Diels-Alder Chemistry to Develop Self-Healing Epoxy Resins and Composites Thereof

Self-healing polymers are a class of smart materials able to recover after sustaining damage. A family of thermosetting epoxy resins, containing Diels-Alder (DA) adducts in the epoxy precursor backbone, has been prepared and characterized. The DA adducts can be reversibly cleaved and reformed under the appropriate thermal conditions, and this feature has been exploited to produce intrinsically self-repairing materials. This chapter focuses on the effects of different structural features, such as average number of cross-linking functionality and molecular mobility of epoxy precursors, on the efficiency of healing process. High cross-linking density and molecular stiffness improve mechanical performances, such as elastic modulus and glass transition temperature, and allow fabrication of self-healing fiber-reinforced composites by conventional manufacturing technologies. Within this chapter, the molecular design, the preparation, and the evaluation of properties of self-healing epoxy and its composites have been discussed

Monitoring of self-healing composites: a nonlinear ultrasound approach

Self-healing composites using a thermally mendable polymer, based on Diels–Alder reaction were fabricated and subjected to various multiple damage loads. Unlike traditional destructive methods, this work presents a nonlinear ultrasound technique to evaluate the structural recovery of the proposed self-healing laminate structures. The results were compared to computer tomography and linear ultrasound methods. The laminates were subjected to multiple loading and healing cycles and the induced damage and recovery at each stage was evaluated. The results highlight the benefit and added advantage of using a nonlinear based methodology to monitor the structural recovery of reversibly cross-linked epoxy with efficient recycling and multiple self-healing capability

A Dietary Assessment Training Course Path: The Italian IV SCAI Study on Children Food Consumption

The eating patterns in a population can be estimated through dietary surveys in which open-ended assessment methods, such as diaries and interviews, or semi-quantitative food frequency questionnaires are administered. A harmonized dietary survey methodology, together with a standardized operational procedure, in conducting the study is crucial to ensure the comparability of the results and the accuracy of information, thus reducing uncertainty and increasing the reliability of the results. Dietary patterns (i) include several target variables (foods, energy and nutrients, other food components), (ii) require several explanatory variables (age, gender, anthropometric measurements, socio-cultural and economic characteristics, lifestyle, preferences, attitudes, beliefs, organization of food-related activities, etc.), and (iii) have impacts in several domains: imbalance diets; acute and chronic exposures affect health, specifically non-communicable diseases; and then sanitary expenditure. On the other hand, food demand has impacts on the food system: production, distribution, and food services system; food wastes and other wastes generated by food-related activities of the households (e.g., packaging disposal) have consequences on the “health of the planet” which in turn can have effects on human health. Harmonization and standardization of measurement methods and procedures in such a complex context require an ad hoc structured information system made by databases (food nomenclatures, portion sizes, food atlas, recipes) and methodological tools (quantification methods, food coding systems, assessment of nutritional status, data processing to extrapolate what we consider validated dietary data). Establishing a community of professionals specialized in dietary data management could lead to build a surveillance system for monitoring eating habits in the short term, thus reducing costs, and to arrange a training re-training system. Creating and maintaining the dietary data managers community is challenging but possible. In this context, the cooperation between the CREA Research Centre for Food and Nutrition and the Italian National Health Institute (ISS) promoted and supported by the Italian Ministry of Health may represent a model of best practice that can ensure a continuous training for the professional community carrying out a nutritional study

MULTISCALE DESIGN AND MANUFACTURING OF ADVANCED COMPOSITES INTEGRATING DAMPING FEATURES

Multi-functionality is a current issue in materials design, in particular, the fast growing application of advanced composites in commercial aeronautic is raising the need to design primary structures with composite material that perform multiple functions: i.e. able to fulfil not only mechanical allowable but also functional requirement such as vibroacoustic and fire reaction. The development of multifunctional design tools integrating structural and damping features enables a next step toward the exploitation of the composite materials benefits. It is worth noting that the structural damping in the case of a composite fuselage is a multiscale problem. The fuselage vibroacoustic requirement is determined by the behaviour of stringers reinforced skin, that is determined by the panel damping behaviour which owns its damping features to its laminate architecture and constituents materials. The requirement chain for a composite structure is formulated by a top-down approach determined by the behaviour of sub-structures which compose the final structural component. Aim of this work is to individuate and implement a design procedure able to describe a composite structure starting from its constituents, moreover for each dimensional scales the behaviour have to be modelled. The through dimensional scales model proposed for describing composite materials use the formulation of constitutive equation for describe the material behaviour at each sub-component. From the homogenization of fibres and hosting matrix it is possible to formulate a micro-scale constitutive matrix describing mechanical and dissipative lamina behaviour, with analogous approach the laminate behaviour is described by the homogenization of the constituents layers. The potential of describe mechanical and dissipative feature for a laminate starting from its elementary constituents gives the chance of imagine hybrid architecture able to improve a desired feature. Keeping in mind the passive damping feature, three possible hybrid architecture have been proposed for suit the requirement of increment material performance, moreover the composite have to maintain its mechanical properties above a defined level to preserve structural safety. The insertion of a viscoelastic layer within the laminate has been individuated as promising architecture for increase damping performance although this configuration is susceptible to interlaminar stress and prone to de-bonding. From theoretically study on the energy allocation within the laminate is formulated the novel idea of an hybrid laminate where the viscoelastic material is embedded as long fiber in the reinforcement preform, this architecture contribute to increment the damping properties withstand the mechanical properties but enhancement level is less than an interleaved containing the same volume of added material. Rather than modifying the fiber arrangement the lamina passive damping could be increased by means of introducing high damping nano-fillers within the hosting matrix. For the prediction of the overall laminate properties an hierarchical procedure has proposed accounting the hybridization at each laminate level. Considering elementary structures, such as a beam, subjected to boundary condition which induce that energy is allocated in only one component, the damping predicted is the overall damping capacity for the considered energy component. A valuable technology for manufacturing composite materials have to be flexible in changing constituents properties as well as the insertion of a softer material as lamina or the use of hybrid layer stacking the fibres or the use of a pre-hybridised hosting matrix. Process technologies allowing the listed item are based on the liquid moulding, in particular the VARTM process is selected as this process could be easily extended on large scale fabrication. Unidirectional composites of the proposed lamina architecture were manufactured and tested. In each case a valuable increment in passive damping were measured. Both the interleaved layer and the hybrid preform lead to a loss in mechanical performances, whilst the hybrid laminates manufactured by the nanofilled hosting matrix kept the its mechanical features leading to an enhancement of loss factor until 40% at temperatures suitable for aeronautical applications. The most promising architecture selected from experimental study was the multiscale laminate, as they are reinforced by microscale long fibres and nanoscale nanotubes. As proof of the industrial feasibility of this solution a simple typical aeronautical component has manufactured. A stiffened composite plate is designed and manufactured for further acoustical testing. In addition the angle ply laminate has fabricated and mechanical tested

Insights on Shear Transfer Efficiency in “Brick-and-Mortar” Composites Made of 2D Carbon Nanoparticles

Achieving high mechanical performances in nanocomposites reinforced with lamellar fillers has been a great challenge in the last decade. Many efforts have been made to fabricate synthetic materials whose properties resemble those of the reinforcement. To achieve this, special architectures have been considered mimicking existing materials, such as nacre. However, achieving the desired performances is challenging since the mechanical response of the material is influenced by many factors, such as the filler content, the matrix molecular mobility and the compatibility between the two phases. Most importantly, the properties of a macroscopic bulk material strongly depend on the interaction at atomic levels and on their synergetic effect. In particular, the formation of highly-ordered brick-and-mortar structures depends on the interaction forces between the two phases. Consequently, poor mechanical performances of the material are associated with interface issues and low stress transfer from the matrix to the nanoparticles. Therefore, improvement of the interface at the chemical level enhances the mechanical response of the material. The purpose of this review is to give insight into the stress transfer mechanism in high filler content composites reinforced with 2D carbon nanoparticles and to describe the parameters that influence the efficiency of stress transfer and the strategies to improve it

Flash sintering in metallic ceramics: finite element analysis of thermal runaway in tungsten carbide green bodies

Flash sintering is a powerful tool for the ultrarapid consolidation of green ceramic compacts, although its activation mechanisms in electrically conductive PTC (Positive Temperature Coefficient for resistivity) materials' is poorly understood. It was argued that a flash event could be initiated and sustained for a transitory period in certain PTC ceramics because of an initial negative dependence of the green material resistivity with temperature. The thermal runaway phenomenon and its activation conditions on binderless tungsten carbide (WC) green bodies are investigated in the present work by numerical simulations using finite element methods (FEM). The flash event is recreated and studied within the COMSOL Multiphysics software at the macroscale, i.e., considering the flash as an electrical power surge driven by an increasing sample's conductivity. During the flash, very high temperatures in the range of 1800–2000 °C can be reached in the WC green sample in a few seconds. The accurate numerical simulation of such event results in heating rates exceeding 1000 °C/s, a condition that theoretically brings a powder compact at temperatures high enough to accelerate and prioritize sintering densifying mechanisms over non-densifying ones. Therefore, the sample's regions where the maximum sintering temperature is reached more slowly because of thermal contacts with the electrodes remain highly porous at the end of the process