Showing papers in "Journal of Composite Materials in 2022"

Physical analysis and statistical investigation of tensile and fatigue behaviors of glass fiber-reinforced polyester via novel fibers arrangement

Abstract: Polymer composite researchers have extensively explored the influences of fiber orientation, volume fraction, type, length, as well as the impacts of matrix type, matrix/reinforcement interface, fibers hybridization, and nanoparticle incorporation on the mechanical behaviors of fiber-reinforced composite materials. The impacts of tailored fiber architectures on the mechanical characteristics of bulk polymeric-based composites, on the other hand, have not been investigated. The purpose of this research is to determine the effect of fiber arrangement on the mechanical characteristics of glass fiber-reinforced polymeric materials (GFRP). Unreinforced (UR) polyester, surface reinforced arranged (SRA) composites and bulk reinforced arranged (BRA) composites were fabricated. Characterizations have been performed using scanning electron microscope rotating bending fatigue machine and a universal testing machine. Results demonstrate that SRA’s lifespan after being exposed to bending fatigue has increased significantly with respect to UR and BRA samples. Average fatigue life for SRA samples is 61 times longer than the life of BRA samples at 56 MPa bending stress. Furthermore, a Weibull distribution function with shape parameter and scale parameter was implemented to analyze the fatigue life dataset statistically. The introduction of SRA novel design has promising results for cost reduction as well as quality improvement.

Potentiality of halloysite nanoclay on crashworthiness performance of polymer composite tubular elements

Abstract: The recent article investigates the impact of the presence of halloysite nanoclay (HNC) on crashworthiness performance of glass/epoxy energy absorbent composite tubes. Specimens filled with 0,1,2,3, and 4 wt. % of HNC were manufactured via wet-wrapping process and tested under quasi-static axial loadings. The crush load-displacement response, initial crushing load ( P ip ) , average crushing load ( P avg ), crushing force efficiency (CFE), absorbed energy (U), and specific absorbed energy (SEA) for the proposed composites were determined. The crushing behaviors for all specimens were traced. It was indicated that the specimens’ failure mechanisms and the energy absorption capacities of nanofilled glass/epoxy composites are highly dominated by the wt. % of the embedded HNC. The inclusion of HNC enhances the energy absorbing capacities of glass/epoxy composites during the crushing process. Composite tubes filled with 4 wt. % of HNC has the highest load carrying and energy absorption capacities which are, respectively, 32.75 kN and 1110.84 J. So, they are the most suitable materials for energy dissipating elements. The inclusion of 1, 2, 3, and 4 wt. % of HNC to glass/epoxy composite tubes exhibits, respectively, an enhancement of 8.56, 35.76, 37.96, and 53.33% in P i p and an enhancement of 169.29, 215.76, 204.60, and 254.19% in the P a v g . Also, an improvement in the energy absorbing by, respectively, 220.43, 270.09, 249.11, and 320.98% was attended. The purpose of this work is to experimentally study the applicability of HNC in the energy dissipating composite tubular elements.

A review of applications of CT imaging on fiber reinforced composites

Abstract: With the development of X-ray computed tomography over the last few decades, it is gradually considered to be a powerful tool in the field of materials research. This paper presents a comprehensive...

Textile reinforcement structures for concrete construction applications––a review

Abstract: The use of non-metallic, textile reinforcement structures in place of steel reinforcement is a key component in making concrete constructions more sustainable and durable than they currently are. The reason for this is the corrosion resistance of textile reinforcements, which makes it possible to reduce the thickness of the concrete cover and at the same time extend the service life of concrete structures. This reduces the amount of cement required and thus also the emission of the greenhouse gas carbon dioxide (CO2). By means of textile manufacturing technologies, customized, load-adapted reinforcement topologies can be adjusted to the requirements of highly stressed and well-designed concrete components. The objective of this paper is to give an overview of recent research literature dedicated to textile reinforcement structures that are already used for concrete applications in the construction industry as well as those currently under development. Therefore, textile reinforcement structures, which are divided into one-, two- and three-dimensional topologies, as well as common materials used for textile-reinforced concrete (TRC) are reviewed. Most research has so far been devoted to two-dimensional textile reinforcement structures. Furthermore, novel approaches to the fabrication of textile reinforcement structures for concrete applications based on robotic yarn deposition technologies are addressed.

Production and processing of pre-impregnated thermoplastic tapes by pultrusion and compression moulding

Abstract: Although there is no doubt that composite materials are the future of lightweight structures and components, most of composites currently produced are made from thermoset polymers, which are not able to be recycled or reprocessed. In contrast, thermoplastic polymers offer the possibility to recycle and reprocess and when combined with a fibrous reinforcement, provide interesting mechanical properties. This work reviews the production of two thermoplastic pre-impregnated materials in a tape form, one of which is produced on new prototype equipment developed in our laboratories. The method for the production of tape is described, and the prepregs presented here were subjected to two processing techniques. The first processing method, pultrusion, is an efficient and autonomous method to produce composite profiles, marking itself as a continuous and cost-effective way to produce these materials. Pultrusion bars were then subjected to heated compression moulding, a process that allows to obtain more complex-shaped parts. The second method, heated compression moulding, is a relatively simple process which was used to obtain composite laminates. The pultrusion bars and composite laminates were then subjected to mechanical testing to evaluate the levels of consolidation of the final material. A microscope testing was also carried out to analyse the dispersion of fibres and polymer, as well as the amount of voids present in the composite.

Thermoplastic matrix material influences on the mechanical performance of additively manufactured carbon-fiber-reinforced plastic composites

Abstract: Materials design and development continue to be more relevant as applications continue to rise for additively manufactured carbon-fiber-reinforced-plastic (CFRP) composites. Plastic matrixes bond and protect the fiber and help to transfer load through the composite to support intended applications. This makes it more necessary to understand the influences of thermoplastic matrixes on the mechanical performance of the composites fabricated through the additive manufacturing (AM) technique. This study investigated Acrylonitrile–Butadiene–Styrene (ABS) and Polyamide (PA) matrixes, which represent the bulk of the amorphous and semicrystalline engineering-grade thermoplastics matrixes, respectively, used in CFRP composite applications. Mechanical properties: tensile, compression, flexural, and thermal properties were examined, with the results showing the thermoplastic matrixes compositions and morphologies influences on the mechanical properties. The CF-PA was found to offer superior strength, ductility, and toughness because of their close-packed ordered lamellar matrix morphology, while the CF-ABS was found to offer superior modulus because of their loose morphology which more easily rearrange in reaction to stress upon elastic deformation. The mechanical properties results were reinforced by the fracture failure modes and the thermal analysis results which showed the CF-PA composite’s ability to withstand higher mechanical performance and temperatures before failure.

A predictive model towards understanding the effect of reinforcement agglomeration on the stiffness of nanocomposites

Abstract: Nanocomposite technologies can be significantly enhanced through a careful exploration of the effects of agglomerates on mechanical properties. Existing models are either overly simplified (e.g., neglect agglomeration effects) or often require a significant amount of computational resources. In this study, a novel continuum-based model with a statistical approach was developed. The model is based on a modified three-phase Mori–Tanaka model, which accounts for the filler, agglomerate, and matrix regions. Fillers are randomly dispersed in a defined space to predict agglomeration tendency. The proposed model demonstrates good agreement with the experimentally measured elastic moduli of spin-coated cellulose nanocrystal reinforced polyamide-6 films. The techniques and methodologies presented in the study are sufficiently general in that they can be extended to the analyses of various types of polymeric nanocomposite systems.

Study of mechanical properties and wear resistance of nanostructured Al 1100/TiO2 nanocomposite processed by accumulative roll bonding

Abstract: Aluminum (Al) composites have been extensively developed for automotive applications due to their high specific strength. Therefore, in this study, an Al-titanium dioxide (TiO2) nanocomposite was processed using the accumulative roll bonding (ARB) process. The mechanical characteristics of monolithic and nanocomposites specimens made with 0, 1, 2, and 3 wt% TiO2 nanoparticles as reinforcement were studied at several ARB passes. According to the microstructure of the composites, rolling after five passes achieves a homogenous distribution of reinforcement particles, ultrafine and elongated grains of the matrix. After five ARB passes, the TiO2 particles were uniformly dispersed. Finally, scanning electron microscopy and energy dispersive spectroscopy revealed that the Al-TiO2 nanocomposite had an appropriate dispersion of TiO2 nanoparticles. Vickers microhardness improves as the number of accumulative roll bonding passes increases. Furthermore, after five passes, Vickers microhardness testing revealed that the sample with 3%TiO2 has the greatest hardness value of 112 HV, which is significantly greater than the 44 HV hardness value of the ARB-processed aluminum. The mechanical properties of the specimens, yield and ultimate strengths, improved with the addition of TiO2 nanoparticles. Due to good bonding among the components, mechanical parameters such as microhardness and tensile strength were more than three times better than the Al matrix.

Static and dynamic deformation response of smart laminated composite plates induced by inclined piezoelectric actuators

Abstract: A Levi-type analytical solution procedure is developed to characterize static and dynamic deformation response of smart laminated simply-supported composite rectangular plates induced by inclined piezoelectric actuators under (1) constant electrical voltage and (2) time-dependent electrical voltage with excitation frequency. The key to development of this analytical solution is to employ higher order finite integral transform and discretized higher order partial differential unit step function equations. Unlike earlier studies, this research aims to investigate the effect of inclination angle of piezoelectric actuators on static and dynamic deformation response of laminated composite plates under both static and dynamic conditions. The developed analytical solution procedure is implemented computationally through Matlab-based computer code. Its accuracy is initially investigated through convergence study and results comparison with the published literature for a particular case when inclination angle is θ = 0°, which is only limited to bending deformation response. Since there is no published benchmark data for twisting deformation response analysis caused by inclination angle of piezoelectric actuators (θ ≠ 0°), a set of robust and realistic numerical analysis using Abaqus finite element analysis (FEA) is conducted. Good agreement between the analytical and numerical results is observed. Unlike applied electrical voltage, inclination angle of a piezoelectric actuator does not have a significant impact on twisting deformation response during static mode; whereas, both the excitation frequency and inclination angle can significantly influence maximum amplitude of vibration.

The effect of graphene and graphene oxide on defective single lap adhesively bonded joints

Abstract: The addition of nano-additives provides a path to improve joint performance. However, it is not clear if the use of these materials can alter the susceptibility of bonded joints to the presence of defects. This work aims to shed some light on this matter, by testing the performance of defective joints bonded with adhesives modified with nano-additives. Two different kinds of carbon-based nano-platelets, including graphene (G) and graphene oxide (GO), were used in this work as additives for adhesives used to bond single lap joints (SLJs). Bulk specimens, as well as three geometrically different SLJs were manufactured and tested. One configuration was manufactured without defects (WO), another with a disbond defect in the middle of the overlap, and another with a disbond defect on the edge of the overlap, known as a side defect (SD). These specimens were bonded with a neat epoxy adhesive and with the same adhesive modified with the addition of 0.3 wt% of G and GO. The addition of G and GO was found to improve Young’s modulus and the strength of the epoxy adhesive, while also decreasing its toughness. Dual effect of G and GO addition on improving the strength of the neat epoxy and WO SLJs while reducing the strength of some defective SLJs is also discussed using FT-IR and Raman spectrometry as well as scanning electron microscope pictures of the fracture surfaces.

Morphological and mechanical characterization of the Al-4032/granite powder composites

Abstract: The main motive of this paper is to prepare a newer composite material using non-conventional reinforcement (industrial waste) for various industrial applications. The aluminium alloy (Al-4032) matrix based composites (AMCs) have been fabricated through bottom pouring stir casting method. The granite powder (GP, ceramic particles) obtained from waste (normally available from construction site) has been used as reinforcement, at 0, 3, 6, 9 % by weight. The particle size of the reinforcement has been up to 54μm. The morphological (microstructure, SEM, XRD) and mechanical (tensile strength, micro-hardness, impact strength) characterization of the AMCs have been carried out. The morphological study reveals that the reinforcement particles (GP) are almost uniformly distributed throughout the matrix phase. The mechanical properties of the AMCs have been observed to be better than the unreinforced alloy. It is expected that the fabricated Al-4032-GP composites will be useful for the automobile parts like piston, disc brakes, high speed machinery and high-speed rotating parts etc.

Quasi-static axial crushing performance of thin-walled tubes with circular hole discontinuities

Abstract: This paper investigates the crashworthiness performance of square pipes with induced holes. Glass reinforced epoxy (GFRP) specimens were fabricated and tested under quasi-static axial crashing. Four design parameters were chosen, each at three levels, to calculate crashworthiness indicators. The design parameters are the hole diameter (d), the hole position to specimen length ratio (P/L), the number of holes and distribution (n), and crosshead speed (V). Taguchi technique has been adapted to get the optimum crashworthiness parameters. Experiments based on Taguchi’s orthogonal array with 9 experimental runs (L9) were performed. Optimal conditions with the maximum absorbed energy (U) and minimum initial peak force ( F i p ) were determined. The main effects, signal to noise ratio (S/N), and analysis of variance (ANOVA) have been investigated. Results indicated that “V” followed by “d” are the highest influencing parameters on the values of “U” with a contribution of 49% and 43%, respectively. The dominant influencing parameter on the values of F i p is “n” with a contribution of 94%. Finally, confirmation tests were carried out to validate the estimated model with respect to experimental results. The optimum U and F i p of GFRP square pipes with circular cutouts were compared with those of non-porous specimens.

Microstructure and tensile properties of in-situ synthesized and hot-extruded aluminum-matrix composites reinforced with hybrid submicron-sized ceramic particles

Abstract: Aluminum-matrix composites (AMCs) reinforced with submicron-sized ceramic particles of Al2O3, TiB2 and TiC were in-situ synthesized by reactive sintering of Al, TiO2, and B4C powder mixtures and further densified by hot-extrusion process. The reaction mechanisms for formation of the reinforcing particles, extrusion behavior, microstructure, and tensile properties of the AMCs have been investigated. The reactions of TiO2 and B4C with molten Al were a stepwise process, and there were many intermediate phases including oxygen deficient titanium oxides (Ti3O5, Ti2O3, and TiO), Al4C3, AlB2, and Al3Ti, before the expected reinforcing particles of Al2O3, TiB2, and TiC were formed. The results showed that hot-extrusion process was an effective means to densify reactive-sintered porous composites, and dense AMCs can be obtained through hot-extrusion in a temperature range of 480–550°C. The microstructure of the resulting AMCs was characterized by fine reinforcing ceramic phases with an average particle size of 0.24 μm, which were homogeneously distributed in Al matrix. Furthermore, no significant change in particle sizes could be found after extrusion, and ceramic particle content and extrusion temperature have small influences on the average particle sizes of the reinforcing phases. The presence of these sub-micron hybrid ceramic particles resulted in significant enhancements in yield and tensile strength of the AMCs. The yield strength improvement is mostly due to the coefficient of thermal expansion (CTE) mismatch between the ceramic particles and Al matrix, followed by Orowan strengthening, while the relative contributions of grain refinement and load-bearing effects are much smaller.

Strength and failure mechanism of single-lap magnesium-basalt fiber metal laminate adhesively bonded joints: Experimental and numerical assessments

Abstract: A quick literature search reveals the significant lack of data and information concerning magnesium-to-magnesium bonded joints as well as fiber-metal laminates (FMLs) made with magnesium alloys. Therefore, a systematic series of experimental and numerical investigations are carried out to assess the performance of single-lap joints mating FML adherends. The primary goal is to better understand the effects of geometrical and material parameters that influence the performance of magnesium-to-magnesium joints. The FML adherends used in this study consist of basalt natural fiber-epoxy laminate sandwiched in between thin sheets of magnesium alloys, which were subsequently adhesively bonded using a room-cured epoxy resin. The effects of two types of surface treatments, namely, “sandblasting” and “sandblasting with resin coating” on the bond strength and failure mechanism of the adhesively bonded joints (ABJs) are investigated. A 3D numerical model developed to simulate the response of the joints subjected to quasi-static lap-shear tests. This model, which accounts for the material and geometrical nonlinearity in the joints, is used to perform a parametric analysis for establishing the optimal overlap bond length. The distributions of the shear and peel stresses in the overlap region and the effects of adhesive thickness on the performance of the joints are systematically examined. The comparison of the experimental data and numerical results confirms the robustness and cost-effectiveness of the numerical model in predicting the response of such single-lap ABJs.

Residual mechanical performance of lightweight fiber-reinforced geopolymer mortar composites incorporating expanded clay after elevated temperatures

Abstract: This research provides an experimental investigation on the properties of fiber reinforced composite materials consisting of lightweight expanded clay aggregates (LECA) and polyvinyl alcohol (PVA) fibers. The influence of temperature (room temperature, 250°C, and 500°C) on the lightweight geopolymer mortar (LWGM) composite materials is also explored. LECA is used as a partial replacement to river sand with 60% and 80%. The base material utilized for LWGM is slag activated by a mixture of sodium silicate and sodium hydroxide solutions. The fresh properties in terms of workability and density were performed. A series of experiments, such as compression, flexural and uniaxial tensile strength tests, were executed to assess the mechanical properties of LWGM composite materials. In addition, the microscopic variations due to the elevated temperature were also evaluated by scanning electron microscopy (SEM) to understand the macro-scale behavior of the samples. The results indicated that increasing the level of LECA replacement caused a reduction in the density and compressive strength of the LWGM. Also, incorporating a 1% PVA fiber volume fraction significantly enhanced the flexural and uniaxial tensile behavior of LWGM composite materials. The compressive strength enhancements were observed at 250°C due to further geopolymerization, while compressive strength reductions were obtained at 500°C due to the vapor impact and difference in thermal expansion. In addition, the load-carrying capacity of all samples increased, and displacement capacity decreased under flexural tests at 250°C. However, the ductile behavior of the PVA incorporating specimens changed to brittle due to the melting of PVA fibers.

Impact behavior of long glass fibre reinforced aluminum metal matrix composite prepared by friction stir processing technique for automotive

Abstract: This work dealt with the fabrication of novel long glass fibre reinforced aluminum metal matrix composite (LGFRAMMC) material for automotive applications. The composite specimens were prepared by incorporating long glass fibre with different fibre volume percentage (50, 66, 80, and 100 vol.%) as reinforcement in aluminium alloy (Al6061) using the friction stir processing (FSP) method. The mechanical behaviour of the composite materials was investigated for their primary loading conditions such as tensile and Izod impact stress. Microstructural characterization and fractured mechanism of the fabricated composites were carried out by scanning electron microscope (SEM) analysis. The tensile strength and elongation of the developed composite specimens decreased with the incorporation of long glass fibre, whereas the Izod impact strength of the developed composite specimens was significantly improved as compared to the conventional base metal (Al6061) body panels used in automobiles. The low tensile strength of LGFRAMMC specimens compared to base metal was because of tunnel defect, brittle fracture and extreme plastic deformation (EPD) as characterized by fibre pull-out, pits, and micro cracks. The synergetic effects of EPD and reinforcing by long glass fibres lead to a remarkable improvement in the impact strength.

Performance evaluation of AlTiN coated carbide tools during machining of ceramic reinforced Cu-based hybrid composites under cryogenic, pure-minimum quantity lubrication and dry regimes

Abstract: In this study, the machining performance of 10 wt.% B-Ti-SiCp particles reinforced Cu-based hybrid composites were investigated under dry, minimum quantity lubrication (MQL) and cryogenic LN2 assisted environments during milling. In-depth analyses comprising of tool wear development, surface roughness, surface texture, cutting temperature, cutting energy, and chip morphologies were thoroughly performed. According to the experimental results, MQL environment was found to be most influential method to prevent build-up-edge formation. In addition, LN2 assisted cryogenic coolant medium is the most powerful method in all machining characteristics as providing better tribological properties. The paper proposes a novel approach for improved machinability performance of Cu-based hybrid composites with sustainable techniques.

Environmental affected mechanical performance of additively manufactured carbon fiber–reinforced plastic composites

Abstract: Due to their attractive strength-to-weight ratios, stiffness-to-weight ratios, thermal expansion, corrosion resistance, and vibration resistance properties, carbon fiber reinforced plastic (CFRP) composites have been widely used in applications ranging from aerospace to sporting goods. Considering some of the advantages of additive manufacturing (AM) over traditional subtractive methods, AM is being used to fabricate CFRP composites. For the fabrication method, several investigations have been conducted on materials and processing effects on the mechanical performance of the composites. However, no studies have investigated the effects of environmental conditions on mechanical performance. This study reports the environmental (temperature and relative humidity) affected mechanical performance of AM fabricated CFRP composites exposed to three different environmental conditions: warm–wet, warm–dry, and cold–dry, compared to samples tested immediately after fabrication under normal ambient conditions. The result was that the warm temperatures have insignificant effects on the mechanical performance of the composites, while near-zero degree cold temperatures have significant effects after the 96 h and 250 h short-term exposure periods. The result also showed the temperature to have more significant effects on mechanical properties than relative humidity. Under the warm conditions, the dry humidity resulted in a slight increase in material mechanical properties over the nominal ambient condition, while the wet humidity showed an insignificant reduction in material mechanical properties.

Polylactic acid and polyhydroxybutyrate coating on hemp fiber: Its effect on hemp fiber reinforced epoxy composites performance

Abstract: The present research work investigated the influence of biodegradable polymer coatings of hemp fiber on the structural, water absorption, mechanical, and tribological properties of hemp fiber and hemp fiber reinforced epoxy composites (HFREC). Hemp fibers were initially treated with sodium hydrogen carbonate and then coated with biodegradable polymers like polyhydroxybutyrate (PHB) and polylactic acid (PLA). Scanning electron microscopy (SEM) images of the coated fibers showed a visible change in fiber surface and improvement in surface roughness, while; X-Ray diffraction (XRD) analysis indicated the improvement in crystallinity of the coated fibers resulting in enhanced interfacial adhesion between the coated fibers and the epoxy matrix. The experimental results also revealed that both PHB and PLA coatings of the fibers have resulted in improvement of water resistance and mechanical properties such as tensile strength, modulus, and impact strength of coated HFREC. Tribological test results also revealed that the coated HFREC have improved wear and frictional properties in comparison to uncoated HFREC. The best tribological and mechanical properties were exhibited by PLA coated HFREC, which was also confirmed through the SEM images of worn and fractured surfaces of the uncoated and coated hemp fiber composites.

Experimental and numerical investigation on the effect of core-shell microcapsule sizes on mechanical properties of microcapsule-based polymers

Abstract: In this study, the effect of various microcapsule sizes on the mechanical properties of microcapsule-based polymeric materials was investigated using the finite element method and validated with experimental outcomes. Specimens containing 5wt. % of microcapsules were fabricated to calculate the elastic modulus, and maximum tensile stress, and to validate numerical results. To consider the error, five tests were performed for all samples, and results were reported on average. The average errors between the numerical outcomes and experimental results were 4.74% and 5.35% for maximum tensile stress and elastic modulus, respectively. The coaxial electrospraying method was used for synthesizing microcapsules made of alginate (shell) and epoxy (core). A scanning electron microscope (SEM) was used to calculate the diameter of the capsules. To develop an empirical model for the average microcapsule diameter (AMD) and carry out the optimization process, response surface methodology (RSM) with central composite design was used. Also, analysis of variance was employed to validate the accuracy of the model. The effects of three parameters, including voltage, needle size, and the distance between the tip of the needle to the collector, on average microcapsule diameter, were investigated. The empirical model was validated by a confirmation run, and the determined error (1.93%) between the predicted and experimental results indicates the precision of the model. The numerical study indicated that microcapsule-based self-healing polymers containing smaller microcapsules tolerate higher stresses. However, the effect of the microcapsules’ size on the elastic modulus of a representative volume element was negligible.

Hybridization effect of functionalized microcrystalline cellulose and liquid acrylonitrile butadiene rubber on epoxy

Abstract: Toughening epoxy resins by adding different agents has been employed as a way to reduce brittleness in composites. Some hybridization strategies combining liquid rubbers and rigid fillers can be found in the literature, but the pair cellulose-based reinforcement, such as microcrystalline cellulose (MCC), and liquid acrylonitrile butadiene rubber (NBR) is hardly studied. The aim of this work is to investigate the effect of hybridizing MCC and amino-functionalized MCC (MCCSi) with NBR on the thermal, mechanical, and dynamic-mechanical behavior of epoxy. X-ray microtomography showed a good dispersion of MCCSi fillers in epoxy/NBR compared to the non-treated MCC filler. NBR with MCCSi was found to slightly increase the thermal stability of epoxy. The addition of MCC, regardless of the functionalization, decreased tensile strength and elastic modulus, but improved impact strength and toughness properties (KIC). Also, MCCSi composites displayed better dynamic-mechanical behavior, attributed to the enhanced chemical interaction, with a small effect on glass transition temperature.

Investigation of mechanical, physicochemical, and thermal properties of new fiber from Silybum marianum bark fiber

Abstract: The present investigation aimed to understand the physicochemical properties of the new cellulosic fiber extracted from the bark of Silybum marianum (SM), in view of using it as a potential reinforcement for polymer composites. The morphological and anatomy, physical, thermal and mechanical properties of fibers were firstly discussed in this paper. The Silybum marianum fibers (SMF) were characterized by scanning electron microscopy, Fourier transform infrared, thermogravimetric analysis (TGA), optical microscope, X-ray diffraction (XRD), and single fiber tensile test. The average Young’s modulus and the breaking stress data presented by the fibers are 15.97 GPa and 201.16 MPa, respectively. XRD reveals the presence of cellulose with a crystallinity index of 45%. Thermal stability (250°C) and maximum degradation temperature (357.72°C) of the SMF are established by the thermogravimetric analysis. An analysis of the mechanical properties was carried out on a population of 35 samples using Weibull statistics with two and three parameters.

Experimental analysis of tensile properties and essential work of fracture of fumed silica filled polypropylene toughened with thermoplastic polyolefin elastomer

Abstract: In this research, tensile and fracture behavior of polypropylene (PP) toughened with two types of thermoplastic polyolefin elastomers (TPOs) and filled with fumed silica are investigated. The TPOs are both propylene- and ethylene-based thermoplastic elastomers. Three percentages of TPO (0, 10, and 20 wt%) and four percentages of fumed silica (0, 1, 3, and 5 wt.%) are used. The addition of ethylene-based TPO to PP show higher values of modulus and tensile strength than propylene-based TPO. In contrast, propylene-based TPO show higher elongation at break which by increasing this type of TPO the elongation at break increase by 788%. The presence of fumed silica in the PP/TPOs blend improve the tensile strength and modulus but declined the elongation at break. Fracture behavior analysis of these compounds is performed by utilizing the essential work of fracture (EWF) approach. The outcomes demonstrate that both types of TPO in PP cause cavitation and fibrillar structures that increased the elastic and plastic work of fracture. Adding 10 wt.% ethylene- and propylene-based TPO to PP, the values of w e and βw p increase by 63%, 100% and 124%, 123%, respectively. Morphological observations show that fumed silica is located mainly around TPOs particles or at the PP/TPOs interfaces. The addition of fumed silica also reduce the size of the pores, which indicate a slight reduction in the amount of plastic work. However, fumed silica with low percentages increase the amount of elastic work and then reduce it. Also, the compound with 10 wt.% propylene-based thermoplastic elastomers and 1 wt.% fumed silica had the best toughness-stiffness-strength balance among the samples based on the optimization results.

A laminated vitrimer composite with strain sensing, delamination self-healing, deicing, and room-temperature shape restoration properties

Abstract: Laminated multifunctional composites are highly desired in modern lightweight engineering structures. The purpose of this study is to develop a composite laminate with impact tolerance, delamination healing, strain sensing, Joule heating, deicing, and room temperature shape restoration functionalities. In this study, a novel self-healable and recyclable shape memory vitrimer was used as the matrix, unidirectional glass fabric was used as reinforcement, and tension programmed shape memory alloy (SMA) wires were used as z-pins. To provide multifunctionality, the programmed SMA wires were further twisted and formed into sinusoidal shape. Copper wire strands were hooked to the sinusoidal SMA z-pins to make them a closed circuit. Low velocity impact, compression after impact, damage self-healing, deicing, and room temperature shape restoration tests were conducted. The tests result show that the desired multifunctionality of the laminated composite was achieved. The hybrid laminate provides a promising design for lightweight load-carrying engineering structures.

Experimental investigation on the mechanical behavior and damage of 3D printed composites under three-point bending

Abstract: Three-dimensional (3D) printing has been triumphantly applied for the manufacture of various composite components. In this work, acoustic emission (AE), X-ray micro-computed tomography (Micro-CT) are used in conjunction with digital image correlation (DIC) measurement to investigate the mechanical behaviors of 3D printed continuous fiber reinforced composites under three-point bending test. Meanwhile, several mechanical experiments are carried out to study the flexural properties of three kinds of composite specimens, among which the specimens with larger glass fiber content exhibit more superior mechanical properties. Furthermore, AE response characterizations and microscopic damage morphology are also examined. In consequence, the complementary nondestructive testing (NDT) technology combining AE, DIC, and Micro CT is successfully applied to evaluate the mechanical behaviors of 3D printed composites, and the flexural deformation and damage are comparatively investigated for different composite specimens. The cross-validation results of cluster analysis (k-means), K-Nearest Neighbor (KNN) and principal component analysis (PCA) show that AE parameters including frequency, amplitude, and RA value (rise time divided by peak amplitude) are closely associated with the damage process of different specimens. The results show that the PCA can confirm the selected K-means cluster analysis parameters (peak frequency and peak amplitude) and the dimensionality reduction effects of 20% glass fiber specimens have the best results, indicating that the proportion of the principal components extracted can represent the original parameters is 81%. It was also confirmed that the supervised learning KNN algorithm corresponding to different damage patterns can verify the unsupervised learning k-means cluster. Correspondingly, the strain fields characterized by DIC are reasonably matched with the AE signal responses. In addition, the critical damage and delamination mechanisms of the 3D printed continuous fiber reinforced composites are clearly revealed by Micro-CT characterization.

Maxwell-Wagner-Sillars interfacial polarization in dielectric spectra of composite materials: Scaling laws and applications

Abstract: An experimental and theoretical investigation of the scaling laws governing the phenomenon of Maxwell-Wagner-Sillars interfacial polarization in composite materials in dependence on morphology, volume fraction, orientation of fillers, form factor and the presence of interphases is presented in the current study. By considering the complex dielectric function of the matrix and of the fillers, the dielectric spectra are calculated in the frequency range from 107 Hz to 10-2 Hz and compared to dielectric measurements by Broadband Dielectric Spectroscopy, carried out in the frequency range from 107 Hz to 0.5Hz and between -90oC and 150oC. The characteristic frequencies of the global dielectric response are reported to strongly vary with the conductivity value of the conductive phase, while a much weaker dependence is observed upon varying the volume fraction, the form factor and the orientation of fillers. The value of permittivity at low frequency does not change with the conductivity value, whereas a significant variation is observed in dependence on the composite morphology, form factor, orientation of fillers and presence of interfaces with different gradients of properties. Two possible applications of our analysis are reported: (i) measuring the conductivity of materials without employing a direct electrical contact between the electrodes and the sample and (ii) discriminating different phenomena of electrical polarization in complex materials by analyzing the scaling laws. Our study delivers thus a useful and necessary analysis of the dielectric behavior of composite materials, where interfacial polarization effects play a major role.

Valorization of Posidonia-Oceanica leaves for the building insulation sector

Abstract: A new bio-composite material appropriate for building thermal insulation is proposed. The hydrophilic, thermal, and mechanical properties of composites made with Posidonia-Oceanica leaves, are experimentally investigated. The effect of two different sizes of fibers (natural and crushed leaves) as well as the effect of the chemical treatment (1% sodium hydroxide) are studied. For this purpose, different parallelepipedic specimens of dimensions 270 × 270 × 30 mm3 (thermal properties tests) and 160 × 40 × 40 mm3 (mechanical properties tests) were prepared by varying densities of leaves (0, 5, 10, 15, 20, and 30% by volume). In comparison to the fiber size effect, the results reveal that fiber loading has a significant impact on the mechanical and thermal characteristics of composites. Alkali treatment can improve the compressive and flexural strength of bio-composites. The novel bio-composites have low thermal conductivity (0.09 W.m−1K−1 when 30% of reduced size Posidonia-Oceanica leaves were loaded into the reference mortar) and acceptable mechanical performances. Results also show (1) The addition of treated fiber improves the ductility of the material. (2) The fracture toughness is 75% greater than reference mortar. (3) The use of crushed fibers decreases the composite’s mechanical strengths. (4) The flexural strength decreases with the fibers content and increase after 1% sodium hydroxide treatment. It can be concluded that the proposed bio-composite can be employed as thermal insulation material.

Drilling of natural fiber-reinforced based polyurethane foam composite

Abstract: The combination of natural fibers and renewable source matrices is an option to replace materials from non-renewable sources used in the manufacture of composites. One example is the use of pinus sawdust and sisal fibers together with a matrix of polyurethane (PU) foam derived from vegetable oils. For the application of composites in sectors such as building or furniture industry, one of the necessary processes is drilling, which allows assembling through different fastening systems. The aim of this work is to investigate the drilling process of the composites of PU foam derived from vegetable oils matrix with only pinus sawdust and hybrid pinus sawdust and sisal fibers taking into account surface damages of the holes and temperature generated during the process. Results showed that drilling parameters influence on the generation of damages mainly at the edges of the holes. Lower cutting speed and feed rate were most appropriate for drilling these types of composites, and temperatures generated during drilling showed relationship with the generation of damages.