Morphology evolution of polysulfone nanofibrous membranes toughened epoxy resin during reaction-induced phase separation

The phase separation process and morphology evolution of 5 wt% polysulfone (PSF) nanofibrous membranes toughened epoxy resin at different temperatures were investigated by synchrotron radiation small angel X-ray scattering (SR-SAXS), phase contrast microscopy (PCM) and scanning electron microscopy (SEM). The onset time of phase separation obtained by different methods was basically identical. As the curing proceeded at constant temperature, the scattering peak corresponding to the maximum scattering intensity shifted to a smaller scattering vector (q_m), and the average diameters of PSF spheres increased, which showed a phase separation pattern of nucleation and growth mechanism. PSF spheres exhibited random alignment in “sea-island” morphology, which was attributed to the in situ phase separation of PSF nanofibers. Also, the effects of phase separation kinetics on the phase morphology and fracture toughness of nanofibrous membranes toughened epoxy resin were investigated. Results showed that the phase separation process was faster than the curing reaction process, which implied that the diffusion coefficient of PSF in epoxy resin increased with increasing the curing temperature, resulting in the increase of PSF sphere size that in turn improved the fracture toughness at higher temperature.     

RTM快速成型环氧树脂时间-温度-转变图的构建及其碳纤维/环氧树脂复合材料评价

针对自行研制的树脂传递模塑工艺（RTM）快速成型环氧树脂,利用唯象动力学模型、DiBenedetto方程和凝胶模型研究了树脂体系的等温及非等温固化动力学,构建了时间-温度-转变（TTT）的关系图,表明树脂体系兼具较长的适用期与快速固化特性。以此设计RTM快速成型工艺,考察了树脂体系对碳纤维织物的浸润流动行为,并评价了快速成型碳纤维/环氧树脂复合材料的界面力学性能与微观形貌。结果表明,注射温度下树脂体系的浸润填充性良好,RTM快速成型碳纤维/环氧树脂复合材料的力学性能和内部成型质量较好。      

Three-Dimensional Flow Simulations for the Resin Transfer Molding Process

In resin transfer molding (RTM) a stack of fiber mats or woven rovings is laid inside the mold cavity. Then the mold is sealed and resin is injected. The computer simulation of the injection phase in resin transfer molding (RTM) can help the mold designer to position properly the injection ports and the air vents, to select an adequate injection presssure and to optimize the cycle time. The purpose of this article is to present a finite element simulation model of the filling process that can be applied to three-dimensional “thin shell” molds. An application to a subway seat is described to illustrate the various stages of the simulation     

Experimental investigation and flow visualisation of the resin transfer mould filling process for non-woven hemp reinforced phenolic composites

Resin transfer moulding (RTM) of glass fibre reinforced polymeric composites offers the advantages of automation, low cost and versatile design of fibre reinforcement. A replacement of glass fibres with natural plant fibres as reinforcement in polymeric composites provides additional technological, economical, ecological and environmental benefits. The resin transfer mould filling process has significant effects on different aspects, such as fibre wetting out and impregnation, injection gate design, “dry patch” and void formation. Flow visualisation experiments were carried out using a transparent RTM mould to develop a better understanding of the mould filling process for hemp mat reinforced phenolic composites. The mould filling of unreinforced phenolics was characterised by a “quasi-one-dimensional steady state” flow. In the case of hemp non-woven reinforced system, the mould filling process can be considered as the flow of fluids through porous media. “Fibre washing” was a typical problem encountered during the injection process, leading to poor property uniformity. In addition, a preferential flow path was usually created near the edges and corners of the mould. The path exhibited low flow resistance and caused the resin flow front to advance much faster in these regions. The edge flow disturbed the steady flow, leading to difficulties in venting arrangement and “dry patch” formation. The edge flow and fibre washing were alleviated by reinforcement manipulation so steady state flow could be achieved. The relationships between the filling time and injection pressure and between filling time and different fibre weight fractions have been established for certain specific injection strategies.     

PCG solver and its computational complexity for implicit control-volume finite-element method of RTM mold filling simulation

For isoparametric element meshes, the control-volume finite-element method for resin transfer molding (RTM) mold filling generates an asymmetric matrix, and the performance of the pre-conditioner conjugate gradient (PCG) solver decreases by almost one order of magnitude, even for meshes with very few trivial asymmetric data points. In this paper, the asymmetric parts of the linear equations were transferred to the right-hand sides, and then the linear equations were transformed into an equivalent set of symmetric equations. The right-hand sides of the system of equations were updated only when the set of filled nodes changed. The time steps were controlled by the rule of “one time step, one element-size distance.” Based on the PCG solver and the time-step strategy, the computational complexity of the implicit control-volume method was analyzed and presented. Both analytical and case studies showed that the computational complexity of the PCG solver was of order N squared (where N is the number of nodes) for both 2.5D and 3D meshes. The proposed approach was very suitable for a 3D mesh and had the capability of simulating a mesh with 50,000 nodes in under one hour using a 2.0 GHz CPU, 512M RAM computer.     

EPON862环氧树脂体系化学流变特性研究

对用于RTM工艺的EPON862环氧树脂体系的化学流变特性进行研究,并根据双阿累尼乌斯方程,建立树脂体系的流变模型。粘度模型与实验结果具有良好的一致性。模型可揭示树脂体系在不同工艺条件下的粘度行为,定量预报RTM工艺树脂的低粘度平台工艺窗口,为合理制定RTM工艺参数、保证产品质量和实现工艺参数的全局优化提供了必要的科学依据。      

海因树脂体系化学流变特性研究

采用DSC热分析技术和粘度测量手段,研究了海因树脂体系的固化特性和化学流变特性,建立了双阿累尼乌斯粘度模型。粘度模型预测的体系粘度变化规律与实验结果具有良好的一致性,模型可有效模拟树脂体系在不同工艺条件下的粘度行为,为复合材料成型工艺模拟分析以及工艺参数的准确制定奠定了基础。     

用于环氧树脂固化过程实时监测的光纤折射率传感器

研究了应用光纤传感技术对环氧树脂固化过程进行实时监测的方法。通过将一段光纤的包层去掉构成光纤折射率传感器, 利用环氧树脂在固化过程中折射率随固化度增大而增大的特性进行固化监测。应用光线追迹法和局部平面波理论导出光纤固化传感器的理论模型。通过在光纤传感区一端的光纤端面镀全反射膜形成探针型传感结构。对E51 环氧树脂的等温固化过程进行了实时监测实验。      

The variation in lateral and longitudinal stress gauge response within an RTM 6 epoxy resin under one-dimensional shock loading

The dynamic response of a commercially important epoxy resin (RTM 6) has been studied using plate impact experiments in the impact velocity regime of 80–960 m/s. Both longitudinal and lateral manganin stress gauges were employed to study the development of orthogonal components of stress both during and after shock arrival. In light of recent work raising doubts about the interpretation of lateral gauge data, lateral response within the RTM 6 resin was also used to investigate the physical phenomena being measured by the embedded lateral gauges. U _S–u _P and σ_X–u _P Hugoniot relationships were in good agreement with data for similar polymer materials from the literature. Derivation of shear strength behaviour both during and after shock arrival showed evidence of strengthening behind the shock front, attributed to compression of the cross-linked epoxy resin polymer chains. Comparison of the change in lateral stress behind the shock to the behaviour of an epoxy resin possessing a similar U _S–u _P Hugoniot from the literature showed a different response; likely attributable to enhanced cross-linking present in this second resin. This result suggests that the embedded lateral gauges were, at least in part, measuring a physical response behind the shock within the resin. A Hugoniot elastic limit of 0.88 ± 0.04 GPa was derived and found to be of the same order of magnitude as results found elsewhere for similar materials.     

Transparency and toughness characterization of epoxy resins modified with liquid chloroprene rubber

Transparent epoxy resins modified with liquid chloroprene rubber (LCR), containing in a category of rubber-toughened resin were found. Transparency and toughness characterization of the modified epoxy resins were investigated as a function of LCR content. Epoxy resins modified with 0–10 vol % LCR showed complete phase-separation microstructure. However, these modified resins were transparent, because the refractive index of LCR was compatible with that of the epoxy resin matrix at room temperature. On the other hand, it was observed that above 10 vol % LCR, a certain amount of LCR dissolved into the epoxy matrix. In this case, the glass transition temperature decreased with increasing LCR content. It was also found that the critical stress intensity factor, K _c, of the modified epoxy resins exhibited a maximum between 10 and 15 vol % LCR.     

A comparative study of the fatigue and post-fatigue behavior of carbon–glass/epoxy hybrid RTM and hand lay-up composites

The paper presents a study of the fatigue and post-fatigue behavior of a hybrid carbon–glass biaxial fabric reinforced epoxy composite manufactured by the resin transfer molding (RTM) and the hand lay-up (HL) processes, with the main objective of assessing whether a material characterization run at the prototype level of a handicraft technology could be significant for a mass production technology and whether a comparison on static properties (a viable task at an industrial level) could ensure the same level of agreement for the fatigue life and residual properties. Tensile and flexural static tests as well as displacement-controlled bending fatigue tests (R ratio of 0.10) were conducted on two sets of standard specimens, having fiber orientation parallel to the loading direction (on-axis specimens) and at 45° to the loading direction (off-axis specimens). Specimens were subjected to different fatigue loading, with the maximum load level up to 60% of the average ultimate flexural strength, and damage in the laminate was continuously monitored through the loss of bending moment during cycling. After 10⁶ cycles, the fatigue test was stopped and residual properties were measured. Micrographs of sample sections revealed some voidage for HL specimens while resin rich areas were observed for RTM specimens. Results of the static tensile and flexural tests pointed out lower mechanical properties for the RTM specimens when tested on-axis and slightly higher properties when tested off-axis. Regardless of specimen fiber orientation, the fatigue and post-fatigue performance of RTM samples was inferior to that of HL specimens with the gap increasing for increasing fatigue load levels. The result was ascribed to the presence in RTM samples of resin-rich areas, which are reported to have limited influence on the laminate static properties but which may act as initiation sites for fatigue cracks.     

三维编织超高分子量聚乙烯纤维-碳纤维混杂增强环氧树脂复合材料摩擦磨损性能

以超高分子量聚乙烯纤维(UHMWPE)-碳纤维(CF)三维混杂编织体为增强体,环氧树脂(ER)为基体,通过树脂传递模塑(RTM)工艺制备了三维编织混杂复合材料,研究了其摩擦磨损性能了,并采用混合正压力模型对摩擦系数进行了预测。结果表明,在纤维总体积含量一定的情况下,随着CF体积含量的增加,复合材料的摩擦系数增大,而其比磨损率降低。UH_3D/ER复合材料的磨损机制以粘着磨损为主,CF_3D/ER复合材料则以磨粒磨损为主,混杂复合材料的磨损机制主要取决于CF与UHMWPE纤维的相对含量 ,通过调节UHMWPE纤维和CF的体积比例可实现对复合材料摩擦磨损性能的有效调控。采用的计算模型可较好地预测UH_3D/ER的摩擦系数。     

Characterisation of the cross-linking process in an E-glass fibre/epoxy composite using evanescent wave spectroscopy

The term “self-sensing composites” is sometimes used to describe the case where the reinforcing glass fibres in advanced fibre-reinforced composites are used as the sensors for chemical process-monitoring (cure monitoring). This paper presents conclusive evidence to demonstrate that reinforcing E-glass fibres can be used for in situ cure monitoring. The cure behaviour of an epoxy/amine resin system was compared using evanescent wave spectroscopy via the reinforcing E-glass fibres and conventional transmission Fourier transform infrared spectroscopy. This paper also reports for the first time that evanescent wave spectroscopy via E-glass fibres can be used to detect the presence of silane coupling agents. Preliminary results indicated that the cure kinetics on the E-glass fibre surface, as observed using evanescent wave spectroscopy, were influenced by the silane coupling agent.     

RTM processing and electrical performance of carbon nanotube modified epoxy/fibre composites

This investigation focuses on nanoparticle filtration in the processing of multiscale carbon and glass fibre composites via resin transfer moulding. Surface modified and unmodified carbon nanotubes (CNTs) were incorporated into a commercial epoxy resin. The dispersion quality was evaluated using electrical measurements of the liquid suspensions. The manufacturing process was adapted to the challenges posed by the modified rheological behaviour of the CNT loaded resin. Nanoparticle filtration was observed; with some of the unmodified systems following so called ‘cake filtration’ behaviour. This resulted in nonlinear flow behaviour that deviated from the ideal response observed in RTM filling in conventional composites. The electrical conductivity of relatively high fibre volume fraction multiscale carbon and glass laminates increased by less than an order of magnitude with the addition of the nanotubes.     

Eliminating volatile-induced surface porosity during resin transfer molding of a benzoxazine/epoxy blend

We studied the mechanism of volatile-induced surface porosity formation during the resin transfer molding (RTM) of aerospace composites using a blended benzoxazine/epoxy resin, and identified reduction strategies based on material and processing parameters. First, the influence of viscosity and pressure on resin volatilization were determined. Then, in situ data was collected during molding using a lab-scale RTM system for different cure cycles and catalyst concentrations. Finally, the surface quality of molded samples was evaluated. The results show that surface porosity occurs when cure shrinkage causes a sufficient decrease in cavity pressure prior to resin vitrification. The combination of thermal gradients and rapid gelation can generate large spatial variations in viscosity, rendering the coldest regions of a mold susceptible to porosity formation. However, material and cure cycle modifications can alter the resin cure kinetics, making it possible to delay the pressure drop until higher viscosities are attained to minimize porosity formation.     

一种中温定型剂及其RTM预制体性能

研究了ES-T321定型剂及其配对的RTM专用环氧树脂3266的混合使用性能(如相容性、流变性和热性能等).ES-T321可以制备成丙酮溶液或粉末定型材料,使用方便.ES-T321的熔点比3266树脂的RTM注射温度窗口高,具有较好的抗流动冲刷性能,能够保证定型织物在树脂注射时不被冲散.ES-T321在3266树脂的固化温度下能溶解在树脂中,并与3266的固化剂反应.加入定型剂对树脂混合体系的热性能几乎没有影响.定型处理的预成型体的回弹效应小,溶液法定型的预成型体的回弹比粉末法更小.     

基于RTM工艺的纤维增强环氧树脂复合材料阻燃改性研究

制备了全新的阻燃定型剂DHQEP/ET3228,利用传统RTM工艺,实现了对纤维增强环氧树脂复合材料的阻燃改性。该定型剂的加入为预成型体提供出色的定型效果,回弹角测试中仅发生了1.24°的回弹,同时还可以有效提升复合材料的阻燃性能（LOI可达36.8%）。另外,阻燃定型剂可以参与环氧树脂的固化反应,使得阻燃定型剂的添加对复合材料的界面性能影响较小,保持了复合材料良好的层间剪切性能。     

Advanced cure monitoring by optoelectronic multifunction sensing system

In this work, a dual functionality fiber optic sensing system for thermoset cure monitoring has been developed and successfully tested. Principle of operation relies on the use of a standard optical fiber in single ended configuration containing a single in-fiber Bragg grating. The change in refractive index directly related to material density at fiber end and the variation in the wavelength reflected by the fiber grating have been monitored simultaneously, throughout an In-Mould curing process of an epoxy resin. A compact and low cost in-fiber dual wavelength demodulation system has been developed and experimental results demonstrate the capability to on line identify the degree of cure, gel point, residual stresses and the glass transition temperature of the cured resin.     

RTM用环氧3266树脂体系化学流变特性的研究

本研究在基本的黏度实验和DSC热分析实验的基础上,采用双阿累尼乌斯方程研究了RTM用环氧3266树脂体系的化学流变特性,建立了相应的化学流变模型,模型与实验结果具有良好的一致性.模型揭示了该树脂体系在不同工艺条件下的黏度变化规律,定量预报了该体系的低黏度工艺窗口平台,为合理制定RTM工艺参数保证产品质量和实现工艺参数的全局性优化提供了必要的科学依据.     

用光纤进行树脂基复合材料的成型过程监测

研究了用光纤对碳纤维环氧树脂复合材料成型监测的方法和系统。通过测量复合材料成型过程中树脂折射率的变化来反映树脂的粘度变化和固化过程。