Yong Lu

Bio: Yong Lu is an academic researcher from Nanjing Institute of Technology. The author has contributed to research in topics: Composite number & Curing (chemistry). The author has an hindex of 2, co-authored 3 publications receiving 18 citations.

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

Abstract: 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.

Reduction of composite deformation based on tool-part thermal expansion matching and stress-free temperature theory

Abstract: Aiming at the serious deformation problem of composite after curing, a new curing technology based on tool-part thermal expansion matching and stress-free temperature theory is presented to reduce the deformation. The thermal expansions of composite tool are designed to match with the composite part in parallel and perpendicular to the fiber direction. The stress-free temperature theory is introduced to reduce chemical shrinkage of resin by modifying the curing parameters. To verify the accuracy of this technology, the deformation of composite samples manufactured by traditional and the new curing technologies are compared. The experiment results indicate that the deformation of composites cured by the new curing technology is reduced to 8.3 % of traditional curing process.

Cooling system during high-pressure microwave curing based on electromagnetic shielding

Abstract: High-pressure microwave curing of fiber-reinforced polymer composites exhibits prominent advantages of fast response, high efficiency, and low energy consumption due to the characteristic of selective volume heating. However, the slow and uncontrollable cooling process in the high-pressure electromagnetic environment will prolong the curing cycle and limit the realization of optimized curing processes in microwave method. And there is currently no suitable solution. Here, a circulation cooling system is invented in the high-pressure electromagnetic environment by the application of porous array electromagnetic shielding theory, which can ensure the microwave shielding and the gas circulation. Results show that the circulation cooling system can satisfy the requirements of microwave shielding more than 99%, the maximal cooling rate of 6°C/min and the cooling rate of this cooling system is 3.6 times higher than that of the traditional high-pressure microwave tank. We anticipate that solving the cooling problem is a step towards the industrial application of composite microwave curing and it will also have applications in heat dissipation of electronic equipment and protection of precision apparatus.

Curing multidirectional carbon fiber reinforced polymer composites with indirect microwave heating

Abstract: Microwave curing technologies have many advantages in manufacturing fiber reinforced polymer composite materials used in aerospace products, compared with traditional autoclave curing technologies. However, multidirectional carbon fiber reinforced polymer composites can hardly be penetrated and heated by microwave directly, which has become a major obstacle in industrial application worldwide. In this paper, an indirect microwave curing method was proposed to solve this problem. The microwave absorption performance of the indirect microwave heating medium was systematically optimized by evaluating its dielectric properties and reflection loss according to the transmission line theory. On this basis, the microwave susceptive mold was carefully designed and manufactured. Subsequently, the multidirectional carbon fiber/epoxy composite was successfully cured with indirect microwave heating, which was demonstrated by the observation of the curing process with infrared thermal imager and differential scanning calorimetry analysis of the final products. Compared with the traditional thermal curing method, the curing cycle and energy consumption were reduced by 42.1% and 75.9% respectively. Results of further characterization experiments indicated that the mechanical properties of indirect microwave cured specimens were slightly higher than those of the thermally cured counterparts.

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

Abstract: 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.

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

Abstract: 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.

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

Abstract: 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.