Flax Fiber-reinforced Composites Research Articles

Temperature and rate dependent shear characterization and modeling of spread-tow woven Flax/PP composite laminates

This paper investigates the in-plane shear behavior of spread-tow woven structured flax fiber-reinforced polypropylene composites, focusing on temperature and displacement rate effects. For this aim, the study includes bias-extension experiments to characterize the shear behavior of the material. Several experiments were conducted at different displacement rates and temperature levels. The temperature levels were chosen to encompass the material's behavior during solid and molten-state thermoforming, given the melting and decomposition temperatures acquired from differential scanning calorimetry and thermogravimetric analysis tests, respectively. A new fixture was designed and manufactured to allow pre-heating of the oven and rapid placement of the samples, which in turn, prevents their degradation for the time duration required to reach a uniform temperature distribution in the oven. During the experiments, the 3D digital image correlation technique accurately measured local deformations and strains on the specimen's surface under varying conditions. Further, a finite element model is developed, incorporating a fiber reorientation algorithm with a hypo-elastic shear model to simulate the material's temperature and rate-dependent behavior. The finite element shear angle distributions, as well as the shear angle-force and shear angle-displacement curves, are compared with the Digital Image Correlation (DIC) data and load measurements for different test conditions, showing good agreement between the numerical and experimental approaches.

Damage and fracture studies of continuous flax fiber-reinforced composites 3D printed by in-nozzle impregnation additive manufacturing

Additive manufacturing (AM) of continuous yarn-reinforced biobased composites presents multi-functional properties and low environmental impact of this technology. Few studies focused on the mechanical damage mechanisms of continuous biobased composites obtained by AM processes, while it is a topic of high interest for the mastery of mechanical behaviors and optimization of the materials for high requirement applications. This study aims to assess the damage and fracture modes of continuous flax yarn-reinforced PLA manufactured by AM, with different yarn orientations. The additively manufactured biobased composites were characterized by tensile test, 3D microscopy and micro-tomography to link the process-structure-properties relationships regarding the damage and fracture modes. The results showed that the 0° manufactured composite had a significant enhancement of tensile properties compared to other configurations. The damage mechanism presented fiber rupture with polymer transverse cracks at 0°, while the 45° and 90°-oriented composites showed premature fiber/matrix interface debonding. This study aims to find the relationship between damage mechanisms, deposition strategy, and anisotropy of the additively manufactured long vegetal fibers-reinforced biobased composite materials. The results bring a new understanding of the anisotropy and defects in printed composite materials regarding their mechanical behaviors during damage.

Dicyanamide ionic liquid mixtures for curing and modifying flax-fiber reinforced epoxy resin composites

Epoxy composites reinforced with natural fibers are a research area that has been growing tremendously in recent years, with increasing reports providing a better understanding of the interactions within such structures, resulting in newer and more specialized applications. This article presents a comprehensive study on the design and application of ionic liquids (ILs) in the development of flax fiber-reinforced epoxy composites with tailored mechanical properties. Three distinct ILs, namely 1-hexyl-3-methylimidazolium dicyanamide [HMIM][DCA], 1-hexyl-1,4-diazabicyclo[2.2.2]octan-1-ium dicyanamide [DABCO-C6][DCA], and trimethyloctadecylammonium dicyanamide [N11118][DCA], were strategically engineered to incorporate longer carbon chains, with the primary objective of influencing the mechanical parameters of the resulting composites, specifically aiming for enhanced flexibility and resistance to bending and stretching. Using these designed ILs, two mixtures were developed and crafted to facilitate the effective curing of epoxy resin, which was examined using Differential Scanning Calorimetry (DSC). Investigation of the resin crosslinking process revealed that the mixtures of ILs exhibited a lower total enthalpy of thermal conversion than single-IL systems. Moreover, shifts in the polymerization onset temperatures were observed for the mixtures, with some systems displaying dual temperature peaks during crosslinking, indicative of potential parallel polymerization reactions.

Investigation of recovery behavior on 3D-printed continuous plant fiber-reinforced composites

The mechanical properties and accuracy of 3D-printed composites can be significantly affected by printing parameters. This work discovered a noteworthy recovery phenomenon during 3D printing of continuous flax fiber-reinforced composites (CFFRCs). The yarn count and printing speed are the critical factors that influence the recovery behavior, which, in turn, affects the thickness, the fiber volume fraction, and the void content of CFFRCs, ultimately impacting the mechanical properties. Smaller yarn counts have a greater effect on the recovery behavior of CFFRCs. Increasing the printing speed from 5 mm/s to 15 mm/s leads to the loss of tensile properties and flexural modulus in CFFRCs up to 30 % and 58 %, respectively. The recovery mechanism of the CFFRCs is further elucidated with the observation of temperature distribution during the printing process. This indicates that recovery is more likely to occur in the compressed yarn with a twisted structure when the deposited thermoplastic matrix exceeds the glass transition temperature. The results and findings have the potential to enhance the process optimization of 3D-printed continuous plant fiber composite parts, ensuring high mechanical properties and dimensional precision.

Modeling and analysis of TiO2 filler's impact on specific wear rate in flax fiber-reinforced epoxy composite under abrasive wear using Taguchi approach

PurposeThis study explores how titanium oxide (TiO2) filler influences the specific wear rate (SWR) in flax fiber-reinforced epoxy composites (FFRCs) through a Taguchi approach. It aims to boost abrasive wear resistance by incorporating TiO2 filler, promoting sustainable and eco-friendly materials.Design/methodology/approachThis study fabricates epoxy/flax composites with TiO2 particles (0–8 wt%) using hand layup. Composites were tested for wear following American Society for Testing and Materials (ASTM) G99-05. Statistical analysis used Taguchi design of experiments (DOE), with ANOVA identifying key factors affecting SWR in abrasive sliding conditions.FindingsThe study illuminates how integrating TiO2 filler particles into epoxy/flax composites enhances abrasive wear properties. Statistical analysis of SWR highlights abrasive grit size (grit) as the most influential factor, followed by normal load, wt% of TiO2 and sliding distance. Grit size has the highest effect at 43.78%, and wt% TiO2 filler contributes 15.61% to SWR according to ANOVA. Notably, the Taguchi predictive model closely aligns with experimental results, validating its reliability.Originality/valueThis paper integrates TiO2 filler and flax fibers to form a novel hybrid composite with enhanced tribological properties in epoxy composites. The use of Taguchi DOE and ANOVA offers valuable insights for optimizing control variables, particularly in natural fiber-reinforced composites (NFRCs).

Evolution of stiffness in flax yarn within flax fiber reinforced composites during moisture absorption

This study aims to investigate the evolution of stiffness in flax yarn within flax fiber reinforced composites (FFRCs) during moisture absorption, focusing on the influence of moisture content on the microstructure of flax fibers. To characterize the hygroscopic mechanical behaviors of flax yarns in FFRCs, the hygroscopicity and tensile properties of dried and impregnated flax yarns were tested at various humidity levels. A multi-scale modeling approach was utilized to simulate the stiffness in flax yarn within FFRCs, encompassing the modeling of cell wall layers of the flax elementary fiber, flax elementary fiber and twisted flax yarn. Specifically, the variation trends of the microfiber angle (MFA) in the S2 layer and the stiffness degradation of the combined amorphous matrix (CAM) with respect to relative moisture content (RMC) were proposed and determined through simulation and inversion calculation. The study reveals that the MFA in the S2-layer is the most crucial parameter affecting the longitudinal elastic properties of flax yarn in FFRCs, while the stiffness degradation of the CAM significantly influences the transverse elastic properties. Finally, this study establishes a relationship between the overall stiffness of flax yarn in FFRCs and the RMC. This relationship provides a parameter foundation for accurately predicting the mechanical properties of FFRCs during moisture absorption.

Creep analysis of the flax fiber-reinforced polymer composites based on the time–temperature superposition principle

Abstract Natural plant fiber-reinforced polymer composites (PFRP) have emerged as an environmental-friendly material in the construction industry, but their creep behavior is a critical concern for load-bearing structures. This study investigates the creep behavior of flax fiber-reinforced polymer composites (FFRP) using the time–temperature superposition principle (TTSP). Due to the application of TTSP on the tensile creep behavior of FFRP is not fully understood, three potential methods for calculating the critical parameters during TTSP are compared to obtain an efficient application method to build the creep master curve. A 2,000-h long-term creep test is conducted parallelly on the same sample to validate the accuracy of the creep analysis results. The study proposes an ideal method to determine the key parameters in TTSP, providing valuable insights for the practical application of PFRP in the construction industry. Meanwhile, the research results in this study would be helpful in better understanding the creep behavior of FFRP via short-term accelerated tests.

Optimization of dry sliding wear performance of TiO2 filled bamboo and flax fiber reinforced epoxy composites using Taguchi approach

PurposeThis paper aims to report the effect of titanium oxide (TiO2) particles on the specific wear rate (SWR) of alkaline treated bamboo and flax fiber-reinforced composites (FRCs) under dry sliding condition by using a robust statistical method.Design/methodology/approachIn this research, the epoxy/bamboo and epoxy/flax composites filled with 0–8 Wt.% TiO2 particles have been fabricated using simple hand layup techniques, and wear testing of the composite was done in accordance with the ASTM G99-05 standard. The Taguchi design of experiments (DOE) was used to conduct a statistical analysis of experimental wear results. An analysis of variance (ANOVA) was conducted to identify significant control factors affecting SWR under dry sliding conditions. Taguchi prediction model is also developed to verify the correlation between the test parameters and performance output.FindingsThe research study reveals that TiO2 filler particles in the epoxy/bamboo and epoxy/flax composite will improve the tribological properties of the developed composites. Statistical analysis of SWR concludes that normal load is the most influencing factor, followed by sliding distance, Wt.% TiO2 filler and sliding velocity. ANOVA concludes that normal load has the maximum effect of 31.92% and 35.77% and Wt.% of TiO2 filler has the effect of 17.33% and 16.98%, respectively, on the SWR of bamboo and flax FRCs. A fairly good agreement between the Taguchi predictive model and experimental results is obtained.Originality/valueThis research paper attempts to include both TiO2 filler and bamboo/flax fibers to develop a novel hybrid composite material. TiO2 micro and nanoparticles are promising filler materials, it helps to enhance the mechanical and tribological properties of the epoxy composites. Taguchi DOE and ANOVA used for statistical analysis serve as guidelines for academicians and practitioners on how to best optimize the control variable with particular reference to natural FRCs.

Resorcinol-Derived Vitrimers and Their Flax Fiber-Reinforced Composites Based on Fast Siloxane Exchange.

Natural fiber-reinforced composites are gaining increased interest for their significantly reduced carbon footprint compared to conventional glass or carbon fiber-based counterparts. In this study, natural fibers are used in a resorcinol-based epoxy resin that is thermally reshapable at higher temperatures (>180°C) by using fast exchanging siloxane bonds, catalyzed by 1,5,7-triazabicyclo[4.4.0]dec-5-ene. Stress relaxation times of only about 6s at 220°C can be reached. A resorcinol-based epoxy compound is selected because it can be derived from cellulose, opening ways for more sustainable and reshapable composite materials. In a last step of the research, the low viscosity vitrimer formulation (<200mPas) is applied to make a flax fiber-reinforced composite using an industrially relevant vacuum-assisted resin infusion process. A section of this composite is successfully reshaped, which allows for envisioning a second life for natural fiber-reinforced composites.

Analysis of Thermomechanical Behavior of the Tubular Braided Fabrics with Flax/Polyamide Commingled Yarns.

Flax fibers are widely used as the strongest natural fibers in composite parts with advanced structures. Due to their excellent mechanical properties and recyclability, they have attracted more attention from the aviation and automotive industries, etc. These composite parts are usually obtained by preforming reinforcements or prepregs at high temperatures, and their mechanical behaviors are greatly affected by temperature variations. To improve the understanding of the mechanical properties of flax fiber materials, especially for the braided fabric with non-orthogonal structures, uniaxial tensile tests at different temperatures and tensile speeds were conducted on hollow tubular braided fabrics. The thermomechanical properties of Flax/Polyamide12 (PA12) prepregs were analyzed. The results show that temperature and tensile speed have obvious effects on the strength and shear stiffness of tubular fabrics. The strength and shear stiffness of the fabric decreases as the ambient temperature increases. Meanwhile, the strength of the fabric can also be improved by appropriately increasing the tensile speed. In addition, according to the experimental results, a theoretical model is established to describe the shear angle on the smallest circumference of the fabric, which provides a theoretical basis for the subsequent simulation process. The test results can provide a reference for the manufacture of flax fiber-reinforced composites with tubular structures.

Measuring material velocity and thickness mapping of flax fiber-reinforced plastic composites using automated ultrasonic rapid motion scanner

The interest in using sustainable materials was a part of the Sustainable Development Goals by the United Nations in 2015, its mission aims to eradicate poverty and conserve the environment by the year 2023. The use of engineered bio-fiber has the potential to replace the usage of synthetic fibers. However, the diversification of the application is limitless. The intended paper investigates the detection of impurities of cured pre-impregnated bio-composite using C-scan ultrasound. The Flax Fiber-Reinforced Plastic Composites were fabricated and cured with heat-assisted curing. The panels were inspected by an automatic ultrasonic rapid motion scanner to measure the material sound velocity of the Flax panel. As a result, the test obtained a reference value of Flax Fiber-Reinforced Plastic Composite material sound velocity of 3.17 (31700 mm/s) for thickness mapping. The obtain sound velocity value can be used as a future reference for inspecting any type of flax material specimen by using the rapid motion scanner from Eddyfi Technologies.

Influence of Oil Palm Nano Filler on Interlaminar Shear and Dynamic Mechanical Properties of Flax/Epoxy-Based Hybrid Nanocomposites under Cryogenic Condition

Natural fiber-reinforced polymer composites are gaining in popularity due to recyclability and availability. This research investigates how oil palm shell (OPS) filler materials impact the interlaminar shear and the dynamic properties of flax fiber-reinforced hybrid composites under cryogenic circumstances. Filler materials in two different proportions (0, 2, 4, and 6 wt.% OPS) and 40 wt.% flax fibers were used to make composites. The OPS filler-filled polymeric materials were invented through typical hand lay-up. The hybrid materials were imperiled to liquid nitrogen for varying amounts of time after production (15 and 30 min). According to the findings, OPS nanoparticles can be used as natural rather than artificial fillers. Furthermore, loading 4 wt.% OPS nanoparticles into organic fabric-strengthened epoxy polymeric materials during 15 min of cryogenic settings resulted in the best interlaminar shear and dynamic performances. The storage and loss modulus of the flax/epoxy composites were improved by adding a 4% OPS nanofiller. The improvement can be ascribed to the hardness and stiffness of the additional OPS nanofillers. The 4% nano-OPS/flax/epoxy hybrid nanocomposite’s damping factor was substantially reduced compared to the flax/epoxy composites. The OPS nanofiller limits the epoxy molecular chain’s free segmental mobility, resulting in a lower damping factor and enhancing the adherence among flax fibers and the epoxy resin. The shattered specimen of the hybrid materials was investigated using a scanning electron microscope.

Effect of milling parameters on the surface quality of a flax fiber-reinforced polymer composite

Flax fiber-reinforced polymer composites are an interesting alternative to synthetic fiber-reinforced polymer composites for many engineering applications. When machining flax fiber-reinforced composite materials that are by definition heterogeneous, the matrix and the fibers react differently and hence many sorts of damage may occur such as poor surface roughness, delamination, and fluffing. The novelty of the current work lies in identifying the major factors that affect the quality of the milled surface of composites reinforced with flax fibers and provides recommendations and collaborative solutions to the composite machining community. In this study, the impact of cutting conditions (cutting speed, feed rate, and fiber orientation) on the cutting forces and surface roughness during milling of the flax/epoxy composite is investigated. For this purpose, slotting tests are performed on flax fiber-reinforced polymer plates using a carbide end mill tool based on a full factorial design of experiment. Furthermore, a randomization in the order in which experimental runs are done is used to reduce bias by balancing the effect of uncontrolled variables that have not been accounted for in the experimental design. It is concluded that the feed rate has the most influence on the cutting forces and roughness parameters. Moreover, the fibers orientation also has a significant effect on the outputs, and the cutting speed has less effect but it remains significant.

Anisotropic behaviors of moisture absorption and hygroscopic swelling of unidirectional flax fiber reinforced composites

This work aims to study the anisotropic moisture absorption characteristics of unidirectional flax fiber reinforced composites (FFRCs) and evaluate the variations of the internal stress caused by the hygroscopic deformation, which might lead to the deterioration of the mechanical properties of the composites. FFRCs were prepared using vacuum-assisted resin infusion molding (VARIM) technology. Moisture absorption tests were designed by sealing the designated surfaces with a polyurethane waterproof coating to keep the moisture absorption of FFRCs only in the desired directions. The deformation caused by moisture absorption in the width direction was also monitored. It confirms that the moisture absorption of FFRCs conformed to the 3D Fick's law, and the influence of moisture absorption in the width direction cannot be ignored, especially for the unidirectional transverse tensile test specimen (UTFRC). The hygroscopic deformation of the unidirectional FFRCs showed that the material expands perpendicular to the fiber direction but shrinks along the fiber direction. The modified 3D Fick’s law based on heat conduction equation was performed to reveal the mechanism of the above moisture absorption and hygroscopic deformation. According to the finite element inversion, it was found that the axial diffusion coefficient along flax fiber bundles was much larger than the transverse diffusion coefficient perpendicular to the fiber bundle direction due to the existence of the unique lumen structure inside flax fibers. In addition, the high internal stress caused by the mismatched swelling properties between the fiber and the matrix was the main reason for the damage of the FFRCs, especially at the interface, which may seriously affect the service life of the composites. The outcome of this study can be used to accurately analyze the hydro-elastic behaviors of plant fiber reinforced composites, which is a prerequisite for predicting the mechanical properties affected by moisture absorption.

A Competitive Study of the Static and Fatigue Performance of Flax, Glass, and Flax/Glass Hybrid Composites on the Structural Example of a Light Railway Axle Tie

The most common studies in the literature are those analyzing fatigue life under cyclic loading for flax fiber-reinforced composites. A novel type of staple fiber yarn made from flax tow with almost unidirectional fiber orientation and a quasi-unidirectional fabric was developed for composite applications. Additionally, a hybrid material made of flax and glass was produced for a demonstrator component (an axle tie of a narrow-gauge railway). For such an application, the investigation of fatigue strength is of particular importance. Therefore, the fatigue behavior of flax, glass, and hybrid flax/glass composites was investigated in the high cycle fatigue range. A total of 106 load cycles were carried out. From about 7³ to 8³ loading cycles, the flax laminate was found to have higher fatigue strength than the glass fiber-reinforced composite. The hybrid materials tend to show a higher fatigue strength than the glass type from approximately 2 × 105 load cycles. Results based on a finite element method also demonstrate better fatigue properties at an increased number of load cycles for flax-based composites than the glass fiber-reinforced component. The flax/glass component’s fatigue strength ranged between the flax values and the glass fiber-reinforced composites. Overall, the hybrid material shows significantly better static bending and impact characteristics than flax and considerably better fatigue properties than the glass fiber-reinforced composite making the hybrid material attractive for an application in an axle tie.

Effectiveness of Sodium Acetate Treatment on the Mechanical Properties and Morphology of Natural Fiber-Reinforced Composites

This paper aims to investigate the ability of an eco-friendly and cheap treatment based on sodium acetate solutions to improve the mechanical properties of flax fiber-reinforced composites. Flax fibers were treated for 5 days (i.e., 120 h) at 25 °C with mildly alkaline solutions at 5%, 10% and 20% weight content of the sodium salt. Quasi-static tensile and flexural tests, Charpy impact tests and dynamical mechanical thermal (DMTA) tests were carried out to evaluate the mechanical properties of the resulting composites. Fourier transform infrared analysis (FTIR) was used to evaluate the chemical modification on the fibers surface due to the proposed treatment, whereas scanning electron microscope (SEM) and helium pycnometry were used to get useful information about the morphology of composites. It was found that the treatment with 5% solution of sodium acetate leads to the best mechanical performance and morphology of flax fiber-reinforced composites. SEM analysis confirmed these findings highlighting that composites reinforced with flax fibers treated in 5% sodium acetate solution show an improved morphology compared to the untreated ones. On the contrary, detrimental effects on the morphology as well as on the mechanical performance of composites were achieved by increasing the salt concentration of the treating solution.

Development and analysis of eco-friendly multi-functional materials

Now a day's automobile industries are developing materials in such a way that, the materials should be light in weight and environmentally friendly with excellent mechanical properties. Flax fiber is a naturally available fiber material own excellent mechanical properties. Two reinforced composites were manufactured. One was a complete flax fiber-reinforced composite, the second one was flax fiber metal laminates (combination of flax fiber and aluminum mesh). The manufacturing process of composite materials is also more important, and it is cost-dependent. The hand lay-up method is one of the manufacturing techniques and the cost is very less as compared to other techniques. Manufactured flax fiber and flax fiber metal laminate reinforced composite materials were tested under experimental tests. The experimental test results of flax fiber and hybrid composite materials were compared with each other. The sound transmission loss of flax fiber-reinforced composite material has 15% higher than flax fiber metal laminate reinforced material at the frequency ranges of (400 Hz). The vibration-damping factor of flax fiber metal laminate has 26% higher than flax fiber-reinforced composite. Electromagnetic radiation absorption of flax fiber metal laminate material has 20 db & 15 db higher than flax fiber-reinforced composite material at frequency ranges of (8.16 GHz &12 GHz). The flexural strength and tensile strength of flax fiber material were higher than flax fiber metal laminate material. Finally, the results of the experimental tests were compared with the simulation results of both flax fiber-reinforced composites and flax fiber metal laminate materials. Except for, vibration-damping factor the remaining properties of flax fiber composite material gave better results than the flax fiber metal laminate.

Enhancement of surface & bulk mechanical properties of Flax reinforced composites with different carbon allotropes

In this study, the effects of carbon allotropes on surface and bulk properties of flax fiber-reinforced composites (FFRC) are examined. Flax reinforced composites were prepared using two different nanofillers as FG & GO. Various surface and bulk properties like heat deflection, hardness, impact & tensile-strength & flexural-strength tests were performed. Addition of nanofillers like GO/ FG enhances the entire surface and bulk properties. Experimental values manifests that at 0.75 wt% of GO, the FFRC has better impact and tensile-strength, hardness, flexural-strength and heat deflection that is 30%, 15%, 18%, 20% and 13% respectively. But for FG as nanofillers, have manifested better properties when contrast to the GO and pure the FFRC. The properties like impact & tensile-strength, hardness, heat deflection & flexural-strength test are improved by 36%, 18%, 22%, 22% and 15% respectively. It was found that, after the addition of optimum weight % of nano-fillers, there was a degradation of surface and bulk properties.

Damping Behavior of Thermoplastic Organic Sheets with Continuous Natural Fiber-Reinforcement

In the field of lightweight construction, the use of natural fibers as reinforcement in composites has been increasingly discussed. Additionally, the damping properties of natural fibers are known from fiber materials such as fiber insulation boards. In the scope of the work presented here, the focus is on identifying the potential of natural fibers for lightweight structures with high vibration damping capacity. For this purpose, test specimens made of flax fiber-reinforced and glass fiber-reinforced thermoplastic composites were manufactured and characterized. Contrary to expectations, the flax fiber-reinforced composite exhibited an almost isotropic damping characteristic. A comparison of the damping and stiffness properties determined by measurement confirms the high potential of natural fiber-reinforced materials for lightweight structures with high damping.

Analysis of Mechanical Properties of Unidirectional Flax Roving and Sateen Weave Woven Fabric-Reinforced Composites

Abstract Natural fiber-reinforced composites are getting more attention from researchers and manufacturing companies to replace metals and synthetic materials that have dominated the manufacturing industries. In this study, the mechanical properties of unidirectional (UD) flax roving-reinforced composites and woven fabric-reinforced composites were investigated. Three different composites were prepared from flax rovings, which have the same linear density and epoxy resin matrix, with different reinforcement and composite preparation methods. The samples were subjected to experimental tests of flexural rigidity and tensile strength in a parallel and perpendicular direction to fiber orientation. The test results showed that flexural rigidity and tensile strength of flax fiber-reinforced composites are highly dependent on the direction of fiber orientation. The results also reveal that in a parallel direction to fiber orientation, UD composites have higher flexural rigidity and tensile strength than woven fabric-reinforced composite.