An official website of the United States government
Laminated multifunctional composites are highly desired in modern lightweight engineering structures. The purpose of this study is to develop a composite laminate with impact tolerance, delamination healing, strain sensing, Joule heating, deicing, and room temperature shape restoration functionalities. In this study, a novel self-healable and recyclable shape memory vitrimer was used as the matrix, unidirectional glass fabric was used as reinforcement, and tension programmed shape memory alloy (SMA) wires were used as z-pins. To provide multifunctionality, the programmed SMA wires were further twisted and formed into sinusoidal shape. Copper wire strands were hooked to the sinusoidal SMA z-pins to make them a closed circuit. Low velocity impact, compression after impact, damage self-healing, deicing, and room temperature shape restoration tests were conducted. The tests result show that the desired multifunctionality of the laminated composite was achieved. The hybrid laminate provides a promising design for lightweight load-carrying engineering structures.
more »
« less
Hybrid hemp/glass fiber reinforced high-temperature shape memory photopolymer with mechanical and flame-retardant analysis
Abstract Cultivated natural fibers have a huge possibility for green and sustainable reinforcement for polymers, but their limited load-bearing ability and flammability prevent them from wide applications in composites. According to the beam theory, normal stress is the maximum at the outermost layers but zero at the mid-plane under bending (with (non)linear strain distribution). Shear stress is the maximum at the mid-plane but manageable for most polymers. Accordingly, a laminated composite made of hybrid fiber-reinforced shape memory photopolymer was developed, incorporating strong synthetic glass fibers over a weak core of natural hemp fibers. Even with a significant proportion of natural hemp fibers, the mechanical properties of the hybrid composites were close to those reinforced solely with glass fibers. The composites exhibited good shape memory properties, with at least 52% shape fixity ratio and 71% shape recovery ratio, and 24 MPa recovery stress. After 40 s burning, a hybrid composite still maintained 83.53% of its load carrying capacity. Therefore, in addition to largely maintaining the load carrying capacity through the hybrid reinforcement design, the use of shape memory photopolymer endowed a couple of new functionalities to the composites: the plastically deformed laminated composite beam can largely return to its original shape due to the shape memory effect of the polymer matrix, and the flame retardancy of the polymer matrix makes the flammable hemp fiber survive the fire hazard. The findings of this study present exciting prospects for utilizing low-strength and flammable natural fibers in multifunctional load-bearing composites that possess both flame retardancy and shape memory properties.
more »
« less
- PAR ID:
- 10469852
- Publisher / Repository:
- Nature Publishing Group
- Date Published:
- Journal Name:
- Scientific Reports
- Volume:
- 13
- Issue:
- 1
- ISSN:
- 2045-2322
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
ACS (Ed.)Synthetic fibers such as glass, carbon, etc., are used as reinforcement in polymer composites due to their high strength and modulus. However, synthetic fibers contribute to high costs and have a significant environmental impact. To overcome this challenge, various natural fibers, including banana, kenaf, coir, bamboo, hemp, and sisal fiber, as reinforced in a polymer matrix are investigated for mechanical properties. In this study, biocomposites with natural fibers as reinforced are developed and characterized. Treated and untreated natural fibers such as flax, maple, and pine as reinforced in thermoplastic, in this study, polypropylene (PP), are investigated for the mechanical properties, including tensile, flexural, and impact test. Mechanical test results exhibited that adding the natural fibers enhanced the tensile, flexural, and impact properties. It can be inferred that these biocomposites can be used as potential materials for the automobile industry.more » « less
-
In the last few decades, fiber reinforced composites have been established as the materials of choice for lightweight applications in a large spectrum of applications ranging from aerospace, defense, and marine industries to automotive products and consumer goods. With the growing shift to sustainable resources, natural fibers, especially plant fibers, received increased interest throughout the years. Among these natural fibers, silks stand out with low stiffness and a high failure strain, unlike conventional fibers such as carbon or glass. Although gaining traction as a natural alternative reinforcement, silk still has little to no commercial uses despite its higher performance. Besides its higher mechanical properties and lightweight, silk exhibits other attractive properties such as improved flame retardancy and biodegradability. To take advantage of these features, proper fiber/matrix adhesion must be achieved. Such silk/matrix bonding can be inferred from the silk/resin affinity during composite manufacturing. In this study, the affinity/wettability of several silk/resin systems were analyzed via static contact angles using imageJ software to determine candidates for silk reinforced composite laminates with better adhesion. To this end, a combination of four silk fibers and three resin systems were investigated. The investigated silk fibers were Ahimsa, Charmeuse, Habotai, and Tussah; and the resins included a vinyl ester (Hydrex) and two epoxies (INF114 and INR). For Tussah fibers, initial contact angles were consistently one of the lowest. However, these fibers exhibited a higher contact angle over time compared to the other silk fibers studied. Conversely, Ahimsa silk fibers showed the highest initial contact angle, then quickly dropped to com-plete wetting. Habotai fibers dropped towards complete wetting quickly, however, consistently slowed considerably shortly after. Charmeuse fibers performed similarly to Ahimsa fibers with Hydrex, however was considerably slower to wetting with the other resins. Among the investigated resins, Hydrex showed the best affinity to silk fibers with the majority of the lowest initial contact angles and the fastest to complete wetting. INF114 consistently receded at a slower, albeit steady, rate until reaching complete wetting apart from Tussah. INR showed the highest initial contact angles and never reached complete wetting after an hour for two of the four silks investigated. Therefore, the best silk/resin affinity was observed for the Ahimsa and Charmeuse silk fibers and the Hydrex vinyl ester resin. In future work, silk composites with these constituents would be investigated.more » « less
-
null (Ed.)In this investigation, multi-walled carbon nanotubes (MWCNTs) were grown over carbon fiber fabrics via a relatively nondestructive synthesis technique. The MWCNTs patches were grown into three different topologies: uniform, fine patterned and coarse patterned. Hybrid carbon fiber-reinforced polymer composites (CFRPs) were fabricated based on the patterned reinforcements. Tensile tests, dynamic mechanical thermal analyses (DMTA) and flexure load relaxation tests were carried out to investigate the effect of the patterned nano-reinforcement on the static, dynamic, glass transition, and viscoelastic performance of the hybrid composites. Results revealed that the hybrid composite based on fine-patterned topology achieved better performance over all other configurations as it exhibited about 19% improvement in both the strength and modulus over the reference composite with no MWCNTs. Additionally, the increase in glass transition for this composite was as high as 13%. The damping parameter (tan δ) was improved by 46%. The stress relaxation results underlined the importance of patterned MWCNTs in minimizing the stress decay at elevated temperatures and loading conditions. Utilizing patterned MWCNTs topology significantly reduced the stress decay percentage at the thermomechanical conditions 60 MPa and 75 °C from 16.7% to 7.8%. These improvements are attributed to both the enhanced adhesion and large interface area by placing MWCNTs and by inducing an interlocking mechanism that allows the interaction of the three constituents in load transfer, crack deflection and hindering undesired viscoelastic deformations under different thermomechanical loadings.more » « less
-
Natural fiber-reinforced polymers are currently used in a variety of low- to high-performance applications in the automotive, packaging, and construction industries. Previous studies have demonstrated that natural fibers (e.g., flax, hemp) exhibit good tensile mechanical properties and have positive environmental and economic attributes such as low cost, rapid renewability, and worldwide availability. However, natural fibers are inherently susceptible moisture-induced changes in physical and mechanical properties, which can be unfavorable for in-service use. This study illustrates how a micromechanics-based modelling approach can be used to help facilitate durability design and mitigate the deleterious effects of freeze-thaw deterioration in wood-plastic composites (WPCs). The model described in this study predicts the critical fiber volume fraction (V_fcrit) at which damage to the composite will occur under certain environmental conditions for different WPC formulations of hardwood and softwood fiber reinforcement and polymer matrix types. As expected, the results show that V_fcrit increases (a positive result) as anticipated in situ moisture content decreases. In addition, results suggest that fiber packing distribution directly influences V_fcrit and that V_fcrit increases as the mechanical properties of the polymer matrix increase. In sum, the study demonstrates how predictive modeling can be applied during the design phase to ensure the durability of WPCs.more » « less
