Composite materials are demonstrating the ability to face the challenge of competitive markets where high-performance, low costs, and reduced manufacturing time are mandatory. Vacuum bagging with autoclave curing is one of the most used manufacturing methods for carbon fiber composite parts. However, it shows some limitations, mainly due to manual operations and long processing time. Out-of-autoclave (OOA) methods, such as pressure bag molding (PBM), can lead to a strong reduction of the manufacturing time through the simplification of lay-up and curing phases. In this paper, a comparative analysis between the autoclave and the PBM processes has been performed, jointly considering both the economic and environmental aspects. An evaluation of the environmental impacts has been carried out following the standardized life cycle assessment (LCA) methodology. In addition, costs related to these two manufacturing techniques have been estimated through a parametric approach and successively compared. Different scenarios have been considered to take into account various production batches, mold manufacturing techniques, and end of life alternatives. The analyses show conflicting results demonstrating that a global optimum scenario does not exist and, depending on the chosen indicator and production batch, the best alternative varies. Considering only the environmental indicators, the autoclave process can be considered the most sustainable option, due to the lower consumption of energy.

Comparative life cycle assessment and cost analysis of autoclave and pressure bag molding for producing CFRP components

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 (Tg) 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.

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

Conductive Polymer Composites (CPCs) have recently gained an extensive scientific interest as feedstock materials in Fused Filament Fabrication (FFF) Three-dimensional (3D) printing. Polylactic Acid (PLA), widely used in FFF 3D printing, as well as its Carbon Black (CB) nanocomposites at different weight percentage (wt.%) filler loadings (0.5, 1.0, 2.5 and 5.0 wt.%), were prepared via a melt mixing filament extrusion process in this study and utilized to manufacture FFF 3D printed specimens. The nanocomposites were examined for their electrical conductivity. The highest loaded 3D printed CPC (5.0 wt.%) was tested as an electrothermal Joule heating device. Static tensile, flexural, Charpy’s impact and Vickers microhardness mechanical properties were investigated for the neat and PLA/CB 3D printed nanocomposites. Dynamic Mechanical Analysis (DMA) revealed a stiffening mechanism for the PLA/CB nanocomposites. Scanning Electron Microscopy (SEM) elucidated the samples’ internal and external microstructural characteristics. The PLA/CB 5.0 wt.% nanocomposite demonstrated also antibacterial properties, when examined with a screening process, against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). It can be envisaged that the 3D printed PLA/CB CPCs exhibited a multi-functional performance, and could open new avenues towards low-cost personalized biomedical objects with complex geometry, amongst others, i.e., surgery tools, splints, wearables, etc.

https://www.mdpi.com/2311-5629/7/3/52/pdf

Fused Filament Fabrication Three-Dimensional Printing Multi-Functional of Polylactic Acid/Carbon Black Nanocomposites

Layered self‐resistance electric heating to cure thick carbon fiber reinforced epoxy laminates

The article at hand presents a novel approach to accelerating the early strength development of mineral-impregnated carbon-fibre composites (MCF) by electrical Joule heating. MCF were produced with a metakaolin-based geopolymer suspension and subsequently cured using Ohmic heating under systemically varied voltages and durations. The MCF produced were characterised in respect of their mechanical and morphological properties. Three-point-bending and uniaxial tension tests yielded significant enhancement of MCF mechanical properties due to curing within only a few hours. Thermogravimetric analysis (TGA), mercury intrusion porosimetry (MIP), environmental scanning electron microscope (ESEM) as well as micro-computed tomography (µCT) confirmed advanced geopolymerisation by the electrical heating process and a strong sensitivity to parameter selection. After only two hours of resistance heating MCF could demonstrate tensile strength of up to 2800 MPa, showing the great potential for applying the Joule effect as a possibility to enhance the strength development of geopolymer-based MCF. Moreover, the applied method offers a huge potential to manufacture automated fast out-of-oven cured MCF with a variety of shapes and dimensions. 

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Joule heating as a smart approach in enhancing early strength development of mineral-impregnated carbon-fibre composites (MCF) made with geopolymer

Carbon fiber reinforced plastic self-resistance electric (SRE) heating has been conceived as an alternative to out-of-autoclave technology due to its characteristics of uniform heating, fast heating/cooling, low energy consumption, and low equipment investment. In this work, a series of SRE heating experiments were conducted, in which the temperature distribution field, energy consumption, and curing time of SRE curing process were characterized. Comprehensive mechanical tests and microscopic characterization were carried out. The experimental results exhibit that the rapid heating rate of SRE curing process resulted in a weaker matrix performance because of the insufficient time of void elimination, which finally leads to an inferior compression and flexural strength for the composite part, while the fiber preferential heating effect can significantly improve the fiber-resin interfacial strength, because the naturally formed temperature difference along the interfacial area enhanced the adhesive strength of the resin around the interface, which improved the macroscopic tension and interlaminar shear strength.

Mechanical performance of carbon fiber/epoxy composites cured by self-resistance electric heating method

The invention relates to a resin-based composite material curing online monitoring method, belonging to the technical field of composite material curing online monitoring, and particularly relates toa curing degree monitoring method for a composite material electric energy loss heating curing process. For the curing technology of accurately measuring the electric energy transmitted into a composite material member, the electric power value and an average temperature change amount of a whole member are monitored and input on line, according to the law of conservation of energy, the chemical energy released by the composite material member is calculated in real time, and finally the degree of the cross-linking and solidity reaction of the whole member is obtained in real time. The method does not need to embed a curing sensor generating influences on the material performances, the composite material can be taken as a heating source and as a sensor, and the composite material member electric power and temperature change are input to represent the average curing degree of the material. The method can greatly enhance the implementability of on-line monitoring of the curing degree of composite materials, can significantly improve the curing quality of composite members, and can achieve high-efficiency adaptive regulation of the curing process.

Liu Shuting

Papers

Mechanical performance of carbon fiber/epoxy composites cured by self-resistance electric heating method

Resin-based composite material curing online monitoring method