acting on its particulate components the rate of energy dissipation is calculated and utilized to evaluate the viscosity and yield stress of the suspension. These rheological parameters depend on the volume fraction and architecture of the agglomerate, the number of fused particles per cluster, and the viscosity of the suspending fluid. The analysis is also extended to include the case of polydispersity of agglomerate sizes.     

Reserve ability of parallel system with failed elements

The aim of the analysis is to define for a system with parallel elements conditions at which the failure of one or several elements does not cause immediate failure of the whole system. The critical number of failed elements of such a system is assessed based on the strength probability properties of its structural elements. The condition of the catastrophic failure of the whole system is defined by the shape and scale parameters of the strength probability function and the number of parallel elements. The proposed probabilistic model allows estimating the ability of the parallel systems to continue operation when some of its elements are broken.     

The effect of dissolved polymers on the rheological properties of coating colours

Coating colours used for the coating of paper and board consist mainly of a mineral pigment, which is very often clay, a synthetic binder such as a styrenebutadiene latex, dispersion agents and water retention aids. The latter are often water soluble polymers. These polymers have a very strong influence on the rheological properties of the coating colours, both on the strain rate dependence of the apparent viscosity and on the viscoelasticity. The effects of two different grades of carboxymethylcellulose (CMC) and one grade of hydroxyethylcellulose (HEC), on the rheological properties at room temperature of a clay-based coating colour at pH 8, have been investigated. It is concluded that the high values of the dynamic modulus of the colours are due to interactions between the cellulose derivatives and the solid particles, i.e. mainly the clay particles. For HEC this interaction is associated with adsorption of the polymeric molecules on the clay particles. In the case of CMC, the adsorption is strongly retarded by the presence of the dispersant (a polyacrylate salt). It is suggested that the marked elasticity of the CMC-containing colour in addition to a possible polymer adsorption may be due to charge interactions and/or depletion flocculation. The effect of CMC and HEC on the water-retention properties of the colour is also discussed.     

Modelling characteristic properties of sandstones

A computer model of a porous medium is described. Written in FORTRAN, it consists of a three-dimensional array of cubes and cylinders representing pores and throats, respectively. The pore-size distribution (p.s.d.) is calculated from the mercury porosimetry curve of Clashac outcrop sandstone, a relatively clay-free, well characterised rock. Surface area and porosity are calculated from the program and the original porosimetry curve is simulated as a check of the p.s.d. Fifty values of the tortuosity factor of the sandstone are then simulated via a weighted random walk through the model. The tortuosity is then defined as the median of the resulting distribution. The tortuosity is simulated for two different cases of an assumed potential field.     

Nonlinear study of the dynamic behavior of a string-beam coupled system under combined excitations

In this paper,the nonlinear dynamic behavior of a string-beam coupled system subjected to external,parametric and tuned excitations is presented.The governing equations of motion are obtained for the nonlinear transverse vibrations of the string-beam coupled system which are described by a set of ordinary differential equations with two degrees of freedom.The case of 1:1 internal resonance between the modes of the beam and string,and the primary and combined resonance for the beam is considered.The method of multiple scales is utilized to analyze the nonlinear responses of the string-beam coupled system and obtain approximate solutions up to and including the second-order approximations.All resonance cases are extracted and investigated.Stability of the system is studied using frequency response equations and the phase-plane method.Numerical solutions are carried out and the results are presented graphically and discussed.The effects of the different parameters on both response and stability of the system are investigated.The reported results are compared to the available published work.     

Physiology,mechanics, and rheology

Biological systems possess rather specialized mechanical properties, acquired as part and parcel of the evolutionary development of the system as a whole. Their optimization permits the system to function physiologically in the context of a biologically essential, but mechanically often widely varying environment with adequate efficiency. The system's environment is its source of food and shelter; it represents the space in which it forages or preys on other creatures and in which it has to defend itself against still others. Thus, the system has to develop an adequately pliant, rheologically matched, energy-use efficient, mechanical interface between it and its surroundings. This must be an interface that both effectively excludes, but also effectively admits, the external. Internally, as well, it has to adapt the mechanical properties of cell and connective tissue to physiological function and the efficient performance of useful work. This will be illustrated by way of examples. Blood rheology is briefly discussed and put into the context of clinical hemorheology and epithelial protection; and function, by way of a mucus coating or a mucociliary clearance system, is reviewed in some detail. The importance of all aspects of rheological matching is demonstrated.Delivered as a Keynote Lecture at the Golden Jubilee Conference of the British Society of Rheology and Third European Rheology Conference, Edinburgh, 3–7 September, 1990.