Multifunctional Composites for Improved Polyimide Thermal Stability

The layered morphology of silicate clay provides an effective barrier to oxidative degradation of the matrix resin. However, as resin thermal stability continues to reach higher limits, development of an organic modification with comparable temperature capabilities becomes a challenge. Typically, phyllosilicates used in polymer nanocomposites are modified with an alkyl ammonium ion. Such organic modifiers are not suited for incorporation into high temperature polymers as they commonly degrade below 200oC. Therefore, the development of nanoparticle specifically suited for high temperature applications is necessary. Several nanoparticles were investigated in this study, including pre-exfoliated synthetic clay, an organically modified clay, and carbon nanofiber. Dispersion of the layered silicate increases the onset temperature of matrix degradation as well as slows oxidative degradation. The thermally stable carbon nanofibers are also observed to significantly increase the resin thermal stability

Electromagnetic Properties of Multifunctional Composites Based on Glass Fiber Prepreg and Ni/Carbon Fiber Veil

Multifunctional composites combine structural and other physicochemical properties, with major applications in aeronautical, space, telecommunication, automotive, and medical areas. This research evaluates electromagnetic properties of multifunctional composites based on glass fiber woven fabric pre-impregnated with epoxy resin laminated together carbon fiber non-woven veil metalized with Ni. In this way, searching for possible application as radar absorbing structures or electromagnetic interference shielding structures. The scattering parameters, in the frequency range of 8.2 to 12.4 GHz, show that the epoxy resin/glass fiber prepreg allows the transmission of the electromagnetic waves through its microstructure, independently of the glass fiber reinforcement orientation (98% transmission, S-24 = -0.09 dB). However, the carbon fiber/Ni veil shows highly reflector behavior (91% reflection, S-22 = -0.43 dB). Energy dispersive spectroscopy of the veil, before and after nitric acid attacks, confirmed the Ni coating removal from the carbon fiber surface. Still, the scattering parameters show reflector behavior (77% reflection, S-22 = -1.13 dB), attributed to the electrical conductivity of carbon fibers. Multifunctional composites based on glass fiber/epoxy/carbon fiber/Ni veil laminates were processed by hot compression molding. The scattering parameters show that the laminates do not behave as good radar absorbing structures. Nevertheless, the laminates present promising results for application as light weight and low thickness structural composites with electromagnetic interference shielding effectiveness (91.4% reflection for 0.36 mm thickness and 100% for similar to 1.1 mm) for buildings, aircraft, and space components.Univ Estadual Paulista, Fac Engn Guaratingueta, Dept Mat & Tecnol, Ave Dr Ariberto Pereira Cunha,333 Portal das Coli, BR-12516410 Guaratingueta, SP, BrazilInst Technol Aeronaut, Dept Ciencia & Tecnol Aeroespacial, Lab Guerra Elect, Sao Jose Dos Campos, SP, BrazilUniv Fed Sao Paulo, Inst Ciencia & Tecnol Curso Engn Mat, Sao Jose Dos Campos, SP, BrazilUniv Fed Sao Paulo, Inst Ciencia & Tecnol Curso Engn Mat, Sao Jose Dos Campos, SP, BrazilWeb of Scienc

Design of multifunctional composites and their use for the 3-D printing of microsystems

Many of today\u27s high-tech products are approaching their technological limits. For example, the microelectronics community is faced with overheating devices with a demand for compact three-dimensional (3D) architectures and lower power consumption, whereas the aerospace industry is seeking lighter, stiffer and more electrically conductive materials for the creation of more energy efficient aircraft. A promising solution is to capitalize on the amazing electrical, thermal and mechanical properties of some nanoscopic materials (one billionth of a meter). However, several challenges in material processing and manufacturing must be resolved, namely exploiting these properties at the industrial scale and overcoming the current planar configuration with a truly 3D method. The nature of work presented is mainly on the development of high-performance materials for the manufacturing of microscopic or larger systems featuring multiple functionalities. On the material side, the design of polymer-based nanocomposite coatings used to protect aerospace composite structures against lightning strike will be presented. A comparative analysis between the standard copper meshes and our novel coating designs (e.g., wet chemical metallization, heterogeneous distribution of conductive fillers, hybrid fillers deposition) was performed under high current (up to 50 kA). On the manufacturing side, different 3D printing methods will be explained. These methods were used to build complex 3D shapes at the microscopic scale and above such as helical freeform microcoils, microstructured fibers and nanocomposite liquid sensors. In conclusion, we believe that the fabrication techniques presented provide an original and promising approach to resolve the aforementioned issues, thus making nanotechnology more accessible to industry, especially in aerospace, microelectronics and biomedicine

High deformation multifunctional composites: materials, processes, and applications

Structural health monitoring (SHM) is a non-destructive process of collecting and analysing data from structures to evaluate their conditions and predict the remaining lifetime. Multifunctional sensors are increasingly used in smart structures to self-sense and monitor the damages through the measurements of electrical resistivity of composites materials. Polymer-based sensors possess exceptional properties for SHM applications, such as low cost and simple processing, durability, flexibility and excellent piezoresistive sensitivity. Thermoplastic, thermoplastic elastomers and elastomer matrices can be combined with conductive nanofillers to develop piezoresistive sensors. Polymer, reinforcement fillers, processing and design have critical influences in the overall properties of the composite sensors. Together with the properties of the functional composites, environmental concerns are being increasingly relevant for applications, involving advances in materials selection and manufacturing technologies, In this scenario, additive manufacturing is playing an increasing role in modern technological solutions. Stretchable multifunctional composites applications include piezoresistive, dielectric elastomers (mainly for actuators), thermoelectric, or magnetorheological materials [1]. In the following, piezoresistive materials and applications will be mainly addressed based on their increasing implementation into applications.Portuguese Foundation for Science and Technology (FCT) in the framework of the Strategic Funding UID/FIS/04650/2019 and UID/EMS/00151/2019. The authors thank the FCT for financial support under SFRH/BPD/110914/2015 (P. C) and SFRH/BPD/117838/2016 (J. Pereira) grants. Financial support from the Basque Government Industry and Education Departments under the ELKARTEK, HAZITEK and PIBA (PIBA-2018-06

Multiscale Modeling of Composites: Toward Virtual Testing ... and Beyond

Recent developments in the area of multiscale modeling of fiber-reinforced polymers are presented. The overall strategy takes advantage of the separa-tion of length scales between different entities (ply, laminate, and component) found in composite structures. This allows us to carry out multiscale modeling by computing the properties of one entity (e.g., individual plies) at the relevant length scale, homogenizing the results into a constitutive model, and passing this information to the next length scale to determine the mechanical behavior of the larger entity (e.g., laminate). As a result, high-fidelity numerical sim-ulations of the mechanical behavior of composite coupons and small compo-nents are nowadays feasible starting from the matrix, fiber, and interface properties and spatial distribution. Finally, the roadmap is outlined for extending the current strategy to include functional properties and processing into the simulation scheme