Investigation of Environmental Durability of Carbon Fiber/epoxy Composites PDF Download

Author: Samet Yağmur
Publisher:
ISBN:
Category : Carbon composites
Languages : en
Pages : 170

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Book Description
Fiber reinforced polymer composites, that have increasing demand in many applications such as aircraft and automotive industry, are usually exposed to different environmental conditions which may be harmful to them. The investigation of their environmental durability is critical for those applications. The objective of this study was to investigate the effects of temperature and moisture on durability of carbon fiber reinforced epoxy composites. For this purpose, 0/90° woven, plain unidirectional and non-crimp biaxial ±45 fabrics were used as reinforcement. The specimens were manufactured using vacuum resin infusion process to obtain relatively high fibre volume fraction ratios. The composites manufactured were exposed to cyclic aging conditions to simulate aircraft flight environment. Hygrothermal, high temperature and freezing conditions were used as in one cycle which was 12 hours long. Moisture absorption was determined by weighing the specimens at regular intervals as a function of aging cycles. Tensile and flexural tests were performed prior to aging and after 500, 1000 and 1500 hours aging. After the completion of aging cycles, the moisture content did not increase significantly due to presence of subzero and high temperatures in aging cycles. The mechanical test results revealed differences based on the fabric types used. It was found that the tensile strength and modulus values of woven composites increased after aging cycles as compared to those of unidirectional and biaxial composites. On the other hand, flexural properties decreased at the end of the aging cycles for the composites aged as test coupons.

Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 17

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Book Description
An investigation has been completed which determines the physiochemical mechanisms of environmental durability and degradation of graphite-epoxy (Thornel T300 in 5208 epoxy) and fiber glass-epoxy S-2 glass in 5208 epoxy) under hydro-thermal (high moisture and temperature) exposure. Surface energy and moisture diffusion analysis provide nondestructive test methods which detect irreversible degradatiion of the fiber-matrix interface. Dynamic mechanical damping detects reversible volumetric plasticization effect on modulus, and the interlaminar shear strength and transfibrous fracture energy distributions. A composite durability characterization program is demonstrated which effectively combines preventative nondestructive evaluation (PNDE) with environmental failure and micromechanics analysis of composite structural reliability.

Author: Christopher C. Pauly
Publisher:
ISBN:
Category : Nature
Languages : en
Pages : 64

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Book Description
The increasing acceptance and incorporation of fiber-reinforced polymer matrix composites (PMCs) as engineering construction materials have led many to look to the infrastructure as an application for these versatile materials. One such system is pultruded graphite fiber-reinforced epoxy (graphite/epoxy). Some PMC systems degrade when subjected to environmental conditions (e.g., moisture, stress, UV light, electrochemical polarization). These variables are typically studied either singularly or in series, but in real applications (e.g., aerospace, marine, infrastructure), these materials are subjected to many of these conditions simultaneously. To simulate field conditions, this study investigated the combined effects of an aqueous environment, electrochemical polarization, and applied bending stress on the durability of a pultruded graphite/epoxy composite. The findings indicate that graphite/epoxy composites cannot be assumed to be insensitive to degradation by environmental variables. Further, electrochemical polarization, as might occur with contact with a metal such as a fastener, can accelerate degradation. This damage requires the presence of moisture. Chloride and sulfate concentrations in rain are sufficient to establish an electrolyte within creviced regions, but deicing salts would overtake these as a contributor to conductivity. Further findings may be summarized as follows: 1.) Application of polarization in an aerated 0.6M NaCl environment led to breakdown of the fiber/matrix interface. The high pH environment created during the oxygen reduction reaction was necessary but not sufficient to create this breakdown, as the unpolarized specimen exposed to a pH 13 environment did not degrade. Cathodic polarization as would occur by coupling to steel or aluminum is required. 2.)Application of cathodic polarization did not significantly alter strength. Average measurements of shear strength, however, did decrease with the application of cathodic polarization for 70 and 90 days.

Author: George S. Springer
Publisher: CRC Press
ISBN:
Category : Technology & Engineering
Languages : en
Pages : 222

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Book Description

Author: Shloka Vemuganti
Publisher:
ISBN:
Category : Electronic dissertations
Languages : en
Pages : 98

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Book Description
The effects of environment on the interfacial bond strength of carbon fiber tow embedded in epoxy resin are being studied through accelerated aging experiments and pull-out tests (PT). The goal is to examine the synergistic effects of hot, cold, wet, dry and stressed environment on interfacial bond strength (IFBS) of carbon/epoxy composites in order to forecast life of composites in severe environments. The PT specimens were prepared by embedding a fixed length of a carbon fiber tow in uncured epoxy. The interfacial debonding between resin and fiber tow is the targeted mode of failure. A spring loaded frame was designed for applying a preset load to multiple PT specimens. All the PT specimens including the frames with the stressed specimens were subjected to accelerated environmental aging conditions for different time intervals. The moisture absorption and desorption data were recorded. The PT tests were then carried out by pulling the carbon fiber tow from the cylindrical resin, mounted in a screw driven MTS testing machine. Average IFBS of approximately 21.5 MPa was observed for the unaged control sample. The hot/wet/stressed (70°C/3% moisture/2 lb) specimens show a significant degradation ( -29.03 %) in bond strength after 176 days of aging time. The degradation due to moisture is seen to be more critical under the influence of temperatures (50°C, 70°C). In order to obtain the maximum interfacial shear strength for various embedded lengths and environmental aging parameters, a numerical analysis has been carried out using a 3D finite element model (FEM). A FEM analysis was done using cohesive elements at the fiber/matrix interface in order to study the environmental aging effects at the interface. The predicted bond strength from the numerical analysis was compared with the experimental data. A reasonable agreement was observed between experimental data and Finite Element Analysis (FEA).

Author: Douglas Chen
Publisher:
ISBN:
Category :
Languages : en
Pages : 118

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Book Description
Carbon fiber/epoxy composites are a vital and heavily used component in a variety of industries, ranging from aerospace to sports. However, major difficulties may soon arise in regard to environmental considerations for their disposal. These composites are designed to be strong and resilient, and thus are difficult to break down or decompose. The only current option for carbon fiber/epoxy composite wastes is to leave them in landfills or plane graveyards. The high price of carbon fiber also makes finding ways to recover and reuse carbon fiber very attractive. The purpose of this dissertation is to investigate an inexpensive method to break down the epoxy in carbon fiber/epoxy composites and recover fibers while maintaining their mechanical strength. A new chemical solvolysis process was utilized to oxidize and decompose the epoxy in carbon fiber-reinforced epoxy composites, allowing for carbon fiber recovery and recycling. This process involved heating the composite in a mixture of ethanol and hydrogen peroxide at elevated temperatures for 4 hours. This process results in significant epoxy removal with minimal fiber strength loss. Epoxy removal was confirmed with visual and mass analysis, scanning electron microscopy and electron dispersive spectroscopy, and thermogravimetric analysis. The liquid byproduct solution remaining was chemically analyzed using gas chromatography/mass spectroscopy and found to contain organic compounds that could be attributed to the degradation of epoxy by the solution. A kinetic model was developed for the purpose of identifying optimal parameters for the reaction. Parameters considered included time, temperature, concentrations of the reactants, and the amount of surface area exposed to the oxidizing solution. Mass loss over time was studied for each reaction variable while keeping the other parameters static, creating a mass loss rate that could be plotted against each parameter. The fittings for these plots were used to identify the constants to be used in the model. The model was compared to experimental data and found to correlate well, with an average error below 8%. The new chemical solvolysis process in this study was compared to using 98% pure sulfuric acid to dissolve the epoxy. The solvolysis process was found to remove epoxy at a higher rate, while keeping similar fiber strength when comparing samples processed for similar fiber recovery performance. These comparisons resulted in the conclusion that the solvolysis process performs better than dissolution by sulfuric acid. A further modification to the solvolysis process involves the same mixture of ethanol and hydrogen peroxide with the addition of ferrous ions in an acidic environment. This process could potentially be done at lower temperatures and lower concentrations of hydrogen peroxide, and thus could allow for a reduction in costs when recovering fibers using this process. Initial experiments did confirm the ability to remove significant amounts of epoxy at much lower temperatures and lower concentrations of hydrogen peroxide.

Author: Avinash Reddy Akepati
Publisher:
ISBN:
Category : Electronic dissertations
Languages : en
Pages : 116

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Book Description
The effect of environmental and loading conditions on the degradation of Interlaminar Shear Strength (ILSS) of the carbon-epoxy composite specimens was studied in the current research. The hygrothermal conditions capture the synergistic effects of field exposure and extreme temperatures. Short beam shear tests (SBST) were performed to determine the Interlaminar Shear Strength (ILSS) of environmentally aged composite specimens in accordance with ASTM D2344-84. Initially, a standard two-dimensional cohesive layer constitutive model with a cubic traction-separation law was employed in order to simulate the experiment using an in-house Finite Element Analysis code (NOVA-3D). Numerical instabilities encountered using the standard elastic cohesive layer model were overcome by incorporating viscoelastic regularization in the constitutive equations of the cohesive layer. This modification also enabled the analysis to continue beyond the point of peak failure load. The model was able to accurately simulate the load-deflection behavior of most of the SBST specimens aged under various hygrothermal and synergistically applied stress conditions. Further, the effect of displacement rate on ILSS of specimens was studied using NOVA-3D. A PC based life prediction software, Composite Performance Predictive Tool (CPPT), was developed using a mechanism-based degradation model in order to predict the life of a composite structure under given environmental and loading conditions. The software was benchmarked using the test data.

Author: Celine A Mahieux
Publisher: Elsevier
ISBN: 0080531059
Category : Technology & Engineering
Languages : en
Pages : 323

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Book Description
Thanks to their low density and tailored properties, polymer matrix composites are attractive candidates for a large number of industrial applications ranging from aerospace to transportation and energy. However, the behaviour of polymer-based materials is strongly affected by a number of environmental factors. Environmental Degradation in Industrial Composites provides vital information on the effects of environmental factors such as temperature, liquid and gas exposure, electrical fields and radiations, and how micro- and micromechanical calculations during design and manufacture must take these effects into account. The book concludes with reviews on standard and specific testing methods for the various environmental factors and their combinations, helping mechanical/materials engineers and specifiers to predict possible changes due to environmental conditions. Each chapter is supplemented by industrial case studies to help in the understanding of degradation of composites in real life situations.This book will help you to...* Understand how environmental factors lead to degradation effects in polymer matrix composite structures* Build these factors into calculations when predicting the part performance and lifetime of structures* Compare real-life situations from case studies with your predicted results* Predict probable composite behaviour with greater accuracy This book will help you to...* Understand how environmental factors lead to degradation effects in polymer matrix composite structures* Build these factors into calculations when predicting the part performance and lifetime of structures* Compare real-life situations from case studies with your predicted results* Predict probable composite behaviour with greater accuracy

Author: Arya Uthaman
Publisher: Elsevier
ISBN: 0443155461
Category : Technology & Engineering
Languages : en
Pages : 448

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Book Description
The usage of composites is a broad and growing area of scientific research, especially in developed and developing countries. These materials are used in a broad range of applications in both structural and civil engineering sectors. In many of these applications FRPs are exposed to one or more environmental influences, so they need to be designed to meet durability requirements to withstand even the harshest of environments. Aging and Durability of FRP Composites and Nanocomposites focuses on the latest developments in durability and long-term ageing studies of composite materials especially for those used in civil and structural engineering applications. The book will be a valuable reference resource for materials scientists and engineers who want to learn more about the long-term service life and durability behaviour of composites under different environmental conditions. Discusses composites and polymer nanocomposites Reviews different types of aging processes and degradation mechanisms in composites Covers different types of accelerated aging tests Presents theory, modeling, and simulation studies of aged composites and nanocomposites Looks at recent trends and future possibilities

Author: Jyotishkumar Parameswaranpillai
Publisher: John Wiley & Sons
ISBN: 3527346783
Category : Technology & Engineering
Languages : en
Pages : 450

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Book Description
Discover a one-stop resource for in-depth knowledge on epoxy composites from leading voices in the field Used in a wide variety of materials engineering applications, epoxy composites are highly relevant to the work of engineers and scientists in many fields. Recent developments have allowed for significant advancements in their preparation, processing and characterization that are highly relevant to the aerospace and automobile industry, among others. In Epoxy Composites: Fabrication, Characterization and Applications, a distinguished team of authors and editors deliver a comprehensive and straightforward summary of the most recent developments in the area of epoxy composites. The book emphasizes their preparation, characterization and applications, providing a complete understanding of the correlation of rheology, cure reaction, morphology, and thermo-mechanical properties with filler dispersion. Readers will learn about a variety of topics on the cutting-edge of epoxy composite fabrication and characterization, including smart epoxy composites, theoretical modeling, recycling and environmental issues, safety issues, and future prospects for these highly practical materials. Readers will also benefit from the inclusion of: A thorough introduction to epoxy composites, their synthesis and manufacturing, and micro- and nano-scale structure formation in epoxy and clay nanocomposites An exploration of long fiber reinforced epoxy composites and eco-friendly epoxy-based composites Practical discussions of the processing of epoxy composites based on carbon nanomaterials and the thermal stability and flame retardancy of epoxy composites An analysis of the spectroscopy and X-ray scattering studies of epoxy composites Perfect for materials scientists, polymer chemists, and mechanical engineers, Epoxy Composites: Fabrication, Characterization and Applications will also earn a place in the libraries of engineering scientists working in industry and process engineers seeking a comprehensive and exhaustive resource on epoxy composites.