Tesi sul tema "Self-healing"

Concrete is a brittle material prone to cracking due to its low tensile strength. Crack repairs are not only expensive and time-consuming but also increase the carbon footprint. Designing a novel concrete material possessing the ability to self-repair cracks would enhance its sustainability. Self-healing can be defined as a material’s ability to repair inner damage without any external intervention. In the case of concrete, the process can be autogenous, based on an optimized mix composition, or autonomous, when additional capsules containing some healing agent and/or bacteria spores are incorporated into the binder matrix. The first process uses unhydrated cement particles as the healing material while the other utilizes a synthetic material or bacteria precipitating calcite which are released into the crack from a broken capsule or activated by access to water and oxygen. The main disadvantages of the autonomous method are the loss of the fresh concrete workability, worsened mechanical properties, low efficiency, low survivability of the capsules and bacteria during mixing and the very high price. On the other hand, the autogenous self-healing was found to be more efficient, more cost effective, safer, and easier to implement in full-scale applications. Knowledge related to mechanisms and key factors controlling the autogenous self-healing is rather limited. Therefore, the aim of this research work was to better understand the autogenous self-healing process of concrete and to optimize the mix design and exposure conditions to maximize its efficiency. This licentiate thesis summarizes the main findings of the first 2.5 years of the PhD project. Several factors affecting autogenous self-healing were studied, including the amount of unhydrated cement, mix composition, age of material, self-healing duration and exposure conditions. The process was investigated both externally, at the surface, and deeper inside of the crack, by evaluating the crack closure and chemical composition of formed self-healing products. In addition, the flexural strength recovery was also studied. It was observed that a large amount of cement in the concrete mix does not ensure an efficient autogenous self-healing of cracks. A very dense and impermeable binder microstructure limited the transport of calcium and silicone ions to the crack and diminished the precipitation of the healing products. Addition fly ash increased the crack closure ratio close to the crack mouth, but its presence did not support the recovery of the flexural strength, presumably due to a very limited formation of load bearing phases inside the crack. Calcium carbonate was detected mainly at the crack mouth, whereas calcium silicate hydrate (C-S-H) and ettringite were found deeper inside the crack. The formation of C-S-H and ettringite presumably resulted in a regain of the flexural strength. On the other hand, calcite crystals formed close to the surface of the specimen controlled conditions inside the crack through its external closure. Healing exposure based on pure water appeared to be inefficient even despite the application of different temperature cycles and water volumes. The application of a phosphate-based retarding admixture in the curing water resulted in the highest self-healing efficiency. The admixture presumably inhibited the formation of a dense hydration shell on the surface of the unhydrated cement grains and promoted the precipitation of calcium phosphate compounds inside the crack. In addition, water mixed with microsilica particles caused a regain of the flexural strength through formation of C-S-H in the crack.

Service life of asphalt roads could be extended by enhancing the natural self-healing ability of asphalt mixtures with encapsulated rejuvenators. When crack damage appears, the capsules release healing agents, which dissolve bitumen to flow into cracks. In this research, a new type of capsules was developed. These capsules contain sunflower oil as a rejuvenating agent. The size, morphology, mechanical strength and thermal stability of these capsules were investigated. The composition of the capsules, which nominally divides these capsules into different types based on their oil content, epoxy-cement shell and polymer amount, and its effect on capsule characteristics were also studied. In addition, the effect of the capsules on the chemical composition of bitumen with time of exposure to broken capsules was evaluated by the FTIR test. Results show that the characteristics of the capsules and their effect on chemical composition allow them to be incorporated in asphalt mixtures for further investigations for their effect on asphalt mechanical performance and self-healing. The mechanical performance of aged asphalt mixtures is investigated by using three nominally different types of capsules. Two of these were protected with a hard shell made of epoxy-cement composite; two coats with 1.0 o/w (oil-to-water), three coats with 1.0 o/w and without the hard shell with 0.5 o/w. The optimum amount of capsules used in all mixtures was 0.5% of total mass of asphalt mixture. Tests started by investigating the effect of mixing and compaction processes on these capsules. Results show that the hard shell (epoxy-cement) was not necessary for the capsules to survive mixing and compaction processes. Capsules deformed and broke with cyclic loading, releasing oil that diffused in the bitumen in less than 24h. Healing of cracks in aged asphalt mixtures led to an increase of stiffness under cyclic loading. However, asphalt specimens with capsules had lower deformation resistance. Computer tomography scanning of specimens showed large reductions in cracks around the capsules, after resting 4 days (96h) at 20oC. The mechanical properties of asphalt mixture containing capsules have been evaluated. Including water sensitivity, particle loss, stiffness and permanent deformation. One type of capsule (0.1 o/w) with three different capsule contents by mass of asphalt mixture were used, 0.1%, 0.25% and 0.5% with oil-to-bitumen ratio 1.1, 2.8 and 5.5, respectively. Capsules were strongly bonded to the asphalt mixture and results showed improved or at least similar mechanical properties to that of asphalt mixtures without capsules. This shows that capsules for asphalt self-healing can be safely used in the road, without affecting its quality. Asphalt containing capsules had slightly lower stiffness (no rest period), which can be easily solved by reducing the size of the capsules in the future. Furthermore, a new method for testing asphalt self-healing by the action of capsules was designed and tested. This method was based on a 3-point bending test (3PB) to beak samples and measure their flexural strength. The test was implemented by comparing the strength recovery of the broken beams after healing to their original flexural strength. The test was first applied to asphalt mastic beams, which are asphalt mixtures with higher bitumen content and fine aggregate and filler. Five different types of capsules used, based on their o/w ratios. These were 0.05, 0.1, 0.2, 0.5 and 1.0 o/w ratios with different amounts depending on their oil content so that they can provide a 7.2% of rejuvenator (sunflower oil) to the asphalt mastic beams. The effect of capsule content on self-healing was investigated by the 3PB on samples containing all those five capsule types (different contents) at one healing temperature, namely 20oC and different healing times. Effect of temperature on healing was investigated as well by 3PB test applied to mastic beams containing one type of capsules with 0.5 o/w ratio at four different temperatures, namely 5oC, 10oC, 15oC and 20oC. The main results showed that the capsules can break inside the asphalt mastic releasing the encapsulated oil to bitumen. Healing levels in the asphalt mastic samples with capsules were greater than samples without capsules, and the healing level of asphalt samples with, and without, capsules increased with the healing time. Additionally, the healing level given by the capsules inside the cracked asphalt mastic depended on the oil/water content of the capsule and on the temperature at which the healing process occurs. Finally, a correlation factor was developed between the healing level of asphalt mastic with and without capsules, independent of the temperature and time evaluated. Self-healing of real asphalt mixture was also investigated by same method of 3PB at different healing times and different temperatures. One type of capsules, namely 0.1 o/w with three different capsule contents, 0.10%, 0.25% and 0.50% by total weight of the mixture, were mixed with the asphalt. Eight different healing temperatures were used in this test, namely -5oC, 5oC, 10oC, 15oC, 20oC, 30oC, 40oC and 50oC. It was proven that the capsules can resist the mixing and compaction processes and break inside the asphalt mixture as a result of applying external mechanical loads, releasing the encapsulated oil. The capsules content in asphalt mixture has a significant influence on the healing level, where a higher capsule content led to higher healing levels. It was found that cracked asphalt mixture with capsules recovered 52.9% of initial strength at 20oC versus 14.0% of asphalt mixture without capsules. Likewise, asphalt with, and without, capsules presents an increase of the healing level when the temperature increases. Finally, it was proved that healing temperature over 40oC has significant influence on the healing levels of the asphalt beams.

A general conclusion from the work is that both systems require considerable development before being ready for industrial application. However, of the two systems investigated, it is the latter which shows the greatest potential to not only greatly enhance the durability of cementitious composites, but also to improve their strength and ductility.

The concept of self-healing materials has emerged from the reticence that exists in composite design, especially in aerospace structures. This concern emanates from composite materials' poor interlaminar properties and therefore tendency to perform badly when subject to impact events, typically manifesting as matrix cracking, delamination, and fibre debonding. With even microscopic damage having the potential to grow under fatigue loading until the structure's mechanical properties are diminished, composite structures are manufactured with high built in safety factors and structural redundancy to counteract inevitable defect creation. By developing self-healing materials, these defects can be addressed before (or after) they are allowed to grow, thus reducing the requirement for structural redundancy and capitalise on the mass savings that result. The chemistry behind healing mechanisms, and. methods of incorporating healing functionality itself, has been intensely researched by many groups in recent years. Whilst impressive results have been observed, and respecting the advancements that have been achieved, there still exist challenges which need to be addressed to allow for effective and fully autonomous self-healing systems. Many studies report thermal activation of polymerisation reactions, pre-mixing of healing agents, manual closing of crack planes to increase the relative volume of healing agent, or artificial opening of crack planes to increase infiltration and alleviate tensile stresses on the healing agent. Fundamentally however, achieving high healing efficiencies relies on delivering an adequate volume of healing agent(s) in a stoichiometric ratio and achieve effective mixing, or relies on exposing embedded catalyst to initiate and sustain polymerisation. We aim to address some of these challenges and reduce the dependency on external stimulus to increase healing efficiency in an autonomous manner through two different approaches. Firstly, the problems associated with incorporation of catalyst into the matrix, achieving stoichiometric ratios, and effective mixing, can be addressed using a single part healing chemistry that requires no additional stimulus or catalyst after release to polymerise. We have therefore investigated a potential route to 'inhibited healing' whereby a resin is actively prevented from undergoing polymerisation until released from the delivery vessel, whereupon polymerisation occurs rapidly and autonomously., Secondly, problems associated with mixing, reducing fibre disruption from vascule incorporation, delivering adequate volume from smaller reserves, achieving high proportions of infiltration, or to address larger damage voids and bridge wider separations, can be achieved by creation of volume in the healing agent , itself. We have investigated different chemical systems to produce a structural polymer with a volume greater than the sum of its constituent parts, explored methods of tailoring its chemical and structural properties, and assessed its ability to repair not only the relatively small volumes associated with damage within laminate structures, but also the larger damage volumes associated with impacted sandwich structures.

Nature provides us with amazingly complex and clever systems, structures and substances that make up the world we see around us. We can refer to nature, borrowing its ingenious solutions to solve engineering challenges or improve existing man-made materials. The process of assimilating real- world biological examples into technology is called 'bio-inspiration', and for many years scientists have been attempting to imitate the design of natural materials. This project seeks to mimic some of the complex architectures with outstanding properties found in nature: the shells of molluscs, with extraordinary toughness due to a highly hierarchical structure of platelets on the micro- and nano- scale, and human bone, with its ability to self-heal and regenerate its complex composite organic/inorganic microstructure after fracture. In this work it will therefore be investigated the effect of composite polymer/ceramic structures obtained via a manufacturing technique called freeze-casting, it is observed and optimised the role of the thin interface in self-healing organic/inorganic composites and the composition of the soft supramolecular phase and the inorganic phase is varied in order to obtain structures with properties closer to the behaviour of natural ones. The study couples interface and composite design with mechanical tests to determine interfacial adhesion in order to understand the factors that control the strength of the composite and the effectiveness and timescale of its self-healing. The same self-healing polymer is moreover used in the production of an innovative light composite exhibiting electrical conductivity and compression and flexion sensing capabilities in the attempt to mimic the outstanding properties of skin.

Self-healing composites are composite materials capable of automatic recovery when damaged. They are inspired by biological systems such as the human skin which are naturally able to heal themselves. Over the past two decades, two major self-healing concepts – based respectively on the use of capsules and vascular networks containing healing agents - have been proposed and material property recovery has been enhanced from 60% to nearly 100%. However, this improvement is still not sufficient to allow self-healing composites to be applied in practice because the healing capability varies with many external factors such as ambient temperatures and damage conditions. The key to the practical application of self-healing composites is to promote the sustainability of healing capacity to make the recovery robust. The thesis presents various techniques to enhance the healing capacity of fibre-reinforced composites to realise strong recovery regardless of ambient temperatures or material types. It presents the effects of various popular configurations of vascular networks on the flexural properties and healing performances of fibre-reinforced composites. The thesis demonstrates a design enabling recovery at ultra-low temperatures by using hollow vascular networks and porous heating elements. It also presents a new healing mechanism to repair the broken structural carbon fibres by incorporating conventional healing agents with short carbon fibres which could be aligned in an in situ electric field. The mechanism was also adopted to enable the restoration of the conductivity of a fibre-reinforced composite incorporating a porous conductive element, a carbon nanotube sheet, which could be used as a heating actuator or a sensing component. Thus, the development reported in this thesis have contributed to promoting the sustainability of the recovery of self-healing composites.

The research within the field of self-healing fibre reinforced polymers has been mainly focused on the development of novel healing chemistries and the application on damage scenarios where the damage volume and progression is contrived and pre-defined by the specimen geometry. Even though the potential of recovering the mechanical properties has been shown, limited amount of examples of the application of self-healing in more complex loading scenarios are found in the literature. The overall aim of this thesis is to apply self-healing within a higher complexity loading scenario resembling industrial relevant applications. Skin-stiffened structures combined with a vascular healing approach have been selected as the target scenario. Skin-stiffener debond specimen, mimicking the stress state at the tip of the flange, have been used to understand experimentally the damage progression under tensile-tensile fatigue. The damage progression has been manipulated by locally changing the fracture toughness with interleaves, transverse vascules and an oblique ply structure in order to steer efficiently the damage into predefined interfaces where the vascules are located. However, only moderate healing was obtained, reason being the small size of the connectivity between the vascules and the damage network. In contrast, efficient healing was demonstrated within strap lap and stringer run-out specimen tested under static tensile loading. The findings within this thesis suggest that there is a potential to recover damage occurring within industrial relevant structural applications, having the capacity to reduce conservative safety margins and therefore permitting to exploit the weight saving potential of fibre reinforced polymers.

Thesis (Ph. D.)--West Virginia University, 2006.
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Wireless sensor networks (WSNs) and pervasive systems are increasingly used for applications such as building monitoring and control, health-care and environmental monitoring. The users are frequently non-technical and devices may not be easily accessible, thus their management and complexity should be transparent to the users. To this extent, the systems need to be self-healing, able to respond to failures. We extend previous work on self-managed cell (SMC), which introduced an infrastructure for autonomous pervasive systems, with fault detection and recovery services. We present a middleware for constrained platforms, which supports dynamic adaptation of network components imposing small overheads. It provides an event-driven paradigm for expressing system behaviour based on policies. We identify and define sensor readings' fault models extracted from long-running, real-world sensor deployments. We describe a fault detection mechanism for sensor readings based on heuristic and Bayesian probabilistic approaches that accurately identifies error occurrences in readings and minimises false positives. We implemented a recovery mechanism that responds to sensor and communication link degradation to dynamically reorganise the original role and task allocation among sensor nodes without disrupting service operations. Finally, we present a case study on a production-quality, multi-hop routing middleware, ITA Sensor Fabric, where we prototyped an adaptive routing mechanism, which set-ups virtual circuits for sensor data subscriptions avoiding recurring communication link and traffic congestion patterns that appear in the network. Evaluation of the framework shows that the embedded policy management system is lightweight for power constrained nodes. The self-healing service accurately identifies erroneous sensors and is capable to effectively reconfigure network assets to improve quality of information while maintaining long life expectancy of the system.

Orientador: Prof. Dr. Jeverson Teodoro Arantes Junior
Dissertação (mestrado) - Universidade Federal do ABC, Programa de Pós-Graduação em Nanociências e Materiais Avançados, 2017.
Uma estrutura que pode autorregenerar em condições ambiente é um desafio enfrentado atualmente e é uma das áreas mais promissoras na ciência de materiais inteligentes. O presente projeto visa a utilização de métodos teóricos para o estudo das propriedades estruturais e funcionais de nanocompósitos intrinsecamente autorregenerativos, permitindo estratégias mais eficientes para o desenvolvimento de novos materiais. As simulações são baseadas na Teoria do Funcional da Densidade (DFT). Estudamos os componentes isolados que constituem o nanocompósito funcional: diarilbibenzofuranona (DABBF), SHP e nanopartículas de (óxido de) níquel. Estudando a formação da DABBF contra a reação da arilbenzofuranona (ABF) e O2 (auto-oxidação), vemos que a reação de formação sem barreira da DABBF é preferida à auto-oxidação porque existe um processo de transferência de carga que resulta no superóxido fracamente ligado. Realizamos um estudo sistemático por meio de cálculos ab initio para investigar a reação de clusters de Ni13 com moléculas de O2. Avaliamos dinamicamente o efeito sobre as propriedades estruturais, eletrônicas e magnéticas e compreendemos o mecanismo de quimissorção do oxigênio (primeiro estágio da oxidação). Finalmente, estudamos as interações entre os oligômeros do SHP e as nanopartículas, levando ao nanocompósito autorregenerativo. Sugerimos como trabalhos futuros simular as interações entre todos esses materiais levando ao nanocompósito autorregenerativo por meio de uma abordagem multiescala via métodos DFT e de dinâmica molecular (MD).
A structure that can sustain self-healing repair under standard conditions is a challenge faced nowadays and is one of the most promising areas in smart materials science. The present project aims at the use of theoretical methods for the study of structural and functional properties of intrinsically self-healing nanocomposites, allowing improved design strategies for novel materials. The simulations are based on Density Functional Theory (DFT). We studied the isolated components that constitute the functional nanocomposite network: diarylbibenzofuranone (DABBF), SHP, and oxidated nickel nanoparticles. Studying DABBF bond formation against arylbenzofuranone (ABF) and O2 reaction (autoxidation), we see that the barrierless DABBF bond formation is preferred over autoxidation because there is a charge transfer process that results in the weakly bonded superoxide. We performed a systematic study by means of ab initio calculations to investigate Ni13 clusters reaction with O2 molecules. We evaluate dynamically the effect on structural, electronic, and magnetic properties and understand the oxygen chemisorption (first oxidation stage) mechanism. Finally, we study the interactions between SHP oligomers and the nanoparticles, leading to the selfhealing nanocomposite. We suggest as future work simulating the interactions between all these materials leading to the self-healing nanocomposite through a multiscale approach via DFT and molecular dynamics (MD) methods.

La robotique souple est une branche émergente de la robotique, qui implique l’incorporation d’élastomères. L’utilisation de matériaux auto-réparants (AR) dans les robots mous présente l’avantage de pouvoir réparer les dommages et donc de prolonger la durée de vie du robot. Dans cette thèse, des élastomères AR à base de caoutchouc naturel époxydé (ENR) ont été synthétisés, qui permettent des mouvements cycliques à 5Hz. Les dommages peuvent être réparés grâce aux liaisons hydrogène et liaisons ester échangeables, à la diffusion des chaînes pendantes et à la micro-séparation de phase. Pour la détection des dommages, des capteurs de déformation piézorésistifs ont été produits en utilisant les mêmes matériaux ENR chargés de particules conductrices de noir de carbone. Des fibres de capteurs ont été intégrées dans la matrice AR et ont montré une récupération des propriétés mécaniques et électriques après auto-réparation. Des actionneurs pneumatiques équipés des capteurs précédents ont été assemblés et testés avec succès. Enfin, de nouveaux matériaux vitrimères ont été synthétisés en utilisant des enzymes comme catalyseurs bio-sourcés, ce qui permet de réduire la température de recyclage à 100 °C
Soft robotics is an emergent branch of robotics, which involves incorporation of elastomers. The use of self-healing (SH) materials in soft robots has the advantage that damage can be repaired and thus prolong the robot’s lifetime. In this work, SH elastomers based on epoxidized natural rubber (ENR) were synthesized, which allow cyclic movements at 5 Hz. Damage of the material can be healed due to hydrogen bonds, exchangeable ester bonds, interdiffusion of dangling chains and microphase separation. For damage detection, piezo-resistive strain sensors were produced using the same ENR materials charged with conductive carbon black particles. Laser-cutted sensor fibers were integrated into SH matrix and showed a recovery of mechanical and electrical properties after cut and self-healing. Sensorized pneumatic actuators were assembled and successfully tested before and after healing. Finally, new vitrimer materials were synthesized using enzymes as bio-based catalysts, which allow to reduce the recycling temperature to 100 °C

Crack formation in concrete structures due to various load and non-load factors leading to degradation of service life is very common. Repair and maintenance operations are, therefore, necessary to prevent cracks propagating and reducing the service life of the structures. Accessibility to affected areas can, however, be difficult and the reconstruction and maintenance of concrete buildings are expensive in labor and capital. Autonomous healing by encapsulated bacteria-based self-healing agents is a possible solution. In this study, a novel bacteria-based healing agent was investigated in order to test the self-healing efficiency of the specimens in comparison to the commonly used healing agents made of lactic acid derivatives. (PLA). The novel integrated healing agent is a non-toxic, biodegradable dissolved inorganic carbon substrate derived from wastewater that has been used as an encapsulation material for spores of cohnii bacteria in the Bacillus gene family and for nutrients made up of yeast extract. This dissolved inorganic carbon substrate is a bioplastic made by the bacteria in wastewater known as alkanoate derivatives (AKD). To assess the effect of these healing agents on the mortar characteristics, quantification and characterization of the self-healing were conducted. The quantification of the self-healing efficiency was performed by various experimental techniques such as light microscopy, water permeability, chloride ion permeability, and thermogravimetric analysis whereas the material characterization was investigated by x-ray diffraction and environmental scanning electron microscope. Moreover, a statistical analysis was performed to study the correlation of self-healing efficiency between various experimental techniques. The incorporated dosages of healing agents adopted were 2.6% and 5% by weight of cement. Complete immersion in water was considered to be the condition of treatment of the specimen for healing at two separate periods of 28 and 56 days. The crack widths investigated were in the range of 0.04 to 0.8 mm. The quantification and characterization tests indicated that bacterial containing mortar series especially PLA and AKD at 5% dosage displayed a higher self-healing performance and an indication of precipitated calcium carbonate in the crack mouth. However, the results from the chloride migration test didn’t show any influence by the self-healing healing agents. Furthermore, the statistical analysis identified a major impact of the internal crack geometry on the difference in self-healing ratios, also in the cases where effective crack width is equal.
Sprickbildning i betongkonstruktioner p.g.a. olika laster och lastoberoende faktorer som leder till förkortning av livslängden är mycket vanligt förekommande. Reparation och underhåll är därför nödvändiga för att förhindra att sprickorna propagerar och reduceras konstruktionernas livslängd. Möjligheterna att komma åt de skadade partierna kan dock vara svåra och reparationerna är vanligen både arbetsintensiva och kostsamma. Självläkning med ingjutna bakteriebaserade, självläkande tillsatser är en möjlig lösning på problemet. I denna studie undersöktes en ny bakteriebaserat självläkande tillsats för att prova den självläkande förmågan i jämförelse med vanligt förekommande självläkande tillsatser av mjölksyrederivat (PLA). Den nya integrerade självläkande tillsatsen är en giftfri, biologiskt nedbrytningsbar, oorganisk kolsubstratslösning utvunnen ur avloppsvatten, en tillsats som har använts som ett inkapslingsmaterial för sporer från cohnii-bakterier från bacillussläktet och från näringsämnen framställda ur jästextrakt. Denna kolsubstratslösning är en bioplast framställd ur avloppsvatten och känd som alkanoatderivat (AKD). För att bestämma effekten av dessa självläkande tillsatser på cement bruks egenskaper genomfördes kvantifiering och karakterisering av självläkningen. Kvantifieringen av självläkningens effektivitet utfördes genom olika experimentella metoder såsom ljusmikroskopi, vattengenomsläpplighet, kloridjonstransport och termogravimetriska analyser medan materialkarakteriseringen utfördes med röntgendiffraktion och svepelektronmikroskop (ESEM). Vidare genomfördes en statistisk analys för att undersöka korrelationen mellan olika experimentella metoder. De doser av självläkande tillsatser som användes var 2,6 och 5 % av cementvikten. Fullständig nedsänkning i vatten ansågs vara den lämpligaste lagringen för självläkning under två olika tidsperioder på 28 respektive 56 dygn. De sprickbredder som studerades låg i intervallet 0.04 till 0.8 mm. Försöken kring kvantifiering och karakterisering indikerade att bruken innehållande bakterier, i synnerhet 5 % PLA och AKD, utvecklade en högre form av självläkande beteende och en förekomst av kalciumkarbonat i sprickspetsen. Resultaten från försöken kring kloridtransport visade emellertid inga tecken på någon effekt från de självläkande tillsatserna. Vidare identifierades i den statistiska analysen att inre sprickbildning har stor betydelse för självläkningseffekten även i fall där den effektiva sprickbredden är lika stor.

The aim of this study was to develop a new single-part healing system for self-healing composites. The self-healing approach to composite repair has been developed in the last two decades and means that a damaged area can be repaired by material already housed within the structure. The background and development of self-healing has been reviewed. The two main self-healing mechanisms are discussed. To date only two part self healing systems have been examined. These require diffusion of the separate constituents to a single location in order to effect cure and restore strength. Single part adhesives do not have this disadvantage and are therefore very attractive. Several candidate single-part adhesive or resin systems were considered and discussed according to the critical requirements of a self-healing system. A series of experiments was undertaken to evaluate the possibility of candidate adhesive systems being effective for self-healing by focusing on the determination of storage stability and bonding efficiency. The results of storage stability testing showed that the stability of cyanoacrylate and polyurethane adhesives was poor. However silane and polystyrene cements showed good storage stability. Very low bonding efficiency was achieved with polystyrene cement but a 22% strength recovery was obtained with the silane 3-[tris(trimethylsiloxy)silyl]-propylamine. Suggestions for further research into single-part healing systems are also given.

A self-sensing and self-healing bolted joint has been developed. This concept encompasses the areas of health monitoring, joint dynamics and smart materials. In order to detect looseness in a joint the impedance health monitoring method is used. A new method of making impedance measurements for health monitoring that greatly reduces the equipment cost and equipment size was developed. This facilitates implementation of the impedance technique in real-life field applications. Several proof of concept experiments are presented and compared to the traditional method of making impedance measurements. Investigations of bolted joint dynamics were conducted. A literature review of bolted joints and their diagnostics is presented. The application of the transfer impedance method is compared to standard modal tests on various bolt tensions. An investigation of damping in bolted joints was also made comparing a bolted and monolithic beam. Practical issues in adaptive bolted joints are investigated. This includes issues on activating/heating SMA actuators, connecting the actuators to the power source, size selection of SMA actuators and insulations. These issues are examined both experimentally and theoretically.
Master of Science

The present work is devoted to establishing of a new generation of self-healing anti-corrosion coatings for protection of metals. The concept of self-healing anticorrosion coatings is based on the combination of the passive part, represented by the matrix of conventional coating, and the active part, represented by micron-sized capsules loaded with corrosion inhibitor. Polymers were chosen as the class of compounds most suitable for the capsule preparation. The morphology of capsules made of crosslinked polymers, however, was found to be dependent on the nature of the encapsulated liquid. Therefore, a systematic analysis of the morphology of capsules consisting of a crosslinked polymer and a solvent was performed. Three classes of polymers such as polyurethane, polyurea and polyamide were chosen. Capsules made of these polymers and eight solvents of different polarity were synthesized via interfacial polymerization. It was shown that the morphology of the resulting capsules is specific for every polymer-solvent pair. Formation of capsules with three general types of morphology, such as core-shell, compact and multicompartment, was demonstrated by means of Scanning Electron Microscopy. Compact morphology was assumed to be a result of the specific polymer-solvent interactions and be analogues to the process of swelling. In order to verify the hypothesis, pure polyurethane, polyurea and polyamide were synthesized; their swelling behavior in the solvents used as the encapsulated material was investigated. It was shown that the swelling behavior of the polymers in most cases correlates with the capsules morphology. Different morphologies (compact, core-shell and multicompartment) were therefore attributed to the specific polymer-solvent interactions and discussed in terms of “good” and “poor” solvent. Capsules with core-shell morphology are formed when the encapsulated liquid is a “poor” solvent for the chosen polymer while compact morphologies are formed when the solvent is “good”. Multicompartment morphology is explained by the formation of infinite networks or gelation of crosslinked polymers. If gelation occurs after the phase separation in the system is achieved, core-shell morphology is present. If gelation of the polymer occurs far before crosslinking is accomplished, further condensation of the polymer due to the crosslinking may lead to the formation of porous or multicompartment morphologies. It was concluded that in general, the morphology of capsules consisting of certain polymer-solvent pairs can be predicted on the basis of polymer-solvent behavior. In some cases, the swelling behavior and morphology may not match. The reasons for that are discussed in detail in the thesis. The discussed approach is only capable of predicting capsule morphology for certain polymer-solvent pairs. In practice, the design of the capsules assumes the trial of a great number of polymer-solvent combinations; more complex systems consisting of three, four or even more components are often used. Evaluation of the swelling behavior of each component pair of such systems becomes unreasonable. Therefore, exploitation of the solubility parameter approach was found to be more useful. The latter allows consideration of the properties of each single component instead of the pair of components. In such a manner, the Hansen Solubility Parameter (HSP) approach was used for further analysis. Solubility spheres were constructed for polyurethane, polyurea and polyamide. For this a three-dimensional graph is plotted with dispersion, polar and hydrogen bonding components of solubility parameter, obtained from literature, as the orthogonal axes. The HSP of the solvents are used as the coordinates for the points on the HSP graph. Then a sphere with a certain radius is located on a graph, and the “good” solvents would be located inside the sphere, while the “poor” ones are located outside. Both the location of the sphere center and the sphere radius should be fitted according to the information on polymer swelling behavior in a number of solvents. According to the existing correlation between the capsule morphology and swelling behavior of polymers, the solvents located inside the solubility sphere of a polymer give capsules with compact morphologies. The solvents located outside the solubility sphere of the solvent give either core-shell or multicompartment capsules in combination with the chosen polymer. Once the solubility sphere of a polymer is found, the solubility/swelling behavior is approximated to all possible substances. HSP theory allows therefore prediction of polymer solubility/swelling behavior and consequently the capsule morphology for any given substance with known HSP parameters on the basis of limited data. The latter makes the theory so attractive for application in chemistry and technology, since the choice of the system components is usually performed on the basis of a large number of different parameters that should mutually match. Even slight change of the technology sometimes leads to the necessity to find the analogue of this or that solvent in a sense of solvency but carrying different chemistry. Usage of the HSP approach in this case is indispensable. In the second part of the work examples of the HSP application for the fabrication of capsules with on-demand-morphology are presented. Capsules with compact or core-shell morphology containing corrosion inhibitors were synthesized. Thus, alkoxysilanes possessing long hydrophobic tail, combining passivating and water-repelling properties, were encapsulated in polyurethane shell. The mechanism of action of the active material required core-shell morphology of the capsules. The new hybrid corrosion inhibitor, cerium diethylhexyl phosphate, was encapsulated in polyamide shells in order to facilitate the dispersion of the substance and improve its adhesion to the coating matrix. The encapsulation of commercially available antifouling agents in polyurethane shells was carried out in order to control its release behavior and colloidal stability. Capsules with compact morphology made of polyurea containing the liquid corrosion inhibitor 2-methyl benzothiazole were synthesized in order to improve the colloidal stability of the substance. Capsules with compact morphology allow slower release of the liquid encapsulated material compared to the core-shell ones. If the “in-situ” encapsulation is not possible due to the reaction of the oil-soluble monomer with the encapsulated material, a solution was proposed: loading of the capsules should be performed after monomer deactivation due to the accomplishment of the polymerization reaction. Capsules of desired morphologies should be preformed followed by the loading step. In this way, compact polyurea capsules containing the highly effective but chemically active corrosion inhibitors 8-hydroxyquinoline and benzotriazole were fabricated. All the resulting capsules were successfully introduced into model coatings. The efficiency of the resulting “smart” self-healing anticorrosion coatings on steel and aluminium alloy of the AA-2024 series was evaluated using characterization techniques such as Scanning Vibrating Electron Spectroscopy, Electrochemical Impedance Spectroscopy and salt-spray chamber tests.
In Anlehnung an den Selbstheilungsmechanismus der menschlichen Haut entwickeln wir ein innovatives Verfahren zur Funktionalisierung von Korrosionsschutzbeschichtungen, um auch diese in die Lage zu versetzen Beschädigungen selbstständig „auszuheilen“. Dazu werden winzige Mikro- und Nanobehälter mit aktiven Substanzen (z. B. Korrosionshemmstoffen, Versiegelungsmitteln, Bioziden etc.) befüllt und anschließend in eine Korrosionsschutzbeschichtung eingebettet. Kommt es nun im Zeitablauf zu korrosionsauslösenden Beschädigungen der Schutzbeschichtung (z. B. durch Kratzer oder Risse) werden an der Defektstelle die eingebetteten Behälter zerstört und aktiv wirkende Gegensubstanzen freigesetzt. Dadurch wird die verletzte Stelle sofort wieder verschlossen und die Korrosionsgefahr eliminiert. Der entscheidende Vorteil derart funktionalisierter Schutzbeschichtungen ist ihre aktive Rückkopplung mit dem Korrosionsauslöser: Die aktive Schutzsubstanz wird nur an der Defektstelle und nur in der zur Korrosionsvermeidung erforderlichen Menge freigegeben. Somit werden eine länger anhaltende Wirkdauer sowie eine deutlich höhere Nachhaltigkeit der Beschichtungen ermöglicht. Dieses „intelligente Verhalten“ der neuen aktiven Korrosionsschutzbeschichtungen ist nur dank ihrer innovativen Mikrostruktur möglich. Die winzigen Mikro- und Nanobehälter beinhalten nicht nur aktive Substanzen in ihrem Inneren sondern besitzen auch eine intelligent konstruierte Hüllenstruktur, deren Durchlässigkeit sich je nach Art des Korrosionsauslösers ändert. Wird die eingekapselte aktive Substanz freigesetzt, fängt diese sofort an gegen die korrosionsverursachenden Einflüsse zu wirken. Ist die Gefahr beseitigt verringert sich die Durchlässigkeit der Behälterhülle wieder. Diese bedingte Reversibilität zwischen geschlossenem und geöffnetem Zustand des Behälters sorgt für einen sehr sparsamen Verbrauch der aktiven Substanz und für die stark verbesserte Schutzwirkung darauf basierender Antikorrosionsbeschichtungen. Diese Arbeit befasst sich mit dem Aufbau polymerer Kern-Schale-Mikrokapseln, die entsprechende Korrosionsinhibitoren und Biocide enthalten. Der Morphologie wird für zahlreiche Lösungsmittel und Polymere mit Hilfe der Hansen-Löslichkeitsparameter in guter Übereinstimmung mit elektronenmikroskopischen Experimenten beschrieben. Die Wirkungsweise in technischen Beschichtungen wird quantifiziert anhand von elektrochemischer Impedanzspektroskopie, Rastervibrationssondenmessungen und industrienahen Testverfahren.

The application of self-healing material in industrial systems has the potential to improve reliability and save cost. This is because faults do occur in systems, and for life critical or remote or difficult to access ones, current maintenance practices may be insufficient. When such systems are self-healed, the materials making up the systems regain some or all of its lost physical properties to keep the systems functioning. However, a majority of self-healing approaches are not yet at the level of industrial integration. These self-healing approaches are passive and do not guarantee a match between the damage and healing rate. A significant step in their advancement is the development of an integrated sensing, fault diagnosis and active self-healing system, which is the focus of this thesis. A mathematical model based on a previously experimented electromechanical self-healing process, whose healing mechanism combines piezoelectricity and electrolysis is developed. The model demonstrates the poor match between the damage and healing rate due to the ineffectiveness of the healing process to counteract the onset of damage, the dominant effect of uncertainties and disturbances on the healing process, the dependence of healing on the location of the healing mechanism relative to the fault location, etc. In addition, nonlinearities, such as the inherent dead-zone of the chosen healing mechanism affect the response of the healing process. The model also provides a benchmark for the work in this thesis. The model is then the foundation for the development of a novel active self-healing system. This is a closed loop system that takes advantage of sensing and adaptive sliding mode feedback control with the modelled healing mechanism to achieve a desired response. Importantly, it is shown in simulation that adaptive feedback control (sliding mode control) can minimize the effect of uncertainties, regulate the healing rate of a self-healing system to meet user or environmental demands, such as the damage rate, and compensate for the non-linear dead-zone associated with this healing mechanism. Finally, a novel fault diagnosis method that combines the beam curvature, proportional orthogonal decomposition, Hölder exponent and supervised regression is presented as a step to define the environmental demands. This essentially captures the effect of damage of a beam structure. It is combined with the active self-healing system, leading to a novel framework for an integrated sensing, fault diagnosis and closed loop active self-healing system. It is shown through simulation that the proposed active system can potentially estimate the damage rate, provide adequate actuation to match the healing rate with the estimated damage rate and provide real time insight into the healing dynamics.

Epoxy coatings are currently the most popular corrosion protection mechanism for steel reinforcement in structural concrete. However, these coatings are easily damaged on worksites, negating their intended purpose. This study investigates self-healing coatings for steel reinforcement to introduce an autonomous healing mechanism for damaged coatings. Coatings were applied to steel coupons, intentionally damaged, and introduced to a corrosive environment via aerated salt-water tanks. Performance of the experimental coatings was evaluated qualitatively and quantitatively. Adhesion strength and effects of coating thickness were also studied. Results from coated steel coupons subjected to damage and submerged in salt-water aeration tanks exhibited improved corrosion resistance performance with self-healing coatings. However, self-healing coatings have comparable poor adhesion to the substrate as do conventional coatings. This paper shows preliminary results demonstrating the potential benefits of self-healing coatings for steel reinforcement and identifies numerous avenues for future research.

When exposed to varying temperatures, water, and stress, concrete develops tiny undetectable cracks that can spread and threaten its integrity until eventually it must be replaced. Self-healing concrete offers significant economic and environmental benefits. The goal of this project is to investigate the feasibility of using bacteria as a self-healing additive, and to design a plant for producing self-healing concrete. The concrete designed by the team includes dormant bacteria that are reactivated by water entering a crack. The bacteria naturally produce calcium carbonate, which seals the cracks resulting in a stronger, longer-lasting concrete. The team designed a system of bioreactors to cultivate the bacteria, Bacillus subtilis, which is added to lightweight aggregate, a component of concrete. The team also designed a plant to produce the cement necessary to make concrete. This design involves balancing the energy needs of several large crushers and grinders, a heating and cooling system, and a large kiln. The cement and aggregate are combined with water to form self-healing concrete.

Concrete is one of the most versatile and common building materials used in industry. However, concrete is prone to cracks, which can eventually lead to collapse of structures. Self-healing concrete, which prevents large cracks by filling micro-cracks as they form, has the potential to mitigate the problems associated with cracking. The mechanism behind self-healing concrete uses a biological agent, such as the Bacillus Subtilis bacteria, which is added to the concrete mix and autonomously heals small cracks by precipitating calcium carbonate. Encapsulating the bacteria with the aggregate not only improves bacterial survival, but also increases the overall tensile strength of the concrete. In addition to the bacteria and aggregate, a cement plant was also designed. Cement is a fine powder which, when mixed with water, has a cohesive property which holds the other components of concrete together. The manufacturing process of cement starts with crushed limestone, which is heated in a kiln until it forms the nodules of calcium silicates that make up clinker, which is then crushed into cement powder. Although more research is necessary to determine the long-term performance and impact, the further development and implementation of self-healing concrete is a worthwhile and potentially profitable pursuit.

A self-healing cementitious material could provide a step change in the design of concrete structures. There is a need to understand better the healing processes, to predict accurately experimental behaviour and to determine the impact on mechanical properties. Micromechanical modelling, with a two-phase Eshelby inclusion solution, is chosen as a suitable framework within which to explore self-healing. The impact of micro-cracking and other time-dependent phenomena are considered alongside self-healing experiments and the numerical mechanical strength response. A new approach describes simulating inelastic behaviour in the matrix component of a two-phase composite material. Quasi-isotropic distributed micro-cracking, accompanying volumetric matrix changes, is combined with anisotropic microcracking arising from directional loading. Non-dilute inclusions are homogenised and an exterior point Eshelby solution is used to obtain stress concentrations adjacent to inclusions. The accuracy of these solutions is assessed using a series of three dimensional finite element analyses and a set of stress/strain paths illustrate the model’s characteristics. The problem of autogenous shrinkage in a cementitious composite is applied using a volumetric solidification and hydration model, which quantifies the effects of micro-cracking. Experiments on early age concrete and mortar beams showed that autogenous healing is primarily due to continued hydration. A novel self-healing model focuses on mechanical strength recovery of micro-cracked material and considers healing whilst under strain as well as allowing for re-cracking the healed material. The constitutive model is combined with a layered beam model to allow successful comparisons with experimental results.

Recent years have seen the growing interest in the novel field of biogeotechnologies. Of particular interest to researchers has been the microbially induced calcium carbonate precipitation (MICP) for geotechnical (stabilisation of soils) and geoenvironmental (immobilisation of contaminants) applications. The MICP process results in the formation of a brittle monolith from sand cemented by the microbial calcium carbonate which will, however, be subjected to chemical and physical deterioration over time. This will bring the need for repair of the earth structure which can be highly difficult and costly. This study investigates the possibility of incorporating a self-healing mechanism in the MICP that will allow the initially formed monolith to be healed after damage. MICP via a spore-forming, ureolytic organism, Sporosarcina ureae, was evaluated for its self-healing potential. The most commonly used organism in biocementation, namely Sporosarcina pasteurii, was found to not form spores. Experiments in aqueous solution showed that encapsulated (in calcium carbonate) sporulated bacteria can survive harsh conditions, starvation for periods of 6 months (while encapsulated within the mineral) and be able to germinate once exposed from the mineral matrix with availability of nutrients. The revived bacteria were then able to form the precipitation of further calcium carbonate. Additionally, the bacterium was able to go through cycles of self-healing multiple times without its activity being significantly affected. Also presented are experiments in particulate media which showed the ability of the organism to cause the cementation of sand columns. S. ureae was able to respond when a physical or chemical damage occurred to the monolith by germinating and producing again calcium carbonate which restored the functionality of the bio-cemented sand columns.

The field of artificial immune system (AIS) is an example of biologically inspired computing that takes its inspiration from various aspects of immunology. Techniques from AIS have been applied in solving many different problems such as classification, optimisation and anomaly detection. However, despite the apparent success of the AIS approach, the unique advantages of AIS over and above other computational intelligence approaches are not clear. In order to address this, AIS practitioners need to carefully consider the application area and design methodologies that they adopt. It has been argued that of increasing importance is the development of a greater understanding of the underlying immunological system that acts as inspiration, as well as the understanding of the problem that need to be solved before proposing the immune-inspired solution to solve the desired problem. This thesis therefore aims to pursue a more principled approach for the development of an AIS, considering the application areas that are suitable based on the underlying biological system under study, as well as the engineering problems that needs to be solved. This directs us to recognise a methodology for developing AIS that integrates several explicit modelling phases to extract the key features of the biological system. An analysis of the immunological literature acknowledges our immune inspiration: granuloma formation, which represents a chronic inflammatory reaction initiated by various infectious and non-infectious agents. Our first step in developing an AIS supported by these properties is to construct an Unified Modelling Language (UML) model agent-based simulation to understand the underlying properties of granuloma formation. Based on the model and simulation, we then investigate the development of granuloma formation, based on the interactions of different signalling mechanisms and the recruitment of different cells in the system. Using the insight gained from these investigation, we construct a design principles to be incorporated into AIS algorithm development. The design principles are then instantiated for a self-healing algorithm for swarm robotic systems, specifically in the case of swarm beacon taxis when there exist failure of robots' energy in the systems. The self-healing algorithm, which is inspired by the granuloma formation of immune systems is then tested in swarm robotics simulation. To conclude, we analyse the process we have pursued to develop our AIS and evaluate the advantages and the disadvantages of the approach that we have taken, showing how a more principled approach with careful consideration the application area can be applied to the design of biologically-inspired algorithms.

Cementitious materials are the most wildly used construction materials in the world, and the development of self-healing cementitious materials are highly beneficial. The aim of the thesis is to use dual-microcapsules or polycaprolactone as self-healing agent, and to study the self-healing properties and fracture mechanics of the self-healing cement. Microcapsule based self-healing cement in this work is fabricated by adding 10, 20 and 30 wt.% of dual-microcapsules to the cement. The dual-microcapsule system contains a bisphenol A diglycidyl ether (DGEBA) epoxy resin in one capsule and pentaerythritol tetrakis (i.e. mercaptan) as hardener in the other capsule. Polycaprolactone (PCL) based self-healing cement is prepared by adding 10, 20 and 30 wt.% of PCL powders to the cement. The study of self-healing efficiency and fracture behaviour of the self-healing cement are carried out using the TDCB (tapered double-cantilever beam) fracture tests. For the microcapsules based self-healing system, microcapsules can be classified by three diameters. The diameters of epoxy microcapsules are 210 μm and 71 μm; the diameters of mercaptan microcapsules are 181 μm and 77 μm. The epoxy TDCB with inserted cement block was adopted in fracture characterization of the virgin cements without and with the healing agent as well as that after healing. The cement block is square or round in shape; the specimens with square shape cement showed inconsistent cracking, and most cracking started from edges rather than the pre-crack. The specimens with round shape cement showed consistent cracking along the pre-crack. 10, 20 and 30 wt.% of large microcapsules were added in the cement. The average healing efficiency of cement specimens is 4.6%, 48.1%, and 25.4%, respectively, for 10%, 20%, and 30% of large microcapsules, increasing with the content of healing agent. For the PCL based self-healing system, the average diameter of PCL powder is 367 μm, and the melting point is 63°C defined by DSC. Rheology of PCL powders shows shear thinning behavior due to a decrease of viscosity under shear rate. The specimens healed at 110°C show better healing efficiency than those healed at 90°C; all of them reach 100% of healing efficiency except the specimens with 10% of PCL healed at 90°C. The maximum healing efficiency reaches 244% for the specimens embedded with 30% of PCL and healed at 110°C. In conclusion, the healing efficiency increases with the content of epoxy microcapsules or PCL particles, because more coverage of the epoxy or PCL on the cracked surfaces. PCL-based cement at a high healing temperature shows better healing efficiency owing to the lower viscosity and better flow of PCL. PCL-based self-healing system shows better healing efficiency than epoxy microcapsules because of some microcapsules ruptured during the mixing process with the cement, losing its function.

The main objective of this thesis is to bring new contributions to the self-healing and secure systems domain. In particular, to develop a self-healing technique for memory systems and to increase security of memory systems, techniques which favor low-power consumption. In order to achieve the main objective, three major research objectives were proposed: design of an error detection and correction scheme for errors that occur in memory systems and integrate them in a memory system, design techniques to increase the security and data privacy of memory systems against different types of attacks and to combine the previous two into a single solution, in order to achieve a self-healing and secure low-power memory system. The low-power aspect of the proposed solutions and techniques is evaluated during design stage and afterwards through simulation. Also, the architectures are evaluated from several other points of view, such as error detecting and correcting performance, area and delay overhead, and security efficiency. The first chapter contains a short introduction of the domain and subject of the thesis, current state of the art in this domain, proposed objectives and thesis organization. The second chapter contains a unidirectional error detecting, correcting and localization scheme, which is used for the self-healing technique. The chapter begins with an introduction and motivation about error detecting and correcting codes and their usage in memory systems and continues with a theoretical background. The chapter continues with the design of the proposed codes, which are explained in detail and illustrated through several figures. Then, they are analyzed from the following points of view: coding scheme, error localization, error correction and error escapes. For the latter three, metrics are defined, in order to evaluate the codes. Afterwards, the implementation of the proposed codes is exposed in several figures. Also, the usage of the codes is explained, as well as DRAM repair strategies. In the end of this chapter, the efficiency of the proposed codes is evaluated and exemplified. The evaluation process contains other metrics: speed and delay, area overhead, power consumption and code redundancy. Chapter 3 contains a proposed scheme to increase security in memory systems against cold-boot attacks. The technique uses data scrambling, hence the chapter begins with a short theoretical background and a review of data scrambling methods. It continues with the proposed solution, which is based on using unique scrambling vectors in an interleaved way, and theoretical performance and efficiency. The chapter ends with evaluation and experimental results for the proposed methodology. Evaluations of area overhead, power consumption and access time are performed in the CACTI simulation tool and on a FPGA development board. Chapter 4 approaches specific types of threats that can prevail in memory systems: simple and differential power or electromagnetic analysis attacks (SPEMA and DPEMA). The chapter begins with short introduction and motivation sections, and continues with a theoretical background about possible threats. In the following section, SPEMA and DPEMA are explained and discussed in detail. Afterwards, the proposed solutions for mitigating SPEMA and DPEMA are exhibited, and ends with evaluation and experimental results. An information leakage function is defined and used in evaluating the security efficiency of the solutions. The implementation costs are assessed with the use of the CACTI simulation tool, with respect to area and delay overhead, and power consumption. The final chapter, 5, contains the conclusions of the work, scientific contributions and future research directions.

The present work addresses poor bone/implant integration and severe bone defects. In both conditions external stimuli is required for new bone to form. A multilayered functional implant coating, comprised of an inner layer of crystalline titanium dioxide (TiO2) and an outer layer of hydroxyapatite (HAP), loaded with bone morphogenetic protein-2 (BMP-2), was proposed as a tool for providing both improved initial bone formation and long-term osseointegration. The in vitro characterization of the implant coatings showed that TiO2 and HAP were more favorable for cell viability, cell morphology and initial cell differentiation, compared to native titanium oxide. Furthermore, significantly higher cell differentiation was observed on surfaces with BMP-2, indicating that a simple soaking process can be used for incorporating bioactive molecules. Moreover, the results suggest that there could be a direct interaction between BMP-2 and HAP, which prolongs the retention of the growth factor, improving its therapeutic effect. For treating severe bone defects a strategy involving BMP-2 delivery from hyaluronan hydrogels was explored. The hydrogels were prepared from two reactive polymers – an aldehyde-modified hyaluronan and a hydrazide-modified poly(vinyl alcohol). Upon mixing, the two components formed a chemically crosslinked hydrogel. In this work the mixing of the hydrogel components was optimized by rheological measurements. Furthermore, an appropriate buffer was selected for in vitro experiments by studying the swelling of hydrogels in PBS and in cell culture medium. A detection method, based on radioactive labeling of BMP-2 with 125I was used to monitor growth factor release both in vitro and in vivo. The results showed a biphasic release profile of BMP-2, where approximately 16 %  and 3 % of the growth factor remained inside the hydrogel after 4 weeks in vitro and in vivo, respectively. The initial fast release phase corresponded to the early ectopic bone formation observed 8 d after injection of the hydrogel formulation in the thigh muscle of rats. The hydrogel formulation could be improved by incorporation of HAP powder into the hydrogel formulation. Furthermore, bone formation could be increased by pre-incubation of the premixed hydrogel components inside the syringe prior to injection. Crushed hydrogels were also observed to induce more bone formation compared to solid hydrogels, when implanted subcutaneously in rats. This was thought to be due to increased surface area of the hydrogel, which allowed for improved cell infiltration.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2018.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 127-136).
The functional versatility and endurable self-healing capacity of soft materials in nature is found to originate from the dynamic supramolecular scaffolds assembled via reversible interactions. To mimic this strategy, extensive efforts have been made to design polymer networks with transient crosslinks, which lays the foundation for synthetic self-healing hydrogels. Towards the development of stronger and faster self-healing hydrogels, understanding and controlling the gel network dynamics is of critical importance, since it provides design principles for key properties such as dynamic mechanics and self-healing performance. For this purpose, a universal strategy independent of exact crosslinking chemistry would be regulating the polymer material's dynamic behavior by optimal network design, yet current understanding of the relationship between network structure and macroscopic dynamic mechanics is still limited, and implementation of complex network structure has always been challenging. In this thesis, we show how the dynamic mechanical properties in a hydrogel can be controlled by rational design of polymer network structures. Using mussel-inspired reversible catechol coordination chemistry, we developed a nanocomposite hydrogel network (NP gel) with hierarchical assembly of polymer chains on iron oxide (Fe3O4) nanoparticles as network crosslinks. With NP gel as a model system, we first investigated its unique dynamic mechanics in comparison with traditional permanent and dynamic gels, and discovered a general approach to manipulate the network dynamics by controlling the crosslink structural functionality. Then we further explored the underlying relationship between polymer network structure and two key parameters in relaxation mechanics, which elucidated universal approaches for designing relaxation patterns in supramolecular transient gel network. Finally, by utilizing these design principles, we designed a hybrid gel network using two crosslinking structures with distinct relaxation timescales. By simply adjusting the ratio of two crosslinks, we can precisely tune the material's dynamic mechanics from a viscoelastic fluid to a rigid solid. Such controllability in dynamic mechanics enabled performance optimization towards mechanically rigid and fast self-healing hydrogel materials.
by Qiaochu Li.
Ph. D.

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2008.
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
"September 2008."
Includes bibliographical references (p. 61-63).
Autonomous self-healing materials offer a novel ability to self-repair damage caused by fatigue or fracture. Applications in many industries, from medical to aerospace, suffer from formation of microcracks, which often result in catastrophic failure of the product when the cracks remain undetected. A self-healing material capable of microcrack elimination would improve the safety of such products, as well as extend their lifetime. This paper presents several recently developed autonomous self-healing designs of polymer composites. The commercialization potential of the designs is explored. Potential applications in four industries are identified, and the helicopter blade is selected as the most likely application to succeed in introducing the novel material into the market. The helicopter market is evaluated based on demand, growth, stability, and ease of entry. Intellectual property landscape is presented and competitors are identified. A combination business strategy of research and development and intellectual property licensing is recommended for entry into the helicopter market.
by Anait Tsinberg.
M.Eng.

Thesis (PhD (Chemistry and Polymer Science)--University of Stellenbosch, 2009.
The work presented in this dissertation describes the development of self-healing coatings based on thiol-ene chemistry. The approach was to synthesize capsules with thiol and ene compounds separately encapsulated. These capsules were embedded in various coating formulations and upon the formation of a crack with a razor blade, these capsules ruptured. This caused the healing agent to flow into the crack via capillary action and the thiol-ene healing mechanism was initiated. This resulted in recovery of the damaged coating and provided continued protection to the substrate. Pentaerythritol tetrakis(3-mercaptopropionate) (TetraThiol), 1,6-hexanediol diacrylate (DiAcrylate) and 1,6-hexanediol di-(endo, exo-norborn-2-ene-5-carboxylate) (DiNorbornene) are the thiol and ene compounds used in this study. Kinetic experiments indicated that both TetraThiol-DiAcrylate and TetraThiol-DiNorbornene monomer pairs undergo rapid polymerization and form a network within minutes upon exposure to UV radiation and with the addition of a photoinitiator. The TetraThiol-DiNorbornene monomer pair also showed a high rate of polymerization without the addition of a photoinitiator and/or exposure to UV radiation. Styrene-maleic anhydride (SMA) copolymers and chain-extended block copolymers with styrene (P[(Sty-alt-MAh)-b-Sty]) were synthesized via Reversible Addition-Fragmentation chain Transfer (RAFT)- mediated polymerization. These copolymers were used as surfactant in miniemulsification for the synthesis of core-shell particles with TetraThiol as the core material. It appeared that P[(Sty-alt-MAh)-b-Sty] block copolymers, sterically stabilized via the addition of formaldehyde, provide optimal stability to the core-shell particles. DiNorbornene is encapsulated via miniemulsion homopolymerization of styrene and well-defined, stable nanocapsules were obtained. TetraThiol and DiAcrylate microcapsules were synthesized via in-situ polymerization of urea and formaldehyde. Microcapsules with a particle size of one to ten micrometers and with a very smooth surface were obtained. These microcapsules and nanocapsules were embedded in poly(methyl acrylate) (PMA), styrene-acrylate and pure acrylic films and the self-healing ability of these coatings, after introduction of a crack with a razor blade, was assessed.

Using web frameworks is becoming more common to build modern websites. Therefore, the robustness and resilience of the web frameworks are critical in production. Automatic software repair is about the software resolving the bugs automatically by itself. A web framework equipped with automatic software repair can improve the resilience of the website at runtime. In this thesis, we investigate the possibility of repairing common web framework errors such as URL interpretation error and database error with self-healing techniques during runtime. The common web framework errors are analyzed by using 16 popular open-sourceweb framework projects from Github. Besides, the self-healing architecture and techniques are implemented in the web framework to resolve the exceptions during runtime. The flexibility and robustness are considered while designing the self-healing techniques. The metrics regarding effectiveness and performance overhead are concerned with evaluating the self-healing techniques. The designed self-healing techniques are found to have resolved entirely the URL interpretation error and partially resolved the database error on two web framework projects. The performance overhead with self-healing techniques has obviously affected both two web framework projects. However, the performance overhead varies depending on the errors and projects. Furthermore, we find that the metrics are enough to evaluate the self-healing techniques while dealing with errors during runtime.
Att använda webbramar blir allt vanligare för att bygga moderna webbplatser. Därför är webbramens robusthet och motståndskraft avgörande i produktionen. Automatisk programvarureparation handlar om att programvaran löser buggen automatiskt av sig själv. Webbramar som är utrustat med automatisk programvarureparation kan vid körtid förbättra webbplatsens motståndskraft. I detta examensarbeten undersöks möjligheten att reparera vanliga fel i webbramen som URL-tolkningsfel och databasfel med självhelande tekniker under körtid. De vanliga webbrams felen analyseras med 16 populära öppna webbramsprojekt från Github. Dessutom implementeras den självhelande arkitekturen och teknikerna i webbramsverket för att lösa undantagen under körtid. Flexibiliteten och robustheten beaktas vid utformningen av självhelande tekniker. Mätetalen av effektivitet och omkostnaden för prestanda beaktas vid utvärdering av självhelande tekniker. De designade självhelande teknikerna har visat sig att ha löst URL-tolkningsfelet fullständigt och delvis löst databasfelet på två webbramsprojekt. Omkostnaden för prestandan med självhelande tekniker har uppenbarligen påverkat de båda två webbramverksprojekten. Omkostnaden för prestanda varierar dock beroende på fel och projekt. Dessutom finner vi att mätetalen är tillräckliga för att utvärdera de självhelande teknikerna medan vi hanterar fel under körtid.

Dans ce mémoire de thèse, nous présentons une approche d’exécution auto-corrective (self-healing) de services composites, basée sur des agents capables de prendre, de manière autonome, des décisions pendant l’exécution des services, à partir de leurs connaissances. Dans un premier temps, nous définissons, de manière formelle, en utilisant des réseaux de Petri colorés, les services composites, leur processus d’exécution, et leurs mécanismes de tolérance aux pannes. Notre approche offre plusieurs mécanismes de reprise sur panne alternatifs : la récupération en arrière avec compensation ; la récupération en avant avec ré-exécution et/ou remplacement de service ; et le point de contrôle (checkpointing), à partir duquel il est possible de reprendre l’exécution du service ultérieurement. Dans notre approche, les services sont contrôlés par des agents, i.e. des composants dont le rôle est de s’assurer que l’exécution des services soit tolérante aux pannes. Notre approche est également étendue afin de permettre un auto-recouvrement. Dans cette extension, les agents disposent d’une base de connaissances contenant à la fois des informations sur eux-mêmes et sur le contexte d’exécution. Pour prendre des décisions concernant la sélection des stratégies de récupération, les agents font des déductions en fonction des informations qu’ils ont sur l’ensemble du service composite, sur eux-mêmes, tout en prenant en compte également ce qui est attendu et ce qui se passe réellement lors de l’exécution. Finalement, nous illustrons notre approche par une évaluation expérimentale en utilisant un cas d’étude
In this thesis, we present a self-healing approach for composite services supported by knowledge-based agents capable of making decisions at runtime. First, we introduce our formal definition of composite services, their execution processes, and their fault tolerance mechanisms using Colored Petri nets. We implement the following recovery mechanisms: backward recovery through compensation; forward recovery through service retry and service replacement; and checkpointing as an alternative strategy. We introduce the concept of Service Agents, which are software components in charge of component services and their fault tolerance execution control. We then extend our approach with self-healing capabilities. In this self-healing extension, Service Agents are knowledge-based agents; that is, they are self- and context-aware. To make decisions about the selection of recovery and proactive fault tolerance strategies, Service Agents make deductions based on the information they have about the whole composite service, about themselves, and about what is expected and what it is really happening at runtime. Finally, we illustrate our approach and evaluate it experimentally using a case study

Recent interest in environmentally friendly alternatives to chromate-based corrosion inhibitors has led to the development of a range of novel coating formulations. The work described in this thesis has been aimed at investigating the mechanism of self-healing and active corrosion protection of the new coatings by searching for active components that have migrated from the coating to a controlled defect. The use of glow discharge optical emission spectroscopy (GDOES) has been investigated as a tool for both the generation of a reproducible controlled defect and for elemental depth profiling of the coatings and corroded substrates. Conclusions drawn from the elemental depth profiles have been validated by a range of characterisation techniques including optical microscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy (EDX) and electrochemical techniques. The work has focused particularly on a comparison of hybrid coatings doped with inhibitors encapsulated in nano-containers, as compared with the direct addition of inhibitor species to the coating matrix. The work also investigates the effects of inhibitor addition to sol-gel coatings or primer systems or both, highlighting possible synergistic effects of mixed inhibitor systems (for example, sol-gel coating doped with strontium aluminium polyphosphate (SAPP)) supporting primers doped with benzotriazol (BZT) or mercaptobenzothiazol (MBT). The various coatings have also been studied in the absence of inhibitor species to assess the effectiveness of the coatings as barriers between the substrate and the corrosive environment. This aspect of the study has highlighted minor inhibitive effects of some of the reagents used in the coating formulations and a major inhibitive effect of the nano-containers. The work therefore concludes with recommendations for a possible coating formulation combining the most beneficial elements of the various coatings investigated.

One of the important design criteria for distributed systems and their applications is their reliability and robustness to hardware and software failures. The increase in complexity, interconnectedness, dependency and the asynchronous interactions between the components that include hardware resources (computers, servers, network devices), and software (application services, middleware, web services, etc.) makes the fault detection and tolerance a challenging research problem. In this dissertation, we present a self healing methodology based on the principles of autonomic computing, statistical and data mining techniques to detect faults (hardware or software) and also identify the source of the fault. In our approach, we monitor and analyze in real-time all the interactions between all the components of a distributed system using two software modules: Component Fault Manager (CFM) to monitor all set of measurement attributes for applications and nodes and Application Fault Manager (AFM) that is responsible for several activities such as monitoring, anomaly analysis, root cause analysis and recovery. We used three-dimensional array of features to capture spatial and temporal features to be used by an anomaly analysis engine to immediately generate an alert when abnormal behavior pattern is detected due to a software or hardware failure. We use several fault tolerance metrics (false positive, false negative, precision, recall, missed alarm rate, detection accuracy, latency and overhead) to evaluate the effectiveness of our self healing approach when compared to other techniques. We applied our approach to an industry standard web e-commerce application to emulate a complex e-commerce environment. We evaluate the effectiveness of our approach and its performance to detect software faults that we inject asynchronously, and compare the results for different noise levels. Our experimental results showed that by applying our anomaly based approach, false positive, false negative, missed alarm rate and detection accuracy can be improved significantly. For example, evaluating the effectiveness of this approach to detect faults injected asynchronously shows a detection rate of above 99.9% with no false alarms for a wide range of faulty and normal operational scenarios.

This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Thesis: S.M., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2019
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 49-50).
Next-generation applications require processing on massive amount of data in real-time, exceeding the capabilities of electronic systems today. This has spurred research in a wide-range of areas: from new devices to replace silicon-based field-effect transistors (FETs) to new circuit and system architectures with fine-grained and dense integration of logic and memory. However, isolated improvements in just one area is insufficient. Rather, enabling these next-generation applications will require combining benefits across all levels of the computing stack: leveraging new devices to realize new circuits and architectures. For instance, carbon nanotube (CNT) field-effect transistors (CNFETs) for logic and Resistive Random-Access Memory (RRAM) for memory are two promising emerging nanotechnologies for energy-efficient electronics. However, CNFETs suffer from inherent imperfections (such as of metallic CNTs, m-CNTs), which have prohibited realizing large-scale CNFET circuits in the past. This work proposes a circuit design technique that integrates and combines the benefits of both CNFETs with RRAM to realize three-dimensional (3D) circuits that are immune to m-CNTs. Leveraging this technique, we show the first experimental demonstration of CNFET-based analog mixed-signal circuits.
by Aya G. Amer.
S.M.
S.M. Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science

2017 - 2018
Main objective of this PhD thesis is the development of a new generation of self-healing multifunctional composites able to overcome some of the current limitations of aeronautical materials, such as: absence of auto-repair mechanisms integrated in the composite structure, reduced electrical conductivity and poor impact damage resistance. Structural aeronautical systems experience a broad spectrum of environmental and operational loads and atmospheric hazards (hail, lightning, storms etc.). Severe and/or prolonged load exposures may trigger the damage accumulation process even in recently deployed structures. Modern airframe design is exploiting new exciting developments in materials and structures to construct ever more efficient air vehicle able to enable ‘smart’ maintenance including self-repair capabilities. Relevant challenges for many of the already developed self-repairing systems are to enhance the structural stability, and the resistance to the atmospheric hazards through specific functions integrated in the material. The traditional approach to the development of aeronautic materials is to address the load-carrying and other functional requirements separately, resulting in a suboptimal load-bearing material with the penalty of added weight. The research activity of this PhD thesis is aimed to develop self-healing, load-bearing materials with all functionalities integrated in a single material able to meet many important requirements of this kind of materials. The main concept underpinning this PhD project is the use of the nanotechnology strategy for the production of new, high mechanical performance multifunctional materials. Based on recent developments in the field of nanotechnologies and successful strategies identified in recently papers and patents, the main objectives of this thesis have been achieved. The performed research activities allowed the implementation of a new generation of self-healing composites, which also considers relevant aspects related to the need of developing environmentally-friendly materials for transports. In this project, many different approaches have been considered for each functionality in order to reduce the risk of failure. Alternative concepts with respect to designs already proposed in literature have been explored. Multifunctional resins prepared using chemicals not commercially available yet have been developed and characterized. ... [edited by Author]
XXXI ciclo

2010 - 2011
This research work rises from collaborative activities between Alenia Aeronautica (Pomigliano D’Arco, Napoli) and the Industrial Engineering Department of University of Salerno. One of the biggest challenge facing materials scientists is the idea to put in action self-healing composites in aeronautical applications. Polymeric composite materials, recently introduced in aeronautics, are subject to weakening due to mechanical, chemical, thermal, stress. This could lead to the formation of microcracks deep within the structure where detection and external intervention are difficult or impossible. The presence of the microcracks in the polymer matrix can affect both the fiber and matrix dominated properties of a composite. In the case of a transport vehicle, the propagation of microcracks may compromise the structural integrity of the polymeric components, and so threatening passengers’ safety. In this work, we have developed a multifunctional autonomically healing composite with a selfhealing functionality active at the severe operational conditions of aircrafts (temperature range: -50 °C/80 °C). The self-repair function in this new self-healing system, inspired by the design of White et al., is based on the metathesis polymerization of ENB (or ENB/DCPD blend) activated by Hoveyda-Grubbs’1st generation catalyst. The self-healing epoxy mixture, containing Hoveyda-Grubbs’1st generation catalyst, allows a cure temperature up to 180 °C without becoming deactivated. A quantitative assessment of self-healing functionality showed very high values of selfhealing efficiency. Before reaching these amazing results several systems were investigated that differ for the nature and the composition of the epoxy matrix, catalysts and active monomers used:these systems have been gradually improved to suit performance requirements for a structural advanced material to be applied to aeronautical vehicles. [edited by the author]
X n.s.

In contrast to classical Field-Programmable Gate Arrays (FPGAs), partial and run-time reconfigurable (RTR) FPGAs can selectively reconfigure partitions of its hardware almost immediately while it is still powered and operative. In this way, RTR FPGAs combine the flexibility of software with the high efficiency of hardware. However, their potential cannot be fully exploited due to the increased complexity of the design process, and the intricacy to generate partial reconfigurations. FPGAs are often seen as a single auxiliary area to accelerate algorithms for specific problems. However, when several RTR partitions are implemented and combined with a processor system, new opportunities and challenges appear due to the creation of a heterogeneous RTR embedded system-on-chip (SoC). The aim of this thesis is to investigate how the flexibility, reusability, and productivity in the design process of partial and RTR embedded SoCs can be improved to enable research and development of novel applications in areas such as hardware acceleration, dynamic fault-tolerance, self-healing, self-awareness, and self-adaptation. To address this question, this thesis proposes a solution based on modular reconfigurable IP-cores and design-and-reuse principles to reduce the design complexity and maximize the productivity of such FPGA-based SoCs. The research presented in this thesis found inspiration in several related topics and sciences such as reconfigurable computing, dependability and fault-tolerance, complex adaptive systems, bio-inspired hardware, organic and autonomic computing, psychology, and machine learning. The outcome of this thesis demonstrates that the proposed solution addressed the research question and enabled investigation in initially unexpected fields. The particular contributions of this thesis are: (1) the RecoBlock SoC concept and platform with its flexible and reusable array of RTR IP-cores, (2) a simplified method to transform complex algorithms modeled in Matlab into relocatable partial reconfigurations adapted to an improved RecoBlock IP-core architecture, (3) the self-healing RTR fault-tolerant (FT) schemes, especially the Upset-Fault-Observer (UFO) that reuse available RTR IP-cores to self-assemble hardware redundancy during runtime, (4) the concept of Cognitive Reconfigurable Hardware (CRH) that defines a development path to achieve self-adaptation and cognitive development, (5) an adaptive self-aware and fault-tolerant RTR SoC that learns to adapt the RTR FT schemes to performance goals under uncertainty using rule-based decision making, (6) a method based on online and model-free reinforcement learning that uses a Q-algorithm to self-optimize the activation of dynamic FT schemes in performance-aware RecoBlock SoCs. The vision of this thesis proposes a new class of self-adaptive and cognitive hardware systems consisting of arrays of modular RTR IP-cores. Such a system becomes self-aware of its internal performance and learns to self-optimize the decisions that trigger the adequate self-organization of these RTR cores, i.e., to create dynamic hardware redundancy and self-healing, particularly while working in uncertain environments.
Partiell och run-time rekonfigurering (RTR) betyder att en del av en integrerad krets kan konfigureras om, medan den resterande delens operation kan fortlöpa. Moderna Field Programmable Gate Array (FPGA) kretsar är ofta partiell och run-time rekonfigurerbara och kombinerar därmed mjukvarans flexibilitet med hårdvarans effektivitet. Tyvärr hindrar dock den ökade designkomplexiteten att utnyttja dess fulla potential. Idag ses FPGAer mest som hårdvaruacceleratorer, men helt nya möjligheter uppstår genom att kombinera ett multiprocessorsystem med flera rekonfigurerbara partitioner som oberoende av varandra kan omkonfigureras under systemoperation. Målet med avhandlingen är att undersöka hur utvecklingsprocessen för partiella och run-time rekonfigurerbara FPGAer kan förbättras för att möjliggöra forskning och utveckling av nya tillämpningar i områden som hårdvaruacceleration, själv-läkande och själv-adaptiva system. I avhandlingen föreslås att en lösning baserad på modulära rekonfigurerbara hårdvarukärnor kombinerad med principer för återanvändbarhet kan förenkla komplexiteten av utvecklingsprocessen och leda till en högre produktivitet vid utvecklingen av inbyggda run-time rekonfigurerbara system. Forskningen i avhandlingen inspirerades av flera relaterade områden, så som rekonfigurerbarhet, tillförlitlighet och feltolerans, komplexa adaptiva system, bio-inspirerad hårdvara, organiska och autonoma system, psykologi och maskininlärning. Avhandlingens resultat visar att den föreslagna lösningen har potential inom olika tillämpningsområden. Avhandlingen har följande bidrag: (1) RecoBlock system-på-kisel plattformen bestående av flera rekonfigurerbara hårdvarukärnor, (2) en förenklad metod för att implementera Matlab modeller i rekonfigurerbara partitioner, (3) metoder för själv-läkande RTR feltoleranta system, t. ex. Upset-Fault-Observer, som själv-skapar hårdvaruredundans under operation, (4) utvecklandet av konceptet för kognitiv rekonfigurerbar hårdvara, (5) användningen av konceptet och plattformen för att implementera kretsar som kan användas i en okänd omgivning på grund av förmågan att fatta regel-baserade beslut, och (6) en förstärkande inlärnings-metod som använder en Q-algoritm för dynamisk feltolerans i prestanda-medvetna RecoBlock SoCs. Avhandlingens vision är en ny klass av själv-adaptiva och kognitiva hårdvarusystem bestående av modulära run-time rekonfigurerbara hårdvarukärnor. Dessa system blir själv-medvetna om sin interna prestanda och kan genom inlärning optimera sina beslut för själv-organisation av de rekonfigurerbara kärnorna. Därmed skapas dynamisk hårdvaruredundans och självläkande system som har bättre förutsättningar att kunna operera i en okänd omgivning.

QC 20151201

The polymer model is incorporated into a simulation for the entire material system which is based on a beam idealisation and in which a strong discontinuity approach is used to simulate cracking. It is shown that this model is able to accurately simulate the experiments carried out on the LatConX system.