Electrolytes have been identified as some of the most influential components in the performance of electrochemical supercapacitors (ESs), which include: electrical double-layer capacitors, pseudocapacitors and hybrid supercapacitors. This paper reviews recent progress in the research and development of ES electrolytes. The electrolytes are classified into several categories, including: aqueous, organic, ionic liquids, solid-state or quasi-solid-state, as well as redox-active electrolytes. Effects of electrolyte properties on ES performance are discussed in detail. The principles and methods of designing and optimizing electrolytes for ES performance and application are highlighted through a comprehensive analysis of the literature. Interaction among the electrolytes, electro-active materials and inactive components (current collectors, binders, and separators) is discussed. The challenges in producing high-performing electrolytes are analyzed. Several possible research directions to overcome these challenges are proposed for future efforts, with the main aim of improving ESs' energy density without sacrificing existing advantages (e.g., a high power density and a long cycle-life) (507 references).

A review of electrolyte materials and compositions for electrochemical supercapacitors

The science and technology of ultracapacitors are reviewed for a number of electrode materials, including carbon, mixed metal oxides, and conducting polymers. More work has been done using microporous carbons than with the other materials and most of the commercially available devices use carbon electrodes and an organic electrolytes. The energy density of these devices is 3¯5 Wh/kg with a power density of 300¯500 W/kg for high efficiency (90¯95%) charge/discharges. Projections of future developments using carbon indicate that energy densities of 10 Wh/kg or higher are likely with power densities of 1¯2 kW/kg. A key problem in the fabrication of these advanced devices is the bonding of the thin electrodes to a current collector such the contact resistance is less than 0.1 cm2. Special attention is given in the paper to comparing the power density characteristics of ultracapacitors and batteries. The comparisons should be made at the same charge/discharge efficiency.

Ultracapacitors: Why, How, and Where is the Technology

: An overview of the virtual crack closure technique is presented. The approach used is discussed, the history summarized, and insight into its applications provided. Equations for two-dimensional quadrilateral elements with linear and quadratic shape functions are given. Formula for applying the technique in conjuction with three-dimensional solid elements as well as plate/shell elements are also provided. Necessary modifications for the use of the method with geometrically nonlinear finite element analysis and corrections required for elements at the crack tip with different lengths and widths are discussed. The problems associated with cracks or delaminations propagating between different materials are mentioned briefly, as well as a strategy to minimize these problems. Due to an increased interest in using a fracture mechanics based approach to assess the damage tolerance of composite structures in the design phase and during certification, the engineering problems selected as examples and given as references focus on the application of the technique to components made of composite materials.

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Virtual crack closure technique: History, approach, and applications

Inspired by the unique and efficient wound healing processes in biological systems, several approaches to develop synthetic polymers that can repair themselves with complete, or nearly complete, autonomy have recently been developed. This review aims to survey the rapidly expanding field of self-healing polymers by reviewing the major successful autonomic repairing mechanisms developed over the last decade. Additionally, we discuss several issues related to transferring these self-healing technologies from the laboratory to real applications, such as virgin polymer property changes as a result of the added healing functionality, healing in thin films v. bulk polymers, and healing in the presence of structural reinforcements.

Self-healing polymers and composites

Carbon nanotubes and graphene are some of the most intensively explored carbon allotropes in materials science. This interest mainly resides in their unique properties with electrical conductivities as high as 104 S cm−1, thermal conductivities as high as 5000 W m−1 K and superior mechanical properties with elastic moduli on the order of 1 TPa for both of them. The possibility to translate the individual properties of these monodimensional (e.g. carbon nanotubes) and bidimensional (e.g. graphene) building units into two-dimensional free-standing thick and thin films has paved the way for using these allotropes in a number of applications (including photocatalysis, electrochemistry, electronics and optoelectronics, among others) as well as for the preparation of biological and chemical sensors. More recently and while recognizing the tremendous interest of these two-dimensional structures, researchers are noticing that the performance of certain devices can experience a significant enhancement by the use of three-dimensional architectures and/or aerogels because of the increase of active material per projected area. This is obviously the case as long as the nanometre-sized building units remain accessible so that the concept of hierarchical three-dimensional organization is critical to guarantee the mass transport and, as consequence, performance enhancement. Thus, this review aims to describe the different synthetic processes used for preparation of these three-dimensional architectures and/or aerogels containing either any or both allotropes, and the different fields of application in which the particular structure of these materials provided a significant enhancement in the efficacy as compared to their two-dimensional analogues or even opened the path to novel applications. The unprecedented compilation of information from both CNT- and graphene-based three-dimensional architectures and/or aerogels in a single revision is also of interest because it allows a straightforward comparison between the particular features provided by each allotrope.

Three dimensional macroporous architectures and aerogels built of carbon nanotubes and/or graphene: synthesis and applications

The introduction of carbon nanotubes (CNTs) into conventional fibre-reinforced polymer composites creates a hierarchical reinforcement structure and can significantly improve composite performance. This paper reviews the progress to date towards the creation of fibre reinforced (hierarchical) nanocomposites and assesses the potential for a new generation of advanced multifunctional materials. Two alternative strategies for forming CNT-based hierarchical composites are contrasted, the dispersion of CNTs into the composite matrix and their direct attachment onto the primary fibre surface. The implications of each approach for composite processing and performance are discussed, along with a summary of the measured improvements in the mechanical, electrical and thermal properties of the resulting hierarchical composites.

Carbon nanotube-based hierarchical composites: a review

Composite Failure Analysis Handbook. Volume 2. Technical Handbook/ Part 2. Atlas of FractographsMetal FailuresMetallography in Failure AnalysisTitanium AlloysFailure Analysis HandbookFractography in Failure Analysis. A Symposium Presented at May Committee Week, American Society for Testing and Materials, ASTM, Toronto,Ont. 1977Failure Analysis of Engineering StructuresCompositional and Failure Analysis of PolymersFRACTOGRAPHY IN FAILURE ANALYSISPAPERS PRESENTED AT A SYMPOSIUM HELD DURING THE MAY COMMITTEE WEEKASTMAMERICAN SOCIETY FOR TESTING AND MATERIALS, COMMITTEE E-24 ON FRACTURE TESTING OF MATERIALS.The Fracture of Brittle MaterialsMetallurgical Failure AnalysisDamage and Fracture MechanicsFracture Failure Analysis of Fiber Reinforced Polymer Matrix CompositesFractography of Ceramic and Metal FailuresPractical Engineering Failure AnalysisAnalyzing FailuresFailure Analysis and PreventionCharacterization and Failure Analysis of PlasticsFailure Analysis Case Studies IINotes on the Value of Fractography in Failure AnalysisFractography of Ceramic and Metal FailuresFractography in Failure Analysis of PolymersFailure Analysis in Engineering ApplicationsFractography in Failure AnalysisFractography and Failure AnalysisFractography and Failure Mechanisms of Polymers and CompositesFailure Analysis and Fractography of Polymer CompositesSpecial Fractographic Techniques for Failure AnalysisFailure Analysis of Heat Treated Steel ComponentsMetallurgy of Failure AnalysisMicroscopy, Fractography and Failure AnalysisFractography in Failure AnalysisPlastics Failure Analysis and PreventionFractography in the Failure Analysis of Corroded Fracture SurfacesFractographyDeformation and Fracture Behaviour of Polymer MaterialsFractography in Failure AnalysisThe Fracture of Brittle MaterialsDamage and Fracture MechanicsFractography in Failure Analysis Fractographic information retrieval from oxidized or corroded fracture surfaces is very important in failure analysis. In order to determine the mode of failure, the surface oxides must be removed without destroying the original surface morphology of the fracture. Over the years, several methods have been utilized in the removal of surface oxides. However, chemical dissolution of the oxides coupled with ultrasonic cleaning has been the most effective. The effectiveness of two commercially available proprietary products and of orthophosphoric acid in the removal of surface oxides without destroying the fracture surfaces is discussed. Three case histories, in which each of the chemicals has been utilized, are presented. The fractographic information obtained in each case was supported by metallography. Orthophosphoric acid, when coupled with ultrasonic cleaning, is very effective in the removal of oxides from fracture surfaces.This book covers the most recent advances in the deformation and fracture behaviour of polymer material. It provides deeper insight into related morphology–property correlations of thermoplastics, elastomers and polymer resins. Each chapter of this book gives a comprehensive review of state-of-the-art methods of materials testing and diagnostics, tailored for plastic pipes, films and adhesive systems as well as elastomeric components and others. The investigation of deformation and fracture behaviour using the experimental methods of fracture mechanics has been the subject of intense research during the last decade. In a systematic manner, modern aspects of fracture mechanics in the industrial application of polymers for bridging basic research and industrial development are illustrated by multifarious examples of innovative materials usage. This book will be of value to scientists, engineers and in polymer materials science.This book covers recent advancement methods used in analysing the root cause of engineering failures and the proactive suggestion for future failure prevention. The techniques used especially non-destructive testing such X-ray are well described. The failure analysis covers materials for metal and composites for various applications in mechanical, civil and electrical applications. The modes of failures that are well explained include fracture, fatigue, corrosion and high-temperature failure mechanisms. The administrative part of failures is also presented in the chapter of failure rate analysis. The book will bring you on a tour on how to apply mechanical, electrical and civil engineering fundamental concepts and to understand the prediction of root cause of failures. The topics explained comprehensively the reliable test that one should perform in order to investigate the cause of machines, component or material failures at the macroscopic and microscopic level. I hope the material is not too theoretical and you find the case study, the analysis will assist you in tackling your own failure investigation case.Recognized for their superior strength, corrosion/oxidation resistance, and biocompatibility, titanium alloys are particularly intriguing to engineers, scientists, and metallurgists in aerospace, biomedical, and other industrial applications. Titanium Alloys: An Atlas of Structures and Fracture Features uses award-winning micrographs and fractographs to illustrate how alloy microstructures are affected by various thermomechanical treatments present in real world operating conditions. This book is the first of its kind to compile microstructural and fracture features for titanium alloys and titanium aluminides as well as capture its fractographic features together with the conditions that produced failure. The author discusses the physical metallurgy of titanium alloys as a standard for observing microstructures and their failures. Then she combines the skillful use of scanning electron microscopy in fracture analysis and an eye for detail to deliver a visual presentation of fracture surfaces generated under different loading conditions, including ductile, fatigue, intergranular, and cleavage fractures. Especially helpful to those engaged in failure analysis of titanium components, the book includes a case study applying key criteria to the service failure of a defective titanium alloy component. Supported byadditional background data such as types, compositions, phase transformations, microstructures, and typical fractographs, Titanium Alloys: An Atlas of Structures and Fracture Features offers exceptional insight into the structure-property correlations of titanium alloys.This book contains analysis of reasons that cause products to fail. General methods of product failure evaluation give powerful tools in product improvement. Such methods, discussed in the book, include practical risk analysis, failure mode and effect analysis, preliminary hazard analysis, progressive failure analysis, fault tree analysis, mean time between failures, Wohler curves, finite element analysis, cohesive zone model, crack propagation kinetics, time-temperature collectives, quantitative characterization of fatigue damage, and fracture maps. Methods of failure analysis are critical to for material improvement and they are broadly discussed in this book. Fractography of plastics is relatively a new field which has many commonalities with fractography of metals. Here various aspects of fractography of plastics and metals are compared and contrasted. Fractography application in studies of static and cycling loading of ABS is also discussed. Other methods include SEM, SAXS, FTIR, DSC, DMA, GC/MS, optical microscopy, fatigue behavior, multiaxial stress, residual stress analysis, punch resistance, creep-rupture, impact, oxidative induction time, craze testing, defect analysis, fracture toughness, activation energy of degradation. Many references are given in this book to real products and real cases of their failure. The products discussed include office equipment, automotive compressed fuel gas system, pipes, polymer blends, blow molded parts, layered, cross-ply and continuous fiber composites, printed circuits, electronic packages, hip implants, blown and multilayered films, construction materials, component housings, brake cups, composite pressure vessels, swamp coolers, electrical cables, plumbing fittings, medical devices, medical packaging, strapping tapes, balloons, marine coatings, thermal switches, pressure relief membranes, pharmaceutical products, window profiles, and bone cements.In order to assist the investigator of service failures, work was performed using electron fractographic methods to resolve three separate problems that have not been solvable using the more conventional macroor light microscopic techniques. Three independent problems were examined, and solutions were achieved. These were: (1) determination of fracture direction in thin sheet metal components, (2) differentiating between hydrogen embrittlement and stress corrosion in high-strength steels, and (3) determination of applied cyclic stress as a function of fatigue striation spacing.The First African InterQuadrennial ICF Conference “AIQ-ICF2008” on Damage and Fracture Mechanics – Failure Analysis of Engineering Materials and Structures”, Algiers, Algeria, June 1–5, 2008 is the first in the series of InterQuadrennial Conferences on Fracture to be held in the continent of Africa. During the conference, African researchers have shown that they merit a strong reputation in international circles and continue to make substantial contributions to the field of fracture mechanics. As in most countries, the research effort in Africa is undtaken at the industrial, academic, private sector and governmental levels, and covers the whole spectrum of fracture and fatigue. The AIQ-ICF2008 has brought together researchers and engineers to review and discuss advances in the development of methods and approaches on Damage and Fracture Mechanics. By bringing together the leading international experts in the field, AIQ-ICF promotes technology transfer and provides a forum for industry and researchers of the 

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Failure Analysis and Fractography of Polymer Composites

The feasibility of reinforcing conventional carbon fiber composites by grafting carbon nanotubes (CNTs) onto the fiber surface has been investigated. Carbon nanotubes were grown on carbon fibers using the chemical vapor deposition (CVD) method. Iron was selected as the catalyst and predeposited using the incipient wetness technique before the growth reaction. The morphology of the products was characterized using scanning electron microscopy (SEM), which showed evidence of a uniform coating of CNTs on the fiber surface. Contact angle measurements on individual fibers, before and after the CNT growth, demonstrated a change in wettability that can be linked to a change of the polarity of the modified surface. Model composites based on CNT-grafted carbon fibers/epoxy were fabricated in order to examine apparent interfacial shear strength (IFSS). A dramatic improvement in IFSS over carbon fiber/epoxy composites was observed in the single fiber pull-out tests, but no significant change was shown in the push-ou...

Hierarchical Composites Reinforced with Carbon Nanotube Grafted Fibers: The Potential Assessed at the Single Fiber Level

Structural power composites

Carbon nanotubes (CNTs) were grafted on IM7 carbon fibres using a chemical vapour deposition method. The overall grafting process resulted in a threefold increase of the BET surface area compared to the original primary carbon fibres (0.57 m 2 /g). At the same time, there was a degradation of fibre tensile strength by around 15% (depending on gauge length), due to the dissolution of iron catalyst into the carbon; the modulus was not significantly affected. The wetting behaviour between fibres and poly(methyl methacrylate) (PMMA) was directly quantified using contact angle measurements for drop-on-fibre systems and indicated good wettability. Single fibre fragmentation tests were conducted on hierarchical fibre/PMMA model composites, demonstrating a significant (26%) improvement of the apparent interfacial shear strength (IFSS) over the baseline composites. The result is associated with improved stress transfer between the carbon fibres and surrounding matrix, through the grafted CNT layer. The improved IFSS was found to correlate directly with a reduced contact angle between fibre and matrix.

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Emile S. Greenhalgh

Papers

Carbon nanotube-based hierarchical composites: a review

Failure Analysis and Fractography of Polymer Composites

Hierarchical Composites Reinforced with Carbon Nanotube Grafted Fibers: The Potential Assessed at the Single Fiber Level

Structural power composites

Carbon nanotube grafted carbon fibres: A study of wetting and fibre fragmentation