Nonlinear Viscoelastic and Viscoplastic Constitutive Equations Based on Thermodynamics

An approach to modeling the mechanical behavior of fiber reinforced and unreinforced plastics with an evolving internal state is described. Intrinsic nonlinear viscoelastic and viscoplastic behavior of the resin matrix is taken into account along with growth of damage. The thermodynamic framework of the method is discussed first. The Gibbs free energy is expressed in terms of stresses, internal state variables (ISVs), temperatureand moisture content. Simplifications are introduced based on physical models for evolution of the ISVs and on experimental observations of thedependence of strain state on stress state and its history. These simplifications include use of master creep functions that account for multiaxial stresses, environmental factors and aging in a reduced time and other scalars. An explicit representation of the strains follows, which isthen specialized to provide three-dimensional homogenized constitutiveequations for transversely isotropic, fiber composites. Experimentalsupport for these equations is briefly reviewed. Finally, physicalinterpretation of some of the constitutive functions is discussed usingresults from a microcracking model as well as molecular rate process andfree volume theories. It is shown that the present thermodynamicformulation leads to a generalized rate process theory that accounts for abroad distribution of thermally activated transformations in polymers.     

“均压”烧结新技术的评述与展望

首次提出了均压烧结的概念；分析了和均压烧结技术提高烧结放产质量的机理；介绍了给上部料层加压和为下部料层减压的试验结果；展望了均压烧结技术在攀钢运用的必要性与可行性。     

环境温度对压降法漏率测试的影响

介绍了差压法测量漏率的原理并结合差压测量的过程对环境温度变化的影响进行了分析 ,给出了温度修正公式 ,提出了被检系统的有效容积的测量方法     

Hybrid model for the diffusion of simple and complex penetrants in polymers

A hybrid model, which combines the characteristic features of the Pace–Datyner molecular model with those of the Kulkarni–Stern free‐volume model, was developed to assess the effect of temperature, penetrant concentration, and polymer crystallinity on penetrant diffusivity. The predictive capabilities of the proposed model were tested by a direct comparison with experimental data. The diffusivity of ethylene and propylene vapors in semicrystalline polyethylene and isotactic polypropylene was experimentally measured using a magnetic suspension microbalance. Sorption kinetic measurements were carried out at temperatures up to 80°C and pressures up to 80 atm. The diffusivity was found to increase with temperature and penetrant concentration. Apparently, there was a very good agreement between the theoretical values predicted by the new hybrid diffusion model and the experimentally determined diffusivities. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

对黄河水沙特性变化的主要认识

编者按由水利部第二届“水沙变化研究基金”和“黄河防汛科技项目”资助的《黄河水沙特性变化综合分析》课题，是黄委水科院和水文局共同主持完成的。本项目主要从河流学和河床演变学出发，充分考虑防洪、防凌和水资源的开发利用，以弄清情况、分析规律为主线，在前人成果...     

粮食通风系统的数学描述

运用热量与质量传递理论、力学定律和体积平均原理，通过深入、系统地研究，得出了粮食通风系统数学描述的热量和质量传递的连续方程，从而把通风储粮技术提到系统化、理论化和科学化的高度。     

A new edge detection method for automatic visual inspection

This paper presents a new edge-detection method which, based on simple arithmetic and logical operations, consists of three procedures: image binarisation, image contraction, and image subtraction. Experiments showed that the proposed algorithm could generate a path one pixel wide with continuous edges, and the proposed algorithm had a better edge-detection accuracy than the 4-connected, 8-connected, and the Sobel techniques. Therefore, the proposed edge-detection algorithm is feasible for use in automatic visual inspection systems.     

设有横缝的高拱坝地震反应分析方法

文中介绍了两种模拟拱坝径向横缝的力学模型，应用非直接对接的自由子结构方法，在模态子空间内建立了拱坝地震反应分析的非线性动力方程，提出了考虑动水压力影响的近似计算方法。最后通过算例说明不同径向横缝模型对拱坝地震反应的影响。     

高压下甲烷在环己烷-乙醇及苯-乙醇中的溶解度测定与研究

利用自己建立的高压下测定气体在液体中溶解度的测定装置,在15-45℃、2.0-12.0 MPa的条件下,首次测定了甲烷在环已烷-乙醇、苯-乙醇混合体系中的溶解度。用PRSV状态方程及3种不同的混合规则对实验测定的气液平衡数据进行了计算。计算结果表明,使用同一种状态方程的不同混合规则计算极性体系的气液平衡数据所得的结果不同,改变传统的混合规则可提高计算精度。同时还使用Aalto-Keskinen模型及本研究提出的Yen-Woods-Aalto-Keskinen模型对实验得到的高压液相摩尔体积进行了估算,均得到满意的结果。     

Thermodynamic properties of R 22 + R 114 mixtures in the high-density region for temperatures from 310 to 370 K

The densities for mixtures of R 22 and R 114 have been measured with the variable-volume method using a metal bellows as a function of temperature and pressure. The results for three different compositions (75, 50, and 25 mol% R 22) cover the high-density region along seven isotherms between 310 and 370 K at 15 pressures from 1.0 to 10 MPa. Based on the present density measurements, the values of the excess molar volume, the volume expansion coefficient, and the isothermal compressibility have been calculated. The excess molar volumes for each mixture below 340 K are positive, whereas those above 350 K decrease with decreasing pressure and become negative at low pressures. The behavior of the volume expansion coefficient and the isothermal compressibility for the equimolar mixture are closer to that for R 114 than the average of those for both pure components.