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Author: Palak B. Patel
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Book Description
Advanced structural fiber composite materials have lightweight, multi-directional, and tailorable properties which are vital for weight-critical applications such as aerospace vehicles. Nanoengineered aerospace-grade composites have been developed to have integrated multifunctionalities while ensuring maintained, or even enhanced, mechanical properties, without significant changes in the dimension or weight of the composite system. While integrating individual multifunctionalities into such composites has been demonstrated in a limited set of cases, integrating more than one multifunctionality has not yet been explored. This thesis focuses on the manufacturing and characterization of a nanoengineered integrated multifunctional composite (IMC), that would enable the inclusion of more than one multifunctional capability, while maintaining or enhancing structural function. To this end, a glass fiber reinforced polymer (GFRP) unidirectional-ply composite laminate was nanoengineered with carbon nanotubes (CNTs) in the composite's interlaminar regions and surfaces, to produce the IMC. A preliminary study, focusing on the compatibility of CNTs in GFRP and on enhancing the laminate's structural function, determined the preferred CNT architectures to reinforce the interlaminar regions and enable various multifunctionalities. The IMC integrated a commercial CNT film on the outer surfaces and two preferred architectures in the interlaminar region: a 10 μm aligned carbon nanotube (A-CNT) film (termed nanostitch) and a patterned and coherently buckled A-CNT film (termed nanostitch 2.0). The resulting IMCs had an equivalent quality (no detectable voids, insignificant difference in the laminate thickness and interlaminar thickness) to the baseline GFRP system, while demonstrating maintained or enhanced mechanical performance. Relative to the baseline, the IMCs h ave enhanced (∼5%) interlaminar shear strength (ILSS) and maintained notched tensile strength with equivalent damage progression as revealed through in situ testing using synchrotron radiation computed tomography (SRCT). The IMCs demonstrated here, with electrically and thermally conductive interlaminar regions and surfaces, support future demonstrations of multifunctionalities through a composite system designed to serve independent yet synergistic functionalities in life-cycle enhancement, energy savings during manufacturing, in situ cure (manufacturing) monitoring, Joule heating ice protection system (IPS) applications, and in-service damage sensing, among others.
Author: Palak B. Patel
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Book Description
Advanced structural fiber composite materials have lightweight, multi-directional, and tailorable properties which are vital for weight-critical applications such as aerospace vehicles. Nanoengineered aerospace-grade composites have been developed to have integrated multifunctionalities while ensuring maintained, or even enhanced, mechanical properties, without significant changes in the dimension or weight of the composite system. While integrating individual multifunctionalities into such composites has been demonstrated in a limited set of cases, integrating more than one multifunctionality has not yet been explored. This thesis focuses on the manufacturing and characterization of a nanoengineered integrated multifunctional composite (IMC), that would enable the inclusion of more than one multifunctional capability, while maintaining or enhancing structural function. To this end, a glass fiber reinforced polymer (GFRP) unidirectional-ply composite laminate was nanoengineered with carbon nanotubes (CNTs) in the composite's interlaminar regions and surfaces, to produce the IMC. A preliminary study, focusing on the compatibility of CNTs in GFRP and on enhancing the laminate's structural function, determined the preferred CNT architectures to reinforce the interlaminar regions and enable various multifunctionalities. The IMC integrated a commercial CNT film on the outer surfaces and two preferred architectures in the interlaminar region: a 10 μm aligned carbon nanotube (A-CNT) film (termed nanostitch) and a patterned and coherently buckled A-CNT film (termed nanostitch 2.0). The resulting IMCs had an equivalent quality (no detectable voids, insignificant difference in the laminate thickness and interlaminar thickness) to the baseline GFRP system, while demonstrating maintained or enhanced mechanical performance. Relative to the baseline, the IMCs h ave enhanced (∼5%) interlaminar shear strength (ILSS) and maintained notched tensile strength with equivalent damage progression as revealed through in situ testing using synchrotron radiation computed tomography (SRCT). The IMCs demonstrated here, with electrically and thermally conductive interlaminar regions and surfaces, support future demonstrations of multifunctionalities through a composite system designed to serve independent yet synergistic functionalities in life-cycle enhancement, energy savings during manufacturing, in situ cure (manufacturing) monitoring, Joule heating ice protection system (IPS) applications, and in-service damage sensing, among others.
Author: Jeonyoon Lee
Publisher:
ISBN:
Category :
Languages : en
Pages : 193
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Book Description
Manufacturing of advanced aerospace-grade structural composites has traditionally utilized autoclaves to impart heat and pressure, in addition to vacuum, to create high-quality, void (defect)- free, reproducible structures. Carbon (micro) fiber reinforced polymer (CFRP) composites, which are pre-impregnated with a thermoset or thermoplastic polymer to form prepreg sheets, are in widespread use via autoclave processing due to their ease of use and high fiber volume fraction. However, autoclaves have high capital costs, and incur high operating costs due to the convective heating and applied pressure. Furthermore, the fixed capacity of an autoclave limits the size and design of composite parts, and the production rate is limited by autoclave availability. As a result, there has been an increasing interest in the development of alternatives, for example, out-of-autoclave (OoA) specially-formulated prepregs that only require heat and vacuum (i.e., pressure is not required). OoA prepreg processing also has drawbacks due to their specialized morphological and chemical formulation for vacuum-only conditions, as well as part quality (especially, composite interlaminar properties) that is below autoclave-processed materials. In light of the limitations described above, this dissertation (1) develops a novel prepreg processing technique, termed 'out-of- oven' (OoO) curing, that conductively cures OoA prepregs via nanoengineered resistive heating; (2) expands the applicability of the OoO process to conventional autoclave-formulated prepregs; and (3) introduces multifunctionality in the form of cure status sensing. Characteristics of the OoO process using a CNT film as a heating element are first examined and compared to those of an oven curing process, focusing on an aerospace-grade OoA-formulated unidirectional aerospace-grade CFRP prepreg system. Thermophysical and mechanical property comparisons suggest that there is no difference in laminates cured via OoO and oven curing as evaluated by void content, degree of cure analysis, short beam shear interlaminar testing, dynamic mechanical analysis, and double-edge notch tensile testing. The OoO process reduces electrical energy consumption by two orders of magnitude (from 13.7 to 0.12 MJ) due to conductive vs. convective heating, under a typical industrial curing condition for a small (60 mm x 50 mm) test panel. Modeling shows that for parts beyond a meter-scale, energy savings will also be at least two orders of magnitude. Moreover, comparative finite element modeling of the OoO and oven curing shows excellent agreement with measured values, including the reduction in electrical energy and instantaneous power consumption. Altogether, these findings show that OoO curing works for OoA prepreg systems, with significant energy savings. Given the results of the first study, the next study effectively removes the need for an autoclave by adapting the OoO process to conventional autoclave-formulated prepreg systems that currently require applied pressure of ~700 kPa in addition to vacuum. This technique entails OoO curing plus insertion of a nanoporous network (NPN, e.g., vertically aligned CNT arrays) into the interlaminar regions of autoclave-formulated composite laminates. Capillary pressure due to the NPN is calculated to be of the same order as the pressure applied in conventional autoclave processing. Results show that capillary-enhanced polymer wetting by the NPN enables sufficient reduction of interlaminar voids to levels commensurate with autoclave-processed composites. Thermophysical property comparisons and short beam shear interlaminar strength testing show that OoO-processed composites with NPN are equivalent to those of autoclave-cured composites, with energy and other savings similar to OoO curing with OoA prepreg in the first study. Conformability of the NPN to the micron-scale topology of the prepreg surface, and continuous vacuum channels created by the NPN, are identified as key factors underlying interlaminar void reduction. Finally, this dissertation introduces a multifunctional aspect of the OoO manufacturing: an in situ cure status monitoring technique utilizing the nanostructured CNT-based heating element of the OoO process. The OoO heating elements are nanoporous and CNT-based, but in this study have different morphology (randomly-oriented or in-plane aligned CNTs) than the NPN (vertically aligned CNTs, A-CNTs). As OoO curing proceeds and the heating element is powered, the adjacent polymer flows into the nanoporous heater via capillary action. Based on cure status sensing experiments and theoretical models, it is found that electrical resistance changes of the heating element correspond to several mechanisms associated with different stages in the cure process, including polymer infiltration into the CNT network that causes the average CNT-CNT junction distance to increase, giving a resistance increase. Later in the manufacturing, as the polymer cross-linking occurs after infiltration into the heating element, chemical cure shrinkage decreases the CNT-CNT junction distance, leading to a decrease in resistance. Thus, the heating element is multifunctional as a cure status sensor, and is found to be highly repeatable, demonstrating a new capability to enhance both quality and productivity of composite manufacturing. OoO curing and related processing techniques introduced here are expected to contribute to the design and manufacturing of next-generation multifunctional composite architectures. These processing techniques have several advantages, including: (1) compatibility with a wide range of composite materials, including OoA- and autoclave-formulated prepregs; (2) removal of size and shape constraints on composite components imposed by the use of a heating vessel; (3) manufacturing cost savings by efficient conductive (as opposed to convective) thermal processing; (4) production improvements via the in situ cure status monitoring by multifunctional heating elements as cure sensors; and (5) the potential for spatial heating control to accommodate structural features such as thick and thin transitions. Future work will expand the techniques to thermoplastics and other high-temperature polymers. The OoO techniques are expected to enable several systems-level production and operational savings, such as accelerated cure cycles, that require further study. Other areas of exploration include on-site composite curing and repair, and leveraging the spatial control of heat flux from the OoO technique into other OoA composite processes, such as resin infusion and resin transfer molding.
Author: Xinchen Ni
Publisher:
ISBN:
Category :
Languages : en
Pages : 177
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Book Description
At present, there is a need for novel, scalable, and high-performance structural materials that offer unprecedented combinations of stiffness, strength, and toughness at a low density, which can serve in a variety of applications in the aerospace, transportation, defense, and energy industries. To date, composite materials, specifically advanced carbon fiber reinforced plastics (CFRPs), which are comprised of high specific stiffness and strength continuous carbon microfibers and lightweight, relatively compliant polymers, have been among the most attractive materials and are used extensively in the aerospace sector. However, most CFRPs are fabricated by stacking plies in a layer-by-layer fashion, resulting in a weak polymer-rich region, known as the interlaminar region, at each ply interface that leads to poor properties through the laminate thickness. Although the mechanically superior microfibers are designed to be the primary load carriers, the much weaker polymer matrix causes the laminates to be prone to premature failure with interlaminar delamination, which negatively affects both in-plane and out-of-plane performance. This key shortcoming is known as the Achilles' heel of CFRPs, which hinders their design and wider adoption in critical structural applications. In this dissertation, a novel nanoengineering approach to address the longstanding problem of weak ply interfaces of CFRPs is developed and demonstrated. High densities (>10 billion nanofibers per cm2) of uniformly-distributed vertically aligned carbon nanotubes (A-CNTs) are placed between neighboring plies to bridge the weak polymer-rich interlaminar region in existing prepreg-based laminated composites, creating a hierarchical architecture termed "nanostitch". The effectiveness of nanostitching is evaluated via various mechanical tests including short-beam shear (SBS), Mode I and II fracture, and double edge-notched tension (DENT), in all of which the nanostitched composites have demonstrated enhanced mechanical performance. Furthermore, the multiscale reinforcement mechanisms resulting from the CNTs are elucidated via a variety of ex situ and in situ damage inspection techniques, including optical microscopy, scanning electron microscopy, lab-based micro-computed tomography, and in situ synchrotron radiation computed tomography (SRCT). Specifically, in SBS, despite no increase in static strength, a 115% average increase in fatigue life across all load levels (60 to 90% of static strength), with a larger increase of 249% in high-cycle (at 60% of static strength) fatigue, is observed. In Mode I and Mode II fracture, it is revealed that the interlaminar crack bifurcates into the intralaminar region from the interlaminar precrack, and then propagates within the intralaminar region parallel to the nanostitched interlaminar region as an "intralaminar delamination" in steady state. This unique crack bifurcation phenomenon has never been previously observed and is attributed to the A-CNTs adding interlaminar toughness to a level that causes the interlaminar crack to bifurcate into the less tough intralaminar region. In DENT, an 8% increase in ultimate tensile strength (UTS) is observed and is attributed to the A-CNTs suppressing critical interlaminar delaminations very close to final failure (greater than 90% UTS) via in situ SRCT. In addition to the positive reinforcement results observed for the nanostitched composites, a next-generation higher volume fraction nanostitched composite with additional levels of beneficial hierarchy termed "buckled nanostitch" or "nanostitch 2.0" is created by exploiting the unique buckling behavior displayed by patterned A-CNT forests under compression. This multilevel hierarchical architecture further enhances the composite mechanical performance: SBS strength by 7% and DENT strength by 28%, compared to the baseline composites. The dissertation not only presents a controllable, scalable manufacturing method to produce engineered structural materials that are hierarchically designed down to the nanoscale with enhanced mechanical performance, but it also establishes key new understanding of the complex and coupled strengthening and toughening mechanisms acting at different scales, as well as their effects on macroscopic laminate-level mechanical properties. A particular focus has been the seminal use of in situ SRCT to study the effects of the hierarchical nanoscale reinforcements, and thus the methods established provide an experimental path forward for future work in this area. Together, these advances open up new opportunities for creating next-generation engineered materials with a suite of programmable properties by controlling their structures and constituents across multiple length scales.
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 19
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Book Description
Interlaminar damage in the form of delamination due to the stress concentration is one of the dominant forms in laminated composite structures. One of the approaches to enhance the delamination resistance of the advanced composite structures is to reduce mismatch of elastic properties and the stress concentrations at the interfaces between the laminated layers by utilizing interleave materials. The interleave material considered in this study is a nano-interlayer which can be fabricated in the form of either a thin film of nano-modified epoxy reinforced with vapor grown nanofibers or a fiber mat that can be fabricated with the electrospun fiber process. The nanofibers in the form of a thin film are functionalized with ozone to enhance the interfacial strength between the nanofibers and the surrounding epoxy. To computationally assess the effectiveness of this approach, continuous interface elements of zero thickness are utilized for the characterization of the nano-interlayer. The interface element formulation is based on a cohesive zone model with softening constitutive law. Meanwhile, the experiment was performed with two types of nano-interlayers that are inserted into the laminated composites to monitor initiation and progression of their damage behavior.
Author: Piyush R. Thakre
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
This research is focused on investigating the effect of carbon nanotubes on macroscale composite laminate properties, such as, interlaminar shear strength, interlaminar fracture toughness and electrical conductivity along with studying the micro and nano-scale interactions of carbon nanotubes with epoxy matrix via thermomechanical and electrical characterization of nanocomposites. First an introduction to the typical advanced composite laminates and multifunctional nanocomposites is provided followed by a literature review and a summary of recent status on the processing and the characterization work on nanocomposites and composite laminates. Experimental approach is presented for the development of processing techniques and appropriate characterization methods for carbon nanotubes reinforced epoxy resin based multi-functional nanocomposites and carbon fiber reinforced polymer composite laminates modified with carbon nanotubes. The proposed work section is divided into three sub-sections to describe the processing and the characterization of carbon nanotube reinforced epoxy matrix nanocomposites, woven-carbon fabric epoxy matrix composite laminates modified with selective placement of nanotubes and unidirectional carbon fiber epoxy matrix composite laminates modified with carbon nanotubes. Efforts are focused on comparing the effects of functionalized and unfunctionalized carbon nanotubes on the advanced composite laminates. Covalently functionalized carbon nanotubes are used for improved dispersion and fiber-matrix bonding characteristics and compared with unfunctionalized or pristine carbon nanotubes. The processing of woven carbon fabric reinforced epoxy matrix composite laminates is performed using a vacuum assisted resin transfer molding process with selective placement of carbon nanotubes using a spraying method. The uni-directional carbon fiber epoxy matrix pre-preg composites are processed using a hot press technique along with the spraying method for placement of nanotubes. These macroscale laminates are tested using short beam shear and double cantilever beam experiments for investigating the effect of nanotubes on the interlaminar shear stress and the interlaminar fracture toughness. Fractography is performed using optical microscopy and scanning electron microscopy to investigate the structure-property relationship. The micro and nano-scale interactions of carbon nanotubes and epoxy matrix are studied through the processing of unfunctionalized and functionalized single wall carbon nanotube reinforced epoxy matrix nanocomposites. The multifunctional nature of such nanocomposites is investigated through thermo-mechanical and electrical characterizations.
Author: Ruquan Ye
Publisher:
ISBN: 9789814877275
Category : Graphene
Languages : en
Pages : 88
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Book Description
LIG is a revolutionary technique that uses a common CO2 infrared laser scriber, like the one used in any machine shop, for the direct conversion of polymers into porous graphene under ambient conditions. This technique combines the preparation and patterning of 3D graphene in a single step, without the use of wet chemicals. The ease in the structural engineering and excellent mechanical properties of the 3D graphene obtained have made LIG a versatile technique for applications across many fields. This book compiles cutting-edge research on LIG by different research groups all over the world. It discusses the strategies that have been developed to synthesize and engineer graphene, including controlling its properties such as porosity, composition, and surface characteristics. The authors are pioneers in the discovery and development of LIG and the book will appeal to anyone involved in nanotechnology, chemistry, environmental sciences, and device development, especially those with an interest in the synthesis and applications of graphene-based materials.
Author: Kamal K. Kar
Publisher: Springer
ISBN: 3662495147
Category : Technology & Engineering
Languages : en
Pages : 694
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Book Description
Composite materials are used as substitutions of metals/traditional materials in aerospace, automotive, civil, mechanical and other industries. The present book collects the current knowledge and recent developments in the characterization and application of composite materials. To this purpose the volume describes the outstanding properties of this class of advanced material which recommend it for various industrial applications.
Author: Joseph H. Koo
Publisher: Cambridge University Press
ISBN: 1316094413
Category : Technology & Engineering
Languages : en
Pages : 719
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Book Description
This book is focused primarily on polymer nanocomposites, based on the author's research experience as well as open literature. The environmental health and safety aspects of nanomaterials and polymer nanocomposites, risk assessment and safety standards, and fire toxicity of polymer nanocomposites, are studied. In the final chapter, a brief overview of opportunities, trends, and challenges of polymer nanocomposites are included. Throughout the book, the theme is developed that polymer nanocomposites are a whole family of polymeric materials whose properties are capable of being tailored to meet specific applications. This volume serves as a general introduction to students and researchers just entering the field and to scholars from other subfields seeking information.
Author: William N. Sharpe, Jr.
Publisher: Springer Science & Business Media
ISBN: 0387268839
Category : Mathematics
Languages : en
Pages : 1100
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Book Description
The Springer Handbook of Experimental Solid Mechanics documents both the traditional techniques as well as the new methods for experimental studies of materials, components, and structures. The emergence of new materials and new disciplines, together with the escalating use of on- and off-line computers for rapid data processing and the combined use of experimental and numerical techniques have greatly expanded the capabilities of experimental mechanics. New exciting topics are included on biological materials, MEMS and NEMS, nanoindentation, digital photomechanics, photoacoustic characterization, and atomic force microscopy in experimental solid mechanics. Presenting complete instructions to various areas of experimental solid mechanics, guidance to detailed expositions in important references, and a description of state-of-the-art applications in important technical areas, this thoroughly revised and updated edition is an excellent reference to a widespread academic, industrial, and professional engineering audience.
Author: Rumiana Kotsilkova
Publisher: iSmithers Rapra Publishing
ISBN: 9781847350633
Category : Science
Languages : en
Pages : 352
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Book Description
Thermoset nanocomposites represent a new technology solution. These new formulations benefit from improved dimensional/thermal stability, flame retardancy and chemical resistance; and have potential applications in marine, industrial and construction markets.This book helps to answer questions related to the design of nanocomposites by controlling the processing technology and structure. The book is addressed not only to researchers and engineers who actively work in the broad field of nanocomposite technology, but also to newcomers and students who have just started investigations in this mul.
