An Approach toward the Realization of a Through-Thickness Glass Fiber/Epoxy Thermoelectric Generator

Capsule-Based Self-Healing and Self-Sensing Composites with Enhanced Mechanical and Electrical Restoration

In this work, we report for the first time the manufacturing and characterization of smart multifunctional, capsule-based self-healing and self-sensing composites. In detail, neat and nanomodified UF microcapsules were synthesized and incorporated into composites with a nanomodified epoxy matrix for the restoration of the mechanical and electrical properties. The electrical properties were evaluated with the use of the impedance spectroscopy method. The self-healing composites were subjected to mode-II fracture toughness tests. Additionally, the lap strap geometry that can simulate the mechanical behavior of a stiffened panel was used. The introduction of the nanomodified self-healing system improved the initial mechanical properties in the mode-II fracture toughness by +29%, while the values after the healing process exceeded the initial one. At lap strap geometry, the incorporation of the self-healing system did not affect the initial mechanical properties that were fully recovered after the healing process.

3R Composites: Knockdown Effect Assessment and Repair Efficiency via Mechanical and NDE Testing

In this study, the mechanical properties of purposefully synthesized vitrimer repairable epoxy composites were investigated and compared to conventional, commercial systems. The purpose was to assess the knockdown effect, or the relative property deterioration, from the use of the vitrimer in several testing configurations. Mechanical tests were performed using ILSS, low-velocity impact, and compression after impact configurations. At modeled structure level, the lap strap geometry that can simulate the stiffening of a composite panel was tested. Several non-destructive evaluation techniques were utilized simultaneously with the mechanical testing in order to evaluate (i) the production quality, (ii) the damage during or after mechanical testing, and (iii) the repair efficiency. Results indicated that the new repairable composites had the same mechanical properties as the conventional aerospace-grade RTM6 composites. The electrical resistance change method proved to be a valuable technique for monitoring deformations before the initiation of the debonding and the progress of the damage with consistency and high sensitivity in real time. In terms of repair efficiency, the values ranged from 70% to 100%.

Printed Single-Wall Carbon Nanotube-Based Joule Heating Devices Integrated as Functional Laminae in Advanced Composites

This work reports the design and fabrication of novel printed single-wall carbon nanotube (SWCNT) electrothermal Joule heating devices. The devices are directly deposited on unidirectional (UD) glass fiber (GF) fabrics. The GF-SWCNT Joule heaters were integrated during manufacturing as "system" plies in carbon fiber reinforced polymer (CFRP) composite laminates. Specific secondary functions were imparted on the composite laminate endowing thus a multifunctional character. The efficient out-of-oven curing (OOC) of a CFRP laminate was demonstrated using a sandwich configuration comprising top/bottom GF-SWCNT system plies. A total power consumption of ca. 10.5 kWh for the efficient polymerization of the thermoset matrix was required. Infrared thermography (IR-T) monitoring showed a uniform and stable temperature field before and after impregnation with epoxy resin. Quasi-static three-point bending and dynamic mechanical analysis (DMA) revealed a minor knock-down effect of the OOC-CFRP laminates properties compared to oven cured CFRPs, whereas the glass transition temperature (T_g) was almost identical. The OOC-CFRP laminates were efficient in providing additional functions such as deicing and self-sensing that are highly sought in the energy and transport sectors, i.e., wind turbine blades or aircraft wings. The novel modular design provides unique opportunities for large-area applications via multiple interconnected arrays of printed devices.