Nomex/氰酸酯树脂夹层复合材料耐湿热性研究

在70℃,85%湿度的环境下对Nomex/氰酸酯树脂夹层复合材料进行了湿热处理,并对其吸湿特性进行了研究.然后,对老化前后的试样进行了力学性能以及介电性能的测试.结果表明:Nomex/氰酸酯树脂夹层复合材料经湿热处理后,其介电性能的保持率很高,具有很好的介电性能与耐湿热性.夹层材料力学性能保持率很高,主要是由于其面板基体树脂为氰酸酯树脂,其更好的耐湿热性给整个夹层结构提供更好的保护.     

湿热环境对PMI泡沫夹芯复合材料性能的影响

采用聚甲基丙烯酰亚胺（PMI）泡沫、碳纤维增强环氧树脂（EW220/5258）复合材料面板制备了PMI泡沫夹芯复合材料,研究了PMI泡沫夹芯复合材料、EW220/5258复合材料面板及PMI泡沫芯材的吸湿特性,并讨论了湿热对PMI泡沫夹芯复合材料的压缩性能及介电性能的影响。结果发现：PMI泡沫夹芯复合材料的饱和吸湿时间...     

湿热循环对Nomex蜂窝/环氧树脂夹层复合材料性能的影响

通过对Nomex/环氧树脂夹层复合材料1(1号材料)和Nomex/环氧树脂夹层复合材料2(2号材料)进行7天和14天湿热循环,测定了其吸湿、脱湿曲线,实验结果表明,1号材料的饱和吸湿率和水分保持率均低于2号材料,1号材料具有更好的耐湿热性,分别对循环前后的材料进行力学性能和介电性能测试。结果表明,湿热循环对材料的剪切性能造成较大影响,其中对2号材料的影响尤为显著,1号材料的力学性能保持能力大于2号材料;同时,还讨论了湿热循环前后两种材料的介电常数和损耗角正切的变化情况。     

超高分子量聚乙烯纤维增强复合材料的性能研究

采用一种结构与超高分子量聚乙烯(UHMWPE)纤维相似、且对纤维表面具有良好浸润性的碳氢树脂(PCH)作基体,通过层压成型方法制得UHMWPE/PCH复合材料.研究了复合材料的力学性能、介电性能、吸湿性能及界面黏结性能.结果表明,UHMWPE/PCH复合材料介电性能优异、力学性能好、耐湿热性能较佳、界面黏结性能好,可用作高性能透微波复合材料.     

湿热老化对玻璃纤维/环氧树脂复合材料性能的影响

为研究玻璃纤维(GF)/环氧树脂复合材料湿热老化机制, 首先, 利用称重法、动态热机械分析仪(DMA)、SEM和矢量网络介电分析仪研究了湿热老化对GF/环氧树脂608(EP608)复合材料性能的影响;然后, 分析了复合材料的吸湿率、力学性能、介电性能与老化时间的关系, 并对其老化机制进行了探讨。结果表明:随老化时间延长, GF/EP608复合材料的力学性能和介电性能均有不同程度的下降;湿热老化对GF/EP608复合材料吸湿率的影响符合Fickian扩散定律;树脂基体的塑化、水解和基体-纤维界面的破坏是造成GF/EP608复合材料力学性能和介电性能下降的主要因素。所得结论可为GF增强环氧树脂基复合材料的应用提供科学依据。      

不同湿热条件下碳纤维/环氧复合材料湿热性能实验研究

对比研究了环氧5228A树脂及碳纤维/环氧5228A树脂复合材料层合板在3种湿热环境(水煮、70℃水浸,70℃85%相对湿度)下的湿热性能,考察了湿热条件对复合材料层间剪切性能的影响规律,并从吸湿特性、物理化学特性、树脂力学性能、湿应力等方面分析了不同湿热环境下复合材料性能衰减的机制。研究表明,碳纤维/高温固化环氧树脂复合材料层间剪切性能主要是由吸湿率决定,相同吸湿率不同湿热条件下性能的下降幅度基本相同;3种湿热条件下该树脂及其复合材料未发生化学反应、微裂纹等不可逆变化,复合材料层合板湿热老化机制主要是吸入水分后基体增塑和树脂、纤维湿应变不一致导致的湿应力对复合材料性能的负面作用。     

湿热环境下复合材料层板拉-压性能

通过对碳纤维环氧复合材料试样进行不同湿热环境下的拉伸和压缩实验,分析其吸湿特性、拉压力学性能、破坏后断口形貌以及动态力学性能,探讨湿热对该复合材料的拉伸和压缩性能的影响。结果表明:碳纤维环氧复合材料的吸湿过程满足Fick定律,饱和吸湿率约为0.86%。吸湿后材料表面变得光滑,有少量纤维拔出和树脂破坏发生,但吸湿后没有发生化学反应和新物质生成。吸湿后在130℃下,复合材料的拉伸性能保持率为96%,而压缩性能保持率仅为69%。吸湿后玻璃化转变温度比干态时下降了33℃。     

复合材料泡沫夹层结构界面的温度-应变分布

复合材料泡沫夹层结构由于其比强度高、比刚度高、耐腐蚀等特点已广泛在土木工程领域中获得应用。然而,由于复合材料面板与夹芯材料在温度荷载作用下热膨胀系数显著不同,因此在面板与芯材之间的粘结层会产生温度应力,因此会降低界面的粘结性能。本文通过试验研究,系统地给出了复合材料泡沫夹层结构界面温度-应变分布规律,并通过理论建模,提出了界面温度-应变分布规律的计算模型,通过对比实验值与理论值,验证了理论分析模型的精确性。     

玻璃纤维立体织物增强环氧树脂泡沫夹层复合材料的制备及力学性能

为了进一步提高泡沫夹层复合材料的承载能力和综合性能,实现其在轨道交通及汽车等工业领域的应用,开展了玻璃纤维立体织物增强环氧树脂泡沫(GF-Fabric/EP)复合材料的制备及其力学性能的研究。制备GF-Fabric/EP复合材料及其夹层结构,探索了GF-Fabric/EP复合材料及其夹层结构的失效行为,以揭示立体织物的增强机制。结果表明：立体织物的引入可显著改善GF-Fabric/EP复合材料的强度、刚度及破坏应变;但在不同承载条件下,各纱线发挥承载作用和效果不同。面板、芯材各自的性能、尺寸及面/芯界面性能均是影响GF-Fabric/EP夹层复合材料力学性能及失效特征的重要因素。以三点加载下的弯曲性能为例,针对不同的GF-Fabric/EP夹层复合材料,需调整跨厚比和试样尺寸并获得理想的失效特征,方可对其弯曲性能或层间剪切性能进行有效、合理的评价。     

蜂窝夹层结构真空袋共固化工艺过程实验研究

针对蜂窝夹层板的共固化工艺 , 以玻纤/环氧 648复合材料为面板 , 以 Nomex蜂窝为夹芯材料 , 采用真空袋法研究了树脂流动对胶瘤面积和面板孔隙缺陷的影响 , 并通过平拉强度的测试考察了胶接强度与胶瘤面积之间的关系。结果表明: 胶瘤面积随加压时机的推迟先增大后减小 , 并且下面板/芯材胶瘤面积要大于上面板/芯材胶瘤面积 ; 在树脂黏度变化的不同阶段 , 面板中的孔隙消除机制不同 , 并与密封袋内抽气通路的分布有关。力学测试结果发现 , 胶瘤面积的增大有利于平拉强度的提高 , 但当胶接强度超过蜂窝抗拉强度时 , 平拉强度的测试方法存在局限性。      

Estimation of Parameters of Universal Distribution of Moments of Failure of Products

A method is proposed for estimating the parameters of a mixture of exponential and Weibull distributions for which the accuracy of preliminary estimates obtained by graphical analysis is refined in accordance with the criterion of maximum likelihood. The efficiency of the proposed method is supported by the results of statistical modeling.     

Evaluation of optical properties of highly scattering media by moments of distributions of times of flight of photons

A novel method for the determination of the optical properties of tissue from time-domain measurements is presented. The data analysis is based on the evaluation of the first moment and the second centralized moment, i.e., the mean time of flight and the variance of the measured distribution of times of flight (DTOF) of photons injected by short (picosecond) laser pulses. Analytical expressions are derived for calculation of absorption and of reduced scattering coefficients from these moments by application of diffusion theory for infinite and semi-infinite homogeneous media. The proposed method was tested on experimental data obtained with phantoms, and results for absorption and reduced scattering coefficients obtained by the proposed method are compared with those obtained by fitting of the same data with analytical solutions of the diffusion equation. Furthermore, the accuracy of the moment analysis was investigated for a range of integration limits of the DTOF. The moment analysis may serve as a comparatively fast method for evaluating optical properties with sufficient accuracy and can be used, e.g., for on-line monitoring of optical properties of biological tissue.     

Analysis of the rate of propagation of the wave of change of boiling modes

An approximate analytical expression is derived for the velocity of the front of the wave of change of boiling modes on a rod and on a plate. The impact of the Thomson effect and of the heater orientation in the gravity field is included. Adequate agreement is demonstrated between the derived relations and experimental data.     

Estimation of potentialities of methods of summation of direct measurement errors

Conventional methods for summation of direct measurement errors are considered. Conditions under which these methods provide consistent results are stated. It is proposed to utilize for characteristic of the total error, its interval estimator or the half-sum of the value obtained by adding up its arithmetic and geometric random errors.Translated from Izmeritel'naya Tekhnika, No. 4, pp. 10–12, April, 1995.     

空压机轴承箱蜗壳温度探头油封改造

由于空压机进气侧轴承箱蜗壳温度探头密封效果不好,使空压机及其后续管道受到油污染。后将温度探头的O形圈密封改为骨架油封,杜绝了轴承箱漏油问题。文章简介空压机的结构和技术参数,详细介绍了骨架油封的制作和优点。     

Characteristics of mechanical properties of materials in studies of conditions of attainment of marginal states

It is shown that conditions of attainment of marginal states in the material of structural components are formulated on the basis of analysis of force and deformation criteria of formation and development of destruction. The parameters of these criteria are data on types of structural materials, standard and special characteristics of their mechanical properties, structural forms of considered elements of the equipment, and their operating stress loading. In this case, the construction of a system of state equations for describing interrelation of current damage, external actions, and responses to them is based on the concept of calculating variations in properties of materials at all stages of the design life cycle.     

Determination of parameters of microstructural inhomogeneity of deformation of metals by the method of modeling

The article suggests a method of evaluating the microstructural inhomogeneity of deformation of metals by modeling. The method includes the measurement of deformations of metal according to meshes of a dividing grid with small base and the calculation of the distribution parameters of microdeformations in model representation. It is shown that the modeling method makes it possible objectively to evaluate the microinhomogeneity of deformation of metals independently of the chosen mesh size of the dividing grid. New structural characteristics are introduced: the base and wave of variation expressing the degree of crumbling or amalgamation of metal grains by inhomogeneity of deformation.Translated from Problemy Prochnosti, No. 7, pp. 40–44, July, 1991.     

水三相点复现的不确定度评定

水三相点是开尔文热力学温度的唯一基准点，也是ITS-90国际温标重要的定义固定点。因此，水三相点不确定度分析对整个温标的建立、温度量值传递起着至关重要的作用。近3年来，中国计量科学研究院研制出一系列高质量的水三相点容器，加强了水三相点的研究，为不确定度的分析提供了更为可靠的实验依据。同时，不确定度的分析也是客观评价新研制容器性能的一个重要指标。因此，根据实验结果对新研制容器所复现的水三相点进行了不确定度评定。评定结果表明，其扩展不确定度为0．16mK(k=2．69，P=0．99)。