【作者】 张伟；

【导师】 柳和生；

【作者基本信息】 南昌大学 ， 机械工程， 2019， 硕士

【摘要】 纤维增强聚合物复合材料不仅能够很好地保留原有聚合物基体的性能,而且还能提高其成型制品的力学性能,现阶段被广泛应用于实际生产生活中。注射成型是纤维增强聚合物复合材料主要成型方式之一,水辅助注射成型(water-assisted injection molding,WAIM)技术是现阶段最具有发展潜力的新兴流体辅助注射成型技术之一,且相比于气体辅助注射成型技术和传统注射成型技术,其优势明显,应用前景也更广泛。通过水辅助注射成型短纤维增强聚合物制品不仅能够很好地保留WAIM纯树脂制品的质量,而且还具有复合材料制品优良的机械性能等优势,但是目前国内外关于水辅助注射成型技术的研究主要集中在成型纯树脂制品方面的研究,而关于纤维增强聚合物水辅助注射成型制品的研究甚少,因此明晰相关参数对短纤维增强聚合物水辅助注射成型制品质量的影响机理至关重要。本文利用三维数值模拟技术与实验相结合的方法进行了短纤维增强聚合物圆管件水辅助注射成型机理研究,以期对以后实际生产加工提供可靠的技术指导。本文的主要工作及相关结论总结如下:(1)对水辅助注射成型技术的两种主要成型工艺的工作原理以及研究进展进行了相关的概述。(2)基于聚合物加工流变学建立了短纤维增强聚合物水辅助注射成型数值模拟中多相流体的充填方程,以及对纤维取向模型的相关演变进行了概述。(3)借助于现有的商业3D注射成型软件进行了数值模拟实验,研究了相关注射成型工艺参数和纤维重量百分比对短射法水辅助注射成型中高压水穿透长度的影响,并进行了实验验证。结果发现:在短射法水辅助注射成型数值模拟中,高压水在20%短纤维增强聚丙烯(short glass fiber reinforced PP,SGFRPP)熔体中的穿透长度随着熔体短射量和注水压力的增加而下降;随着注水延迟时间的增加而增加;而随着熔体温度的升高只是略微的变化;此外,还发现高压水的穿透长度随着纤维含量的增加而减小。实验结果与数值结果相一致。(4)通过数值模拟和水辅助注射实验研究了相关工艺参数和纤维含量百分比对溢流法水辅助注射成型圆管件制品残余壁厚的影响,结果表明:制品的残余壁厚随着注水压力的升高而降低,随着注水延迟时间的增加而增加,而熔体温度对制品残余壁厚影响不明显;实验结果与数值模拟结果相一致。此外,还发现制品的残余壁厚随着注水压力的升高而越来越均匀,而随着注水延迟时间的增加而变得较不均匀;当注水压力较低时(6MPa)时,高压水穿透过程平稳性随着纤维含量的增加而下降,而且在制品中后段这种现象表现出较为显著。(5)通过数值模拟研究了OWAIM一个成型周期内制品整个厚度不同位置处的纤维取向状态随时间的变化情况,结果表明:当未注入高压水时,在制品厚度不同位置处的纤维取向呈现出典型的“皮芯”结构;随着高压水的注入,制品芯层的纤维取向得到了很好地改善。此外,还发现可以根据纤维取向将WAIM制品厚度分为三个区域(即水道层、芯层、壳层),制品的壳层区域的纤维只是沿聚合物流动方向稍微形成取向,数值模拟结果与实验结论相一致。(6)通过数值模拟研究了相关工艺参数对OWAIM制品中纤维取向的影响,发现随着注水压力的升高,制品初始段位置的纤维取向无序区域变短;当注水延迟时间为3s时,制品初始段位置的纤维取向无序区域变短,而在中后段位置随着注水延迟时间的增加,纤维取向的有序区域减少;相较于210℃和270℃,成型熔体温度为250℃时,制品中的纤维有序区域相对最厚。数值模拟与实验结论相一致。(7)通过实验对比了较低水压(6MPa)和较高水压(10MPa)下纤维含量对OWAIM制品不同区域的纤维沿流动方向形成有序取向区域的影响,发现当水压6MPa时,在制品的初始段区域纤维的有序区域随着材料中纤维含量的增加而减小;而在制品的中后段纤维的有序区域随着材料中纤维含量的增加而增加,且这种现象在制品末端S5区域表现的最显著。而当注水压力较高(10MPa)时,随着成型材料中纤维含量的增加,制品初始段S1处的纤维沿流动方向的有序区域逐渐减小,但在制品的末端区域S4、S5区域的随着纤维含量的增加,水道层纤维分布更有序。更多还原

【Abstract】 Fiber reinforced polymer composites is not only can retain the properties of the original polymer matrix,but also can improve the mechanical properties of the molded parts.At this stage,they are widely used in actual production and life.Injection molding is one of the main processing methods of fiber reinforced polymer composites.Water-assisted injection molding(WAIM)technology is one of the most promising newly fluid-assisted injection molding technologies at this stage.Compared with gas-assisted injection molding technology and traditional injection molding technology,it has obvious advantages and wider application prospects.And water-assisted injection molding short fiber reinforced polymer products is not only can well retain the quality of WAIM pure resin,but also it has the advantages of excellent mechanical properties of composite products.However,the research on water-assisted injection molding technology at our country or abroad mainly focuses on the research of pure resin,while the research on water-assisted injection molding of fiber reinforced polymer is rare.Therefore,it is important to study the influence mechanism of relevant parameters on the short fiber reinforced polymer water-assisted injection molding products.In this paper,the combination of three-dimensional numerical simulation technology and experiment is used to study the mechanism of water-assisted injection molding of short fiber reinforced polymer round pipe parts,in order to improve the technical guidance for the actual production and processing in the future.The main work and related conclusions of this paper are summarized as follows:(1)The working principle and research progress of two molding methods for water-assisted injection molding technology were summarized.(2)Based on the rheology of polymer processing,the filling equation of multiphase fluid in the numerical simulation of short fiber reinforced polymer water-assisted injection molding was established,and the related evolution of fiber orientation model was summarized.(3)The numerical simulation experiment was carried out with the help of the existing commercial 3D injection molding software to study the effects of relevant injection molding process parameters and fiber weight percentage on the penetration length of high pressure water in short-shot water-assisted injection molding,and which was verified by experiments.It was found that in the numerical simulation of short-shot water-assisted injection molding,the penetration length of high-pressure water in 20% short glass fiber reinforce PP(SGFRPP)melts decreased with the increase of short shot size and water injection pressure;it increased with the increase of the water injection delay time;and the melt temperature increased only had slightly effected on water penetration length;in addition,it was found that the penetration length of the high pressure water decreased with the increase of the fiber content.The experimental results are consistent with the numerical results.(4)The effects of relevant process parameters and fiber content percentage on the residual wall thickness of overflow water-assisted injection molding round pipe were studied by numerical simulation and experiments.In the numerical simulation of overflow water-assisted injection molding,the results showed that the residual wall thickness of the product decreased with the increase of water injection pressure,and increased with the increase of water injection delay time,and the melt temperature had slightly effected on the residual wall thickness of the product;the experimental results are consistent with the numerical simulation results.In addition,it was also found that the residual wall thickness of the product became more and more uniform with the increase of the water injection pressure,and became more uneven with the increase of the water injection delay time;when the water injection pressure is low(6MPa),the stability of high-pressure water penetration process decreased with the increase of fiber content,and this phenomenon was more obvious in the end of the product.(5)Numerical simulation was carried out to study the change of fiber orientation across the thickness of the product in a molding cycle of OWAIM.It was found that when the high pressure water was not injected,the fiber orientation of the product along the different thickness showed a typical "skin-core" structure.With the injection of high pressure water,the fiber orientation at the core layer of the product was well improved.In addition,it has been found that the WAIM product can be divided into three regions(water channel layer,core layer,and shell layer)according to the fiber orientation across the thickness,and the fibers in the shell region of the product are only slightly oriented along the polymer flow direction,numerical simulation results consistent with the experimental conclusions.(6)The effects of relevant process parameters on fiber orientation in OWAIM products were studied by numerical simulation.It was found that with the increase of water injection pressure,the fiber orientation disordered region at the initial segment of the product became shorter;when the water injection delay time is 3s,the fiber orientation disordered region at the initial segment of the product becomes shorter,and in the middle and rear segment positions,the ordered orientation of the fiber orientation decreases as the water injection delay time increases.Compared to 210°C and 270°C,when the molding melt temperature is 250°C,the fiber ordered regions in the product are relatively thickest.Numerical simulations are consistent with experimental conclusions.(7)The effects of fiber content at lower pressure(6MPa)on the ordered orientation of fiber orientation in different regions of OWAIM products were compared by experiments.It was found that the ordered regions of fibers in the initial segment of the product decreased with the increase the fiber content of the material;while the ordered region of the fibers in the middle and rear segments of the part increased with the increases of fiber content in the material,and this phenomenon is most pronounced in the S5 region of the end of the part.When the water injection pressure is higher(10MPa),as the fiber content in the molding material increased,the ordered region of the fiber at the initial stage S1 of the product gradually decreased,but in the end regions S4 and S5 of the product,as the fiber content in the molding material increased,the fiber orientation in the water channel is more orderly.更多还原