超高分子量聚乙烯纤维的液相氧化改性及其环氧树脂基复合材料的力学和摩擦性能

为增强超高分子量聚乙烯(UHMWPE)纤维与环氧树脂(EP)基体之间的界面粘结强度,采用重铬酸钾溶液对UHMWPE纤维进行表面改性并制备UHMWPE纤维/EP复合材料。结果表明,UHMWPE纤维经液相氧化后表面刻蚀痕迹明显,表面粗糙度明显增加,结晶度增加了11.3%,与乙二醇的接触角减小了14.12°。与纯环氧树脂相比,纤维含量为0.4%的未改性UHMWPE纤维/EP复合材料的拉伸强度降低18.04%,纤维含量为0.6%的液相氧化改性UHMWPE纤维/EP复合材料的拉伸强度降低51.55%,未改性UHMWPE(纤维含量0.5%)和液相氧化改性UHMWPE(纤维含量0.4%)纤维/EP复合材料的冲击强度分别提升了3.29%和4.39%。当纤维含量为0.3%时,液相氧化改性UHMWPE纤维/EP复合材料的弯曲强度比纯环氧树脂增加6.55%,比未改性UHMWPE纤维/EP复合材料增加19%。当纤维含量由0增大到0.5%时,改性和未改性UHMWPE纤维/EP复合材料的摩擦系数先增加后减小。     

酸刻蚀对玄武岩纤维表面偶联剂吸附量及纤维/环氧树脂复合材料力学性能的影响

纤维与树脂的复合需要有一个良好的界面相,以便能将载荷从基体有效地传递给增强纤维,纤维表面改性处理是达到这一要求的主要方法。采用盐酸刻蚀法对玄武岩纤维（BF）表面进行处理,讨论了酸刻蚀对纤维单丝拉伸性能、表面硅烷偶联剂吸附量的影响以及盐酸浓度对BF/环氧树脂复合材料力学性能的影响。结果表明：纤维的单丝拉伸强度随着盐酸浓度的升高呈加速下降趋势;1 mol/L盐酸处理后的纤维表面对硅烷偶联剂KH550的吸附量最大;1 mol/L盐酸刻蚀后再经硅烷偶联剂KH550处理的纤维制成的BF-KH550/环氧树脂复合材料的弯曲性能、拉伸性能和层间剪切强度最优。     

偶联剂处理SiC纤维增强PTFE复合材料的性能

用共混冷压成型法制备了SiC短纤维(未处理和偶联剂表面处理)增强聚四氟乙烯(PTFE)复合材料,测试了复合材料的力学和摩擦磨损性能,研究了表面处理对PTFE复合材料性能的影响,用扫描电子显微镜(SEM)对拉伸断面形貌进行观察,探讨了纤维增强复合材料的机理。研究结果表明:偶联剂处理SiC纤维表面后,复合材料的拉伸强度、冲击强度、减摩耐磨性能均比未处理的有所提高。拉伸断面的SEM分析表明,未处理SiC纤维与PTFE的界面黏结较差,界面出现了许多空隙,偶联剂处理后,SiC纤维与PTFE界面黏结较好,在拉伸过程中多数SiC纤维被基体牢固黏附而难以拔出。     

单宁酸协同改性超高分子量聚乙烯纤维与环氧树脂复合材料

将单宁酸共混改性的环氧树脂与单宁酸-金属Na~+络合改性超高分子量聚乙烯(UHMWPE)纤维进行复合,从而改善了UHMWPE纤维与环氧树脂的界面强度,提高了纤维增强复合材料的整体性能。改性后纤维表面的单宁酸与树脂基体中的单宁酸在界面处形成"桥联"作用。单宁酸共混改性环氧树脂是为了在环氧树脂中引入羟基以增强其力学强度。结果表明,当单宁酸在环氧树脂中的负载量为1%时,树脂基体的拉伸强度、弯曲强度达到最大值,分别为55.41 MPa, 74.24 MPa,与纯环氧树脂相比分别提高了67.5%和63.5%。同时界面剪切强度达到2.22 MPa,与原复合材料相比提高了64.8%。纵向纤维束使环氧树脂复合材料的拉伸强度增加到89.52 MPa,弯曲强度达到118.82 MPa,与纯复合材料相比,分别提高了120.2%,47.3%。通过扫描电镜图分析可以得出,纤维增强复合材料的破坏方式为黏接剂破坏。     

Al2O3颗粒增强聚氨酯基复合材料耐磨性研究

本文研究了Al2O3颗粒增强聚氨酯基复合材料在浆料冲蚀下的耐磨性.结果表明,复合材料的耐磨性随着Al2O3颗粒含量的增加先升高,达到一个峰值后,开始下降.在一定Al2O3颗粒含量下,复合材料的耐磨性好于纯聚氨酯弹性体.这是由于复合材料中的Al2O3颗粒硬度高,可以抵抗浆料的冲蚀磨损,保护周围和下层的基体组织.Al2O3颗粒与基体界面的结合强度对复合材料耐磨性有明显的影响.用KH550处理的复合材料的界面结合强度比用KH560处理的好,所以耐磨性更好.     

表面改性和混杂对超高分子量聚乙烯纤维/环氧树脂复合材料性能的影响

采用紫外接枝和与芳纶纤维混杂的方式改善UHMWPE纤维的缺点,详细研究了接枝单体种类、浓度和纤维混杂等对UHMWPE纤维/环氧树脂复合材料性能的影响。结果表明,以丙酮为溶剂采用一步接枝法在紫外光辐射下将丙烯酸接枝到UHMWPE纤维表面上,可显著提高UHMWPE纤维增强的复合材料的弯曲强度、冲击强度和拉伸强度;随着接枝单体浓度的提高弯曲强度和冲击强度没有明显的变化,而拉伸强度不断提高。同时,将UHMWPE纤维与芳纶纤维混杂可提高其与树脂基体生成的复合材料的耐热性。UHMWPE纤维与芳纶纤维按1∶1的质量比混杂,混杂纤维增强的复合材料在90℃的形变量比UHMWPE纤维增强的复合材料减少66.7%,显著提高了复合材料的耐热性。     

玄武岩纤维增强环氧树脂复合材料复合机制

用三种硅烷偶联剂KH550、KH560和KH570分别处理玄武岩纤维(BF), 以未经偶联剂处理的BF为对照组。X射线电子能谱(XPS)分析三种偶联剂对BF的改性, 发现BF表面的Si元素与偶联剂中的Si元素形成了Si—O—Si键, 其含量顺序为KH550>KH570>KH560。测定了不同方法处理后的BF增强环氧树脂(BF/EP)复合材料水浴前后的弯曲性能和层间剪切强度(ILSS), 同时用SEM观察了BF/EP水浴前后的断裂面微观形貌, 结果发现水浴前三种偶联剂处理BF后都能提高BF/EP的界面粘结性能, 提高效果为KH550>KH560>KH570, 试样破坏时界面无脱粘, 主要发生的是基体破坏, 界面力学性能优于基体力学性能; 水浴处理后, 不同BF/EP的力学性能下降程度不同, 耐水性较差, 试样断裂面呈脆性断裂, 界面脱粘, 部分纤维被拔出后在基体中留下空洞。      

超高分子量聚乙烯(UHMWPE)纤维表面处理对UHMWPE/环氧树脂复合材料界面性能的影响机制

从工程化应用角度研究了常压空气等离子体改性对超高分子量聚乙烯（UHMWPE）纤维/环氧树脂复合材料界面性能的调节机制,主要分析了不同处理时间对UHMWPE纤维表面状态变化的影响,及其对UHMWPE/环氧树脂复合材料界面黏结性能的影响规律。采用SEM及纤维吸水测试研究了等离子体处理对UHMWPE纤维表面物理形貌及纤维表面浸润性能的影响,分别以拉伸和弯曲的方式,通过纤维表面脱黏力及层合板层间剪切强度对UHMWPE/环氧树脂复合材料的界面黏结性能进行表征。结果表明,仅经过4 s的空气等离子体处理之后,UHMWPE纤维表面脱黏力的提高幅度为84.0%,UHMWPE/环氧树脂复合材料层合板的层间剪切强度由未处理的7.01 MPa提高至15.81 MPa,增幅高达125.5%。研究发现,通过常压空气等离子体处理改变了UHMWPE纤维的表面状态,可以显著高效地调节UHMWPE/环氧树脂复合材料的界面性能,为扩大该材料的后续工程化应用提供了理论基础。      

KH550修饰Al_2O_3及其对PI/Al_2O_3薄膜性能的影响

通过调整KH550的含量对Al2O3粉体表面进行改性,并用红外光谱(FT-IR)和X射线衍射(XRD)对改性后的粉体进行表征,表征结果显示KH550成功的键合到Al2O3粉体表面。然后分别使用Al2O3以及改性Al2O3制备了一系列无机粉体含量为16%(质量分数)的PI复合薄膜,通过扫描电子显微镜(SEM)对复合薄膜的断面微观形貌进行表征,并对复合薄膜的力学性能和击穿场强进行测试。测试结果显示KH550的含量对无机粉体分散情况有较大影响。当KH550含量为2%(质量分数)时,PI/KH550-Al2O3复合薄膜的拉伸强度和断裂伸长率最优,分别为130 MPa,12%,与PI/Al2O3薄膜相比,拉伸强度和断裂伸长率分别提高了22.8%,44.5%,击穿场强与其相近。     

超高分子量聚乙烯纤维复合表面改性及其橡胶基复合材料的力学性能

针对超高分子量聚乙烯(UHMWPE)纤维与基体之间界面结合强度低的问题,采用超声波结合铬酸溶液氧化的复合工艺对UHMWPE纤维进行表面处理,并将处理后的纤维加入到天然橡胶(NR)中制备短切UHMWPE纤维/NR复合材料。结果表明:复合改性工艺可有效增加纤维表面粗糙度及表面含氧官能团含量,最佳改性工艺条件为:按照重铬酸钾、水及浓硫酸的质量比7∶12∶150配置铬酸溶液,将含有一定质量UHMWPE纤维的铬酸溶液放入35℃的超声波清洗仪中氧化5min,其中超声波频率为100kHz。与纯NR样品相比,在UHMWPE纤维与NR的质量比为0~6∶100范围内,随着处理后短纤维含量的增加,复合材料的拉伸强度逐渐减小,最大损失量达到50%;复合材料的硬度不断增大,最大增加量达到96%;复合材料的撕裂强度先增大后减小,在UHMWPE纤维与NR的质量比为5∶100时达到最大值,最大增加量达到49%。     

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.     

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.     

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.     

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)。