自然复合材料的强韧化机理和仿生复合材料的研究

本文评述了一个新的研究方向─—自然复合材料强韧化的细观机理及其仿生复合材料的研究。着重考察了木、人骨、贝壳珍珠层、昆虫外骨骼及翅等自然复合材料的研究现状,基于这些研究,部分仿生材料已被设计和制造出来并达到商用程度．复合材料在细观层次的仿生,是将对复合材料及其结构设计产生潜在冲击的重要发展方向．      

激光-载荷联合作用下碳纤维／环氧树脂板的断裂阈值研究

 介绍了激光 载荷联合作用下碳纤维/环氧树脂编织复合材料单边缺口板断裂的实验和理论研究。实验测量了断裂阈值曲线,并结合显微观察确定了三种断裂模式：热应力、热减薄和热击穿模式。获得了热应力模式断裂的理论判据,与实验结果基本吻合。该判据建立了断裂临界条件下热－力和几何参数与材料性能参数之间的关系。     

Echo-Planar Imaging of Porous Media with Spatial Resolution below 100 μm

A modified version of the echo-planar imaging technique incorporating a Carr–Purcell train of 180° rf pulses (PEPI) has been implemented on a standard spectrometer. It is demonstrated that artifacts in the image due to cumulative errors in the rf field can be reduced by replacing each 180° pulse by a composite sequence of three rf pulses. Artifact-free 3D images at 94 μm voxel resolution are obtained within 15 min. This technique has been applied to study the drying process in an initially water-saturated model porous medium with characteristicT^*₂of order 700 μs.     

Spin susceptibility of interacting electrons in one dimension: Luttinger liquid and lattice effects

The temperature-dependent uniform magnetic susceptibility of interacting electrons in one dimension is calculated using several methods. At low temperature, the renormalization group reveals that the Luttinger liquid spin susceptibility approaches zero temperature with an infinite slope in striking contrast with the Fermi liquid result and with the behavior of the compressibility in the absence of umklapp scattering. This effect comes from the leading marginally irrelevant operator, in analogy with the Heisenberg spin 1/2 antiferromagnetic chain. Comparisons with Monte Carlo simulations at higher temperature reveal that non-logarithmic terms are important in that regime. These contributions are evaluated from an effective interaction that includes the same set of diagrams as those that give the leading logarithmic terms in the renormalization group approach. Comments on the third law of thermodynamics as well as reasons for the failure of approaches that work in higher dimensions are given. Received 2 March 1999     

Poly(styrene-b-ethylene oxide) copolymers as stabilizers for the synthesis of silica–polystyrene core–shell particles

Following previous works [1, 2], silica–polystyrene core–shell particles have been synthesized by dispersion polymerization of styrene in an ethanol/water mixture in the presence of a poly(styrene-b-ethylene oxide) block copolymer as stabilizer. Besides the formation of composite core–shell particles, a large number of free latex particles that do not contain silica were also formed. This number decreases as the size of the silica beads decreases from 300 to 29 nm in diameter, and becomes very low compared to the number of composite particles for the smallest silica beads used. In every case, the composite particles could be easily separated from the free latex particles by centrifugation, providing a material made of regular core–shell composite particles. On the basis of the mechanisms involved in dispersion polymerization, hypotheses were formulated to account for the formation of the silica–polystyrene composite particles. Received: 6 May 1999 Accepted in revised form: 29 June 1999     

掺希土离子Eu3+的BaTiO3超细微粉的制备及物性表征

近年来人们对材料及由材料制备的元件提出了高可靠性、多功能等要求。为了达到这种要求,人们从多种途径进行了探索,其中,对现有材料进行掺杂就是很有效的方法之一［１,２］。本文报道对ＢａＴｉＯ３超细微粉进行Ｅｕ３＋的有效掺杂并对其进行了物性表征。１实验部分１...     

Residual strength of GFRP at high-cycle fatigue

Degradation of the residual strength of a glass-fiber-reinforced polyester composite of a lay-up typical of the wind rotor blade material is studied at low-cycle fatigue. A gradual reduction of the residual strength is observed as expected for GRP, accompanied by an increasing scatter of strength. The residual strength model based on the strength-life equal rank assumption yields an accurate approximation of experimental data. The strength reduction at a stress level corresponding to high-cycle fatigue (N>10 ⁶ cycles) appears to correlate well with the test results at higher stress levels, which indicates that the strength degradation at the design stress level can be evaluated using low-cycle tests. Assuming that the parameters of the strength degradation model do not depend on the applied stress level, the residual strength data obtained in low stress level tests of comparatively short duration can be used to estimate the average fatigue life at the same stress thus reducing the total test time. Translated from Mekhanika Kompozitnykh Materialov, Vol. 35, No. 5, pp. 595–604, September–October, 1999.     

A generalized self-consistent method for composites with random elastic properties of inclusions

The generalized self-consistent method is extended to the problems of statistical mechanics of composites with random elastic properties of inclusions. This approach makes it possible to reduce the problem of predicting the effective elastic properties of composites with random structures to a sequence of simpler homogenized boundary-value problems for solitary inclusions with inhomogeneous elastic transition layers in a homogeneous effective elastic medium and with the corresponding boundary conditions. The elastic properties of a solitary inclusion for the gth homogenized problem are found from the solutions of the gth and (g+1)th homogenized problems. The elastic properties and sizes of the transition layers account for the random distribution, random sizes, and random elastic properties of inclusions in the composite. A test problem of predicting the effective elastic properties of a transversely isotropic layer composite with random elastic properties of some layers is solved by using the method proposed. The solution obtained coincides with the known exact solution [1].Perm State Technical University, Perm, Russia. Translated from Mekhanika Kompozitnykh Materialov, Vol. 35, No. 6, pp. 785–796, November–December, 1999.     

竹纤维增强制动摩阻材料摩擦学性能研究

采用竹纤维为增强相制备新型无石棉树脂基复合摩擦材料.通过热失重分析、定速摩擦试验及磨损表面形貌观察等手段探讨竹纤维的含量对材料在不同温度下摩擦学性能的影响.试验结果表明:在树脂基摩阻材料中加入适量竹纤维能改善材料摩擦磨损性能,并具有一定的减震降噪的效果,但在超过其热解温度时会造成竹纤维的碳化、挥发,对基体增强失效;竹纤维质量百分数为13%时试样能获得较稳定的摩擦系数及较低的磨损率;竹纤维含量过多会造成摩阻材料制备工艺性变差,且高温下大量竹纤维碳化剥落会破坏摩擦表面膜的连续性,使摩阻性能显著下降.     

纤维与基体的轴对称界面端附近的奇异应力场

基于各向性弹性力学空间轴对称问题的基本方程,研究了纤维与基体的轴对称界面端的应力奇异性,并给出了界最佳 近的奇异应力场。研究结果表明,该轴对称界面端的应力奇异性与平面应变状态下相应模型的应力奇异性完全相同,材料对界面端附近奇异应力场的影响可用丰个双材料组合参数描述。