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Journal ArticleDOI

Comparison of the mechanical and physical properties of a carbon fibre epoxy composite manufactured by resin transfer moulding using conventional and microwave heating

01 Jun 2008-Composites Science and Technology (Elsevier)-Vol. 68, Iss: 7, pp 1854-1861
TL;DR: In this paper, microwave heating was incorporated into the resin transfer molding technique, and a 50% cure cycle time reduction was achieved by using carbon fiber/epoxy composites.
About: This article is published in Composites Science and Technology.The article was published on 2008-06-01 and is currently open access. It has received 131 citations till now. The article focuses on the topics: Flexural strength & Void (composites).

Summary (3 min read)

Introduction

  • This is the author’s final version of the work after peer review.
  • The article was originally published in Composites Science and Technology in 2008 by Elsevier.
  • The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form.
  • The implementation of microwave heating into common manufacturing methods for polymer composites, such as resin transfer moulding [24], however, has not yet been fully exploited.

2.1. Materials

  • The resin system used in this study was Araldite LY5052 / Aradur HY5052 (supplied by Huntsman).
  • The resin/hardener mix ratio was 100:38 parts by weight.
  • The reinforcement used was high strength T300 carbon fibre fabric (supplied by Hexcel Composites) with ACCEPTED MANUSCRIPT 3 balanced 50/50 warp/weft five-harness satin weave architecture.
  • Seven layers of carbon fibre reinforcement were used for each laminate panel.

2.2.1. Conventional thermal RTM processing

  • Conventional thermal RTM processing was based on the Hypaject Mark II RTM Injection system , as illustrated schematically in Fig.1.
  • The system comprised an inlet valve, a heated homogenizer, a pneumatic valve, a metal mould with 16 electric-cartridge heaters (8 for each mould part) giving a total power output of 4 KW, two K-type thermocouples and two PID temperature controllers.
  • Prior to the curing process, the metal mould was coated with Frekote 44-NC release agent.
  • The fibres were then placed inside the mould cavity (200 x 300 x 3 mm dimensions) and the mould was inclined at 45 0 from horizontal in a steel stand in order to minimize air entrapment during the injection.
  • The resin was drawn into the homogenizer through the inlet valve and left for 10-15 minutes under vacuum in order to remove any air bubbles created at the initial resin-hardener mixing stage.

2.2.2. Microwave RTM processing

  • Microwave RTM processing differed from conventional thermal RTM processing in how the resin-loaded mould was heated after the injection stage.
  • Preparation of the Macor mould prior to resin injection involved applying ACCEPTED MANUSCRIPT 4 Chemlease C15 sealer agent and PMR Chemlease release agent.
  • The maximum amplifier output power that could be used in this configuration was 250 W.
  • The computer control system was designed in such way that the NA would continuously step through the excitation frequencies, while simultaneously regulating the microwave power in order to maintain the desired cure temperature.
  • 5 where, T was the maximum of the measured sample temperatures, Tcure was the cure temperature and Tmin was a pre-set temperature limit.

2.3.1. Flexural modulus and flexural strength

  • The flexural properties of the composite samples were determined according to ASTM Standard D 6272 [25].
  • The apparatus used was an Instron 4301 equipped with a four-point bend jig and a 5 KN load cell.
  • For each composite panel six samples were tested and an average value was taken.

2.3.2 Interlaminar shear strength

  • Interlaminar shear testing of the composite samples was conducted on an Instron 4301 equipped with a three-point bend jig and a 5 KN load cell, according to ASTM Standard D 2344/D 2344M [26].
  • For each composite panel eight samples were tested and an average value was taken.

2.4 Fibre and void volume fraction

  • The percentage fibre volume fraction Vr and the percentage void volume fraction Vv were determined using matrix digestion with nitric acid in a microwave oven according to ASTM Standard D 3171 [27].
  • Prior to that, the density of the samples was determined according to Airbus UK Test Specification [28].
  • For each panel ten samples were tested and an average value was taken.

2.5 Rheology

  • The viscosity of the neat LY/HY5052 resin system was determined as a function of time using a RMS 800 rheometer.
  • The neat resin was heated between two parallel 50 mm aluminium plates under a 1.
  • Hz oscillating frequency at 2°C/min, 5°C/min and 10°C/min from room temperature until gelation occurred.

2.6 Differential scanning calorimetry (DSC)

  • Differential scanning calorimetric studies were carried out on a TA Instruments MDSC 2920 to ensure that the fabricated composite panels were fully cured.
  • Samples were taken from different locations on each composite panel.
  • 7 Dynamic mechanical thermal analysis (DMTA) Dynamic mechanical thermal analysis was carried out on a TA Instruments DMA Q800 to obtain the glass transition temperatures for both conventional thermal and microwave cured composites.
  • For each composite panel six samples were tested.

2.8 Scanning electron microscopy (SEM)

  • The composite samples were examined using Philips XL30 FEG SEM microscope.
  • Small sections of the fracture surfaces were cut from test samples subjected to mechanical testing and placed on metal stubs using double-sided carbon tabs.
  • The stubs with the fracture surfaces were then coated with a very thin layer of gold using Edwards S150B sputter coater in order to make them electrically conductive.

3. Results and discussion

  • Based on previous work by Yusoff [29], the cure cycle employed for conventional thermal processing was 100°C for 3 hours.
  • As depicted in Fig.3, the dielectric loss stabilised after about 90 minutes, thus the cure cycle employed for microwave processing was 90 minutes at 100°C.
  • Table 1 shows the average values of flexural modulus, flexural strength, interlaminar shear strength, fibre volume fraction, void content and panel thickness obtained for composite panels manufactured by both conventional thermal and microwave RTM processing.
  • The flexural moduli of both thermally and microwave cured composites were found to be comparable.
  • The fluidity of the resin is thought to provide better contact between the resin and the fibre surface contour, allowing the resin to effectively enter any formed micro-holes which where previously occupied by trapped air.

4. Conclusions

  • A modification of the conventional RTM method incorporating the use of microwave heating was presented.
  • The method was based on the Hypaject Mark II RTM Injection system.
  • The microwave heating equipment comprised a network analyser, a travelling wave tube amplifier, an isolator, a multi-mode applicator and optical temperature sensing.
  • This increase is not profound as it falls within the experimental error.
  • The mechanical and physical properties of the microwave cured composites were found to be similar and, in some cases, superior compared to their thermally cured counterparts.

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Citations
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Journal ArticleDOI
TL;DR: In this paper, most of the significant phenomena that cause heating during microwave-material interaction and heat transfer during microwave energy absorption in materials are discussed. But, the mechanisms associated with the processing are less understood; popular mechanisms such as dipolar heating and conduction heating have been mostly explored.
Abstract: Efforts to use microwaves in material processing are gradually increasing. However, the phenomena associated with the processing are less understood; popular mechanisms such as dipolar heating and conduction heating have been mostly explored. The current paper reviews most of the significant phenomena that cause heating during microwave–material interaction and heat transfer during microwave energy absorption in materials. Mechanisms involved during interaction of microwave with characteristically different materials – metals, non-metals and composites (metal matrix composites, ceramic matrix composites and polymer matrix composites) have been discussed using suitable illustrations. It was observed that while microwave heating of metal based materials is due to the magnetic field based loss effects, dipolar loss and conduction loss are the phenomena associated with the electric field effects in microwave heating of non-metals. Challenges in processing of advanced materials, particularly composites have been identified from the available literature; further research directions with possible benefits have been highlighted.

502 citations

Journal ArticleDOI
TL;DR: In this article, the authors provide a comprehensive review of microwave composites research, from processing to structural and property evaluations with a focus on the multi-functionalities presented in these microwire composites.

286 citations

Journal ArticleDOI
TL;DR: In this article, the most recent and prominent applications of microwave radiation in biomaterials have been reviewed, and the unmet goals and the perspectives for a technology that probably has the potential to make biom materials more accessible pharmaceutical excipients and the products that involve them more affordable to patients.

117 citations

Journal ArticleDOI
TL;DR: In this paper, the fundamental principles behind efficient accelerated curing of composites using microwave radiation heating are reviewed and presented, especially focusing on the relation between penetration depth, microwave frequency, dielectric properties and cure degree.
Abstract: Accelerated curing of high performance fibre-reinforced polymer (FRP) composites via microwave heating or radiation, which can significantly reduce cure time and increase energy efficiency, has several major challenges (eg uneven depth of radiation penetration, reinforcing fibre shielding, uneven curing, introduction of hot spots etc) This article reviews the current scientific challenges with microwave curing of FRP composites considering the underlying physics of microwave radiation absorption in thermoset-matrix composites The fundamental principles behind efficient accelerated curing of composites using microwave radiation heating are reviewed and presented, especially focusing on the relation between penetration depth, microwave frequency, dielectric properties and cure degree Based on this review, major factors influencing microwave curing of thermoset-matrix composites are identified, and recommendations for efficient cure cycle design are provided

87 citations


Cites background from "Comparison of the mechanical and ph..."

  • ...Many studies related to mechanical performance of microwave cured thermoset composites have looked up the undesirable effects caused by carbon fibre arcing (due to the distinguished strong microwave absorption properties by carbon) during microwave curing of composites, and consideration in microwave power control has been taken to avoid such phenomenon [28, 90, 127-130] while maintaining the nominal post-cure structural integrity comparable to that of composites cured by conventional heating....

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References
More filters
Journal ArticleDOI
TL;DR: In this paper, the fundamentals of electromagnetic theory, dielectric response, and applications of microwave heating to materials processing, especially fiber composites, are reviewed in this article, and a knowledge of electromagnetic theories and dielectrics is essential to optimize the processing of materials through microwave heating.
Abstract: In microwave processing, energy is supplied by an electromagnetic field directly to the material. This results in rapid heating throughout the material thickness with reduced thermal gradients. Volumetric heating can also reduce processing times and save energy. The microwave field and the dielectric response of a material govern its ability to heat with microwave energy. A knowledge of electromagnetic theory and dielectric response is essential to optimize the processing of materials through microwave heating. The fundamentals of electromagnetic theory, dielectric response, and applications of microwave heating to materials processing, especially fiber composites, are reviewed in this article.

1,296 citations


"Comparison of the mechanical and ph..." refers background in this paper

  • ...It is, thus, more appropriate to consider microwave heating as conversion of electromagnetic energy to thermal energy rather than heat transfer [5]....

    [...]

Journal ArticleDOI
TL;DR: In this paper, the physical aspects of a cross-disciplinary science and technology field: the microwave processing of materials are reviewed, including the absorption of electromagnetic waves, heat transfer and the electrodynamics of single and multimode microwave cavities.
Abstract: This article reviews the physical aspects of a cross-disciplinary science and technology field: the microwave processing of materials. High-temperature microwave processing has a clear industrial perspective in such areas as the production of advanced ceramics, the deposition of thermal barrier coatings, the remediation of hazardous wastes etc. This review starts with the relevant fundamental notions regarding the absorption of electromagnetic waves, heat transfer and the electrodynamics of single- and multimode microwave cavities. Useful formulae, estimates, and interrelations between process variables are presented. This is followed by a review of process examples illustrating the specific features of microwave processing: reduction in energy consumption and process duration, rapid and controllable heating, peculiar temperature distribution, and selectivity of energy deposition. Much attention is given to the advantages of higher-frequency millimetre-wave processing, which include the enhanced absorption in many materials of industrial interest, improved uniformity of electromagnetic energy and temperature, and the possibility of surface treatment. The phenomenon of microwave process rate enhancement is addressed in connection with the problem of the non-thermal microwave effect on mass transport in solids. Both experimental and theoretical approaches to the identification of the mechanism responsible for this effect are illustrated. Finally, the physical and technical factors influencing microwave technology scaleup and transfer to industry are discussed.

462 citations


"Comparison of the mechanical and ph..." refers background in this paper

  • ...One such alternative route is microwave processing, which offers several advantages over the conventional thermal processing methods, including rapid, selective and volumetric heating, energy savings, reduced processing time and improved processing control [1-4]....

    [...]

Journal ArticleDOI
TL;DR: In this paper, the authors investigated the use of two epoxy systems where the choice of resin and hardener was based on their measured dielectric loss factors and found that System 1 composites had greater flexural properties and interlaminar shear strengths than System 2 composites when autoclave cured.
Abstract: The ease of heating an epoxy resin with microwaves depends, among other factors, on the dielectric properties of its components at the frequency of the radiation used The majority of the papers published on the microwave curing of reinforced epoxy resin composites have used widely available DGEBA type resins and amine hardeners such as 4,4’-diaminodiphenylsulphone (DDS) This paper investigates the use of two epoxy systems where the choice of resin and hardener was based on their measured dielectric loss factors System 1 contained a resin and hardener with higher loss factors than those used in System 2 The two systems were formulated with polyetherimide (PEI) as a toughening agent Unidirectional carbon fibre prepregs were prepared from both systems Composites were laid up from these prepregs which were then cured in three different ways: autoclave curing, partial autoclave curing followed by microwave post-curing, and microwave curing System 1 composites had greater flexural properties and interlaminar shear strengths than System 2 composites when autoclave cured Flexural properties and interlaminar shear strengths were greater for System 2 in the microwave post-cured composites When fully microwave cured the properties were similar In the microwave cured composites the flexural and interlaminar shear properties were influenced by the structure of the phase separated PEI and the void content

115 citations


"Comparison of the mechanical and ph..." refers background in this paper

  • ...A considerable amount of research has been devoted on microwave curing of different polymer [2, 6-13] and composite systems [14-23]....

    [...]

Journal ArticleDOI
TL;DR: In this paper, the use of the Quickstep method for the processing of an epoxy/carbon fiber aerospace material was compared to equivalent composites produced using an autoclave process.

113 citations

Frequently Asked Questions (11)
Q1. What contributions have the authors mentioned in the paper "Comparison of the mechanical and physical properties of a carbon fibre epoxy composite manufactured by resin transfer moulding using conventional and microwave heating" ?

In this paper, microwave heating was incorporated into the resin transfer moulding technique. Furthermore, both types of composites yielded minimal void content ( 

However, further research is necessary in order to understand and explain the differences in the reaction mechanism between thermally and microwave cured composites. 

Within the composite it is likely that the microwave electric field generates an electric current in the carbon fibres and thus resistive heating. 

The increase in the interlaminar shear strength could be also partly attributed to extended plastic deformation and hence increased crack-tip blunting, as a result of the greater amount of resin between the fibre layers in the microwave cured samples compared to those cured thermally, given the lower fibre volume fraction of the former. 

The enhancement in the interlaminar shear strength can be ascribed to a lowering in the resinviscosity at the initial curing stage of microwave processing, before the cross-linking density starts to rise rapidly and the resin becomes very viscous; in which case no significant change in the composite physical properties could occur. 

due to the complexity of woven fabric composites compared to unidirectional composites, the interlaminar fracture behaviour under Mode I, Mode II and mixed Mode The authorand II loading could also be investigated in order to have a more in depth understanding of the main failure modes. 

Calculations based on the dielectric data measured for Hexply 6376 by Atkinson [31] show that the skin depth at the frequencies used in the present work is between 0.5 and 2.2 cm. 

The sample temperature was constantly monitored by the computer via a serial connection (RS-232) with the fluoroptic thermometer. 

This 50% cure cycle time reduction between conventional and microwave RTM processing wasachieved due to the different nature of interaction between the resin and microwave radiation, which in turn yields a different heating mechanism compared to conventional thermal heating. 

Previous work suggests that by lowering the resin viscosity, improved resin-fibre adhesion and fibre wet-out can be achieved [33-35]. 

As can be seen from Eq.1, the amplifier output power used was proportional to the square of the difference between the set cure temperature and the actual temperature.