The mechanical characteristics of natural fibre composites (NFCs) are closely linked to fibre-matrix and fibre-fibre interactions. This work investigates the improvement of tensile properties of a flax/epoxy composite through the application of click chemistry reaction to a unidirectional-mat (UDM) reinforcement with modifications made on the short fibre mat and unidirectional flax fibre phases of the reinforcement. The surface of short flax fibres was fibrillated to increase the accessibility of hydroxyl groups for all preliminary reactions and the final click chemistry cross-linking, which creates stable covalent triazole bonds between azide and alkyne groups. A small percentage of treated nanocellulose was incorporated to further enhance the reinforcement properties. FTIR and EDX analysis confirmed the presence of the various functional groups on the surface of nanocellulose and flax fibres with very high degrees of substitution. The treatment significantly improved the mechanical properties of the dry reinforcement, including a 220% mean increase in the tensile strength. However, the treatments, particularly the addition of nanocellulose, resulted in a reduction in the permeability to liquid resin of the reinforcements, highlighting the need for compromises in their manufacture. Nonetheless, marked improvements in tensile strength and Young’s modulus were obtained for composites made of pre-compacted and cross-linked fibre preforms. Increases in elastic modulus, strength and strain at break of up to 50.1%, 53.8% and 10.1% were obtained, respectively.

In this study, the low energy impact properties of flax/epoxy, glass/epoxy and hybrid flax-glass/epoxy laminates are evaluated for two different stacking sequences: a unidirectional [0] 8 and a cross-ply [0/90] 2s . For flax laminates, the base reinforcement is made of the combination of a unidirectional flax layer and a flax mat layer, where the mat phase consisted of short flax fibers used as a binder for the unidirectional phase. All laminates were tested under uniaxial tension both before and after impact and were molded at a fiber volume fraction of 40%. The results indicate that the specific stiffness of the flax fiber composite is approximately 7% higher than that of the glass fiber composite, regardless of the stacking sequence used. Concerning low-energy impact resistance, the cross-ply laminate demonstrates superior performance with higher impact resistance and less permanent deformation compared to the unidirectional laminate. The study also explores the hybridization of flax and glass fibers, suggesting a promising approach that leverages the synergistic effects of employing two different types of fibers in the composite. The comparison of energy absorption during impact shows that the hybrid fibers/epoxy composite has a higher energy absorption capacity than the glass fiber/epoxy composite. Additionally, hybridization helps mitigate the degradation of tensile properties caused by impact, representing an effective strategy to enhance the mechanical properties of the flax fiber composite post-impact.

The mechanical properties of composite materials are strongly related to the fiber–matrix interface properties. This study focuses on the click chemistry modification of short flax fibers using the Cu(I)-catalyzed Huisgen cycloaddition type, to strengthen the fiber–fiber interface for composite applications. The flax fibers are functionalized in three steps: a mechanical fibrillation pre-treatment of the fibers surface, followed by a chemical cleaning treatment to eliminate pectin, lignin, hemicelluloses and waxes, allowing exposure of the hydroxyl groups in flax fibers in view of the final treatment of click chemistry. The chosen strategy allows the adaptation of propargylation and tosylation reactions to flax fibers in aqueous media. FTIR and EDX analysis of fibers treated at intermediate stages confirmed the presence of various surface functions of modified fibers with a very high degree of substitution. The properties obtained are strongly improved for reinforcements containing covalent fiber–fiber contacts. Tensile, tearing and bursting tests performed on dry mat reinforcements showed increases in the tensile index, elongation at break, tensile stiffness, burst and tear indexes of 519

The Cu(i)-catalyzed Huisgen cycloaddition click chemistry reaction is of particular interest in the production of paper sheets or natural fiber composites since it leads to the formation of chemically stable bonds between two fibers.

High performance composite materials are mostly synthesized from non-renewable resources with a detrimental environmental impact. In this work an innovative flax fiber -reinforced soy -based polyurethane composite prepreg was developed from a soy -based polyol crosslinked with glycerin and isocyanate. The flax reinforcement was manufactured by binding unidirectional flax strings with short flax fibers. Composite prepregs were fabricated using a three rolls mill and oven pre -curing to obtain a beta stage. Vacuum assisted molding was used to manufacture laminates with a fiber volume fraction up to 41 %. Electron beam and optical microscope images of the composite cross-section indicated an adequate microstructure. Tensile strength (209 MPa), flexural strength (231 MPa), and short beam shear strength (25 MPa) demonstrated that the composites had good specific mechanical properties comparable with composites containing glass fibers studied in previous works, while having a significantly lower expected environmental impact. These properties demonstrate the appropriateness of the ecoresponsible composite material.

Unidirectional (UD) and cross-ply flax and glass fiber reinforced composites (FFRC and GFRC) are tested under four out-of-plane low velocity impact loads. A hybrid flax reinforcement was used, denoted UD-mat, which is made of a UD layer of continuous flax fibers bound to a flax fiber mat layer. For the mat binder, two types of short flax fibers are considered: unmodified fibers and refined ones. The laminates made of refined fibers show the highest permanent and maximum displacements. Moreover, the peak load for the unidirectional FFRC with refined fibers is lower than that with unmodified fibers, for example it is 25% lower at 11 J. When comparing with flax fiber laminates, the absorbed energy and energy absorption ratio are on average 40% lower for glass laminates but less damage is observed. Several failure modes are observed in the flax laminates, while the main failure of the glass/epoxy laminates is delamination.

The natural fiber composites (NFC) market is growing at fast rate in markets such as automotive interiors, construction and wind energy. The major driving force is the rise in demand for lightweight and environmentally sustainable materials. This research aims at developing high performance NFC, made from hybridizing short flax fibers and unidirectional flax filaments in the fabrication of mat and combined UD flax-mat reinforcement, by studying the mechanical surface fibrillation of the short flax fibers to improve the fiber–matrix load transfer. The results show an increase in the longitudinal tensile properties up to about 500 mill revolutions, after which a deterioration of the fiber structure occurs with corresponding reductions on properties. However, fibrillation reduces permeability to liquid resin, except in the transverse direction of UD flax-mat reinforcement. Globally, the mechanical fibrillation has a positive impact on mechanical properties and fracture behavior while impregnation can be further improved to ease manufacturing.

Carbon fiber-reinforced polymer (CFRP) composite materials are massively used since the last decades in many contemporary applications, especially in aerospace for their strength to density and stiffness to density ratios which are higher than alloys. On the other hand, CFRP are known to be difficult to machine compared to metals due to their heterogeneous and anisotropic structure. Common damages like delamination, fiber loosening and pull out, uncut fibers, and mechanical and thermal damages to the epoxy matrix are observed after machining. This research studies the effect of graphene particles addition in epoxy matrix of CFRP on the cutting temperature, in a global objective of improving the machinability and cutting tool life. Thereby, four modified resin plates (0%wt, 0.25%wt, 3%wt, and 10%wt of graphene) without carbon fibers (nanocomposite plates only) were first molded. Next, three CFRP laminates with different percentages of graphene (0%wt, 0.25%wt, and 3%wt) were manufactured using a combination of vacuum bagging and hydraulic pressing in order to guarantee a good fillers’ distribution within the composite plates and a consistent fiber volume fraction. The trimming experiments were performed using a polycrystalline diamond (PCD) tool which was selected for its well-known machining performance. As expected, the tool wear was nonexistent on nanocomposites. For CFRP plates, the tool wear remained in its break-in zone throughout the experiment (final Vb $$\approx 0.051\ll 0.3 \mathrm{mm}$$ for a final length cut of 4.5 m). The cutting tool’s temperature increases with graphene concentration for both nanocomposites and CFRP samples. However, the temperature increase of CFRP plates was reduced by 30% with a graphene concentration of 3%wt. The feed forces were also greatly reduced (up to 43%) with graphene when machining CFRP.

Materials used in many sectors like building or transportation must respect flame resistance standards. In this work, a dispersion of flame retardant phosphorylated kraft fibers (PKF), used in replacement of aluminum trihydroxide (ATH) in a polyester resin of a glass-reinforced composite laminate, and their impact on the flame retardancy of the material was investigated. SEM and EDS images showed a regular and homogeneous distribution of PKF in the resin matrix. The addition of PKF in the resin has a significant impact on the flammability parameters of the composite. For the tested experimental conditions, powdered PKF can be dispersed into the resin at a maximum powder/resin ratio of 20 wt% to maintain a low enough viscosity of resin for molding and procure a significant weight reduction of the laminate. However, there seems to be several unprotected areas in the material, by either PKF or ATH, that could promote flame propagation and smoke emission. Complete coverage of laminate with PKF will need to be achieved for a complete substitution of ATH.

Transverse compaction of fibre reinforcements has significant importance in the production of complex dry fibre preforms for the resin transfer moulding (RTM) process of composite materials. This work investigates, for the first time, the planar compaction of phosphorylated stacks of unidirectional (UD) reinforcements made of flax yarns held together by a thin layer of short flax fibres. Planar compaction tests were carried out to evaluate the influence of temperature and humidity on the creep percentage, thickness recovery, and permanent deformation of UD reinforcements prepared with and without phosphorylation. It appears that the creep percentage and permanent deformation are more important for phosphorylated reinforcements than for untreated ones. Increasing the compaction temperature and humidity results in an increase of the creep and permanent deformation of phosphorylated fibres. The tensile strength of phosphorylated fibres-reinforced composites is lower than that of untreated ones while there is no effect on the tensile modulus.

Carbon Fiber-Reinforced Plastic (CFRP) and Titanium alloy (Ti6Al4V) stacks are used extensively in the modern aerospace industry thanks to their outstanding mechanical properties and resistance to thermal load applications. Machining the CFRP/Ti6Al4V stack is a challenge and is complicated by the differences in each constituent materials’ machinability. The difficulty arises from the matrix degradation of the CFRP material caused by the heat generated during the machining process, which is a consequence of the low thermal conductivity of Ti6Al4V material. In most cases, CFRP and Ti6Al4V materials are stacked and secured together using rivets or bolts. This results in extra weight, while the drilling process required for such an assembly may damage the CFRP material. To overcome these issues, some applications employ an assembly that is free of bolts or rivets, and which uses adhesives or an adapted curing process to bond both materials together. The present research analyzes a thermal distribution and its effect on quality during the edge trimming process of a CFRP/Ti6Al4V stack assembly. Different types of tools and cutting parameters are compared using thermocouples embedded within the material and others on the tool cutting edge. In contrast to previous studies, the feed rate was the most significant factor affecting the cutting temperature and quality of the workpiece, while the cutting speed had no significant impact. The temperature in the workpiece increases as the feed per tooth decreases.

Using natural fibers as reinforcement in polymer matrix composites necessitates evaluating the latter under different modes of solicitation. This allows extracting its material properties for engineering design and research purposes. The main objective of the study is preparing a consistent set of material properties for unidirectional flax fiber-reinforced epoxy composite with defined composition and basic configuration. These data are prerequisites for growing researches on flax fiber-reinforced epoxy composites, especially for numerical analysis purposes using the finite element method. In this work, partially green unidirectional-flax fiber-reinforced epoxy composites are tested for physical and mechanical properties and studied for their failure modes. Tension, compression, flexion, and shear properties, as well as physical properties like density, specific heat capacity and thermal diffusivity, are evaluated according to ASTM standard test methods. Flax fibers, which are composites by themselves, come in bundles in the composites and demonstrate a complex behavior. Therefore, a fractographic analysis has been conducted to understand the macro and microscale failure mechanisms to correlate them with the material properties. The results are in good agreement with those of the literature, when available, but they mainly show the specific behavior of unidirectional-flax composites subject to different solicitation modes, especially compression and direct shear modes evaluated this way for the first time for unidirectional-flax fiber-reinforced epoxy composite. They cover most of the data required for engineering design and numerical analysis by methods like finite element method, particularly for simulating the machining process of flax fiber-reinforced epoxy composite in the ongoing works.

Density is a decisive factor in determining one of the most important advantages of flax fiber-reinforced polymer (FFRP) composites, i.e. their relatively low weight leading to high specific properties.As a fundamental physical property of composites, density enters in many engineering design and quality control calculations and its value is a determining factor for several applications.Especially, we need precise material properties including density so as to develop efficient numerical models to these materials.In this work, three density measurement methods were evaluated and compared: Helium-gas pycnometry and Archimedes with two different immersing liquids, water and ethanol.The results show that Helium-gas pycnometry and Archimedes with ethanol gave similar and repeatable results, whereas using water resulted in much lower values.The density values were all in the range of reported values.However, Helium-gas pycnometry or Archimedes using ethanol are recommended for more precision in measuring the density of FFRP composites.

Composite materials are widely used in various manufacturing fields from aeronautic and aerospace industries to the automotive industry. This is due to their outstanding mechanical properties with respect to their light weight. However, some studies showed that the major flaws of these materials are located at the fiber/matrix interface. Therefore, enhancing matrix adhesion properties could significantly improve the overall material characteristics. This study aims to analyze the effect of graphene particles on the adhesion properties of carbon fiber-reinforced polymer (CFRP) through interlaminar shear strength (ILSS) and flexural testing. Seven modified epoxy resins were prepared with different graphene contents. The CFRP laminates were next manufactured using a method that guarantees a repeatable and consistent fiber volume fraction with a low porosity level. Short beam shear and flexural tests were performed to compare the effect of graphene on the mechanical properties of the different laminates. It was found that 0.25 wt.% of graphene filler enhanced the flexural strength by 5%, whilst the higher concentrations (2 and 3 wt.%) decreased the flexural strength by about 7%. Regarding the ILSS, samples with low concentrations (0.25 and 0.5 wt.%) demonstrated a decent increase. Meanwhile, 3 wt.% slightly decreases the ILSS.

This work aims to analyze the impact of using carbon fibers based materials in the process of generating electrical power based energy harvesting. The harvester is a piezoelectric element exposed to vibrations of a vehicle in motion. The combination of fiber carbon material associated to the piezoelectric transducer are used as a source to generate electrical energy to power cars onboard wireless sensors. Many works treated the possibility to implement the vibrations energy harvesting using piezoelectric components. The approaches are oriented towards flexible piezoelectric materials subjected to flexion efforts for instance. In this work, we choose to use a carbon based material to which we fix a mass placed on a piezoelectric material. This combination is equivalent to a spring mass system. This paper highlights the advantages of such a solution compared to a classic spring mass system.

Having environmental and economic advantages, flax fibers have been recognized as a potential replacement for glass fibers as reinforcement in epoxy composites for various applications. Its widening applications require employing failure criteria and analysis methods for engineering design, analysis, and optimization of this material. Among different failure modes, delamination is known as one of the earliest ones in laminated composites and needs to be studied in detail. However, the delamination characteristics of unidirectional (UD) flax/epoxy composites in pure Mode I has rarely been addressed, while Mode II and Mixed-mode I/II have never been addressed before. This work studies and evaluates the interlaminar fracture toughness and delamination behavior of UDflax/epoxy composite under Mode I, Mode II, and Mixed-mode I/II loading. The composites were tested following corresponding ASTM standards and fulfilled all the requirements. The interlaminar fracture toughness of the composite were determined and validated based on the specific characteristics of natural fibers. Considering the variation in the composite structure configuration and its effects, the results of interlaminar fracture toughness fit in the range of those reported for similar composites in the literature and provide a basis for the material properties of this composite.