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This investigation examines the transient deformation and heat generation of a solid polyurethane subjected to dynamic compression. A special method is presented to prepare the solid polyurethane from raw materials which are commonly used to make polyurethane foams. Testing methods including infrared spectrum, differential scanning calorimetry, quasi-static and dynamic compression were applied to study the basic physical properties of the solid polyurethane. High-speed optical and infrared imaging systems are used to obtain visual and thermo-graphic images during impact tests. Under quasi-static compression, the solid polyurethane presents a good performance in toughness. This is confirmed by its Poisson's ratio. Under impact compression, the adiabatic heat generation are identified statistically. Temperature distribution confirms the fact of transient heat generation in specimens. Adiabatic self-heating mechanism provides a consideration to understand the negative strain-rate effect and post-yield softening effect found in the solid polyurethane. Mechanical properties including quasi-static and dynamic responses are related with the composition of molecular and structure of polymer. 相似文献
154.
《Journal of computational chemistry》2017,38(13):998-1004
Aiming at developing an affordable and easily implementable computational protocol for routine prediction of spectral properties of rigid molecular dyes, density functional theory, and time‐dependent density functional theory were used in conjunction with a vibronic coupling scheme for band shape estimate. To predict the perceived color of molecules in solution, a model has been setup linking the UV‐vis spectra predicted at ab initio level to the L *a *b * colorimetric parameters. The results show that a mixed protocol, implying the use of a global hybrid functional for the prediction of adiabatic energy differences and a range separated hybrid for the prediction of potential energy curvature, allows perceived colors to be quantitatively predicted, as demonstrated by the comparison of L *a *b * colorimetric parameters obtained from computed and experimental spectra. © 2017 Wiley Periodicals, Inc. 相似文献
155.
本文定量分析了"瑞利球"实验的动力学过程。"瑞利球"实验中构建了一个"怪坡",通过对两导轨的控制,使均质圆球看起来像在"爬坡"。文中据刚体运动原理构建了物理模型,并分析系统的受力情况和运动过程,导出了均质圆球"爬坡"的最大高度的公式。在忽略空气阻力与摩擦力情况下,当两导轨杆初始距离远小于圆球半径、小球刚好不能掉落时突然合拢两导轨使其平行、两导轨初始夹角等于两倍导轨倾斜角时,均质圆球可以达到最大高度和最远距离。 相似文献
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A parallel-plate rheomete was constructed and used to study the development of dynamic shear modulus and cell opening under forced adiabatic conditions for a series of flexible slabstock polyurethane foams. Typical industrial formulations were used. The plates were heated to follow the adiabatic temperature profile of a real foam bun during foaming. The rheometer overcomes difficulties encountered in other methods such as heat loss and bubble damage caused by the probe.A four-stage modulus development profile was observed: initial bubble growth, bubble network, polymer stiffening and final curing. Chemical structure development was also studied under forced adiabatic conditions, using Fourier transform infrared spectroscopy. Polymer stiffening coincided with bidentate (hydrogen-bonded) urea formation.The normal force exerted by the expanding foam on the plates was found to be a function of the rate of foam expansion and the foam modulus. A sudden drop in the normal force typically coincides with the visually observed blow-off in the reacting foam bun, thus the normal force profile is a new and accurate indicator of cell opening. The normal force profile clearly shows that cell opening occurs just after the onset of polymer stiffening, thus illustrating the role of polymer rheology in the cell opening mechanism.Dedicated to the memory of Professor Tasos C. PapanastasiouPortions presented at the SPI Polyurethanes Technical/Marketing Conference, October 9–12, 1994, Boston, massachusetts, USA (Best paper award) and at the XIIth International Congress on Rheology, August 18–23, 1996, Québec City, Québec, Canada. 相似文献
158.
玻璃纤维增强聚氨酯泡沫塑料的压缩力学性能研究 总被引:12,自引:0,他引:12
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。 相似文献
159.
本文将空间轴对称问题的Папковиц-Neuber通解用复变量广义解析函数表示,推导出用复变函数法求解空间轴对称问题的基本公式,并以此为工具求得了含球形空腔或刚性夹杂的中厚圆板在轴对称弯曲变形时的完全解. 相似文献
160.