Shrinkage influenced by chain rupture during tensile deformation

Tests are described in which wet shrinkage is observed subsequent to strain annealing of nylon 6 fibers. The wet shrinkage studies demonstrated a large mobilizing effect by water present in the polymer structure even after very high temperature annealing treatments. Transitions in shrinkage behavior after strain-annealing treatments were experimentally observed at strains corresponding to the onset of chain rupture. The shrinkage might be attributed to chain refolding. The apparent activation energy for the processes was approximately 10 kcal/mole for the annealed nylon 6 samples, compared to published values of 14 kcal/mole for nylon 66 fibers.

An analysis of the tension required to maintain a fixed strain on the material indicates that an entropic rearrangement is predominent up to 5% strain. Above this strain, apparently, an enthalpic rearrangement takes over.     

用布喇格光纤光栅传感器测定口腔复合树脂材料光固化收缩与温度演化特性

复合树脂材料已成为重要的牙齿美容修复材料.本文利用两种布喇格光纤光栅传感器测定了口腔复合树脂材料在光固化过程中的收缩与温度演化特性.一种为普通的光纤布喇格光栅,另一种为经过了化学镀镍的光纤布喇格光栅,同时埋入复合树脂样品中,用光照射使其固化,测得光纤布喇格光栅在固化过程中温度和应力随时间的演化曲线.实验结果表明,在光固化过程中,因为聚合反应,树脂产生了强烈的收缩应力和温度变化.掌握复合树脂的光固化收缩特性和温度变化特性对不断改良材料性能以及优化口腔材料的治疗效果具有实际意义.     

用布喇格光纤光栅传感器测定口腔复合树脂材料光固化收缩与温度演化特性

复合树脂材料已成为重要的牙齿美容修复材料.本文利用两种布喇格光纤光栅传感器测定了口腔复合树脂材料在光固化过程中的收缩与温度演化特性.一种为普通的光纤布喇格光栅,另一种为经过了化学镀镍的光纤布喇格光栅,同时埋入复合树脂样品中,用光照射使其固化,测得光纤布喇格光栅在固化过程中温度和应力随时间的演化曲线.实验结果表明,在光固化过程中,因为聚合反应,树脂产生了强烈的收缩应力和温度变化.掌握复合树脂的光固化收缩特性和温度变化特性对不断改良材料性能以及优化口腔材料的治疗效果具有实际意义.     

Simulation of injection-compression molding for thin and large battery housing

Injection compression molding (ICM) is an advantageous processing method for producing thin and large polymeric parts in a robust manner. In the current study, we employed the ICM process for an energy-related application, i.e., thin and large polymeric battery case. A mold for manufacturing the battery case was fabricated using injection molding. The filling behavior of molten polymer in the mold cavity was investigated experimentally. To provide an in-depth understanding of the ICM process, ICM and normal injection molding processes were compared numerically. It was found that the ICM had a relatively low filling pressure, which resulted in reduced shrinkage and warpage of the final products. Effect of the parting line gap on the ICM characteristics, such as filling pressure, clamping force, filling time, volumetric shrinkage, and warpage, was analyzed via numerical simulation. The smaller gap in the ICM parting line led to the better dimensional stability in the finished product. The ICM sample using a 0.1 mm gap showed a 76% reduction in the dimensional deflection compared with the normal injection molded part.     

光漂白聚合物波导折射率轮廓的确定

通过实验发现了光漂白聚合物薄膜厚度随光照时间按指数衰减的规律收缩,在此基础上,利用ｍ线法和精确的转移矩阵理论,由数值拟合得到的聚合物波导的折射率轮廓为费米函数。     

Self degradation of polymer electrolyte based dye-sensitized solar cells and their remedy

Self degradation of dye-sensitized solar cells (DSSC) has been observed due to shrinkage of the polymer electrolytes at room temperature with a relatively high humidity atmosphere. The cell efficiency has also shown to depend on the shrinkage of the polymer. The actual interface area between the polymer electrolyte and the dye soaked nanoporous TiO₂ electrode has been observed to become reduced for alkali salt complexed poly(ethylene oxide) (PEO) polymer electrolyte. This problem can relatively easily be reduced by two step casting and by incorporating ionic liquids in the polymer electrolyte. A possible reason has been sought as the reduced crystallinity and growth of spherulites in the polymer matrix.     

Raman study on the pressure-induced disordered state of polystyrene

The pressure-induced disordered state was first reported for iPS, the polymer showing thermal shrinkage. The low-frequency Raman study showed clearly that pressure introduces irregularity into the polymer backbone of iPS. It has also been revealed that there exist two types of vibrational modes, which show different sensitivities on the regularity of the main chain. These modes indicate two distinctive features of dispersion in the ordered form. In the disordered state, the dispersive modes smear out and the dispersionless one survives to be observed. We conclude that pressure causes the ordered-disordered conversion like thermal shrinkage. This conversion will be a common feature of the polymers showing thermal shrinkage and would be able to take place at relatively low pressure.     

Structural and phase changes in metals during formation of the fatigue fracture surface in metals and alloys

The mechanisms of deformation-induced structural and phase changes, which accompany crack nucleation and growth during fatigue fracture of metals and alloys, are considered. It is shown that the crack steady growth phase is determined by the processes of local melting of the material in extension phase, and melt crystallization processes with formation of shrinkage pores in front of the crack tip in the unloading phases and crack narrowing.     

Nano-sized patterns derived from a SiCN preceramic polymer: Fabrication and their characterization

A microfabrication of ceramic materials with a low shrinkage has created inevitable demands in the fields of micro total analysis systems (μ-TAS) and microfluidic devices with thermal, chemical, and mechanical stability. In this study, nano-sized patterns were prepared using a soft lithographic technique, followed by the UV and thermal curation of a non-oxide SiCN preceramic polymer. The characterization of the thermal and mechanical properties of the cured preceramic polymer revealed that it becomes ceramic-like after the heat treatment at higher temperature than 600 °C. The heat-treated nano-sized patterns showed a low linear shrinkage as well as good chemical stability and optical properties. The results showed the feasibility of enormous potentials of the cured preceramic polymer because of the low shrinkage, the high optical transparency, and the thermal and chemical stability.     

Total Strain of Newtonian Fluids in a Vane Extruder

The vane extruder, which makes a polymer suffer elongation stress much larger than shearing stress, is an innovational equipment in polymer processing. A physical model and a mathematical model are established to analyze the mixing characteristics in polymer processing, namely, the two important functions of residence time distribution and strain distribution function are obtained. It is shown that the direction of total strain gradient is consistent with the orientation of the material flow. The results show that the vane extruder has an advantage over traditional screw extruders due to it being based on elongational rheology.     

Tensile drawing of high and low molecular weight polyethylene terephthalate

The tensile drawing of polyethylene terephthalate fibers spun from polymer of high and low molecular weight over a range of windup speeds has been studied. An analysis of the mechanical properties, orientation, and shrinkage behavior for different draw ratios leads to two conclusions. First, the network structure is the same for both polymers and the same as that described for a medium molecular weight polymer in an earlier paper. Secondly, an increase in molecular weight has an effect similar to an increase in the windup speed on the spun fiber molecular structure, which affects the ultimate mechanical properties obtainable by the chosen processing routes.     

Massive lepton pair production and the size of the photon

An intuitive picture for understanding scaling in hadronic as well as non hadronic processes is proposed which makes use of shrinkage of the size of the particle with its mass. An explicit model in agreement with experiment is also discussed.     

Fabrication of reflective holographic gratings with polyurethane acrylate (PUA)

The effects of prepolymer molecular structure were studied in terms of reflection efficiency, polymer grating shrinkage and electro-optic property. Especially, efforts have been made to quantify holographic grating shrinkage during fabrication by modifying the chemical structure of segmented polyurethane acrylates.     

Al-Mg合金中锯齿形屈服现象的热分析

研究了在室温、定加载应变率拉伸的情况下Al-Mg合金中的锯齿形屈服现象.伴随着锯齿形屈服现象的发生,试件表面温度场会发生变化.而红外相机能以较高的时间、空间分辨率记录下随时间变化的试件表面温度场图像.通过分析这些热图像,探讨了A,B两种类型带的传播规律,得到了局域变形带的带宽、倾角、传播速度等特征参数.在此基础上,引入热传导方程,求得了带内的应变率.实验和计算都发现B类型带产生时试件表面带外区域存在弹性收缩现象,由此提出以是否存在带外收缩变形作为划分A,B类型带的新标准.     

Relaxation dynamics at different time scales in electrostatic complexes: time-salt superposition

In this Letter we show that in the rheology of electrostatically assembled soft materials, salt concentration plays a similar role as temperature for polymer melts, and as strain rate for soft solids. We rescale linear and nonlinear rheological data of a set of model electrostatic complexes at different salt concentrations to access a range of time scales that is otherwise inaccessible. This provides new insights into the relaxation mechanisms of electrostatic complexes, which we rationalize in terms of a microscopic mechanism underlying salt-enhanced activated processes.     

Dependence of solvent crazing in bisphenol–A polycarbonate on molecular weight of organic liquids

Solvent crazing has been investigated for bisphenol-A poly-carbonate exposed to the liquids of n-alcohols, di-n-alkylphthalates, and adipic acid polyesters. The critical strain at which crazes appeared was determined with a Bergen elliptical strain device. In the case of the n-alcohol and di-n-alkylphthalate liquids with a small number of carbons in the alkyl chain, crazes spread rapidly to areas of lower strain with time and ceased within 30 min at room temperature. Such a lower limiting value of critical strain can be predicted by using polar-nonpolar solubility parameter plotting representations employing the molar volume term. On the other hand, craze initiation was more delayed for two higher molecular weight liquids, di-n-octylphthalate and adipic acid polyester. Sorption studies were also conducted on polycarbonate immersed in both liquids. The values of the activation energy and diffusion coefficient estimated from the experimental data on craze initiation were found to be nearly comparable with the ones from the sorption experiments. In conclusion, the induction time-that is, the time at which crazes appear for a given strain–is controlled by the diffusion of the crazing liquid into the polymer. Thus, in the case of these liquids, which are miscible with the polymer, the crazing mechanism can be explained in terms of facilitated craze formation of a plasticized polymer.     

Nanostructural self-organization and dynamic adaptation of metal–polymer tribosystems

The results of investigating the effect of nanosize modifiers of a polymer matrix on the nanostructural self-organization of polymer composites and dynamic adaptation of metal–polymer tribosystems, which considerably affect the wear resistance of polymer composite materials, have been analyzed. It has been shown that the physicochemical nanostructural self-organization processes are developed in metal–polymer tribosystems with the formation of thermotropic liquid-crystal structures of the polymer matrix, followed by the transition of the system to the stationary state with a negative feedback that ensures dynamic adaptation of the tribosystem to given operating conditions.     

Method for measuring wave parameters in films from electric signal detection

The complex method for determining the characteristics of wave processes, which was approved earlier in testing fibers, is modified to the case of polymer film samples. Registration of electric signals by antennas in the rf range at the instants of passage of an elastic longitudinal unloading wave in a narrow film strip after a preset initial quasi-static tension makes it possible to determine the wave velocity. The mass velocity behind the wave front was determined from the frames of high-speed video recording of motion of the free edge of the strip after its failure. These data are used for determining the jumps in strain and stress at the wave front and the instantaneous Young modulus corresponding to this wave process.