Showing papers in "Composites Part A-applied Science and Manufacturing in 2009"
TL;DR: In this article, the authors examined the research in shape memory polymers (SMPs) composites and blends achieved by numerous research groups around the world, mainly for five aims: (1) to improve shape recovery stress and mechanical properties; (2) to decrease shape recovery induction time by increasing thermal conductivity; (3) to create new polymer/polymer blends with shape-memory effect (SME); (4) to tune switch temperature, mechanical properties, and biomedical properties of SMPs; (5) to fabricate shape memory materials sensitive to electricity,
Abstract: Shape memory polymers (SMPs) are a kind of very important smart polymers. In order to improve the properties or obtain new functions of SMPs, SMP composites and blends are prepared. We thoroughly examine the research in SMP composites and blends achieved by numerous research groups around the world. The preparation of SMPs composites and blends is mainly for five aims: (1) to improve shape recovery stress and mechanical properties; (2) to decrease shape recovery induction time by increasing thermal conductivity; (3) to create new polymer/polymer blends with shape-memory effect (SME); (4) to tune switch temperature, mechanical properties, and biomedical properties of SMPs; (5) to fabricate shape memory materials sensitive to electricity, magnetic, light and moisture. The trend of SMP composite development is discussed. SMP composites and blends exhibit novel properties that are different from the conventional SMPs and thus can be utilized in various applications.
525 citations
TL;DR: In this article, the authors describe the production and the mechanical characteristics of composites made completely of renewable raw materials, such as cotton, hemp, kenaf and man-made cellulose fibres.
Abstract: The paper describes the production and the mechanical characteristics of composites made completely of renewable raw materials. Composites of different kinds of natural fibres like cotton, hemp, kenaf and man-made cellulose fibres (Lyocell) with various characteristics were processed with a fibre mass proportion of 40% and poly(lactic acid) (PLA) by compression moulding. Additionally, composites were made of fibre mixtures (hemp/kenaf, hemp/Lyocell). The composites were tested for tensile strength, elongation at break, Young’s modulus and Charpy impact strength. Their characteristics varied markedly depending on the characteristics of the raw fibres and fibre bundles and fibre mixtures used. While kenaf and hemp/PLA composites showed very high tensile strength and Young’s modulus values, cotton/PLA showed good impact characteristics. Lyocell/PLA composites combined both, high tensile strength and Young’s modulus with high impact strength. Thus, the composites could be applied in various fields, each meeting different requirements.
503 citations
TL;DR: In this paper, the effect of size on the tensile strength of composite laminates containing circular holes was investigated, showing that there is a large difference both in failure stress and mechanism due to changes in test configuration.
Abstract: Investigations of the effect of size on the tensile strength of composite laminates containing circular holes show that there is a large difference both in failure stress and mechanism due to changes in test configuration. This is particularly true of the ply and laminate thickness, and hole diameter. Interrupted tests have been performed on open hole tensile specimens at different load levels to determine the progressive damage development, evaluated through non-destructive testing (X-ray and C-scanning). The tests were also analysed using a novel Finite Element Modelling technique. This was able to accurately predict the wide range of ultimate strengths measured with variation in test parameters, principally through incorporation of the sub-critical damage in the analysis. A significant damage mechanism was seen to be delamination at the hole edge which generally occurred at a lower stress for a smaller hole diameter to ply block thickness ratio. Delaminations allowed damage to join up through the thickness of the laminate and propagate. In ply-level scaled specimens, the delamination propagation was the ultimate failure mode of most of the specimens. In sub-laminate level scaled specimens, localised damage relieved stress in the 0° fibres at the hole edge, delaying the onset of fibre failure. Less damage was seen for larger holes, thus leading to a decreasing failure stress with increasing hole diameter.
339 citations
TL;DR: In this article, a combined molding process with abaca and man-made cellulose fibres was used to improve the E-Modulus and tensile strength of PLA/abaca.
Abstract: PLA biocomposites with abaca and man-made cellulose fibres were processed by using combined moulding technology: two-step extrusion coating process and consecutively injection moulding. By adding 30 wt% of man-made cellulose, the Charpy impact strength at ambient temperature increased by factor 3.60, compared to unreinforced PLA. Tensile strength rose by factor 1.45 and stiffness by approx. 1.75. Reinforcing with abaca fibres (30 wt%) enhanced both E-Modulus and tensile strength by factor 2.40 and 1.20, respectively. The Charpy A-notch impact resistance of PLA/abaca could be improved by factor 2.4. SEM photographs show fibre pull-outs from the polymer matrix. The fibre orientation was analysed via optical microscopy. The after-process fibre length was significantly affected already during compounding process.
335 citations
TL;DR: In this paper, the life cycle energy of fiber-reinforced composites manufactured by using the pultrusion process was analyzed and the potential for composite materials to save energy in automotive applications was evaluated.
Abstract: Life cycle assessment is a technique to assess environmental aspects associated with a product or process by identifying energy, materials, and emissions over its life cycle. The energy analysis includes four stages of a life cycle: material production phase, manufacturing phase, use phase, and end-of-life phase. In this study, the life cycle energy of fiber-reinforced composites manufactured by using the pultrusion process was analyzed. For more widespread use of composites, it is critical to estimate how much energy is consumed during the lifetime of the composites compared to other materials. In particular, we evaluated a potential for composite materials to save energy in automotive applications. A hybrid model, which combines process analysis with economic input–output analysis, was used to capture both direct and indirect energy consumption of the pultrusion process in the material production and manufacturing stages.
334 citations
TL;DR: In this article, Salimian et al. examined the mechanical properties such as tensile, flexural and impact strength of fiber-reinforced composites and found that the permanganate treatment caused a reduction in the impact strength.
Abstract: Sisal fibers were subjected to various chemical and physical modifications such as mercerization, heating at 100 °C, permanganate treatment, benzoylation and silanization to improve the interfacial bonding with matrix. Composites were prepared by these fibers as reinforcement, using resin transfer molding (RTM). The mechanical properties such as tensile, flexural and impact strength were examined. Mercerized fiber-reinforced composites showed 36% of increase in tensile strength and 53% in Young’s modulus while the permanganate treated fiber-reinforced composites performed 25% increase in flexural strength. However, in the case of impact strength, the treatment has been found to cause a reduction. The water absorption study of these composites at different temperature revealed that it is less for the treated fiber-reinforced composites at all temperatures compared to the untreated one. SEM studies have been used to complement the results emanated from the evaluation of mechanical properties.
318 citations
TL;DR: In this article, the effects of surface modification on characteristics of jute fiber and mechanical properties of the biocomposite were evaluated, and the experimental results show that surface modification can remove surface impurities and reduce diameter of the jute fibres.
Abstract: A biocomposite was originally fabricated with biodegradable polymer PBS and jute fibre, and the effects of fibre surface modification on characteristics of jute fibre and mechanical properties of the biocomposite were evaluated in this paper. The experimental results show that surface modification can remove surface impurities and reduce diameter of jute fibres. Regarding the mechanical properties of biocomposites, it is observed that the biocomposites with jute fibres treated by 2% NaOH, 2 + 5% NaOH or coupling agent, respectively, an optimum in mechanical properties can obtain at fibre content of 20 wt.%, which exhibit an obvious enhancement in mechanical strength and modulus compared to the ones with untreated jute fibre. Furthermore, surface modification also exhibits less effects on flexural properties compared to tensile properties and more on flexural or tensile modulus than on the strength.
281 citations
TL;DR: In this article, a thermally conductive plastic composite was prepared from a mixture of silicon nitride (Si 3 N 4 ) filler particles and an ultrahigh molecular weight polyethylene-linear low density (PLD) blend.
Abstract: A novel thermally conductive plastic composite was prepared from a mixture of silicon nitride (Si 3 N 4 ) filler particles and an ultrahigh molecular weight polyethylene–linear low density polyethylene blend. The effects of Si 3 N 4 particle sizes, concentration, and dispersion on the thermal conductivity and relevant dielectric properties were investigated. With proper fabrication the Si 3 N 4 particles could form a continuously connected dispersion that acted as the dominant thermally conductive pathway through the plastic matrix. By adding 0–20% Si 3 N 4 filler particles, the composite thermal conductivity was increased from 0.2 to ∼1.0 W m −1 K −1 . Also, the composite thermal conductivity was further enhanced to 1.8 W m −1 K −1 by decreasing the Si 3 N 4 particle sizes from 35, 3 and 0.2 μm, and using coupling agent, for the composites with higher filler content. Alumina short fibers were then added to improve the overall composite toughness and strength. Optimum thermal, dielectric and mechanical properties were obtained for a fiber-reinforced polyethylene composite with 20% total alumina–Si 3 N 4 (0.2 μm size) filler particles.
261 citations
TL;DR: In this article, a critical review of research progress in modelling the structural response of polymer matrix composites exposed to fire is presented, where models for analysing the thermal, chemical, physical, and failure processes that control the structural responses of laminates and sandwich composite materials in fire are reviewed.
Abstract: This paper presents a critical review of research progress in modelling the structural response of polymer matrix composites exposed to fire. Models for analysing the thermal, chemical, physical, and failure processes that control the structural responses of laminates and sandwich composite materials in fire are reviewed. Models for calculating the residual structural properties of composites following fire are also described. Progress towards validation of the models by experimental characterisation of the structural properties of composites during and following fire is assessed. Deficiencies in the fire structural models are identified in the paper, which provide the focus for future research in the field.
253 citations
TL;DR: In this paper, the authors used the Darcy law to determine the porosity and the diameter of the fibres in a 3D random fibrous media and derived a semi-empirical constitutive model for the permeability of the media.
Abstract: Fluid flow analyses for porous media are of great importance in a wide range of industrial applications including, but not limited to, resin transfer moulding, filter analysis, transport of underground water and pollutants, and hydrocarbon recovery. Permeability is perhaps the most important property that characterizes porous media; however, its determination for different types of porous media is challenging due its complex dependence on the pore-level structure of the media. In the present work, fluid flow in three-dimensional random fibrous media is simulated using the lattice Boltzmann method. We determine the permeability of the medium using the Darcy law across a wide range of void fractions (0.08 ⩽ ϕ ⩽ 0.99) and find that the values for the permeability that we obtain are consistent with available experimental data. We use our numerical data to develop a semi-empirical constitutive model for the permeability of fibrous media as a function of their porosity and of the fibre diameter. The model, which is underpinned by the theoretical analysis of flow through cylinder arrays presented by [Gebart BR. Permeability of unidirectional reinforcements for RTM. J Compos Mater 1992; 26(8): 1100–33], gives an excellent fit to these data across the range of ϕ. We perform further simulations to determine the impact of the curvature and aspect ratio of the fibres on the permeability. We find that curvature has a negligible effect, and that aspect ratio is only important for fibres with aspect ratio smaller than 6:1, in which case the permeability increases with increasing aspect ratio. Finally, we calculate the permeability tensor for the fibrous media studied and confirm numerically that, for an isotropic medium, the permeability tensor reduces to a scalar value.
247 citations
TL;DR: In this article, closed-loop thermoset composite recycling through grinding and reincorporation is investigated, and it is shown that by careful attention to the separation and reformulation procedure, the mechanical integrity of recycled composites can be improved, and the use of substantially larger volumes of recyclate is possible.
Abstract: This study investigates closed-loop thermoset composite recycling through grinding and reincorporation. Contrary to many other studies, it is shown that by careful attention to the separation and reformulation procedure, the mechanical integrity of recycled composites can be improved, and the use of substantially larger volumes of recyclate is possible. Both factors are important aspects affecting the economic viability of regrinding as a possible future solution to the composites recycling problem.
TL;DR: In this article, the uncertainty in FRP composites has been quantified and a review of different stochastic modelling approaches suggested in the literature can be found in Section 2.1.
Abstract: The extensive use of FRP composite materials in a wide range of industries, and their inherent variability, has prompted many researchers to assess their performance from a probabilistic perspective. This paper attempts to quantify the uncertainty in FRP composites and to summarise the different stochastic modelling approaches suggested in the literature. Researchers have considered uncertainties starting at a constituent (fibre/matrix) level, at the ply level or at a coupon or component level. The constituent based approach could be further classified as a random variable based stochastic computational mechanics approach (whose usage is comparatively limited due to complex test data requirements and possible uncertainty propagation errors) and the more widely used morphology based random composite modelling which has been recommended for exploring local damage and failure characteristics. The ply level analysis using either stiffness/strength or fracture mechanics based models is suggested when the ply characteristics influence the composite properties significantly, or as a way to check the propagation of uncertainties across length scales. On the other hand, a coupon or component level based uncertainty modelling is suggested when global response characteristics govern the design objectives. Though relatively unexplored, appropriate cross-fertilisation between these approaches in a multi-scale modelling framework seems to be a promising avenue for stochastic analysis of composite structures. It is hoped that this review paper could facilitate and strengthen this process.
TL;DR: In this article, a series of carbon fiber/epoxy composite specimens using a simulated lightning strike generator was used to understand the fundamental damage response of this material form, and the results showed that residual tension strength counter intuitively increases after the infliction of damage, while residual compressive strength is much more dramatically and negatively affected.
Abstract: Damage is inflicted in a series of carbon fiber/epoxy composite specimens using a simulated lightning strike generator in the effort to understand the fundamental damage response of this material form. The strikes up to 50,000 A and 28,000 V are inflicted on both pristine specimens and specimens containing a Hilok stainless steel fastener. Damage area is evaluated via ultrasonic scanning, and advanced optical microscopy is used to gain further understanding in the morphology of damage. Subsequent mechanical testing to assess the residual tensile and compressive strength and modulus of the material is performed according to ASTM standards. Results show that residual tension strength counter intuitively increases after the infliction of damage, while residual compressive strength is much more dramatically and negatively affected. Furthermore, the presence of the fastener influences dramatically both the state of damage in the specimen and its residual strength by spreading throughout the thickness rather than limiting it to the specimen surface.
TL;DR: In this article, a hybrid biocomposites based upon a biodegradable poly(lactic acid) (PLA) matrix reinforced with microfibrillated cellulose (MFC) and bamboo fiber bundles was developed.
Abstract: In this research we develop novel hybrid biocomposites based upon a biodegradable poly(lactic acid) (PLA) matrix reinforced with microfibrillated cellulose (MFC) and bamboo fiber bundles. Due to the relative difference in scale between microfibrillated cellulose and bamboo, a hierarchy of reinforcement is created where bamboo fiber bundles are the primary load-carrying reinforcement and cellulose creates an interphase in the polymer matrix around the bamboo fiber that prevents sudden crack growth. The influence of MFC dispersion on the properties of the PLA matrix was investigated and substantial improvements in the strain energy until fracture observed. By adding just 1 wt% of MFC with a high degree of dispersion an increase in fracture energy of nearly 200% was obtained. In the hybrid bamboo/MFC/PLA composites there is also a dramatic change in the fracture morphology around the bamboo fiber bundles.
TL;DR: In this article, the authors used cellulose fibrils generated from several cellulose sources by ultrasonic treatment in order to utilize biomass to fabricate high-value products and investigated the geometrical and morphological characteristics of the cellulose fibers in micro and nanoscales.
Abstract: Cellulose fibrils in micro and nanoscales generated from biomass are relative new reinforcing materials for polymer composites, which have potential lightweight and high strength and are biodegradable. The objective of this study was to reinforce biodegradable polymers by cellulose fibrils generated from several cellulose sources by ultrasonic treatment in order to utilize biomass to fabricate high-value products. The geometrical characteristics of the fibrils were investigated by polarized light microscopy (PLM) and atomic force microscopy (AFM). The degree of fibrillation of the fibers evaluated by water retention value was significantly increased after treatment. The treated cellulose and separated fibrils were used to reinforce poly(vinyl alcohol) (PVA) to make biodegradable nanocomposites by film casting. The mechanical properties of PVA were significantly improved by most of the small fibrils. The morphological characteristics of the nanocomposites were investigated with PLM, scanning electron microscopy, and AFM.
TL;DR: In this paper, a detailed study on the moisture sorption characteristics of bamboo strips and their influence on the interfacial shear strength (IFSS) of bamboo/vinyl ester composite was performed.
Abstract: Moisture absorption is a major concern for natural fibers used as reinforcement in structural composites. This paper reports a detailed study on the moisture sorption characteristics of bamboo strips and their influence on the interfacial shear strength (IFSS) of bamboo/vinyl ester composite. The IFSS determined by pull-out test decreased dramatically as the fabrication humidity increased. The bamboo strips provide a reservoir of moisture which diffuses into the interfacial region and inhibits the hardening of vinyl ester matrix. The interface of the bamboo/vinyl ester composite can also be damaged due to moisture exposure after fabrication. Post-fabrication exposure of composites to moisture was found to be less damaging than the moisture exposure during the composite fabrication. The IFSS of the composite decreased by nearly 40% in the first 9 d of water immersion. Further immersion up to 100 d did not cause any further reduction in interfacial shear strength.
TL;DR: A facile method with the advantage of using only one single solvent throughout the whole processing was introduced to prepare graphite nanoplatelet (GNP) filled thermoplastic polyurethane (TPU) nanocomposites as mentioned in this paper.
Abstract: A facile method with the advantage of using only one single solvent throughout the whole processing was introduced to prepare graphite nanoplatelet (GNP) filled thermoplastic polyurethane (TPU) nanocomposites. Morphological studies showed that the employed method could provide the uniform dispersion of GNPs in the TPU matrix. Storage modulus of the nanocomposites was increased with increasing GNP content, and the improvement was more obvious at temperatures below the glass transition temperature (Tg) of TPU. For the nanocomposite that contains 3.9 vol% (the maximum loading employed in this study) of GNP, it still showed a long elongation at break of over 600%. Thermogravimetric analysis (TGA) showed that the incorporation of GNPs could improve the thermal stability of the nanocomposites. In addition, cone calorimetry results showed that the GNPs could act as intumescent flame retardant and significantly reduced the heat release rate (HRR), thus improved the flame retardancy of the TPU matrix.
TL;DR: In this article, the roles of processing method and fiber size on the properties of wood-plastic composites were investigated and a better understanding of the relationships between processing method, fiber characteristics, and composite behavior was provided.
Abstract: The aim of this study was to understand the roles of processing method and fiber size on the properties of wood–plastic composites (WPC). Composites were manufactured using extrusion or injection molding (IM) and fibers of different fiber length-to-diameter (L/D) ratio. IM resulted in better mechanical properties and lower water absorption and swelling than extrusion. These differences can be explained by the structure and surface quality of the composites. Fiber L/D ratio had a beneficial effect on mechanical properties but resulted in decreased water absorption characteristics. These results allow identifying a suitable forming process and/or fiber size according to application needs. This study provides a better understanding of the relationships between processing method, fiber characteristics, and composite behavior.
TL;DR: In this article, the effects of fiber variability, size, and content on selected mechanical and physical properties of wood plastic composites were investigated, and the effect of fiber size on water uptake was minimal.
Abstract: We investigated the effects of fiber variability, size, and content on selected mechanical and physical properties of wood plastic composites. HDPE and fibers were compounded into pellets by twin-screw extrusion and test specimens were prepared by injection molding. All tested properties vary significantly with fiber origin. Higher fiber size produces higher strength and elasticity but lower energy to break and elongation. The effect of fiber size on water uptake is minimal. Increasing fiber load improves the strength and stiffness of the composite but decreases elongation and energy to break. Water uptake increases with increasing fiber content.
TL;DR: In this article, a literature review of acoustic emission applications in studies on natural fiber composites is presented, including interface studies in single fibre composite (SFC) tests, damage evolution and failure mechanisms detection and crack propagation.
Abstract: In recent years, natural fibres are increasingly used as reinforcements for the production of low-cost and lightweight polymer composites: other advantages include non-abrasive nature, high specific properties, and biodegradability. However, their limitations, including moisture absorption, poor wettability and large scattering in mechanical properties, and the not sufficient understanding of mechanisms controlling their mechanical behaviour and failure modes, still confine the use of natural fibre reinforced composites in non-structural applications. Acoustic emission (AE) proved useful for its capability of real-time monitoring over the whole material volume and high sensitivity to any process generating stress waves. This paper presents a literature review of AE applications in studies on natural fibre composites. The following fields of application are covered: (1) interface studies in single fibre composite (SFC) tests, (2) damage evolution and failure mechanisms detection and (3) crack propagation, including also current limitations of existing literature and future work.
TL;DR: In this article, abaca was chemically treated with benzene diazonium salt in order to improve the mechanical properties of the abaca-PP composites and the results showed that interfacial bonding between the treated filler and the matrix has significantly improved.
Abstract: In the present study, abaca was chemically treated with benzene diazonium salt in order to improve in the mechanical properties of the abaca-PP composites. Both raw and treated abaca samples were utilized for the fabrication of the composites. The mechanical properties of the composites prepared from chemically treated abaca are found to increase substantially compared to those of untreated ones. Tensile strengths of the composites of both raw and chemically treated abaca-PP composites showed a decreasing trend with increasing filler content. However, the values for the chemically treated abaca-PP composites at all mixing ratios are found to be higher than that of neat PP. The surface morphologies of the fracture surfaces of the composites were recorded using scanning electron microscopy (SEM). The SEM micrographs reveal that interfacial bonding between the treated filler and the matrix has significantly improved, suggesting that better dispersion of the filler into the matrix has occurred upon treatment of abaca.
TL;DR: In this article, a comparison of in-plane tensile properties of two single-ply non-crimp 3D orthogonal weave E-glass fiber composites on one side and a laminate reinforced with four plies of plain weave Eglass fabric on the other is presented.
Abstract: Composites fabricated by VARTM technology with the use of single-ply non-crimp 3D orthogonal woven preforms 3WEAVE ® find fast growing research interest and industrial applications. It is now well understood and appreciated that this type of advanced composites provides efficient delamination suppression, enhanced damage tolerance, and superior impact, ballistic and blast performance characteristics over 2D fabric laminates. At the same time, this type of composites, having practically straight in-plane fibers, show significantly better in-plane stiffness and strength properties than respective properties of a “conventional” type 3D interlock weave composites. One primarily important question, which has not been addressed yet, is how the in-plane elastic and strength characteristics of this type of composites compare with respective in-plane properties of “equivalent” laminates made of 2D woven fabrics. This 2-part paper presents a comprehensive experimental study of the comparison of in-plane tensile properties of two single-ply non-crimp 3D orthogonal weave E-glass fiber composites on one side and a laminate reinforced with four plies of plain weave E-glass fabric on the other. Results obtained from mechanical testing are supplemented by acoustic emission data providing damage initiation thresholds, progressive cracks observation, full-field surface strain mapping and cracks observation on micrographs. The obtained results demonstrate that the studied 3D non-crimp orthogonal woven composites have considerably higher in-plane ultimate failure stresses and strains, as well as damage initiation strain thresholds than their 2D woven laminated composite counterpart. Part 1 presents the description of materials used, experimental techniques applied, principal results and their mutual comparisons for the three tested composites. Part 2 describes in detail the experimentally observed effects and trends with the main focus on the progressive damage: detailed results of AE registration, full-field strain measurements and progressive damage observations, highlighting peculiarities of local damage patterns and explaining the succession of local damage events, which leads to the differences in strength values between 2D and 3D composites.
TL;DR: In this article, surface modification of cellulose pulp fibres was performed with Methacryloxypropyltri-methoxysilane (MPTS) and Aminopropyltrihexilane(APTS) in an attempt to improve their durability into fibre-cement composites.
Abstract: The objective of the present work is to evaluate the effect of surface modification of cellulose pulp fibres on the mechanical and microstructure of fibre–cement composites. Surface modification of the cellulose pulps was performed with Methacryloxypropyltri-methoxysilane (MPTS) and Aminopropyltri-ethoxysilane (APTS) in an attempt to improve their durability into fibre–cement composites. The surface modification showed significant influence on the microstructure of the composites on the fibre–matrix interface and in the mineralization of the fibre lumen as seen by scanning electron microscopy (SEM) with back-scattered electron (BSE) detector. Accelerated ageing cycles decreased modulus of rupture (MOR) and toughness (TE) of the composites. Composites reinforced with MPTS-modified fibres presented fibres free from cement hydration products, while APTS-modified fibres presented accelerated mineralization. Higher mineralization of the fibres led to higher embrittlement of the composite after accelerated ageing cycles. These observations are therefore very useful for understanding the mechanisms of degradation of fibre–cement composites.
TL;DR: In this article, the authors investigated the thermo-mechanical behavior of hemp fibres by means of a dynamic mechanical analyser, which was performed at a frequency of 1-Hz, over the temperature range between 20°C and 220°C.
Abstract: In this paper, the thermo-mechanical behaviour of hemp fibres ( Cannabis sativa L . ) is investigated by means of a dynamic mechanical analyser. Experiments were performed at a frequency of 1 Hz, over the temperature range between 20 °C and 220 °C. When a periodic stress is applied to an elementary fibre, an increase in its rigidity and a decrease in its damping capacity are observed. These changes in its mechanical properties tend to stabilize after an identified number of cycles, thus providing evidence of an “adaptation” phenomenon. This specific mechanical behaviour certainly involves biochemical and/or structural modifications, such as microfibril reorientation, in the material’s organisation. In addition, the behaviour of hemp fibres is affected by temperature, which acts not only as an activation factor, but also as a degradation factor with respect to the visco-elastic properties of the fibres. The rigidity and endurance of the fibres are highly affected by thermal treatment at temperatures above 150 °C, and up to 180 °C. Taking these results into account, polypropylene–hemp fibre composites were manufactured using a specific processing cycle. By respecting the integrity of the fibres during manufacturing, it is found that with such composites, comparatively high performance can be achieved with some specific mechanical properties. This is highly encouraging for applications requiring high mechanical performance.
TL;DR: In this paper, polypropylene (PP) and microcrystalline cellulose (MCC) composites were prepared containing poly(propylenegraft-maleic anhydride) (PP-g-MA) and MCC treated with silicone oil, stearic acid or alkyltitanate coupling agent to promote matrix-filler dispersion and compatability.
Abstract: Polypropylene (PP)–microcrystalline cellulose (MCC) composites were prepared containing Poly(propylene-graft-maleic anhydride) (PP-g-MA) and MCC treated with silicone oil, stearic acid or alkyltitanate coupling agent to promote matrix–filler dispersion and compatability. Infrared spectroscopy confirmed surface treatment. MCC content and PP-g-MA increased PP thermal stability and crystallisation temperature (Tc), though reduced crystallinity due to cellulose II crystals. Tensile stress–strain analysis revealed increased modulus with MCC content, PP-g-MA, alkyltitanate and stearic acid. MCC and PP-g-MA reduced creep deformation and increased permanent strain. Storage modulus, loss modulus and glass transition temperature increased with MCC concentration due to effective interaction between PP and MCC.
TL;DR: In this article, the static and dynamic mechanical properties of nonwoven based flax fiber reinforced polypropylene composites were investigated. And the effect of zein modification on flax fibres was also reported.
Abstract: This paper presents an experimental study on the static and dynamic mechanical properties of nonwoven based flax fibre reinforced polypropylene composites. The effect of zein modification on flax fibres is also reported. Flax nonwovens were treated with zein coupling agent, which is a protein extracted from corn. Composites were prepared using nonwovens treated with zein solution. The tensile, flexural and impact properties of these composites were analysed and the reinforcing properties of the chemically treated composites were compared with that of untreated composites. Composites containing chemically modified flax fibres were found to possess improved mechanical properties. The viscoelastic properties of composites at different frequencies were investigated. The storage modulus of composites was found to increase with fibre content while damping properties registered a decrease. Zein coating was found to increase the storage modulus due to enhanced interfacial adhesion. The fracture mechanism of treated and untreated flax reinforced polypropylene composites was also investigated from scanning electron microscopic studies.
TL;DR: In this article, a combined experimental and 3D dynamic nonlinear finite element approach was used to study the progressive damage behaviors of hybrid woven composite panels (101.6mm × 101.6 mm) impacted by drop-weights at four different velocities.
Abstract: The progressive damage behaviors of hybrid woven composite panels (101.6 mm × 101.6 mm) impacted by drop-weights at four different velocities were studied by a combined experimental and 3-D dynamic nonlinear finite element approach. The specimens tested were made of plain-weave hybrid S2 glass-IM7 graphite fibers/toughened epoxy (cured at 177 °C). The composite panels were damaged using a pressure-assisted Instron-Dynatup 8520 instrumented drop-weight impact tester. During these low-velocity simpact tests, the time-histories of impact-induced dynamic strains and impact forces were recorded. The damaged specimens were inspected visually and using ultrasonic C-Scan methods. The commercially available 3-D dynamic nonlinear finite element (FE) software, LS-DYNA, incorporated with a proposed user-defined damage-induced nonlinear orthotropic model, was then used to simulate the experimental results of drop-weight tests. Good agreement between experimental and FE results has been achieved when comparing dynamic force, strain histories and damage patterns from experimental measurements and FE simulations.
TL;DR: In this article, the authors performed tensile tests on a PSF Al-Si alloy reinforced with multiwalled carbon nanotubes (MWCNTs) and found that the addition of CNTs leads to a 78% increase in the elastic modulus of the composite.
Abstract: Uniaxial tensile tests were performed on plasma spray formed (PSF) Al–Si alloy reinforced with multiwalled carbon nanotubes (MWCNTs). The addition of CNTs leads to 78% increase in the elastic modulus of the composite. There was a marginal increase in the tensile strength of CNT reinforced composite with degradation in strain to failure by 46%. The computed critical pullout length of CNTs ranges from 2.1 to 19.7 μm which is higher than the experimental length of CNT, leading to relatively poor load transfer and low tensile strength of PSF nanocomposites. Fracture surface validates that tensile fracture is governed strongly by the constitutive hierarchical microstructure of the plasma sprayed Al–CNT nanocomposite. The fracture path in Al–CNT nanocomposite occurs in Al–Si matrix adjacent to SiC layer on CNT surface.
TL;DR: In this paper, the effect of functionalization on the interfacial adhesion between epoxy and MWCNTs was examined and the results showed that as the loading of the carbon nanotubes increased, improved flexural strength and flexural modulus were observed.
Abstract: Nanocomposites based on epoxy resin and different weight percentages of unmodified, oxidized, and silanized multi-walled carbon nanotubes (MWCNTs) were prepared by cast molding method. Effects of MWCNTs content on the flexural properties were examined. The results showed that as the loading of the MWCNTs increased, improved flexural strength and flexural modulus were observed. The mechanical properties decreased when the MWCNTs content exceeded 0.2 wt.% due to agglomeration of MWCNTs. These results prove the effect of functionalization on the interfacial adhesion between epoxy and MWCNTs. This was further confirmed by morphology study of fractured surfaces of nanocomposites by SEM and TEM.
TL;DR: In this paper, VARIM was used to produce multiscale fiber reinforced composites (M-FRCs) based on carbon nanofibers dispersed in an epoxy resin.
Abstract: Vacuum assisted resin infusion molding (VARIM) was used to produce multiscale fiber reinforced composites (M-FRCs) based on carbon nanofibers dispersed in an epoxy resin. Flexural, interlaminar shear strength (ILSS) and thermomechanical tests are presented for the 0.1 wt% and 1 wt% M-FRCs and compared with the neat fiber reinforced composites (FRCs). Flexural strength and modulus increased (16–20%) and (23–26%), respectively for the 0.1 wt% and 1 wt% M-FRCs when compared to the neat FRCs. ILSS properties increased (6% and 25%) for the 0.1 wt% and 1 wt% M-FRCs, respectively when compared to neat FRCs. The glass transition temperatures ( T g ) of both M-FRC samples were 25 °C higher than the neat FRC. Coefficients of thermal expansion (CTE) of the M-FRC samples improved compared to the neat FRC. The improved T g and CTE properties in the M-FRC samples are attributed to synergistic interactions between the CNF/PNC matrix and glass fibers.