Effect of cellulose and lignin content on the mechanical properties and drop-weight impact damage of injection-molded polypropylene-flax and -pine fiber composites

Designing bio-composites for structural applications requires a thorough understanding of their mechanical behavior. In this study, we examined the differences in the tensile strength and drop-weight impact response between polypropylene reinforced with flax fibers and that reinforced with pinewood short fibers, as both fibers differ in composition (cellulose, hemicellulose, and lignin) and length-to-diameter ratio. We found that flax fibers, which have higher cellulose content and are twice as long as pine fibers, increased the stiffness and shock resistance of bio-composite materials. However, pine fibers, which contain more lignin, showed increased material ductility and energy absorption. Impulse excitation, acoustic emission and micro-CT techniques were used to evaluate the post-impact mechanical properties and the contribution of each damage mechanism to the final material failure (tearing). The experimental results were used to validate a model based on finite elements. Our results revealed that the experimental and finite-element analyses were in good agreement

Mechanical properties and drop-weight impact performance of injection-molded HDPE/birch fiber composites

Natural-fiber-reinforced composites offer various advantages over synthetic composites, including low density, useful mechanical properties and environmental friendliness. In spite of the progress achieved in the field, the mechanical performance of these composite materials has yet to be fully characterized, particularly in terms of impact resistance. In this study, we measured the drop weight impact, Izod impact strength, hardness, tensile strength and elastic modulus of birch-fiber-reinforced HDPE obtained by injection molding. Drop weight impact energy absorbed was constant and independent of fiber content whereas impact strength was inversely proportional to fiber content. Material toughness decreased slightly at 40% fiber. The Shore D hardness of virgin HDPE increased from 50.6 at 0% fiber to 74.6 at 30% fiber. The improvement of the elastic modulus of a composite containing 40% fiber was 27.2% superior to that reported for similar material made by compression molding. The corresponding improvement in tensile strength was superior by 19.7%. Birch-fiber-reinforced HDPE could be an adequate alternative to technical polymers widely used in several industrial sectors. © 2020 The Author

Gear fatigue life and thermomechanical behavior of novel green and bio-composite materials VS high-performance thermoplastics

In many applications, metal gears have been replaced by plastic gears because of their functionality and cost advantages. Despite their many benefits, the intensive use of plastics and composites raises sustainability issues because of the depletion of non-renewable petroleum resources and the pollution that is generated. Thus, alternative ecological solutions for plastic gears are necessary; however, little is known regarding ecologically designed gears. In this study, we propose two types of innovative gear materials. The first is a semi-ecological polyethylene bio-composite gear reinforced with birch fibers, and the second is a fully bio-sourced natural polyethylene gear with birch fibers. This study is the first time such fully ecological composite-plastic gears have been tested. The tests record the evolution of the fatigue and temperature over time under various operating conditions. Furthermore, acoustic emission is used to assess the evolution of fatigue cracks. The results indicate that the fully ecological gears are feasible and offer an alternative to traditional materials, such as engineering plastics, likely at a lower cost. © 2017 Elsevier Lt

Influence of UV irradiation on mechanical properties and drop-weight impact performance of polypropylene biocomposites reinforced with short flax and pine fibers

The design of biocomposite structures for outdoor applications should consider the influence of ultraviolet (UV) irradiation on the mechanical performances to more accurately determine their durability characteristics and prevent significant damage. Ultraviolet radiation causes the discoloration, surface roughness, mass loss, and degradation of the mechanical properties of biocomposites. In this study, the flexural strength and low-velocity impact response of polypropylene reinforced with short flax or pine fibers, which differed with respect to their physical and chemical properties, were investigated. Flax fibers are twice the length of pine fibers, and exhibit higher cellulose contents. Moreover, flax fibers have been demonstrated to increase the flexural strength and impact resistance of biocomposites. However, under UV irradiation, pine fibers containing more lignin dampened the degradation. Under photo-oxidative conditions, lignin is degraded to protect crystalline cellulose by acting as a light-absorbing compound. Non-destructive techniques such as Fourier transform infrared spectroscopy (FTIR), colorimetry, confocal imaging, acoustic emission, and CT scanning were therefore used to evaluate the effect of UV radiation on the chemical properties, color change, surface roughness, bending behavior, and drop-impact damage

Ultrasonic evaluation of friction stir welds and dissimilar intermixing using synthetic aperture focusing technique

Friction stir welding (FSW) is a recently developed solid-state joining process that uses a specially shaped rotating tool to produce lap or butt joints. At the National Research Council, an inter-institute collaboration was started in 2007 with the goal of exploiting the NDE expertise and applying it for the characterization of friction stir welds for various industrial applications. In particular, very good performance was obtained using ultrasonic immersion or laser-ultrasonics combined with the synthetic aperture focusing technique (SAFT) for detecting lack of penetration in butt joints, discontinuities such as wormholes and hooking in lap joints. Dissimilar metal welds of aluminum and magnesium by FSW are also considered for automotive and aerospace applications. Complex vortex flows are produced during the FSW process that may create intercalated lamellar structures with the possible formation of intermetallic compounds, causing variable hardness and degradation in mechanical properties. A modified version of SAFT that takes into account the difference of ultrasonic velocity in the joint between that of Al and Mg has been developed to study the dissimilar intermixing. Welded samples in the butt configuration with different welding speeds and seam offsets are tested using the immersion technique with the modified SAFT. Results will be presented for both defect detection and weld characterization, and the capabilities and limitations will be discussed.La soudure par friction-malaxage (SFM) est un proc\ue9d\ue9 d\u2019assemblage \ue0 l\u2019\ue9tat solide r\ue9cemment d\ue9velopp\ue9 qui fonctionne au moyen d\u2019un outil rotatif de forme sp\ue9ciale et qui sert \ue0 faire des joints de recouvrement ou des joints bout \ue0 bout. Au Conseil national de recherches du Canada, on a commenc\ue9 une collaboration inter-institut en 2007, avec pour objectif l\u2019exploitation de l\u2019expertise en \ue9valuation non destructive et son application pour la caract\ue9risation de soudures par friction-malaxage pour diverses applications industrielles. En particulier, on a obtenu une tr\ue8s bonne performance par immersion dans des ultrasons ou par une technique ultrasonique \ue0 laser combin\ue9e \ue0 la technique de focalisation \ue0 ouverture synth\ue9tique (TFOS) pour la d\ue9tection du manque de p\ue9n\ue9tration dans des joints bout \ue0 bout, de discontinuit\ue9s comme des tunnels ou des crochets dans des joints de recouvrement. Des soudures m\ue9talliques asym\ue9triques d\u2019aluminium et magn\ue9sium par SFM ont aussi \ue9t\ue9 \ue9tudi\ue9es pour des applications automobiles ou a\ue9rospatiales. Au cours du proc\ue9d\ue9 de SFM, des \ue9coulements complexes avec vortex sont produits. Ceci peut conduire \ue0 la cr\ue9ation de structures lamellaires intercal\ue9es avec formation possible de compos\ue9s interm\ue9talliques, provoquant une duret\ue9 variable et une d\ue9gradation des propri\ue9t\ue9s m\ue9caniques. Une version modifi\ue9e de la TFOS qui tient compte de la diff\ue9rence des vitesses ultrasoniques dans Al et Mg dans le joint a \ue9t\ue9 d\ue9velopp\ue9e afin d\u2019\ue9tudier le m\ue9lange asym\ue9trique. On a test\ue9 des \ue9chantillons soud\ue9s bout \ue0 bout avec diff\ue9rentes vitesses de soudage et diff\ue9rents d\ue9ports de soudage au moyen de la technique par immersion avec TFOS modifi\ue9e. Les r\ue9sultats sont pr\ue9sent\ue9s sur le plan de la d\ue9tection de d\ue9faut et de caract\ue9risation de la soudure. On discute des capacit\ue9s et des limites de cette technique.Peer reviewed: YesNRC publication: Ye

Fuzzy logic response to Young's modulus characterization of a flax-epoxy natural fiber composite

Most design approaches use the experimental elastic modulus as input variable to describe the material properties. In most cases the uncertainty and the variability of the modulus are neglected. In the worst case this can lead to bad estimations of the material performance and more iterations to the final solution. The purpose of this work is to reconcile the Young's modulus of three configurations ([0]10, [0]20 and [±45]10) of flax-epoxy composites obtained by different techniques including acoustic impulse, tensile and bending tests, according to ISO and ASTM standards. Results obtained with these techniques all show different levels of variability in Young's modulus values. A fuzzy logic model is used to obtain a simplified view of linguistic variables representing the modulus of elasticity and to reconcile different modules by including the uncertainty inherent to the different measuring techniques. Results have shown a strong potential for fuzzy logic to reconcile the disparity of Young modulus of natural fiber composites. © 2015 Elsevier Ltd

Hygrothermal aging effects on mechanical and fatigue behaviors of a short-natural-fiber-reinforced composite

A new natural fiber composite made of high density polyethylene (HDPE) and 40% wt of short birch fibers (SBF) was developed to replace polyamide (better known under its industrial name “Nylon”) in spur gear manufacturing. The effect of hygrothermal aging on quasi-static and fatigue bending behaviors of this new composite has been studied in this work. Once hygrothermal aging is completed, flexural quasi-static tests have been performed on aged specimens and results compared with those obtained from unaged specimens. It has been observed that hygrothermal aging has no significant effect on flexural mechanical properties of this composite. After characterization, bending fatigue tests have been conducted on aged specimens and results have been compared with those of unaged specimens. These fatigue tests show that hygrothermal aging decreases the high cycles fatigue strength (HCFS) of this composite. The cause of this fatigue durability decrease has been investigated using Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA) and a scanning electron microscope (SEM). These tests show that the chemical composition and thermal behavior of this composite are not affected by hygrothermal aging. On the contrary, these tests show that damage mechanisms of this composite (HDPE/40% wt of SBF) are directly affected by this type of aging

Fatigue life and residual strength of a short-natural-fiber-reinforced plastic vs Nylon

A new natural fiber composite made of high density polyethylene (HDPE) and short birch fibers (SBF) was developed to replace high-performance thermoplastics (Polyamide) commonly used in gears manufacturing. 3-point flexural quasi-static tests were achieved on bending specimens to assess mechanical properties. Comparison between these results and those of polyamide (PA) and neat polyethylene has showed that the polyethylene reinforced with 40%wt of SBF presents tensile and flexural mechanical properties that are higher than those of the PA11 or the neat polyethylene. After static characterisation, fatigue tests were performed to determine ε-N curves and the evolution of residual strength. Then, the fatigue behavior of the studied composite has been compared with that of PA66 and of ultra-high molecular weight polyethylene (UHMWPE). It has been noticed that polyethylene reinforced with 40%wt of SBF presents a high cycle fatigue strength (HCFS) that is more important than that of PA66 and UHMWPE. Consequently, the studied composite represents a good alternative to replace Nylon in spur gears manufacturing

Mechanical properties,wettability and thermal degradation of HDPE/birch fiber composite

Wood-plastic composites have emerged and represent an alternative to conventional composites reinforced with synthetic carbon fiber or glass fiber-polymer. A wide variety of wood fibers are used in WPCs including birch fiber. Birch is a common hardwood tree that grows in cool areas such as the province of Quebec, Canada. The effect of the filler proportion on the mechanical properties, wettability, and thermal degradation of high-density polyethylene/birch fiber composite was studied. High-density polyethylene, birch fiber and maleic anhydride polyethylene as coupling agent were mixed and pressed to obtain test specimens. Tensile and flexural tests, scanning electron microscopy, dynamic mechanical analysis, differential scanning calorimetry, thermogravimetry analysis and surface energy measurement were carried out. The tensile elastic modulus increased by 210% as the fiber content reached 50% by weight while the flexural modulus increased by 236%. The water droplet contact angle always exceeded 90°, meaning that the material remained hydrophobic. The thermal decomposition mass loss increased proportional with the percentage of fiber, which degraded at a lower temperature than the HDPE did. Both the storage modulus and the loss modulus increased with the proportion of fiber. Based on differential scanning calorimetry, neither the fiber proportion nor the coupling agent proportion affected the material melting temperature. © 2021 by the authors. Licensee MDPI, Basel, Switzerland