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。     

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.     

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。     

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。     

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.     

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。     

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.     

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.     

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.     

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.     

LiFePO_4/graphene锂离子电池复合正极材料的制备与性能

通过溶胶-凝胶烧结法制备了LiFePO4/graphene锂离子电池复合正极材料。采用X射线衍射(XRD)、扫描电镜(SEM)、透射电镜(TEM)、循环伏安(CV)以及各种电化学检测技术对合成材料的结构、形貌进行了表征。LiFePO4/graphene复合材料的表面上和其中的LiFePO4微小颗粒之间都有石墨烯,说明石墨烯与LiFePO4已很好地融合在一起,形成了具有三维空间结构的立体导电网络,大大地提高了复合材料的电子导电性能及减少了电荷转移电阻,从而充分发挥了活性材料的全部潜力。电化学测量表明LiFePO4/graphene的电化学性能比LiFePO4/C更好。LiFePO4/graphene具有较高的比容量和优良的大倍率性能,在0.1和5C电流充放时,LiFePO4/graphene的比容量分别为163.81和101.57 mAh/g,而LiFePO4/C仅为146.05和54.67mAh/g。LiFePO4/graphene也具有优良循环性能,0.5C循环100次,容量保持率为98.48%。     

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。     

Acoustic emission of composite materials in tensile tests at cryogenic temperatures

Tensile tests of fibre reinforced plastics are performed at cryogenic temperatures and simultaneously acoustic emission (AE) is observed to examine the microscopic deformation and fracture processes of these materials. AE behaviours at liquid helium temperature are different from those at liquid nitrogen temperature, although the mechanical behaviours are similar. From these results, correlations of the AE sources with the microscopic deformation and fracture processes are discussed.     

Fire resistance certification of aircraft composite materials

The Federal Aviation Administration (FAA) requires fire resistance certification of aircraft composite materials used in civil aircraft exterior structure and engine compartments. This paper presents an FAA approved process for accomplishing certification testing at minimum cost and time using an oxygen-acetylene heating tip. The test stand and process minimized human factors and quantified backside flame visibility for comparing aluminum and composite materials. The process focus was on demonstratingfire resistant characteristics, but could also be applied to thefireproof test process. Backside flame visibility was defined as the visual observance of light from the oxygen-acetylene flame. This definition was uniformly applied to both the aluminum test panels and the composite test panels. This presentation of the fire resistant certification process for aircraft composite materials will enable others to efficiently set up and perform both fire resistant and fireproof certification testing.     

气体分离复合膜制备中材料匹配和孔渗现象的研究

介绍了气体分离复合膜的基本构型、制备方法及近期的发展,阐述了制备气体分离复合膜时遇到的两个问题;材料匹配和孔渗现象。模拟计算了孔渗对复合膜分离性能的影响,并对如何防止孔渗现象的发生进行了讨论。