The relation between rheological and mechanical properties of PA6 nano- and micro-composites

A series of nanocomposites was prepared with two different methods leading to different levels of exfoliation, and the dynamic properties were measured in the solid state and the melt. The results were compared with micro-composites containing various shapes of glass filler. The higher modulus of nanocomposites at higher concentrations is accompanied by an increase in melt viscosity and the occurrence of a yield stress in the melt. The modulus at room temperature and the melt viscosity are influenced by the aspect ratio and the concentration of the filler particles. These results were used to calculate the aspect ratios of the reinforcement using the Halpin-Tsai composite model and several modified Einstein viscosity models. The experiments showed that the Simha theory for oblate and prolate spheroids predicts platelet aspect ratios from melt viscosity data that are close to the results from the Halpin-Tsai composite model and from TEM observations. The results of the analysis show the advantages and disadvantages of the various shapes and sizes of fillers and the level of exfoliation, both from a processing and a mechanical properties point of view.     

滤网板面罩落料冲孔拉伸复合模设计

本文分析了汽车滤网板面罩的结构工艺性，介绍了面罩落料冲孔拉伸复合模的总体结构及其工作过程。模具结构新颖，结构紧凑，操作简单，生产效率高。     

Considerations on Drying Frozen Spruce Wood and Effects upon Its Properties

The aricle presents the results of a research performed in order to establish whether drying lumber from frozen state (in winter) has repercussions upon its properties, compared to drying under the same conditions lumber parts originating from the same log and position within the log section but that were not frozen prior to drying. To this purpose, spruce (Picea abies L.) lumber specimens, 35 mm and 55 mm thick, cut from the same log, half frozen at - 30°C and half unfrozen, were dried under the same conditions in a climate chamber. Some mechanical properties (hardness, bending strength, and modulus elasticity in static bending), as well as workability (expressed by means of the absorbed power and specific resistance to cutting during milling), were determined The results revealed slight differences between the frozen and the unfrozen samples both during the drying process and afterwards. It was noticed that a significant amount of water was removed from wood during the very beginning of the heating phase (thawing). With regards to wood properties after drying, a slight lowering of the mechanical properties and better workability could be established for the initially frozen samples.     

A fast computation method for time scale signal denoising

This paper presents a novel and fast scheme for signal denoising in the wavelet domain. It exploits the time scale structure of the wavelet coefficients by modeling them as superposition of simple atoms, whose spreading in the time scale plane formally is the solution of a couple of differential equations. In this paper, we will show how the numerical solution of such equations can be avoided leading to a speed up of the scale linking computation. This result is achieved through a suitable projection space of the wavelet local extrema, requiring just least squares and filtering operations. Intensive experimental results show the competitive performances of the proposed approach in terms of signal to noise ratio (SNR), visual quality and computing time.     

Visual analysis of particle bouncing and its effect on pressure drop in dilute phase pneumatic conveying

During the pneumatic conveying of plastic pellets, it has been observed that materials with similar physical characteristics may develop substantial difference in pressure drop, whose cause is not fully understood. This experimental study focused on the dynamic behavior of the particles during conveying and its influence on pressure drop.The bouncing of the particles during pneumatic conveying in dilute phase was visually analyzed by means of a high speed video camera. The experiments included two different plastic pellets of similar size and density but different modulus of elasticity. The conveying trials were carried out in a 0.052 m I.D. aluminum pipe conveying system approximately 35 m long. The loading was controlled by an airflow control valve and a variable speed drive rotary valve. For each material, a series of tests were performed creating a matrix of six solids rates for five different air velocities. During the conveying trials a high speed video camera was used to record the actual particle motion in a horizontal section with fully accelerated flow. The videos showed significant difference in bouncing between the soft and the hard pellets. The soft pellets showed very random and intense bouncing with strong rotation, which affected the rebound considerably. In fact, some particles bounced even backwards. On the other side, the hard pellets showed significantly less bouncing and rotation.In addition to the high speed videos, in each test the pressure drop was measured in the horizontal and vertical directions. As expected, a significant difference in pressure drop was recorded for the same conveying settings when using the different materials. The pressure drop showed a close relation to the bouncing of the particles, being much higher for the soft pellets.It can be concluded that the increased pressure drop, developed by the soft polyethylene pellets, is in part due to the multiple times the particles must be reaccelerated during their transit through the conveying system. Additionally, the reduction in the average particle velocity increases the drag force. All of this resulted in up to 3-fold increase in pressure drop across the conveying line compared to the hard polyethylene pellets that showed significantly less bouncing.     

汽车差壳铸件的铸造工艺探讨

汽车重要的零部件之一差速器壳铸件的壁厚差异大,导致差壳铸件局部极容易出现缩松、缩孔类铸造缺陷。本文通过对模数、补缩通道的运用,在实际生产过程中有效、快速地解决了铸件的缩松、缩孔问题。     

Mechanical Properties Improvement of Waterborne Polyurethane Coating Films After Rewetting and Drying

Drying behavior of waterborne polyurethane coating under ambient conditions displays the typical three-stage drying process on compact hard substrates. When the naturally dried samples are further dried at thermal condition of 105°C, the loss of residual water was accompanied with an increase in the hardness of the films. When the coating films were immersed in water and dried at ambient condition again, the hardness and modulus increased significantly. After 180-min immersion followed by natural drying, the hardness of the film increased to almost 10 times that of the initial value. The possible reason is that the interaction between water and the hydrophobic amorphous phase of polyurethane led to a compacted amorphous phase, which decreased the free volume of the films, resulting in the increase in the hardness and modulus of the coating films.     

自编EXCEL程序调整混凝土用砂细度模数及颗粒级配

砂细度模数以及颗粒级配对混凝土和易性影响较大,砂级配不良易导致混凝土拌合物离析泌水。本文采用EX-CEL软件编制程序,以快速确定砂混合比例,使其混合后能符合Ⅱ区中砂的要求。     

Texturized alginate gels: Screening experiments to identify the important variables on gel formation and their properties

A screening experiment for the formation of alginate gels with eight variables like sodium alginate (3-5 g/100 g), calcium orthophosphate (1.5-2.5 g/100 g), glucono-δ-lactone (GDL) (1.5-2.5 g/100 g), pineapple juice (0-78 g/100 g) and sugar (0-12 g/100 g) and gel-setting variables such as pH (7-9), temperature (10-40°C) and time of gel setting (6-24 h) has been designed by employing Plackett-Burman experimental design. The response functions were the compressive textural parameters namely peak force, irrecoverable compression area or energy and strain, Young’s modulus, and the model parameters like rigidity constant (k) and degree of concavity (n). The formation of an elastic gel is favored at high pH and temperatures while the level of pineapple juice and sugar should be low. Addition of pineapple juice offers a soft gel with low stiffness/rigidity. The experimental results relating the variables and response functions fitted well (0.938 ≤ r ≤ 0.996, p ≤ 0.01) by multivariate linear equations indicating the suitability of the Plackett-Burman design to identify important variables of gel formation. Among the variables, in general, the effect of pineapple juice > glucono-δ-lactone (GDL) > sodium alginate > temperature while other variables had marginal effects.     

一种抵抗水声信道多途干扰的新的盲均衡算法

由于在时变水声信道中会产生随机相位失真，CMA算法的误码性能严重下降。在双模式盲均衡算法的基础上，提出了一种适用于水声信道的新的盲均衡算法——NCMA算法。计算机仿真结果表明，在时变水声信道中，该算法性能优于双模式算法，能够达到对信号相位失真的恢复，并且收敛性能优于双模式算法。