Simultaneous measurement of transient stress and flow birefringence in one-sided compression (biaxial extension) of a polymer melt

Summary Investigation of time dependent behaviour of a polystyrene melt is carried out with the aid of a new apparatus for biaxial extension. Use is made of the method of two impinging fluid streams guided by lubricated trumpet shaped metal walls. The flow birefringence is measured in the plane of symmetry and, at the same time, the force is measured which tends to separate the trumpets. The linear stress-optical relation turns out to be valid in this new flow geometry. An accurate value for the stress-optical coefficient can be determined from the relaxation experiments. The stress build-up as calculated from the optical measurements, is compared with the pertinent result of the theory of linear viscoelasticity. For the desired interconversion of dynamic moduli use is made of the approximation by Schwarzl and Struik. The steady state measurements are checked by the results of the non-linear model of Acierno et al.With 16 figures and 2 tables     

颗粒型砂介质的受压力学特征及屈服滑动

提出颗粒型砂介质在压实过程中的两种特征：孔隙填充状态和颗粒滑动状态；针对孔隙填充状态的力学行为特征，提出相对体积改变量(压实量)作为表征此状态的特征参量，研究了瞬时压缩模量与压实量的函数关系；针对型砂的颗粒滑动状态，提出具有强化效应的Mohr-Coulomb屈服条件，推导描述颗粒屈服滑动状态的增量本构方程、以及三轴压实过程条件下的状态本构方程，最后，就不同侧向压力下的三轴压缩试验、带模样的型砂压实试验的大量试验数据进行处理和验证。     

圆钢管型钢再生混凝土短柱偏压力学性能退化研究

为研究圆钢管型钢再生混凝土短柱在偏压荷载作用下的性能退化,进行了10个短柱试件偏心受压试验。主要分析了再生粗骨料取代率、圆钢管径厚比、型钢配钢率和偏心距等参数对试件的荷载-挠度曲线、变形能力、刚度退化及耗能能力的影响。结果表明:该短柱具有较高的承载力和抗弯刚度;与普通混凝土相比,取代率的增加对短柱的承载力和变形是不利的,试件的挠度变形随着取代率的增加而增大,再生粗骨料取代率为100%的试件偏压承载力降低了8.98%,试件刚度退化速率随着取代率的增加而加快,耗能能力逐渐降低;试件的挠度变形随着圆钢管径厚比的增大或型钢配钢率的减小而增大;试件刚度退化速率随圆钢管壁厚、型钢配钢率的增加逐渐变慢,耗能能力增强;另外,偏心距对试件偏压性能影响较为显著,随着偏心距的增大,试件刚度退化和承载力降低更加明显。     

准静态离散元方法和线性粘弹性问题的模拟

离散元方法是近年发展起来的一种新数值方法,但原则上只能用于动态问题。从静力平衡条件出发建立了离散元系统的准静态演化方程并证明了系数矩阵具有对称正定、稀疏、带状分布等特点,适用于“有效列”方法求解,该解法比高斯消去法节省更多的内存和机时。通过引入广义Maxwell体的元间作用模型建立起线性粘弹性材料准静态响应的离散元模拟方法。该方法独立于传统动态离散元方法,是传统动态离散元方法的拓展,可望在更多领域获得应用。     

自动消除载荷偏心影响的引伸计研究

本文基于拉伸圆截面试样圆周上各点的应变分析，提出一种自动消除载荷偏心影响的引伸计。该引伸计结构简单、可靠、使用方便。特别是在测定金属杨氏模量中更为适用。用电测实验对比校核的数据表明，自动消除载荷偏心影响引伸计安装在不同位置上测量的相对误差不超过０．５％。     

玻璃纤维增强聚氨酯泡沫塑料的压缩力学性能研究

本文研究了两种不同密度的玻璃纤维增强聚氨酯泡沫塑料在准静态压缩下的力学性能。给出了与相应密度的普通泡沫塑料力学性能的比较，实验结果表明：两种增强泡沫塑料在压缩载荷作用下，具有不同于普通泡沫塑料的应力－应变特性，压缩模量和强度一般均有不同程度的提高，而且对相同纤维含量的增强泡沫塑料来说，密度较高的材料增强效果较好。     

改进的 Morse 势和冲击压缩

用分子动力学方法模拟凝聚介质中一维分子链上的激波传播，以得到与冲击压缩实验相一致的结果。通过比较分子链上的孤立波解与激波的实验结果，提出对分子间Ｍｏｒｓｅ作用势进行与考虑量子效应相一致的修正，从而使分子动力学模拟得到的激波Ｕｓ－Ｕｐ关系与实验结果在波后粒子速度达到声速的范围内一致。     

POST-BUCKLING AND IMPERFECTION SENSITIVITY OF A COLUMN WITH AN EQUILATERAL TRIANGULAR CROSS-SECTION IN THE PLASTIC RANGE

The asymmetric initial post-buckling corresponding to the lowest bifurcation load andthe imperfection sensitivity are analysed in detail for a compressed simply supported column with anequilateral triangular cross-section in the plastic range.The effect of elastic unloading is taken into ac-count in the analysis.The asymptotic relations,including high order terms,among the load,the am-plitude of imperfection and the amplitude of the bifurcation mode are realized.The results show thatthe maximum supported load is very sensitive to imperfection.     

Heat transfer in bubble layers at elevated pressures

Heat transfer with steam condensation under moderate pressure on the surface of a horizontal tube immersed in a bubbling layer was experimentally investigated. A copper test section 16 mm in outer diameter and 400 mm in length was placed in a bubbling column 455 mm in diameter. Experiments were made under pressures of 0.14–0.8 MPa, with void fraction 0.04–0.23, vapor superficial velocities 0.05–0.42 m/s, liquid-wall temperature differences 47–105 K, and heat flux densities 0.12–0.8 MW/m². The heat transfer process in the bubbling layer is shown to be of a high intensity: with moderate values of steam content, heat transfer coefficients reach 12–14 kW/(m² · K). Data obtained showed that the known correlations do not consider the influence of pressure on heat transfer. For the first time, data on radial steam content distribution under pressures higher than atmospheric were obtained by an electroprobe method. A table of experimental data is presented.     

Pertubation solution of non-newtonian fluid axial laminar flow through eccentric annuli

Using the perturbation method, the axial laminar flow of Non-Newtonian fluid through an eccentric annulus is studied in the present paper. The relative eccentricity ε is taken as a perturbation parameter, and the first order perturbation solutions of the problem, such as velocity field, limit velocity and pressure gradient, are all obtained.