RTM工艺干斑缺陷形成分析及其两相流仿真预测研究

本文针对干斑形成过程的两相流仿真预测技术进行了研究。首先分析了树脂宏观流动前沿包络形成干斑及之后的演变过程,讨论了排除干斑的方法。然后建立了RTM充模过程中树脂-空气两相流动数学模型,通过对Fluent软件进行二次开发实现了充模过程以及干斑缺陷形成过程的两相流仿真预测。最后,通过对边缘效应导致的干斑形成过程进行仿真,验证了上述算法的正确性。     

RTM工艺中气泡形成及消除研究

总结了关于RTM（树脂压铸）工艺中气泡缺陷的文献报道，对RTM中气泡缺陷的形成机理、影响因素及各研究者提出的消泡方法、理论和模型进行了概述，同时对RTM工艺中气泡缺陷的研究现状给予充分关注，并对RTM缺陷研究的未来方向进行了展望。     

正弦波形梁构件的RTM工艺模拟研究

本文采用PAM-RTM软件对航空用正弦波形梁典型构件进行了模拟分析,对构件进行了几何建模及有限元划分,选择构件不同位置采用线注胶或点注胶的注射方式对构件进行了常压力注射下RTM工艺模拟研究,由此确定了最佳注射方式以及注胶口、出胶口位置,根据干斑缺陷可能出现的位置优化了出胶口的设置,得到了无缺陷的构件制品并对预成型体铺放过程中可能出现的边缘效应对树脂流动及干斑缺陷的影响进行了研究。研究表明：合理设置出胶口是一种较好的消除干斑缺陷的方法,计算机RTM模拟为复合材料模具设计及构件制造提供了重要依据。     

一种新型抛晶干粒的试制

探讨了一种陶瓷专用试剂――新型抛晶干粒的试制,并针对其在使用过程出现的缺陷问题如釉层透明度、釉面针孔和釉层气泡、干粒和砖坯膨胀系数不相匹配等进行了分析和讨论。     

PC注塑制品常见缺陷分析及解决方法

针对聚碳酸酯(PC)粘度高、热稳定性较差、成型加工困难的情况，对多年来注塑过程中遇到的各种制品缺陷及所采取的措施进行了深入的分析、总结。介绍了PC的加工特性及注塑制品中常见的变色、银纹、气泡、冷料斑及内应力等缺陷，分析其成因并提出了相应的解决方案。     

泡沫玻璃气泡缺陷与解决方案

泡沫玻璃是一种具有均匀气泡结构的玻璃制品,具有隔热、吸声、防潮、防火等特点的轻质高强建筑材料和装饰材料。泡沫玻璃的生产过程中,经常会遇到气泡结构不均或大气泡等气泡缺陷。本文从气泡的产生机理分析入手,针对具体的气泡缺陷种类,分析产生原因,提出解决方案,更好地实现泡沫玻璃的内在和外观质量。     

真空辅助RTM工艺中孔隙的形成机理及实时控制研究

根据国内外的研究成果对真空辅助树脂传递成型(RTM)工艺过程中气泡的形成机理进行了分析总结,同时介绍了几种真空辅助RTM实时过程控制方法.研究结果表明,实时过程控制能够减少孔隙形成的几率,改善流动前沿均匀性,缩短注胶时间,是提高复合材料产品质量的重要方法.     

汽车夹层玻璃高压气泡、脱胶原因分析及解决方案

本文针对汽车夹层玻璃生产过程中出现的常见缺陷,如高压气泡、脱胶,从生产过程的各个环节着手分析,探讨了各种影响高压气泡、脱胶的因素,并提出了相应的工艺解决方案和生产防范措施。     

陶瓷大板表面装饰胶合保色釉的研究应用

建筑陶瓷产品表面缺陷一般有色差、针孔、气泡等,相对传统规格增大4～8倍的陶瓷大板而言,其表面缺陷率和产品不良率增加。针对陶瓷大板表面缺陷及干粒不均等问题,笔者研究一种胶合保色釉及其应用。     

RTM工艺过程缺陷产生机理分析

本文全面分析了RTM工艺过程中缺陷产生的原因,并讨论了如何根据缺陷的特征找出问题的根源。     

Influence of alcohol pre‐infusion on the quality of VARTM composites

In the vacuum assisted resin transfer molding (VARTM) process, part‐to‐part variations such as the uncertainty in the permeability and race tracking phenomenon make it difficult to achieve consistent mold filling and ensure part quality of composites. Alcohol pre‐infusion was presented in this study as a novel real‐time monitoring and control approach for the flow process in the VARTM process, alcohol test fluid is infused before the actual resin infusion to locate the potential dry spots without using the large quantity of sensors. Then corresponding process control strategy is designed, such as opening the auxiliary gate at specific moment on those predicted dry spot locations to compensate flow defects. Moreover, alcohol can be easily removed by heat without changing the local permeability. The influence of alcohol pre‐infusion on the quality of VARTM composites were investigated in this study. The mechanical tests were conducted to verify that the alcohol pre‐infusion approach has no significant effect on composite properties because alcohol can be removed from fiber by heat and air flow. Specifically, DMA, TGA, and FTIR spectrum proved that negligible difference existed on the resin–fiber interface between the composites with or without alcohol pre‐infusion. Finally, the microscopy results revealed a similar failure path in a resin matrix. TMA results also demonstrated similar dimension stability. This alcohol pre‐infusion approach was effective when compared with computer simulation and could eliminate the occurrence of dry spots and voids without using sensors or data‐acquisition system. The control schemes were shown in a case study to be capable of compensating the flow defects and achieving desired fill patterns in the face of permeability uncertainty. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers     

Property modifications in poly(p-phenylene benzobisthiazole) fibers with high-tension and high-temperature drying versus postprocessing heat treatment

Modifications in the structure and mechanics of poly(p-phenylene benzobisthiazole) (PBT) fibers have been attempted through high-tension and hightemperature drying and subsequent postprocessing heat treatment experiments. High-tension drying results in an enhancement in tensile properties by offsetting compressive shrinkage stresses during the drying process and improving the molecular alignment within the fiber. Elevated temperature drying under tension further improves the extent and perfection of the lateral molecular order. The increased molecular ordering and improved tensile properties are believed to result from the removal of water and residual acid at elevated temperatures. The final fiber properties after subsequent postprocessing heat treatment are independent of the drying conditions. These results suggest that the ultimate fiber properties are a function of the total strain imposed in all the processing operations (dry jet stretch region, coagulation and drying process, postprocessing heat treatment). The attainment of the fiber's theoretical highmodulus/high-strength properties appears limited by defects such as voids and internal stresses which, in turn, restrict the amount of strain imposed during the fiber process.     

Void formation model and measuring method of void formation condition during hot pressing process

For resin matrix composites, voids are common defects that can seriously deteriorate the properties of the composite parts. Thus, the elimination of voids is a crucial element in controlling the manufacturing process of composite parts. This article focuses on void formation originating from hygroscopic water for resin matrix composite laminates prepared with hot pressing process. The Kardos void formation model was developed to analyze the critical resin pressure for the initiation of voids, and the influencing factors were investigated experimentally to validate the modified model. It is found that resin pressure and gel temperature are the two key parameters to control void defects and that entrapped air in prepreg stacks must be considered in the void formation model. Furthermore, a simple method was established to measure the relationship between porosity and the processing parameters, and the void formation conditions of the resin and the prepreg stack were also studied. The theoretically predicted void formation conditions and the experimental results were compatible for the studied cases. These results are valuable for eliminating void defects, optimizing processing parameters, and enhancing the performance of composite parts. POLYM. COMPOS., 31:1562–1571, 2010. © 2009 Society of Plastics Engineers     

Effect of electrostatic assist and gravure process parameters on voids and dot skips reduction in shrink PVC film

Gravure is the most popular process used to print on shrink films for larger volume runs and high-quality reproduction. Polyvinyl chloride (PVC) holds the major share in shrink application. However, print defects such as voids and dot skips are the major concern while printing on shrink PVC film. The presence of these defects degrades the print quality and causes print rejections. The electrostatic assist (ESA) in gravure is designed to eliminate dot skips; however, the effect of ESA parameters such as air gap and voltage on print defects needs to be explored in depth. Thus, this study aims to minimize print defects by optimization of gravure process parameters. The study investigates the effect of process parameters such as line screen, air gap (distance between charge bar and impression roller), viscosity, voltage and speed on voids and dot skips. A general full factorial was designed and statistical model was developed to determine the influence of each process parameter on defect minimization. The results showed the significance of all the process parameters in reduction of dot skips and void area. The improved ink transfer with ESA resulted in elimination of dot skips and minimization of void area by 96%.     

Synthesis,characterization of hierarchical TS-1 and its catalytic performance for cyclohexanone ammoximation

A hierarchical titanium silicate (TS-1) that possesses large open voids has been prepared by using a dissolution/re-crystallization process. Carbon black was introduced as a hard template during the synthesis process to generate defects both inside and on the surface of crystals, then TPAOH post-treatment was applied, as a result, a novel TS-1 zeolite crystal with large open voids was successfully synthesized. The synthesized hierarchical TS-1 was characterized by XRD, FTIR, SEM, TEM and N₂ physisorption. Compared with the traditional TS-1 and hollow TS-1, the activity of hierarchical TS-1 in cyclohexanone ammoximation was improved and attributed to the macropores that linked the voids inside the zeolite directly to the outer surface.     

Phase transformation and oxidation behavior of Pt-modified MCrAlY coatings

The effects of platinum (Pt) layer on phase transformation and oxidation behavior of MCrAlY (M = Co, Ni) coatings were investigated by isothermal and cyclic oxidation tests at temperature of 1100 °C. Pt layer of about 5 μm thickness was deposited on MAR M247-DS superalloy by an electroplating method, and then the MCrAlY layers were coated with air plasma spray (APS) and vacuum plasma spray (VPS) methods. APS process creates internal oxides and interface voids, whereas the VPS process shows fewer voids in the interface between the MCrAlY layer and the superalloy used as substrate. The oxides and voids formed in the APS process deteriorate the oxidation resistance, indicating that the oxides and voids are transferred to Al₂O₃ compounds during the oxidation tests. The Pt layer shows a strong affinity with Ni element and a weak affinity with Co and Cr elements, resulting in the formation of β-(Ni,Pt)Al phase. The Pt pre-coated layer forces down for the diffusion of soluble elements to get the reduced deplete zone in the superalloy. The VPS process enhances the oxidation resistance of the MCrAlY coating and shows better bonding strength, owing to the generation of homogenous microstructure in the coating and less processing defects.     

Absorption of water into carbon fibre composites

The environmental behaviour of carbon fibre composites is being investigated. Water pick-up data obtained during these studies are analysed in an attempt to develop an understanding of the absorption mechanism. There is evidence which indicates that voids and defects in the composite have a marked effect on the absorption process and may assume greater significance than the diffusion process through the resin. Comments are made as to the possibility of the reversible behaviour of the composites on drying out being associated with hydrogen bonding phenomena. The need to know the size and location of voids is also stressed.     

Effect of gravure process variables on void area in shrink film

The gravure print quality on shrink film depends on process parameters and is fairly gaged by minimum print defects such as voids. The visibility of these defects is visually disturbing and could result in product rejection. This article investigates the effect of process parameters such as viscosity, speed, hardness, and line screen frequency on ink transfer from recess gravure cells and hence on print voids in an attempt to minimize them. A general full factorial design with the abovementioned four independent variables was analyzed by variance, main, and interaction effects. The results revealed line screen, hardness, and ink viscosity as the most influential factors in minimizing the defect. A regression model was developed to predict void area. The model was validated by conducting an additional 11 runs on the press. The predicted values from the model were in close agreement with the press results. The results showed a commendable decrease in the void area by 65%.     

大丝束CF/EP汽车地板VARTM模拟与高温力学性能

汽车轻量化是全球面临的共同问题,采用更具成本优势的大丝束碳纤维（CF）增强复合材料是实现汽车轻量化结构化的重要途径。然而,大丝束碳纤维在液体成型时,单束过多的纤维丝易导致纤维束内微观浸润困难,易产生干斑、气泡等缺陷。同时,传统的汽车电泳烘干工艺对复合材料的高温性能提出了挑战。鉴于此,本文采用0°/90°双轴向缝编大丝束碳纤布和耐高温环氧树脂（EP）,开展了纤维渗透率测试和汽车地板真空辅助树脂传递成型（VARTM）模拟优化研究,设计、制造了成型模具,成功试制出汽车地板样件,超景深显微镜观测显示纤维束内和层间浸润良好,无明显缺陷。高温在线拉伸和应变测试显示,温度对材料拉伸模量影响显著而对强度影响不大,180℃高温下应变恢复能力良好,表明该材料在高温下仍具备较好的强度和抗蠕变性能,该结果对指导复合材料能否通过传统汽车的电泳烘干工艺具有重要意义。     

Concerning the microstructure of dry-RO membranes

The microstructure of cellulose acetate reverse osmosis membranes which have been prepared by the Kesting dry process has been elucidated with the aid of scanning and transmission electron microscopy. The dry-RO membranes consist of three layers: skin, transition layer, and substructure. The gel morphology of each of these layers originates in its sol precursors within the nascent membrane which manage to survive the sol → gel transition intact. The dense skin layer is composed of aggregates of tiny, slightly ellipsoidal nodules which are believed to be paracrystalline in nature. Immediately beneath the skin lies the transition layer, a narrow band of intermediate density consisting of widely separated closed cells. Below the latter lies the porous substructure which is composed of micrometer-sized, open-celled voids. Because of the size of their substructural voids, dry-RO membranes are able to reversibly undergo wet–dry cycling without densification and loss of permeability.