膨体聚四氟乙烯微孔薄膜的透湿性

采用干燥剂法系统测试了ePTFE微孔薄膜的透湿情况,分析了透湿性影响因素,得出以下结论:在实验范围内,ePTFE薄膜的孔隙率、孔径和厚度等结构参数对透湿速率影响较小,透湿的主要影响因素是环境温度和湿度。在相同的湿度下,环境温度对透湿量和透过系数的影响显著,并随温度提高急剧增加;在相同温度下,透湿量随湿度的增加而增加,而透过系数变化不大。     

SiO2含量与粒径对PLA/SiO2复合膜性能的影响

目的 为了提高聚乳酸材料的力学性能和气体阻隔性,选择二氧化硅为共混材料,通过改变二氧化硅的粒径和含量,研究SiO2对SiO2/PLA复合膜性能的影响.方法 用流延法制备二氧化硅/聚乳酸(SiO2/PLA)复合膜.采用力学性能测试、结晶性测试、热稳定测试和透氧、透水蒸汽测试等分析手段对制备的复合膜进行力学性和阻隔性的表征.结果 在PLA材料中添加适量的SiO2对复合膜的拉伸强度和弹性模量会有增强作用,并且粒径越小,增强效果越明显;粒径为50 nm,质量分数为2％时复合膜表现出更佳的力学性能.同时,随着SiO2含量的增加,氧气透过系数呈先降低后升高的趋势,在SiO2质量分数为2％时透过系数最小,复合膜的氧气阻隔性最好;不同粒径不同含量的SiO2透湿性测试结果表明,SiO2粒径为50 nm,质量分数为2％时复合膜的阻隔性效果最好.结论 二氧化硅的加入能够提升聚乳酸的弹性模量和阻隔性,并且二氧化硅的粒径和不同添加量对复合膜的性能有很大影响.     

防潮包装中的干燥剂包装

叙述防潮包装中干燥剂的材料选择,包装干燥剂的薄膜厚度计算方法以及双梯度法包装干燥剂时、干燥剂包装袋的总透湿速度要求大于产品包装容器的总透湿速度之理由。     

升压法测量静态蒸发率理论分析及试验研究

通过对低温介质热力性质在自然升压传热过程的理论分析,基于热力学能量守恒定律,推导出升压法测量静态蒸发率的理论计算公式。分析了测试过程中充满率和有效容积对自然升压过程的影响规律,研究了用升压法测量时24 h内各时间节点的压力变化。结果表明:"压力-时间"曲线呈线性变化且近似为正比例函数,初始充满率越大自然升压速率越慢,当充满率小于80%时,自然升压速率差值逐渐增大,当充满率大于等于80%时,升压速率相差很小;有效容积越小升压速率越快;当升压法测试时间小于6 h时,相比称重法和流量计法,对静态蒸发率的测量结果误差较大,但随着测试时间的延长相对误差呈逐渐减小趋势,当测试时间在6～24 h时,升压法测量结果较称重法和流量计法的误差均小于3%。研究结果验证了理论分析的合理性及计算公式的准确性。研究证明,采用升压法可将静态蒸发率测试时间缩减至6 h,该结果为今后标准的制修订提供了参考。     

纺织品水萃取液pH值测定影响因素的探讨

本文从pH计的选择、测试用水、剪碎后试样大小、取样部位、振荡时间、萃取液静置时间六个方面,较全面地探讨了纺织品pH值测试的影响因素。结果表明：pH计的选择、pH值相差较大的三级水以及不同取样部位对pH值测定结果的影响很大;而其它三个因素往往对于pH值偏高的试样影响较大,而对于大多数pH值较低的试样影响较小。但是有些布样比较特殊,其测试值的影响因素不存在上述规律,这可能与面料的整理工艺有关。     

沙尘在防沙堤附近沉积特性的数值模拟

为研究沙尘在防沙堤附近的沉积特点,基于FLUENT软件,采用标准K-ε湍流模型和DPM模型对沙尘在防沙堤附近的运动轨迹进行数值模拟。结果表明,沙尘的运动轨迹受自身粒径、风速及防沙堤迎风面坡度的综合影响,沙粒粒径越小,风速越大,防沙堤迎风面坡度越缓,沙粒越过防沙堤的能力越强;除风速较低时部分小粒径颗粒沉积在防沙堤后端外,其余情况下沙尘沉积主要发生在防沙堤前端。     

沥青燃烧性能测试中试样状态调节时间的研究

采用氧指数法测试不同状态调节时间后沥青试样的燃烧性能,分析试样状态调节时间对沥青燃烧性能测试的影响。实验结果表明,当试样状态调节时间<12h时,对沥青燃烧性能测试结果影响较大;而当试样状态调节时间≥12h时,对沥青燃烧性能测试结果影响较小,测试结果趋于稳定。因此,当采用氧指数法测试沥青的燃烧性能时,建议沥青试样的状态调节时间应不小于12h。     

粉料粒度对氮化硅陶瓷性能的影响

用球磨的方式将平均粒径为6.46μm的β-氮化硅原料粉细化为不同粒度的亚微米级起始粉料,加入适宜的添加剂,以无压液相烧结的方法研究起始粉料粒度对氮化硅陶瓷的强度、硬度等机械性能的影响。用扫描电镜、X射线衍射等方法测试分析试样的显微结构、相组成等。结果表明,试样密度、强度、硬度等均随起始粉料粒度的减小而增大;试样显微结构显示了烧结体晶粒尺寸随起始粉料粒度的减小而减小,且粒度小的试样烧结的晶粒均匀、致密;烧结后试样的物相主要是β-氮化硅和少量黄长石,粉料的粒度对烧结后样品的物相没有影响。     

6101铝合金时效过程中析出相对电阻率的影响

采用硬度测试、原位电阻测试及TEM等手段,研究了6101铝合金在175~195℃下时效析出相对相对电阻率(Δρ%)的影响,利用修正的马蒂森定则计算了175℃时不同时效时间析出相对相对电阻率的影响,得到了影响合金力学性能和导电率的温度时间判断依据。结果表明,随着温度的升高,时效初期团簇形成的时间越短,相对电阻率越低,硬度峰值也越低;175℃时效后期,析出相的密度增加,相间距减小,析出相对相对电阻率的影响基本稳定,导电率基本稳定。借助研究结果,确定了以力学性能优先和导电率优先的时效制度175℃/680min和195℃/220min,性能测试显示选取依据合理。     

水平直管内冰浆流动过程冰晶粒径演化研究

本文采用实验研究与数值模拟相结合的方法,研究了冰浆在水平直管内流动过程中冰晶粒径的分布及其演化规律。通过CFD-PBM耦合模型模拟研究冰浆在不同过冷度、流速、含冰率下冰晶粒径分布及其演化规律,并通过实验对数值模拟结果进行验证。结果表明:在含冰率为15%的冰浆管道入口处,冰晶粒径数量密度分布均近似高斯分布;随着冰浆流速和含冰率的增加,沿流动方向中心轴的冰晶平均粒径增大,截面冰晶粒径分布越不均匀;流速越小、含冰率越大,冰晶粒径的长度数量密度分布曲线的峰值升高,峰值所对应冰晶粒径的平均值减小。     

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)。