Investigation of strength of carbon-carbon composite materials at temperatures from 293 to 3300 K under high-rate heating

The paper presents the results of the investigation into the influence of temperatures from 293 to 3300 K on the strength of carbon-carbon composite materials in tension and in compression. The character of specimen fracture is studied in the temperature range from 293 to 3300 K. It is shown that qualitatively similar changes in the material strength are observed both in tension and in compression.Translated from Problemy Prochnosti, No. 1, pp. 136–143, January–February, 2005.     

超声化学法制备介孔复合材料的研究

将超声技术引入介孔材料的合成中是近年来研究的热点 ,用超声诱导的方法可大大缩短合成时间 ,又可获得性能优良的介孔复合材料。从超声化学的基本原理和特点出发 ,主要介绍了超声法在制备硅基介孔材料和非硅基介孔材料方面的应用 ,并对超声化学法在该领域的发展前景进行了展望。     

GNP法制备固体氧化物燃料电池复合阳极材料CuxCo1-x-SDC的研究

采用甘氨酸-硝酸盐法制备了CuxCo1-xO-SDC复合阳极材料。利用电化学工作站测试了其电化学性能,使用SEM、电导率、红外、差热-热重分析仪对CuxCo1-xO-SDC进行表征。研究结果表明,在Cu基阳极中加入一种具有高催化活性的金属钴,阳极表现出很好的催化活性,提高了电池的电化学性能。     

聚丙烯/蒙脱土纳米复合包装材料的制备与力学性能研究

采用熔融插层法在双螺杆挤出机中制备了聚丙烯(PP)/蒙脱土(MMT)纳米复合材料,纳米复合材料机械性能测试结果表明,当有机蒙脱土(MMT)质量比为2%时,复合材料的综合力学性能明显优于聚丙烯(PP).扫描电镜观测不到纳米复合材料中明显的有机-无机相畴,表明蒙脱土(MMT)片层分散均匀,分散尺度已基本达到纳米级.     

低温烧结铁氧体/陶瓷复合材料的电磁性能研究

采用MgCuZn铁氧体(MCZF)分别与少量CaTiO3(CT)和BaTiO3(BT)复合,以Bi2O3为助熔剂,通过标准陶瓷工艺在900和950℃烧结得到适合低温共烧陶瓷(LTCC)工艺的两类复合材料MCZF/CT和MCZF/BT。对比研究铁氧体与两类复合材料的磁性能和介电性能发现,与陶瓷复合后材料的截止频率可以从13.9MHz提高到136.5MHz,而1MHz处的介电损耗可以从0.741降低到0.012。对比研究不同烧结温度下复合材料的电磁性能发现,950℃烧结的样品比900℃烧结时有更高的起始磁导率、Snoek产量、介电常数及更低的介电损耗,其中MCZF/CT的起始磁导率达到51.8,明显高于MCZF/BT,但后者有更优良的介电频率特性。此外,结合微结构分析讨论了950℃烧结样品的电磁性能变化原因。     

Estimation of thermal properties of composite materials without instrumentation inside the samples

Recent contributions of parameter estimation in the measurement of thermal properties are of great importance. In comparison with other techniques such as steady state (hot guarded plate, etc.) or transient (line source method, flash method, etc.), the use of parameter estimation provides more information and, in most cases, produces faster results. With this technique the thermal conductivity and the volumetric specific heat are estimated simultaneously and as a function of time, temperature, or position. This method requires experimental data, such as transient temperature and heat flux measurements. Previously, the temperature measurements came from thermocouples embedded in the sample. These thermocouples are introduced in the sample either by drilling holes or by molding the material around a series of thermocouples. Both operations are time-consuming and costly and are needed for each sample. In this study, temperature measurements are made only on the two sides of the samples with thin resistance thermometers. Since the sensors are not inside the material, the effect of the thermal contact conductance between sensor and sample was first investigated. The value of this thermal contact conductance was estimated by using samples of high-conductivity material. Using these values, the estimated thermal properties obtained with surface temperature measurements are compared with values provided by other methods for several low-thermal conductivity materials; agreement has been very good.     

纳米SiO2改性环氧树脂及其复合材料性能研究

先采用机械搅拌和超声分散方式在环氧树脂中分散纳米SiO2微粒,通过扫描电镜表征断面的形貌来分析纳米SiO2分散效果,再采用力学性能测试,研究纳米SiO2对环氧树脂及其玻璃纤维增强复合材料性能的影响,结果表明,超声分散效果明显优于机械搅拌分散;纳米SiO2含量对分散效果、环氧树脂及其复合材料力学性能具有显著影响;采用超声分散的1%(质量分数)纳米SiO2改性环氧树脂浇铸体的弯曲强度比未改性的提高了21.2%,其玻璃纤维增强复合材料的弯曲和拉伸强度分别提高了9.7%和7.9%,但层间剪切强度则降低了10.6%。     

非均相超声法制备纤维素-聚苯胺导电复合材料及其导电性能研究

用非均相超声法制备了纤维素-聚苯胺导电复合材料,通过红外光谱(FT-IR)、扫描电镜(SEM)、和热重(TG)以及四探针仪(SDY-4)对其结构及导电性能进行了表征。经过超声处理的纤维素表面部分细胞初生壁(P)和次生壁外层(S1)脱除,次生壁中层(S2)裸露,表面粗糙。苯胺单体均匀地附着于其表面,并进一步聚合得到颗粒状聚苯胺,有效地抑制了团聚现象的产生。复合材料的热稳定性和导电性都有相应的提高。     

挤压浸渗法制备Csf/Al复合材料的组织与性能

以M40石墨短纤维为增强体，LY12铝合金为基体，用挤压浸渗法制备了短碳纤维增强铝基复合材料，研究了浸渗工艺对复合材料的界面反应和组织与性能的影响，以及不同碳纤维体积分数下的常温及高温力学性能，结果表明，在冷却速度相同的情况下，浸渗温度即铝液的浇注温度对界面反应及复合材料的组织与性能影响较大，740～780℃时界面反应不明显或有轻微的界面反应，材料的性能较好．高于800℃时，碳纤维有氧化现象发生，材料的性能严重下降，甚至低于基体性能，随着碳纤维体积分数的增加，复合材料的常温及高温力学性能提高。     

预测复合材料导热系数的热阻网络法

借助计算机模拟复合材料的空间结构,直接迭代求解热阻网络,得到复合材料的导热系数。分析了在随机分布条件下取样尺度对导热系数的影响,以及二维和三维条件下导热的差别。与文献中实验数据的比较表明,所述方法能够较好地预示颗粒弥散型复合材料的导热系数。     

Structure and mechanical properties of reaction-sintered ceramic composite materials based on titanium and hafnium diborides

The structure and mechanical characteristics of ceramic composite materials based on titanium and hafnium diborides produced by reaction sintering in the course of hot pressing have been studied. It has been shown that ultradispersed structure is responsible for high mechanical characteristics of the synthesized composites.     

复合材料调制热像检测的数值模拟

为了给复合材料结构的调制热波成像检测提供基础理论依据和操作参数窗口,用基于有限单元法的计算机数值模拟研究了复合材料层压板分层、脱粘的调制热像检测规律。分析了相位差与调制频率及缺陷深度的关系,提出了最佳检测频率、半高频带和盲频的预测方法,验证了利用盲频来估计缺陷深度的方法,提出利用最佳检测频率来估计缺陷深度的新方法。研究结果表明：最佳调制频率和盲频近似与缺陷深度的平方成反比;最大相位差及半高频带宽随缺陷深度的增大而减小;利用盲频和最佳调制频率都可以对缺陷深度进行定量估计,在缺陷深度为1~4 mm的范围内,两种方法的估计误差分别在约9%和11%以内。     

Investigation into engineering properties and strength mechanism of grouted macadam composite materials

To further understand engineering properties of grouted macadam composite materials (GMCM) used as a surfacing layer in pavement, the mechanical properties and durability characteristics of GMCM were evaluated, and the relevant strength mechanisms were investigated at the micro level. Results indicate that GMCM has better high-temperature stability, fatigue performance and moisture stability than that of conventional asphalt mix, while it shows an acceptable decrease in low-temperature crack resistance due to the relative brittleness of hardened cement paste. The hardened cement paste also generates a spatial network crystalline lattice in asphalt mix skeleton to form a three-dimensional integral coagulation-crystalloid structure. This facilitates the asphalt mix skeleton and hardened cement paste to bear loads in unison and increase durability of the GMCM. Further, the fibre-like hydrated products of fresh cement slurry on the bitumen film surface increase the interfacial strength between bitumen and hardened cement paste due to toughening and bridging effects, which plays an important role to enhance mechanical properties and durability of GMCM. Finally, GMCM strength is from the internal friction of asphalt mix skeleton, the network structure of hardened cement paste and the adhesion between porous asphalt mix and hardened cement paste. It is concluded that GMCM can better meet the requirements of mechanical properties and durability characteristics than the conventional asphalt mix.     

Multiscale analytical sensitivity analysis for composite materials

We describe a methodology aimed at determining the sensitivity of the global structural behaviour, such deformation or vibration modes with respect to the local characteristics such as material constants of micro‐constituents. An analytical gradient computation, which involves the direct differentiation of the multiple scale strong forms with respect to the design parameters is developed. Comparison of the multiple scale sensitivity analysis (MASA) to the central finite difference (CFD) approximation in terms of accuracy and computation efficiency is carried out. We demonstrate the robustness of the MASA approach compared to the CFD approximation, which has been found to be highly sensitive to the choice of the step size, whose optimal value is problem dependent. Copyright © 2001 John Wiley & Sons, Ltd.     

结构吸波复合材料透波层的研究

采用弓形法测试反射率,研究透波层的厚度、材质对结构吸波复合材料电磁性能的影响。结果显示,在4~18GHz范围内,厚度对其吸波性能具有显著影响,厚度分别为0.25、0.50和1.25mm的透波层,其结构吸波复合材料的最大吸收峰分别为-37.03,-33.45和-33.22dB;随厚度的增加,吸收峰的位置随向低频段显著漂移,-10dB的有效吸收带宽也显著变窄,分别为11.5,11和6.5GHz;与厚度相比,材质对结构吸波复合材料电磁性能影响较小。     

Flight service environmental effects on composite materials and structures

NASA Langley and the U.S. Army have jointly sponsored programs to assess the effects of realistic flight environments and ground-based exposure on advanced composite materials and structures. Composite secondary structural components were initially installed on commercial transport aircraft in 1973; secondary and primary structural components were installed on commercial helicopters in 1979; and primary structural components were installed on commercial aircraft in the mid-to-late 1980's. Over 5.3 million total component flight hours have been accumulated on 350 composite components since 1973. Service performance, maintenance characteristics, and residual strength of numerous composite components are reported. In addition to data on flight components; 10-year ground-based exposure test results on material coupons are reported. Comparisons between flight and ground-based environmental effects for several composite material systems are also presented. Test results indicate excellent in-service performance with the composite components during the 15 year evaluation period. Good correlation between ground-based material performance and operational structural performance has been achieved.     

Applications of thermoelastic stress analysis to composite materials

A number of applied thermoelastic stress analysis (TSA) studies on composite components and assemblies are described, for the purpose of illustrating the potential of the technique for use with composite materials.     

电场激活压力辅助SHS法合成TiC-Ni-Fe复合材料

采用电场激活压力辅助SHS法制备了TiC 15%Ni 20?物相体系金属间化合物基复合材料.分析表明TiC 15%Ni 20?物相体系生成物中主要相为TiC,基体成分为NiTi2与FeNi金属间化合物;随着压力增加,生成物成分更均匀,密度增大,表面硬度和显微硬度值也显著提高.     

石墨/树状大分子复合材料的分子动力学模拟

在COMPASS(Condensed-phase optimized molecular potentials for atomistic simulation studies)力场下, 对以氨(Amine)、 丁二胺(Butanediamine)为核的1代~3代(1G~3G)石墨/树状大分子纳米复合材料进行了分子动力学模拟(Molecular dynamics simulation)。介绍了复合体系的构建过程及分子动力学模拟细节, 从微观构形、 能量变化研究了正则系综(恒定的NVT)中6种插层复合物的稳定性及其机理, 最后利用径向分布函数(Radial distribution function)对能量变化结果进行了分析。结果表明, 当树状大分子体积较小时, 石墨层容易弯曲, 体系能量较高, 导致复合体系不稳定; 随着树状大分子代数的增加, 石墨层形变减小, 体系能量降低, 3代时树状大分子体系最稳定。      

掺合材对水泥基材料雷达吸波效能实验研究

采用弓形法,对以水泥为基体,以掺合材硅灰和粉煤灰、石墨和碳纤维、纳米TiO2和钢纤维为吸波剂的试样,在8～18GHz频段内的吸波性能进行了分析,实验表明硅灰和粉煤灰、纳米TiO2和钢纤维与水泥复合制成的吸波材料具有良好的吸波效能,在8～18GHz频段内,其吸波效能随掺合材的含量增加而增大,但有一极限值。石墨和碳纤维与水泥复合制成的吸波材料的吸波效能较差,当石墨和碳纤维掺量为6%(质量分数)以上时,材料的吸波性能下降。硅灰和粉煤灰混合的最佳含量为30%(质量分数)左右,而纳米TiO2和钢纤维的最佳含量为纳米TiO24%(体积分数)、钢纤维4%(质量分数)左右。掺合材超过一定极限后,材料的透波能力增强,吸波性能便会下降。