熔融树脂法(干法)制备单向纤维预浸带的工艺研究

本文通过对单向玻璃纤维预浸带的浸透性、含胶量及其厚度研究,论述了环氧648-BF₃MEA体系熔融树脂法制备单向预浸带工艺的可行性,并通过模拟浸带装置,确定了相应工艺参数及其主要工艺参数的质量控制方法。      

Residual stress distribution in carbon fibre/thermoplastic matrix pre-impregnated composite tapes

The distribution of residual strain in carbon fibre (P75) reinforced thermo-plastic (polyetheretherketone, PEEK) composites has been studied by monitoring the Raman frequencies of the embedded carbon fibres at the microscopic level. The average longitudinal strain in the fibre measured in a 100 mm² section of a P75/PEEK prepreg was found to be compressive and comparable in magnitude to residual strain values computed analytically. The combined effects of differential thermal expansion of the two materials, differences in fibre size and in the thickness of resin layer, are offered as likely explanations for the incurred variations in the Raman frequency values and the considerable spread of the fibre Raman frequency distribution in the prepreg tape. Finally, it is demonstrated that the previously reported high values of apparent compressive strain in similar composite tapes by means of Raman spectroscopy were artefacts of the experimental procedure.     

纤维增强热塑性树脂预浸料的制备工艺及研究进展

热塑性复合材料因冲击韧性高、环境适应性强、可回收利用等优点,被广泛应用于汽车制造、航空航天、国防军工等领域。但因热塑性树脂加热熔融后较高的黏度使其很难与纤维充分浸渍。预浸料作为制造复合材料的中间材料,现阶段制备工艺已相对成熟,预浸料中纤维已被树脂浸润,因此通过预浸料制备的复合材料孔隙率较低。本文介绍了现阶段常用的热塑性预浸料制备方法及各自的优缺点,包括溶液浸渍法、熔融浸渍法、粉末浸渍法、薄膜叠层法、纤维混杂法以及反应链增长浸渍法。阐述了热塑性树脂熔体浸润纤维的浸渍机理,对浸渍机理的部分研究成果进行了概括。概述了浸渍温度、浸渍压力和牵引速率对预浸带性能的影响。最后指出了国内预浸料生产中存在的主要问题,未来可采用多学科结合、纤维树脂改性、对浸渍过程进行计算机模拟等方法促进热塑性预浸带的产业化发展。     

连续预浸带的制备工艺研究

本文介绍了用预浸带铺制机湿法制备单向碳纤维预浸带的工艺方法,讨论了影响预浸带树脂含量、外观及挥发分含量的有关因素,优化了工艺条件,确定了制备单向预浸带的最佳工艺参数.制备的预浸带最大宽度为300毫米,连续长度可达200米.可以批量稳定地进行生产.      

Effects of fibre surface silanisation on silica fibre/phenolics composites produced by resin transfer moulding process

Abstract

The effects of fibre surface silanisation on silica fibre/phenolics composites produced by the resin transfer moulding (RTM) solution impregnation route were investigated. Diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy and micro-Wilhelmy method were used to evaluate the surface properties of silanised silica fibre. The interlaminar shear strength (ILSS) measurements and morphological observations of the silica fibre/phenolics composites were also performed. The interactions occurring between silica fibre and the components of phenolic resin solution affect the dynamic adsorption behaviour of phenolic resin onto fibre reinforcement. The competitive adsorption of ethanol as solvent onto silica fibre suppresses that of phenolic resin. Fibre surface silanisation by γ-aminopropyl-triethoxysilane (γ-APS), γ-glycidoxypropyl-trimethoxysilane (γ-GPS) and γ-methacryloxypropyl-trimethoxysilane (γ-MPS) leads to the improvement of mechanical interfacial properties of silica fibre/phenolics composites on one hand and decreases the inhomogeneities of resin distribution and mechanical interfacial properties at different regions of the RTM product on the other hand.     

Mechanical properties of natural fibre reinforced polymer composites

During the last few years, natural fibres have received much more attention than ever before from the research community all over the world. These natural fibres offer a number of advantages over traditional synthetic fibres. In the present communication, a study on the synthesis and mechanical properties of new series of green composites involving Hibiscus sabdariffa fibre as a reinforcing material in urea-formaldehyde (UF) resin based polymer matrix has been reported. Static mechanical properties of randomly oriented intimately mixed Hibiscus sabdariffa fibre reinforced polymer composites such as tensile, compressive and wear properties were investigated as a function of fibre loading. Initially urea-formaldehyde resin prepared was subjected to evaluation of its optimum mechanical properties. Then reinforcing of the resin with Hibiscus sabdariffa fibre was accomplished in three different forms: particle size, short fibre and long fibre by employing optimized resin. Present work reveals that mechanical properties such as tensile strength, compressive strength and wear resistance etc of the urea-formaldehyde resin increases to considerable extent when reinforced with the fibre. Thermal (TGA/DTA/DTG) and morphological studies (SEM) of the resin and biocomposites have also been carried out.     

The experimental determination of prepreg tack and dynamic stiffness

A new peel test has been developed which quantifies the tack and dynamic stiffness of uncured prepreg. The test is designed to simulate the automated tape lay-up (ATL) and automated fibre placement (AFP) processes. It includes a pressure controlled application stage, where contact time is inversely proportional to peel rate. The use of a thin film allows stiffness to be isolated from peel resistance in a continuous two stage test. A repeatability study revealed consistent results with 16% standard deviation. Tack and stiffness variability has been observed across roll width and between faces in commercial hand lay-up prepregs. The overall tack and stiffness values for commercial hand lay-up prepregs were found to be inconsistent with the levels specified by manufacturers.A temperature increase revealed inconsistent effects on tack between materials. The contradictory results were rationalised by observing failure modes. The two failure modes observed appeared equivalent to those found in pressure sensitive adhesive (PSA) peel. The shear storage modulus of the prepreg resin was compared to the PSA Dahlquist criterion and found to support the principle of contact efficiency. However, the actual value for the criterion is expected to be a function of prepreg specific conditions such as resin content, fibre distribution and surface pattern.     

Negative Poisson's ratios in angle-ply laminates: theory and experiment

A series of composite panels has been prepared by laminating unidirectional prepreg tapes of epoxy resin reinforced with continuous carbon fibres. Each panel was a balanced, symmetrical laminate with the plies alternating at ± θ to a reference direction where θ = 0, 10, 15, 20, 25, 30 and 40°. The full set of nine elastic constants was determined for each panel using ultrasonic velocity measurements. The experimentally determined elastic constants were then compared with theoretical predictions obtained using standard laminate theory. The Poisson's ratios of the composites were of particular interest in showing negative values for θ in the range between 15 and 30°, as predicted by the theory.     

Interface and impregnation relevant tests for continuous glass fibre-polypropylene composites

An experimental investigation was performed in order to compare the effect of the adhesive strength between fibres and matrix, contra the effect from the degree of impregnation on the mechanical properties of melt impregnated continuous glass fibre—polypropylene composites. Single fibre pull-out tests were performed in order to compare the interfacial bond strength. The degree of impregnation was measured using opacity and scattering from reflected light measurements of the prepregs. The testing included transverse tensile, ±45° tensile, double-notch shear, compression shear and double cantilever beam (DCB). These tests can to a certain degree be given interface relevance (InR) as well as impregnation relevance (ImR). With regard to InR sensitivity, the tests can be ranked in descending order according to prepreg transverse, laminate transverse, intralaminar, and interlaminar double-notch shear tests. With regard to ImR sensitivity, the tests can be ranked in descending order according to prepreg transverse, compressive interlaminar double-notch shear and laminate transverse tests. The measured shear and transverse modulus values showed limited relevance regarding the interface strength and degree of impregnation. The transverse and shear elastic modulus scored low regarding InR and ImR sensitivity. This was also true for the G_IC and G_ICPROP values.     

The development of composite carbon fibres of large diameter—macro fibres

This paper describes the development of a process for manufacturing carbon fibres of larger diameter than those normally available from the “RAE process” [1] or other routes which have so far been described (e.g. the hot-stretching of pitch [2] or cellulose-based [3] fibres). The method consists of impregnating a bundle of carbon fibres or their precursors with resin and after curing, subjecting the composite fibre to a controlled carbonization. The end-product is a thin rod or fibre of carbon-fibre reinforced carbon, which can, in principle, have any desired cross-sectional shape or area [4]. Experiments have been conducted to discover the effect of various processing variables on the properties of the composite fibre. Having chosen a suitable resin for impregnation the principal variables are (a) the degrees of pyrolysis of the initial fibre before impregnation, (b) the rate of cure of the resin to form the “intermediate” and (c) the rate of temperature rise and the maximum temperature during the carbonization process. Fibres of reasonable properties (Young's modulus 76.8 GN m^?2 and ultimate tensile strength of 267 MN m^?2) have been produced but improvements should be obtainable by optimization of this basic process as fibres with strengths up to 400 MN m^?2 have been observed.     

The application of near infrared spectroscopy in the quality control analysis of glass/phenolic resin prepreg

During the manufacture of glass/phenolic resin prepreg cloth, the feasibility of near infrared (NIR) spectroscopy as a technique for the quality control analysis of the resin content, the volatile content and the resin pre-curing degree has been verified. The partial least square (PLS) regression was used to develop the calibration models by utilizing several different spectral pretreatments. The optimum models had determination coefficients (R ²) of 98.29 for the resin content, of 99.50 for the volatile content and of 97.66 for the pre-curing degree, respectively. The root mean square errors of prediction (RMSEP) for the resin content, the volatile content and the pre-curing degree were 0.376%, 0.169% and 0.105%, respectively. The results of the paired t-test revealed that there was no significant difference between the NIR method and the standard method. In the manufacture process of the prepreg cloth, the NIR on-line monitoring results were used to be the instructions for the quality control.     

Effect of Polymer Form and its Consolidation on Mechanical Properties and Quality of Glass/PBT Composites

The aim of this study was to understand the role of the processing in determining the mechanical properties of glass fibre reinforced polybutylene terephthalate composites (Glass/PBT). Unidirectional (UD) composite laminates were manufactured by the vacuum consolidation technique using three different material systems included in this study; Glass/CBT (CBT160 powder based resin), Glass/PBT (prepreg tapes), and Glass/PBT (commingled yarns). The different types of thermoplastic polymer resin systems used for the manufacturing of the composite UD laminate dictate the differences in final mechanical properties which were evaluated by through compression, flexural and short beam transverse bending tests. Microscopy was used to evaluate the quality of the processed laminates, and fractography was used to characterize the observed failure modes. The study provides an improved understanding of the relationships between processing methods, resin characteristics, and mechanical performance of thermoplastic resin composite materials.     

Quality inspection of laid fabric epoxy resins prepreg by near infrared spectroscopy

Near infrared (NIR) spectroscopy has been applied for non-contact quality inspection of the laid fabric prepreg. The cure process of the epoxy resin and the prepreg sample has been studied using near infrared spectroscopy. Abundant information of prepreg related to the resin content and the volatile content was observed in the spectra. Multivariate calibration method based on partial least square (PLS) regression could be used to obtain the relevant analytical information and determine the quality indexes. Sixteen samples were collected randomly, and were analyzed by the reference and NIR methods. The results of the paired t-test revealed that there was no significant difference between the two methods.

The NIR spectroscopy method can be used to predict the resin content and the volatile content simultaneously. Besides, the prepreg could be analyzed once within 30 s without sample destruction. The change of the processing parameters could be used to control the resin content and the volatile content. The study indicates that the NIR analysis is sufficiently rapid and effective for quality inspection in the laid fabric prepreg.     

Processing of Ti-SiC metal matrix composites by tape casting

Abstract

Titanium-silicon carbide (Ti-SiC) continuous fibre composites are very attractive for aerospace applications. Although development of various components is under way, a cost effective method to manufacture the material still has to be identified. Here, a tape casting technique is investigated as a viable method of producing the composites. It involves relatively large inexpensive titanium powder and simple apparatus. Furthermore, the powder particles ensure good fibre distribution, reduced consolidation time, and little damage to the reinforcement. It is shown that uniform powder tapes with good packing density can be readily produced using appropriate casting parameters. Both thermogravimetry and mass spectrometry are used to analyse the burnout process of a fugitive binder system used to produce the tapes. Removal of the organics is found to take place in two stages, separated by over 100 K. composite materials processed by the tape casting route exhibit good fibre distribution and no signs of fibre damage.     

Natural fibre reinforced sheet moulding compound

This paper describes a newly developed system, which enables utilisation of short flax fibres for SMC (Sheet Moulding Compound) production. It is shown that by using an evenly distributed layer of short dried flax fibres, after controlled impregnation and maturation, a homogeneous flow of the prepreg in the mould is obtained, and accordingly a flax fibre reinforced SMC can be produced. Mechanical data indicates that for applications designed with respect to stiffness, flax fibre reinforced SMC materials compete with glass fibre SMC, especially when the fibre length exceeds 25 mm.     

Influence of surface treatment on adhesion of polyethylene fibres

Abstract

A detailed examination has been undertaken of the influence of surface treatment on the adhesion of polyethylene fibres to epoxy resin. The pull-out adhesion has been determined for untreated, chromic acid treated, and plasma etched monofilaments with different draw ratios and thermal annealing treatments. In a few cases, additional chemical treatments were applied to plasma treated fibres before the pull-out test. The polyethylene surface energy also has been determined by measurement of contact angle. The results, taken together, suggest that the adhesion depends on three factors: (i) the wettability (or physicochemical interactions), which is affected by the extent and nature of the surface treatment as well as the fibre draw ratio; (ii) the surface roughness, after plasma etching only, where a honeycomb structure of pits permits mechanical keying between the fibre and the resin (this structure has been examined by scanning electron microscopy); and (iii) the number of chemical bonds per unit area between the fibre and the resin. It is concluded that these three factors can be regarded as additive and that optimum results are obtained when their respective pull-out strengths reach their maximum values, ~2, ~3, and ~1·7 MN m^?2.

MST/640     

A process model for the compaction and saturation of partially impregnated thermoset prepreg tapes

Automated manufacturing of composite materials is key to reducing cost and improving consistency in part quality. Modeling of manufacturing processes can identify influential material, geometric, and process variables, while providing a framework for their optimization and control. A process model has been formulated to describe the compaction and saturation of partially impregnated thermoset prepreg tapes during their placement, using a roller compaction and vacuum consolidation. The roles of various parameters that characterize the initial prepreg tape state and the final prepreg tape state are investigated. The model yields the degree of resin saturation in the tape with changes in its thickness after being compacted, due to an external pressure. The results estimate the degree of dry fiber region within the tape, which can provide vacuum pathways for air or volatile removal before consolidation and cure. The model can be adapted for different material constitutive relationships of tape compaction and saturation.     

Sources of variability in uncured aerospace grade unidirectional carbon fibre epoxy preimpregnate

Two sources of variability have been investigated in uncured unidirectional carbon epoxy preimpregnate (prepreg). The variability in mass/unit area properties has been measured at various scales and compared to the specification limits as defined by the manufacturer. Both random variability and a structured variation in mass properties across the width of the roll can be detected; and as might be expected the variability rises rapidly as the scale on which the measurements are performed is reduced. The variability in fibre straightness has been studied in two ways, by direct measurements of fibre misalignments in as-delivered prepreg, and by inference from measurements of the tensile load response of uncured prepreg. A significant level of fibre misalignment is detectable in as-delivered prepreg, largely as in-plane wrinkling, although both macroscopic out of plane wrinkling and very localised small scale out of plane wrinkling can also be detected. This misalignment increases with forming, both in and out-of plane wrinkling becoming more severe. The influence of these variabilities on laminate and component response are considered.     

Hybrid filler composition optimization for tensile strength of jute fibre-reinforced polymer composite

In present research work, pultrusion process is used to develop jute fibre-reinforced polyester (GFRP) composite and experiments have been performed on an indigenously developed pultrusion experimental setup. The developed composite consists of natural jute fibre as reinforcement and unsaturated polyester resin as matrix with hybrid filler containing bagasse fibre, carbon black and calcium carbonate (CaCO₃). The effect of weight content of bagasse fibre, carbon black and calcium carbonate on tensile strength of pultruded GFRP composite is evaluated and the optimum hybrid filler composition for maximizing the tensile strength is determined. Different compositions of hybrid filler are prepared by mixing three fillers using Taguchi L₉ orthogonal array. Fifteen percent of hybrid filler of different composition by weight was mixed in the unsaturated polyester resin matrix. Taguchi L ₉ orthogonal array (OA) has been used to plan the experiments and ANOVA is used for analysing tensile strength. A regression model has also been proposed to evaluate the tensile strength of the composite within 7% error by varying the above fillers weight. A confirmation experiment was performed which gives 73.14 MPa tensile strength of pultruded jute fibre polymer composite at the optimum composition of hybrid filler.     

Continuous-fibre CMC fabrication using pre-impregnated sheets

A new fabrication technology is presented for long fibre-reinforced ceramic matrix composites (CMCs) using pre-impregnated (prepreg) sheets. The monolayer prepreg sheets were fabricated by a modified doctor blade method using a Si–Ti–C–O long fibre/Al₂O₃ laminated composite as an example. These were flexible enough to allow handling during subsequent processing steps. At the final step of fabrication, the multilayer-preforms of fibre containing prepreg sheets were pressureless-sintered in the furnace. The key point of this fabrication method is that the SiO₂–B₂O₃-based glass powder is previously mixed with Al₂O₃ powder to be dispersed in the slurry, in order to lower the sintering temperature and thus to avoid the degradation of fibres during sintering of the fibre contained green body. Continuous fibre CMC fabrication using such a technique has the advantage of not requiring expensive fabrication facilities (and is thus cost-effective) in addition to its potential for significantly increasing/tailoring mechanical properties such as static strength, fracture toughness, and fatigue resistance.