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The present work aims at studying the damping response of a NiTi auxetic structure fabricated through additive manufacturing. Furthermore, an electropolishing route has been accounted for improving the roughness on the external surface of the printed samples. The damping capacity of the manufactured auxetic NiTi components is evaluated through the amount of energy dissipated per cycle and through the loss factor index. Results show that the damping capacity of the auxetic NiTi cell takes advantage of electropolishing and it is superior to that of traditional materials. Particularly, a maximum dissipated energy of 55 mJ was registered in the austenite state after 10 min of electropolishing; additionally, the loss factor shows a maximum of 0.0523 in the R-phase.

Self-healing materials offer a potential solution to the problem of damage to fibre-reinforced plastics (FRPs) by allowing for the in-service repair of composite materials at a lower cost, in less time, and with improved mechanical properties compared to traditional repair methods. This study investigates for the first time the use of poly(methyl methacrylate) (PMMA) as a self-healing agent in FRPs and evaluates its effectiveness both when blended with the matrix and when applied as a coating to carbon fibres. The self-healing properties of the material are evaluated using double cantilever beam (DCB) tests for up to three healing cycles. The blending strategy does not impart a healing capacity to the FRP due to its discrete and confined morphology; meanwhile, coating the fibres with the PMMA results in healing efficiencies of up to 53% in terms of fracture toughness recovery. This efficiency remains constant, with a slight decrease over three subsequent healing cycles. It has been demonstrated that spray coating is a simple and scalable method of incorporating a thermoplastic agent into an FRP. This study also compares the healing efficiency of specimens with and without a transesterification catalyst and finds that the catalyst does not increase the healing efficiency, but it does improve the interlaminar properties of the material., This research was funded by the State Research Agency of Spain (AEI), under grant number PID2019-107501RB-I00/AEI/10.13039/501100011033

Tallenna OA-artikkeli, kun julkaistu Bromination is herein exploited to promote the emergence of elastic behavior in a short peptide—SDSYGAP—derived from resilin, a rubber-like protein exerting its role in the jumping and flight systems of insects. Elastic and resilient hydrogels are obtained, which also show self-healing behavior, thanks to the promoted non-covalent interactions that limit deformations and contribute to the structural recovery of the peptide-based hydrogel. In particular, halogen bonds may stabilize the β-sheet organization working as non-covalent cross-links between nearby peptide strands. Importantly, the unmodified peptide (i.e., wild type) does not show such properties. Thus, SDSY(3,5-Br)GAP is a novel minimalist peptide elastomer.

Self-healing materials have become more and more interesting for the space industry, since they can lead to the creation of space systems and structures able to repair autonomously after accidental damages caused by collision with micrometeoroids and orbital debris during the entire operational life. The implementation of these novel materials results in higher protection and safety for astronauts, and longer missions in the perspective of lunar bases establishment and manned exploration of Mars. The present study aims to experimentally and numerically characterize an intrinsic self-healing supramolecular polymer that is potentially applicable to space suits, habitats and inflatable structures in general. A dedicated test device has been developed to evaluate the sealing performance of the material through flow rate measurements after a puncture event. The experimental part is followed by the study of the material's constitutive relations including hyperelastic and viscoelastic responses. The related model parameters are computed and calibrated through optimization and data matching tools in order to simulate damage and healing events. Results show that the selected supramolecular polymer possesses effective self-healing abilities also under pressurized conditions, demonstrating its applicability to the considered specific fields in the space sector. Furthermore, for what concerns the analyzed puncture experiments and field of solicitation, the developed model can follow the relaxation process related to the self-healing behavior, since it can predict whether the material is effectively able or not to flow and repair.

Our research investigated the energy absorption characteristics of chiral auxetic lattices filled cylindrical composite tubes subjected to a uniaxial and lateral quasi-static load. The lattice structures were manufactured using a 3D printing technique. Carbon fiber composite tubes without filler material were initially subjected to uniaxial and lateral quasi-static crushing load. The same types of experiment were then performed on chiral lattices and chiral lattices filled composite tubes. For the different cases, the load–displacements curves were analyzed and the specific energy absorption (SEA) values were compared. The SEA capability for the axial quasi-static crushing of the chiral lattices filled composite tubes decreased in comparison with the hollow composite design. However, the most significant result was that the average SEA value in the case of lateral loading increased dramatically in comparison with the hollow composite configuration.

In this work, near fully dense NiTi components have been fabricated using a 55.2Ni-Ti (wt.%) powder through selective laser beam melting. The effect of the manufacturing process on mechanical and functional properties of the selected NiTi alloy has been systematically investigated by tuning the hatching distance, h, and the scanning speed, v, in order to define a set of 12 NiTi families. The as-built NiTi parts present phase transformation temperatures higher than those of the feedstock, ascribed to the depletion of Ni during the process. Pseudoelasticity and shape memory responses have been evaluated through uniaxial compression and bending measurements, respectively. Both quasi-static and dynamic analyses have been considered. It is shown that the resulting material may exhibit distinct damping and strain recovery responses depending on the used process parameters.

Directed energy deposition (DED) is an additive manufacturing technique that enables rapid production and repair of metallic parts with flexible geometry. The complex nature of thermal and material transport during DED can yield unwanted microstructure heterogeneity, which causes scatter in parts performance. Here, we investigate microstructure variations at different length scales in Inconel 718 produced by powder-blown DED using different deposition rates. We quantify spatial trends in grain structure, texture, composition, and solidification structure within parts and correlate them with variations in hardness, yield strength, and Young's Modulus to highlight the effect of the thermal environment during solidification. We find that the high energy input employed when using high deposition rates is conducive to significant microstructure heterogeneity along both the build and transversal directions, which stems from the asymmetric cooling rates generated by the deposition strategy used. We also find that standard heat treatments employed on Inconel 718 are not suitable to homogenize the microstructure. These results have important implications for the development of industrially relevant build rate strategies for additively manufactured parts. Ministry of Education (MOE) Nanyang Technological University National Research Foundation (NRF) Published version This research was funded by the National Research Foundation (NRF) Singapore, under the NRF Fellowship program (NRFNRFF2018–05), and by STE Aerospace Pte. Ltd. YYC and EJ are supported by Nanyang Technological University Singapore (NTU) and the Ministry of Education of Singapore through an Industrial Postgraduate Programme (IPP) scholarship (M4062246) and the collaboration with the University of Strathclyde, UK, respectively.

The thermo-elastic properties of a novel class of ceramic composites based on an ultra-refractory matrix and containing short carbon fibre to provide failure tolerance and thermal shock resistance were experimentally characterised and numerically simulated. The composites samples were fabricated with fibre volume fractions ranging from 5 to 60 vol% and were featured by homogeneous dispersion of fibre along the basal plane due to the processing route. A random sequential adsorption algorithm was implemented to generate Representative Volume Elements (RVEs), following which finite element (FE) analyses were conducted to determine the elastic modulus and the coefficient of thermal expansion of the composites . Comparison of the experimental and modelling results showed good agreement for the modulus at low fibre volume fractions, and for CTE at higher volume fractions. Discrepancies are attributed to significant evolution of the composite microstructure upon processing at high temperatures, as revealed by microscopic analysis. The observations emphasise the need to account for the effects of microstructural changes on the constituent properties in the modelling of the thermo-mechanical properties in sintered ceramic composites.

This article reviews some of the intrinsic self-healing epoxy materials that have been investigated throughout the course of the last twenty years. Emphasis is placed on those formulations suitable for the design of high-performance composites to be employed in the aerospace field. A brief introduction is given on the advantages of intrinsic self-healing polymers over extrinsic counterparts and of epoxies over other thermosetting systems. After a general description of the testing procedures adopted for the evaluation of the healing efficiency and the required features for a smooth implementation of such materials in the industry, different self-healing mechanisms, arising from either physical or chemical interactions, are detailed. The presented formulations are critically reviewed, comparing major strengths and weaknesses of their healing mechanisms, underlining the inherent structural polymer properties that may affect the healing phenomena. As many self-healing chemistries already provide the fundamental aspects for recyclability and reprocessability of thermosets, which have been historically thought as a critical issue, perspective trends of a circular economy for self-healing polymers are discussed along with their possible advances and challenges. This may open up the opportunity for a totally reconfigured landscape in composite manufacturing, with the net benefits of overall cost reduction and less waste. Some general drawbacks are also laid out along with some potential countermeasures to overcome or limit their impact. Finally, present and future applications in the aviation and space fields are portrayed., This research was funded by ASI (Italian Space Agency), grant agreement 2018-5-HH.0 and Ministry of Science and Innovation of Spain, Ramon y Cajal Contract (RyC-2017-22837).

ZrB2 is an ultra-high temperature ceramic (UHTC) possessing a melting point exceeding 3000°C and a combination of exceptional engineering and physical properties. As such, ZrB2 ceramics are potential candidates for space and hypersonic components. The main drawbacks that restrict the employment of ZrB2 ceramics for a wider spectrum of applications are related to the low damage tolerance, poor oxidation resistance and relatively high density. However, the introduction of discontinuous C fibers can increase both ZrB2 robustness and notably decrease the total weight. Moreover, the addition of secondary phases, such as MoSi2, can further improve the high-temperature strength and, most importantly, the oxidation performance of the boride matrix owing to an in-situ development of a complex multilayer oxide structure. However, detrimental chemical reactions between Mo-compounds and C fibers occur during sintering at high temperature thus leading to degradation of the fibers and loss of their toughening function. Therefore, an accurate choice of the sintering additive is paramount to preserve the fiber structural function. Here we present a functionally graded (FG) composite made up of a ZrB2-MoSi2 outer scale, to provide oxidation and ablation resistance, and a progressively C fiber-rich body, to guarantee failure tolerance and lighten the whole structure. To define the best FG architecture and exploit residual stress toughening upon layering, thermo-elastic simulation by finite element modeling is adopted.

In the last decade, self-healing materials have become extremely appealing for the field of space applications, due to their technological evolution and the consequent possibility of designing space systems and structures able to repair autonomously after damage arising from impacts with micrometeoroids and orbital debris, from accidental contact with sharp objects, from structural fatigue or simply due to material aging. The integration of these novel materials in the design of spacecraft structures would result in increased reliability and safety leading to longer operational life and missions. Such concepts will bring a decisive boost enabling new mission scenario for the establishment of new orbital stations, settlement on the Moon and human exploration of Mars.The proposed review aims at presenting the newest and most promising self-healing materials and associated technologies for space application, along with the issues related to their current technological limitations in combination with the effect of the space environment. An introductory part about the outlooks and challenges of space exploration and the self-healing concept is followed by a brief description of the space environment and its possible effects on the performance of materials. Self-healing materials are then analysed in detail, moving from the general intrinsic and extrinsic categories down to the specific mechanisms.

The macroscopic interfacial healing behaviour in a series of urea-urethane networks as function of the hydrogen bonds and disulphides content is presented. The polymers were prepared with different crosslinking densities but with the same amount of dynamic covalent bonds (disulphide linkages). Tensile and fracture measurements were adopted to evaluate the degree of recovery of the mechanical properties after damage. Healing kinetics and healing efficiencies were quantitatively determined as a function of network composition, healing temperature and contact time. Finally, the recovery of mechanical properties was correlated with the viscoelastic response of the networks through rheological measurements and time-temperature superposition principle (TTS). The application of the TTS approach on both fracture healing and DMTA and subsequent mathematical descriptive model led to a better understanding of the influence of polymer architecture and that of the amount of reversible groups on the healing process.

The main aim of this work is to study the respective contribution of the hard and soft blocks of a metal-ligand containing block copolymer to the self-healing behavior. To this aim, different block copolymers containing terpyridine were synthesized using reversible addition-fragmentation chain transfer (RAFT) polymerization. These block copolymers consisted of polystyrene as the hard block, n-butyl acrylate (BA) as soft block and terpyridine units as the ligand moiety placed at different locations in the soft block. These block copolymers were complexed with manganese(II) chloride to introduce transient crosslinks and, thus, self-healing behavior. Homopolymers with the hard and soft block only were also synthesized and tested. A quasi-irreversible crosslinking, i.e. by using nickel(II) nitrate, was performed in order to study the dynamics of the permanently (strongly) crosslinked network. Rheological master curves were generated enabling the determination of the terminal flow in these networks and the reversibility of the supramolecular interactions. Additionally, the macroscopic scratch healing behavior and the molecular mobility of the polymer chains in these supramolecular networks were investigated. A kinetic study of the scratch healing was performed to determine the similarities in temperature dependence for rheological relaxations and macroscopic scratch healing. In our previous work, we have explored the effect of strength of the reversible metal-ligand interaction and the effect of changing the ratio of hard to soft block. This work goes further in separating the individual contributions of the hard and soft blocks as well as the reversible interactions and to reveal their relative importance in the complex phenomenon of scratch healing.

A self-healing sulfur vulcanized natural rubber (NR) is here reported using the common ingredients in a traditional NR formulation. The dynamic character of the di- and polysulfide bonds naturally present in covalently cross-linked rubbers was found to be responsible for the healing ability and the full recovery of mechanical properties at moderate temperatures provided the material was employed in a nonfully cured starting state. Results show that a compromise between mechanical performance and healing capability can be reached by tailoring the amount of sulfur, the cross-linking density, and the disulfide/polysulfide ratio. The healing efficiency was found to depend on the postcuring storage time, the time between damage creation and re-establishment of mechanical contact, and the actual healing time. Furthermore, a dedicated electron spin resonance (ESR) test allowed establishing the underlying healing principle based on temperature-induced free sulfur radicals. The main observations presented here can serve as the basis for the design and preparation of other self-healing polymers with long-term durability based on di-/polysulfide bridges and other reversible moieties.

In this study, self-healing and anti-sloshing materials are investigated for mitigation of impact-induced damage. The integration of these systems, for the prevention of fire or explosion due to impact or bullet damage, may significantly improve the safety of aerospace fuel tanks. Leakage, after bullet penetration or debris impact, may be prevented or at least limited if the container&rsquo, s walls are made by materials with self-healing capabilities. The aim of this work is to define the self-healing behavior of the EMAA ionomer (poly-Ethylene-MethAcrylic Acid copolymer), with reference to the energy dissipation mechanisms involved during damage and autonomic healing. An experimental investigation on the healing capacity of the material when perforated by bullets shot at medium velocity (250 m/s&minus, 450 m/s) was carried out. In these tests, the influence of friction, temperature, and multiple impacts on the healing process was examined and discussed. Moreover, the material response in operating conditions similar to those encountered in actual aeronautical applications, that is, in presence of pressurized fluid and anti-sloshing material (Explosafe&reg, ) was tested. Results show that the presence of the liquid increases the self-healing capabilities, which are, however, slightly affected by pressurization and internal anti-sloshing filler, the contribution in terms of sloshing reduction remains relevant.

While ionomers are well known for their healing ability under ballistic impact conditions, the present work focusses on elucidating the effect of both the free carboxylic content and the cluster state on well-controlled isothermal low temperature healing of surface scratches in ionomer blends. It is shown that under the conditions explored the healing efficiency depends primarily on the amount of free carboxylic groups and the presence of clusters plays a secondary role. A free carboxylic end group concentration of about 3 mol% is required to obtain optimal healing.

In the present study, a comparative compression investigation of anti-tetrachiral and modified re-entrant lattices was conducted in-plane direction using experimental and numerical analyses. Lattice structures were manufactured using fused deposition modelling (FDM) 3D printing technology and crushed at quasi-static condition. Nonlinear finite element (FE) models of both structures were established, and the FE results were systematically compared with the experimental results. The onset of densification phases of both structures was determined numerically. Results indicate that deformation modes strongly affect the force-deflection response of both designs. In this manner, failure locations and buckling deformation in the tests were identified to find a relation with theory and to modify geometries. The anti-tetrachiral design exhibits higher specific energy absorption than modified re-entrant hexagonal lattices. Beyond the auxetic characteristics, deformation mechanism of the anti-tetrachiral lattices provides an opportunity to construct excellent crush absorption in-plane direction thanks to its high shear strength stem from its unique deformation mechanism.

The impressive mechanical properties of natural composites, such as nacre, arise from their multiscale hierarchical structures, which span from nano- to macroscale and lead to effective energy dissipation. While some synthetic bioinspired materials have achieved the toughness of natural nacre, current production methods are complex and typically involve toxic chemicals, extreme temperatures, and/or high pressures. Here, the exclusive use of bacteria to produce nacre-inspired layered calcium carbonate-polyglutamate composite materials that reach and exceed the toughness of natural nacre, while additionally exhibiting high extensibility and maintaining high stiffness, is introduced. The extensive diversity of bacterial metabolic abilities and the possibility of genetic engineering allows for the creation of a library of bacterially produced, cost-effective, and eco-friendly composite materials.

In this work, the mechanical and the self-healing behaviors of an ethylene-co-methacrylic acid ionomer were investigated in different testing conditions. The self-healing capability was explored by ballistic impact tests at low-velocity, midvelocity, and hypervelocity bullet speed; different experimental conditions such as sample thickness and bullet diameter were examined; in all impact tests, spherical projectiles were used. These experiments, in particular those at low and midspeed, allowed to define a critical ratio between sample thickness and bullet diameter below which full repair was not observed. After ballistic damage, the healing effi- ciency was evaluated by applying a pressure gradient through tested samples. Subsequently, morphology analysis of the affected areas was made observing all tested samples by scanning electron microscope. This analysis revealed different characteristic features of the damaged zones affected at different projectile speed. Stress-strain curves in uniaxial tension performed at different temperatures and strain rates revealed yield strength and postyield behavior significantly affected by these two parameters. A rise of temperature during high strain rate tests in the viscoplastic deformation region was also detected. This behavior has a strong influence on the self-repair- ing mechanism exhibited by the studied material during high-energy impact tests. V C 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 000: 000-000, 2013

The development of self-healing materials, based on polymer blends, is an important issue either from a scientific or a technological point of view. The application of such materials can be remarkably extended if healing effects can be maintained even in polymers that are modified in order to tune their physical and mechanical behavior. In this research the self-healing behavior of blends made of ionomers (sodium and zinc salts of poly(ethyelene-co-methacrylic acid)—EMNa and EMZn) with functionalized elastomers (epoxidized natural rubber with different epoxidation levels—ENR50 and ENR25, polyisoprene—PISP) of different compositions is investigated. The role of processing conditions, phase morphology, functionalization level, polymers compatibility over self-healing response are discussed. Rubber functionality and phase dispersion are recognized as crucial factors affecting the healing efficiency of blends. Results of ballistic tests, DSC thermal analysis, FTIR spectroscopy, optical and electron (SEM and TEM) microscopy observations, rheological and mechanical tests are presented as supporting evidences.

In the present work we show the effect of graphene loading on the restoration of the mechanical properties and thermal and electrical conductivity of a self-healing natural rubber nanocomposite. The graphene loading led to a minimal enhancement of mechanical properties and yielded a modest increase in thermal and electrical conduction. The polymer nanocomposites were macroscopically damaged (cut) and thermally healed for 7 h in a healing cell. Different healing trends as function of the graphene content were found for each of the functionalities: (i) thermal conductivity was fully restored independently of the graphene filler loading; (ii) electrical conductivity was only restored to a high degree above the percolation threshold; and (iii) tensile strength restoration increased more or less linearly with graphene content but was never complete. A dedicated molecular dynamics analysis by dielectric spectroscopy of the pristine and healed samples highlighted the role of graphene-polymer interactions at the healed interphase on the overall restoration of the different functionalities. Based on these results it is suggested that the dependence of the various healing efficiencies with graphene content is due to a combination of the graphene induced lower crosslinking density, as well as the presence of strong polymer-graphene interactions at the healed interphase.

Traditional polyetherimides (PEIs) are commonly synthesized from an aromatic diamine and an aromatic dianhydride (e.g., 3,4′-oxidianiline (ODA) and 4,4′-oxidiphtalic anhydride (ODPA)) leading to the imide linkage and outstanding chemical, thermal and mechanical properties yet lacking any self-healing functionality. In this work, we have replaced the traditional aromatic diamine by a branched aliphatic fatty dimer diamine (DD1). This led to a whole family of self-healing polymers not containing reversible chemical bonds, capable of healing at (near) room temperature yet maintaining very high elastomeric-like mechanical properties (up to 6 MPa stress and 570% strain at break). In this work, we present the effect of the DD1/ODPA ratio on the general performance and healing behavior of a room temperature healing polyetherimide. A dedicatedanalysis suggests that healing proceeds in three steps: (i) an initial adhesive step leading to the formation of a relatively weak interface; (ii) a second step at long healing times leading to the formation of an interphase with different properties than the bulk material and (iii) disappearance of the damaged zone leading to full healing. We argue that the fast interfacial adhesive step is due to van der Waals interactions of long dangling alkyl chains followed by an interphase ormation due to polymer chain interdiffusion. An increase in DD1/ODPA ratio leads to an increase in the healing kinetics and displacement shift of the firsthealing step toward lower temperatures. An excess of DD1 leads to the cross-linking of the polymer thereby restricting the necessary mobility for the interphase formation and limiting the self-healing behavior. The results here presented offer a new route for the development of room temperature self-healing thermoplastic elastomers with improved mechanical properties usingfatty dimer diamines.

The development of materials with the ability of intrinsic self-repairing after damage in a fashion resembling that of living tissues has important scientific and technological implications, particularly in relation to cost-effective approaches toward damage management of materials. Natural rubbers with epoxy functional groups in the macromolecular chain (ENR) and ethylene-methacrylic acid ionomers having acid groups partially neutralized with metal ions possess self-repairing behavior following high energy impacts. This research investigates the self-repairing behavior of both ENR and ionomers during ballistic puncture test on the basis of their thermal and mechanical properties. Heterogeneous blending of ionomers and ENR have also been used here as a strategy to tune the thermal and mechanical properties of the materials. Interestingly, blends of sodium ion containing ionomer exhibit complete self-repairing behavior, whereas blends of zinc ion containing ionomer show limited mending. The chemical structure studied by FTIR and thermal analysis shows that both ion content of ionomer and functionality of ENR have significant influence on the self-repairing behavior of blends. The mobility of rubbery phases along with its interaction to ionomer phase in the blends significantly changes the mending capability of materials. The healing behavior of the materials has been discussed on the basis of their thermal, mechanical, and rheological tests for each materials.

The development of Resin Transfer Moulding technology for advanced applications requires a detailed analysis and control of the process. Fibres optics and Fibres Bragg Gratings are useful tools to investigate composite structures during their lifetime service. They are here employed for the monitoring of manufacturing phase and the acquisition of strains during product usage in service. The adopted monitoring procedure allows to follow all the stages of the production process, evidencing their possible influences over final laminate characteristics. Resin injection, curing and cooling, mould extraction, sensor position, deformation control during mechanical testing are analysed on the basis of the signal output from fibre optic sensors embedded in a model component.

In the present work we show the effect of the crosslinking degree on the mechanical and healing behaviour of a healable thermoset dual-network polymer. A hyphenated rheological test (i.e. simultaneous rheology and FTIR) was used to follow the effect of the curing process on the mechanical behaviour in relation to the underlying chemical reactions. The effect of curing on the bulk properties and the polymer interfacial healing was studied using gap closure kinetics and a fracture mechanical test. The increased crosslinking density at longer curing times led to a more temperature-stable polymer network with significantly higher mechanical properties (elastic modulus and strength at break). It was found that the damage closure kinetics decrease with the curing degree but the ultimate interfacial healing efficiency does not. The results here reported highlight the effect of the crosslinking density on the kinetics of damage closure with a low impact on the maximum interfacial healing efficiency as long as the amount of reversible bonds remains constant.

Broadband dielectric spectroscopy (BDS) is introduced as a new and powerful technique to monitor network and macroscale damage healing in an elastomer. For the proof of concept, a partially cured sulfur-cured natural rubber (NR) containing reversible disulfides as the healing moiety was employed. The forms of damage healed and monitored were an invisible damage in the rubber network due to multiple straining and an imposed macroscopic crack. The relaxation times of pristine, damaged, and healed samples were determined and fitted to the Havriliak−Negami equation to obtain the characteristic polymer parameters. It is shown that seemingly full mechanical healing occurred regardless the type of damage, while BDS demonstrates that the polymer architecture in the healed material differs from that in the original one. These results represent a step forward in the understanding of damage and healing processes in intrinsic self-healing polymer systems with prospective applications such as coatings, tires, seals, and gaskets.

This work presents a detailed study into the rheological properties and fracture healing behaviour of two poly(urea-urethane) polymers containing (i) hydrogen bonds and (ii) hydrogen bonds and disulphide linkages. The experimental procedure here presented using the temperature and time superposition allowed for the identification of the contribution of each reversible bond type to the network behaviour (rheology) and healing (fracture). During the experimental data analysis it was found that the same shift factors required to construct the rheological master curves from separate isothermal small-amplitude oscillatory shear (SAOS) measurements at different temperatures could also be applied to obtain a master curve for the fracture healing data as a function of healing time and temperature. This work shows therefore the apparent direct relationship between rheological response and macroscopic fracture healing.

The effect of substitution and oxidation-reduction on the thermal conductivity of perovskite-like layered structure (PLS) ceramics was investigated in relation to mass contrast and non-stoichiometry. Sr (acceptor) was substituted on the A site, while Ta (donor) was substituted on the B site of La2Ti2O7. Substitution in PLS materials creates atomic scale disorders to accommodate the non-stoichiometry. High resolution transmission electron microscopy and X ray diffraction revealed that acceptor substitution in La2Ti2O7 produced nanoscale intergrowths of n = 5 layered phase, while donor substitution produced nanoscale intergrowths of n = 3 layered phase. As a result of these nanoscale intergrowths, the thermal conductivity value reduced by as much as ∼20%. Pure La2Ti2O7 has a thermal conductivity value of ∼1.3 W/m K which dropped to a value of ∼1.12 W/m K for Sr doped La2Ti2O7 and ∼0.93 W/m K for Ta doped La2Ti2O7 at 573 K.

In this work the self-healing behaviour of a supramolecular elastomer showing healing at room temperature was studied by mechanical testing. Tensile experiments on pristine and healed samples were conducted and a critical analysis of the material response under the testing conditions applied pointed out that simple tensile test only allows a restricted quantification of the healing process. A fracture mechanics approach based on the J-integral was adopted to measure the healing behaviour across the restored interface between the original fracture surfaces. The processes involved in the repair were identified by combining the information obtained with the different techniques. A substantial improvement in the assessment of the interfacial healing was achieved.

Over the last few years, several testing methods have been introduced for the detection and quantification of autonomous and thermally stimulated healing in polymers. This review summarizes some of the most prominent state-of-the-art techniques for the characterization of polymer healing occurring at the microscopic and macroscopic levels during the repair of damage such as scratches, cracks, or ballistic perforations. In addition to phenomenological investigation of the self-healing process, a range of physical characterization techniques have been explored for elucidation of the underlying healing mechanism at the molecular or polymer network level. The present state of visual methods, spectroscopic techniques, scattering techniques, and dynamic methods is described. A short outlook is provided, discussing the future challenges and expected new trends in the characterization of self-healing polymers.

The integration of different tools for the prevention of fires or explosions due to impact or bullet damage may significantly improve the safety of fuel tanks. Self-healing polymers have demonstrated their ability to autonomous mending bullet punctures. The results of ballistic tests to check the response of multilayer structures based on self-healing ionomer and aramid fabric or carbon foam are presented in view of their potential employment as safety materials for dangerous liquids containment. Considerations related to the effect of coupling of different materials over self-healing response are discussed. A conceptual solution that integrates self-healing polymers or composites with cellular filler made of wrinkled aluminium foil for fuel tanks is proposed and discussed. Keywords fillers, fuel tanks, impact, self-healing Language: en

This paper addresses the various strategies to induce self-healing behaviour in fibre reinforced polymer based composites. A distinction is made between the extrinsic and intrinsic healing strategies. These strategies can be applied at the level of the fibre, the fibre/matrix interface or at the level of the matrix. It is shown that the degree of healing depends on the type of damage and the testing mode used and examples are given both for extrinsic and for intrinsic healing systems. The conclusion is drawn that self-healing in fibre reinforced composites is possible yet unlikely to become a commercial reality in the near future.

The availability of new materials with uncommon characteristics and functionalities gives the opportunity to develop and possibly integrate new conceptual solutions for the improvement of safety in the design and manufacture of containers for critical substances. Numerous examples can be devised where a proper containment of liquid, even after tank damage, is essential with regard to safety issues. Bullet penetration or debris impact of fuel tanks are two relevant examples where specifically designed configuration and materials may significantly improve safety margins. In such situations, deflagration can be activated by sudden variation of internal pressure and temperature or liquid spilling due to wall container perforation. Cellular filler material in the container can remarkably dispel fire heat and limit pressure wave peaks generated by a bullet explosion; moreover, the overall response to impact loads in case of a crash is remarkably improved. Different fillers with particular configurations, ranging from porous structure to expanded aluminium foil, have been tested as tank explosion suppression media with remarkably positive results. In traditional multilayer wall fuel tanks, self-sealing capability can be obtained as a result of swelling or chemical reaction of rubber/foam layer when it comes in contact with the spilling internal liquid. A usual drawback of these materials is the limited resistance to aging which reduces their effectiveness with time. Moreover, the sealing material does not give structural contribution furthermore consistently increasing the weight of the component. Polymeric materials with intrinsic self-healing capability may become a valid alternative to traditional configurations. In this context, ethylene-methacrylic acid based ionomers can be adopted as self-healing layers. The coupling of such selfSafety and Security Engineering V 379 doi:10.2495/ 3 SAFE 0 1 1 34 www.witpress.com, ISSN 1743-3509 (on-line) WIT Transactions on The Built Environment, Vol 134, © 2013 WIT Press healing polymer with a rigid cellular filler can have multiple benefits such as high impact resistance, repeatable and environmentally stable self-healing capability, lightness, mechanical stiffness and strength.

This paper discusses the impact behavior of a self-healing ionomeric polymer and compares its protection capability against space debris impacts to that of simple aluminium-alloy bumpers. To this end, 14 impact experiments on both ionomer and Al-7075-T6 thin plates with similar surface density were made with 1.5 mm aluminium spheres at velocity between 1 and 4 km/s. First, the perforation extent in both materials was evaluated vis-a-vis the prediction of well known hole-size equations; then, attention was given to the damage potential of the cloud of fragments ejected from the rear side of the target by analysing the craters pattern and the momentum transferred to witness plates mounted on a ballistic pendulum behind the bumpers. Self-healing was completely successful in all but one ionomer samples and the primary damage on ionomeric polymers was found to be significantly lower than that on aluminium. On the other hand, aluminium plates exhibited slightly better debris fragmentation abilities, even though the protecting performance of ionomers seemed to improve at increasing impact speed.

This research deals with the investigation of the self-healing behavior after ballistic damage of ethylene-methacrylic acid ionomers and theirs blends with epoxidized natural rubber (ENR). The self-healing capability was studied by ballistic puncture tests under different experimental conditions as sample thickness, bullet speed, diameter and shape. Bullet speed ranging from few hundreds meters per second to few km/s were employed. The healing efficiency was evaluated by applying a pressure gradient trough the plates and by checking for possible flow at the damage zone. A morphology analysis of the impact area was made observing all samples by scanning electron microscope.