Microwave Processing Of Fiber Reinforced Composites (Optimization of Glass Reinforced Epoxy Curing Process)

Microwave curing of polymer matrix composites has proven to be an attractive substitute for conventional thermal curing. Industrial applications are currently developed including telecommunications, aerospace, food industry, enhancement concrete setting, composites manufacturing, and many others. Many universities and research centers around the globe are endeavoring to make use of this technology to the most. Common research objectives include homogeneity of the cure, the acceleration of cure kinetics, cure reaction mechanism, and enhancement of mechanical properties. In order to efficiently utilize this form of energy, precise control over power, temperature, and time were applied to achieve set goals: reduce cure time and thermal overshoots, assure complete cure, and maximize mechanical properties. This work discusses an optimization scenario to achieve these set goals by combining data from calorimetric analysis, insitu temperature and power monitoring, and energy conservation studies. An experimental setup is assembled consisting of laboratory equipped multi mode microwave applicator and programmable feedback controllers. For thermal curing, a typical electric furnace is used with three thermocouples measuring the cavity, mold, and sample temperatures. Test samples consisted of both neat blend of DGEBA resin together with samples of glass fiber reinforced epoxy. Prior to testing, the microwave cavity has been calibrated to approximate heat losses in the system and thus determine the expected data accuracy. Curing experiments for a specific temperature-time profile show that microwave applicator not only follows the set temperature but also eliminates thermal lag and temperature overshoot. While holdback technique could not deliver the required cure cycle, PID control strategy succeeded in homogenously curing successful epoxy and epoxy/fiberglass samples. Kinetic knowledge is enriched using DSC to determine expected curing times at different curing temperatures. Based on these data, a selected isothermal temperature of 100°C was used with variable dwell times between 13-30 minutes for microwave curing. Mechanical testing data shows that microwave cured samples have relatively exceeded the conventionally cured ones in both flexural strength and modulus. The DSC recommended time of cure 13 minutes, at 100 °C, is a good approximate which suggests similar curing mechanism of cure kinetics in both thermal and microwave· methods. High ramp rate, 200 °C/min could also be achieved without material degradation or temperature overshoot by carefully controlling power during the ramp stage. Effect of gelation time and vacuum degassing, being a major time saving area, were also tested. The gelation time has particularly enhanced the flexural modulus of the epoxy samples. In short, the use of efficient process controller resulted in superior mechanical properties at practically optimum time durations

Simulation of carbon fibre composites in an industrial microwave

The ability of microwave radiation to penetrate and interact directly with materials has led to its extensive use in food and drug industries, and more recently in composites manufacturing. Microwave heating of composites allows rapid heat transfer throughout the material thickness with reduced thermal gradients and processing times as well as energy efficiency. Design of microwave systems to process composite parts with various geometries and sizes demands improved understanding of electromagnetic energy distribution and factors influencing it. Finite-element (FE) models can be efficient design tools in such cases, as physical experimentation can be impractical. In this study, a fully-coupled FE model of a carbon fibre composite in an industrial microwave environment is developed using COMSOL Multiphysics®. The effects of the heating process parameters including the number of active magnetrons, specimen thickness and the variation in the frequency of radiation on the electromagnetic field distribution are studied. The FE model showed that a substantial difference in the electromagnetic field distribution exists for the frequencies above 1 GHz compared to the lower frequencies in the microwave regime, resulting in non-uniform heating

Accelerated microwave curing of fibre-reinforced thermoset polymer composites for structural applications: A review of scientific challenges

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 (e.g. 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

Electromagnetic Energy Coupled to Nanomaterial Composites for Polymer Manufacturing

Polymer nano-composites may be engineered with specific electrical properties to achieve good coupling with electromagnetic energy sources. This enables a wide range of novel processing techniques where controlling the precise thermal profile is critical. Composite materials were characterized with a variety of electrical and thermographic analysis methods to capture their response to electromagnetic energy. COMSOL finite element analysis software was used to model the electric fields and resultant thermal profiles in selected samples. Applications of this technology are demonstrated, including the use of microwave and radio frequency energy to thermally weld the interfaces of 3D printed parts together for increased interlayer (Z) strength. We also demonstrate the ability to bond various substrates with carbon nanotube/epoxy composite adhesives using radio frequency electromagnetic heating to rapidly cure the adhesive interface. The results of this work include 3D printed parts with mechanical properties equal to injection molded samples, and RF bonded joints cured 40% faster than traditional oven curing

Fabrication of functional micro/nano-carbon composites based on structural design for electromagnetic shielding （構造設計による機能性マイクロ・ナノコンポジットの開発および電磁波遮蔽への応用）

信州大学(Shinshu university)博士（工学）この博士論文は、次の学術雑誌論文を一部に使用しています。COMPOSITES SCIENCE AND TECHNOLOGY. 172:108-116 (2019); doi:10.1016/j.compscitech.2019.01.013. © 2019 Elsevier Ltd.MATERIALS LETTERS. 245:98-102 (2019); doi:10.1016/j.matlet.2019.02.101. © 2019 Elsevier Ltd.RSC ADVANCES. 9(17):9401-9409 (2019); doi:10.1039/c9ra00028c. © The Royal Society of Chemistry 2019.MATERIALS LETTERS. 236:116-119 (2019); doi:10.1016/j.matlet.2018.10.101. © 2018 Elsevier B.V.ThesisYAN YONGJIE. Fabrication of functional micro/nano-carbon composites based on structural design for electromagnetic shielding　（構造設計による機能性マイクロ・ナノコンポジットの開発および電磁波遮蔽への応用）. 信州大学, 2019, 博士論文. 博士（工学）, 甲第715号, 令和01年09月30日授与.doctoral thesi

Internal Model Control of a Domestic Microwave for Carbon Composite Curing

This paper outlines the conversion of a domestic microwave oven for use in composite curing applications. It compares several strategies for temperature control. The converted oven has vacuum ports, connectors, and fiber optic thermocouple sensors. Experimental data are provided for each control strategy based on a 200 mm× 200 mm eight-ply prepreg laminate. The degree of cure is established for the test samples by thermal analysis techniques. Multiphysics simulation is used to model the electromagnetic and heating effects in the system, and a common and inexpensive method of approximating the available microwave power is used. The low cost of the microwave components and the ease of conversion are desirable characteristicsin this application

Electro-magnetic Responsive Ni0.5Zn0.5Fe2O4 Nano-particle Composite

The purpose of this study is to simulate and synthesize a Radar (or Radiation) Absorbent Material (RAM) by using polymers and nickel zinc ferrite (Ni0.5Zn0.5Fe2O4) magnetic nanoparticles. There is an ardent desire in military, space and electronics for lighter, faster, cheaper and widespread bandwidth providing RAM materials. Electromagnetic property such as magnetic permeability and electric permittivity play a major in controlling the radiation. The appropriate combination of permeability and permittivity properties is acquired for the synthesis of RAM providing wide-ranging bandwidth. The apt property is achieved by rule of mixture, mixing of particular composition of epoxy polymer having low permeability and permittivity with the nickel zinc ferrite magnetic nanoparticle having high permeability and permittivity. In this investigation, we studied the effective relative permeability and permittivity of Ni0.5Zn0.5Fe2O4 nanoparticles encapsulated within the epoxy polymer resin through Finite Element Analysis (FEA) and several various analytical experiments to verify and match both the simulation and experimental results. The FEA model was explored in two different aspect. First, shape of the nanoparticle is assumed to be spherical, cubic and bar structure. Secondly, the distribution of nanoparticle in the epoxy polymer matrix is assumed to be Simple Cubic (SC), Body Center Cubic (BCC), Face Center Cubic (FCC) and Random distributed unit cell. The result is compared with analytic approaches (Maxwell-Garnett (M-G) theory, Bruggeman theory) and Vibrating Sample Magnetometer (VSM) experimental data

Induction heating of carbon fibre reinforced polymer composites : Characterization and modelling

Carbon fibre reinforced polymers (CFRP) are lightweight materials with great potential due to their high strength and stiffness relative to their weight. This enables weight reduction in, for example, vehicles, which is important in reducing energy consumption. Their high strength and stiffness along the fibre direction also enable the development of new types of construction parts. The manufacturing of thermoset-based CFRP is often a time-consuming process with relatively low energy efficiency. Common manufacturing methods such as resin transfer moulding, compression moulding, and autoclaving use significantly more energy than is needed to cure the CFRP part. This is because the heat is transferred conductively via the part surface from a tool with a large mass. However, other potential heating methods are available. Due to the electrical conductivity of carbon fibres, it is possible to use induction heating. This means that the heat is generated directly within the CFRP part without the need to heat a tool with a large thermal mass. The idea of using this technique to heat CFRP is not new, but the anisotropy of the material means that it is associated with a higher level of complexity than the induction heating of metals.To make the heat and temperature distribution more predictable, there is a need for better models and knowledge of how the heat is generated and how the temperature is distributed within CFRP during induction heating. In this thesis, different CFRP configurations were characterized and modelled to provide knowledge and methods for predicting the induction heating behaviour of CFRP. The development of the models has resulted in temperature prediction tools, useful for a wide range of fibre volume fractions, and for both woven and cross-ply layups. Methods for characterization of thermal and electrical input parameters to the models were identified and developed. The temperature distributions predicted by the models were proven to be valid

Study of thermoplastic composite joining technology by electromagnetic induction heating

The development of light structures in the transport field is closely related to the development of manufacturing and processing technologies. The thermoplastic matrix composite materials are very interesting also for the possibility of hot forming by deformation, and their use is continually increasing. Moreover, these materials allow the possibility of performing welded joints of the parts. The automotive industry and aerospace industry seem to be the industrial sectors that have the most significant potential for application of thermoplastic composite materials. The joining of thermoplastic composites could be carried out using hot melt adhesives or with fusion welding of the thermoplastic matrix. The heating of a hot melt adhesive, or the thermoplastic matrix could be carried out with electromagnetic induction technology. This PhD thesis deals with the electromagnetic induction heating of thermoplastic matrix composite materials for adhesive bonding, and also study for the first time the influence of the current frequency on the heat penetration depth. A numerical model was developed using two different Multiphysics Software, such as Jmag and COMSOL; then the models were validated using an experimental campaign. The main original result of the work is that in the case of thermoplastic matrix composites, the higher the current frequency the higher is the depth of the heat penetration, unlike the case of the metal alloys

Characterization and performance of eco and crack-free high-performance concrete for sustainable infrastructure

The main objective of this study is to develop, characterize, and validate the performance of a new class of environmentally friendly, economical, and crack-free high-performance concrete referred to as Eco and crack-free HPC that is proportioned with high content of recycle materials. Two classes of Eco-HPC are designed for: (I) pavement (Eco-Pave-Crete); and (II) bridge infrastructure (Eco-Bridge-Crete). Eco-HPC mixtures were designed to have relatively low binder content up to 350 kg/m3 and develop high resistance to shrinkage and superior durability. A stepwise mixture design methodology was proposed to: (i) optimize binder system and aggregate skeleton to optimize packing density and flow characteristics; (ii) evaluate synergy between shrinkage mitigating materials, fibers, and moist curing duration to reduce shrinkage and enhance cracking resistance; and (iii) validate performance of Eco HPCs. The composition-reaction-property correlations were developed to link the hydration kinetics of various binder systems to material performance in fresh state (rheological properties) and hardened state (strength gain and shrinkage cracking tendency). Results indicate that it is possible to design Eco-HPC with drying shrinkage lower than 300 µstrain after 250 days and no restrained shrinkage cracking even after 55 days. Reinforced concrete beams made with Eco-Bridge-Crete containing up to 60% replacement of cement with supplementary cementitious materials and recycled steel fibers developed significantly higher flexural toughness compared to the reference concrete used for bridge applications. In parallel, autogenous crack healing capability of concrete equivalent mortar mixtures was monitored using microwave reflectometry nondestructive testing technique. Research is in progress towards analyzing life cycle assessment of Eco-HPCs under field condition --Abstract, page iii