Mechanical Performance Of Composites Research Articles

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

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

Ramie fiber reinforced composites with flame retardant structure design: flammability, smoke suppression, and mechanical properties

Abstract In this work, the structure of composite was designed as Core Stack and Surface Stack, which was treated with the expandable graphite (EG) and metal oxides such as iron oxide (IO), hydroxyapatite (HA), and aluminum tri-hydroxide (ATH). The mechanical performance of composites was characterized via flexural performance and interlaminar shear strength analysis. The flame retardance and smoke suppression of composite was explored in detail by LOI, UL-94, and cone calorimeter test. The findings presented that flexural properties of composites were observed to decrease due to delamination of surface stack, whilst no significant effect on interlaminar shear strength. In comparison with control composite, the loading of metal oxide into composite Surface Stack led to the reduction of peak heat release rate, total heat release, and fire growth index effectively. Moreover, the remarkable decrease in total smoke production could be observed due to the addition of iron oxide and the flame retardant mechanism was discussed. This study was the preliminary exploration of composite with flame retardant design which could be potential solution to improve flame retardancy and smoke suppression of composite with better mechanical structure preservation.

Investigation of the thermomechanical performance of hybrid polymer composite using micro bamboo powder and graphite flakes

AbstractThe current research project is dedicated to tackling the issue of fiber alignment and composite material delamination. Alkali treatment is performed to enhance the bamboo filler reinforced composite's mechanical performance as well as interfacial bonding strength. The hybrid composite is developed with varied bamboo powder content from 2.5 to 12.5 wt% and graphite nanoplatelets (GN) are reinforced in the polymer matrix. The hybrid composite is manufactured with bamboo powder approximately 65 μm sized and GN for electrical and electronics packaging, heat sink, conductive paste, light back cover for thermal management, automobile parts, and packaging goods. The developed material is investigated experimentally through the tensile test, modulus of elasticity, storage modulus, thermal conductivity, corrosion and tribological analysis. Results revealed that 5 and 7.5 wt% bamboo filler with 1 wt% GN gives the best property among others.

Evaluating mechanical efficiency of glass fibres in a polymer profile

This study focuses on the mechanical performance of pultruded glass fibre-reinforced polymer (GFRP) profiles developed for structural applications. Fibre content determines the tensile resistance of such components, and technical specifications describe this essential parameter. However, it does not determine the actual reinforcement efficiency. This manuscript illustrates the above inference both experimentally and analytically, investigating a GFRP square hollow section (SHS) profile available at the market. Standard tensile coupon test defines the material characteristics; a three-point-bending test determines the mechanical performance of the profile. A digital image correlation system captures deformations and failure mechanism of the SHS bending specimen. The developed finite element model with smeared reinforcement estimates the efficiency of the glass filaments, i.e. the ability to predict the actual mechanical resistance (flexural stiffness) under the assumption of the experimentally determined elasticity modulus of bare fibres. Scanning electron microscopy relates the composite microstructure and mechanical performance of the selected profile.

Substitution of virgin carbon fiber with low-cost recycled fiber in automotive grade injection molding polyamide 66 for equivalent composite mechanical performance with improved sustainability

Recycled carbon fiber has historically proven challenging to integrate into composite manufacturing due in no small part to the low-density, randomly oriented, discontinuous fiber format that results from typical recycling. Discontinuous fiber requires the use of alternative technologies than those traditionally applied to continuous fiber (e.g., hand lay-up, winding). Extrusion compounding is one such applicable technology, but material transfer into the system requires alternative feeding equipment or the use of an altered procedure as trialed in this research. In this study, an injection molding compound for automotive applications was prepared with recycled carbon fiber and compared against an existing commercial compound. Input fibers and molded compound were evaluated for mechanical performance, while relevant variables such as compounded fiber alignment and aspect ratio were compared to the existing baseline material to confirm a like-for-like composite material structure. Analysis indicates that recycled fiber performs similarly to virgin fiber reinforcement, demonstrating that recycled fiber may be a viable drop-in replacement for short-fiber discontinuous applications.

Influence of the Kind and the Shape of Insulating Materials on the Mechanical Properties of the Composites Plaster- Granular Cork and Plaster- Fiber Alpha

The objective of our work is to study the influence of nature and the shape of the insulating materials on the mechanical performance of composites based on plaster. The study aims to increase the thermal performance of the building envelope and the same time maintains sufficient mechanical properties of the composites studied. Plaster was combined with two additives (alpha fiber and granular cork). A physical and mechanical characterization of the composites plaster-fiber alpha and plaster-cork was carried on. Authors obtained an important gain in term of lightness 27 % concerning the composite plaster-fiber alpha, however for the composite plaster-cork, the value is 34 %. Concerning the mechanical properties, authors found a decrease in flexural strength of 60 % for the plaster-cork, and an increase of 33 % for the plaster-alpha fiber. For the compressive strength, a reduce of 87 % for the plaster-alpha fiber and 80% for the plaster-cork was observed. Those finding are justified by the scanning microscopic electron tests which show the distribution of the two insulators and adhesion within the plaster matrix.

Flame Retardancy of Biobased Composites-Research Development.

Due to the thermal and fire sensitivity of polymer bio-composite materials, especially in the case of plant-based fillers applied for them, next to intensive research on the better mechanical performance of composites, it is extremely important to improve their reaction to fire. This is necessary due to the current widespread practical use of bio-based composites. The first part of this work relates to an overview of the most commonly used techniques and different approaches towards the increasing the fire resistance of petrochemical-based polymeric materials. The next few sections present commonly used methods of reducing the flammability of polymers and characterize the most frequently used compounds. It is highlighted that despite adverse health effects in animals and humans, some of mentioned fire retardants (such as halogenated organic derivatives e.g., hexabromocyclododecane, polybrominated diphenyl ether) are unfortunately also still in use, even for bio-composite materials. The most recent studies related to the development of the flame retardation of polymeric materials are then summarized. Particular attention is paid to the issue of flame retardation of bio-based polymer composites and the specifics of reducing the flammability of these materials. Strategies for retarding composites are discussed on examples of particular bio-polymers (such as: polylactide, polyhydroxyalkanoates or polyamide-11), as well as polymers obtained on the basis of natural raw materials (e.g., bio-based polyurethanes or bio-based epoxies). The advantages and disadvantages of these strategies, as well as the flame retardants used in them, are highlighted.

Poly(ε-Caprolactone)/Brewers’ Spent Grain Composites—The Impact of Filler Treatment on the Mechanical Performance

Waste lignocellulose materials, such as brewers’ spent grain, can be considered very promising sources of fillers for the manufacturing of natural fiber composites. Nevertheless, due to the chemical structure differences between polymer matrices and brewers’ spent grain, filler treatment should be included. The presented work aimed to investigate the impact of fillers’ reactive extrusion on the chemical structure and the poly(ε-caprolactone)/brewers’ spent grain composites’ mechanical performance. The chemical structure was analyzed by Fourier-transform infrared spectroscopy, while the mechanical performance of composites was assessed by static tensile tests and dynamic mechanical analysis. Depending on the filler pretreatment, composites with different mechanical properties were obtained. Nevertheless, the increase in pretreatment temperature resulted in the increased interface surface area of filler, which enhanced composites’ toughness. As a result, composites were able to withstand a higher amount of stress before failure. The mechanical tests also indicated a drop in the adhesion factor, pointing to enhanced interfacial interactions for higher pretreatment temperatures. The presented work showed that reactive extrusion could be considered an auspicious method for lignocellulose filler modification, which could be tailored to obtain composites with desired properties.

Properties of core-half wrapped shell structure wood-polymer composites containing glass fiber-reinforced shells

Glass fiber (GF) is commonly applied as a filler in the preparation of polymer composites. Due to the presence of GF, composite mechanical performance, flame resistance, and thermal performance could be greatly improved. The influence of a GF-filled polymer shell layer was investigated relative to the morphology, mechanical, thermal, and fire flammability performance of the core-half wrapped shell structured wood high-density polyethylene (HDPE) composites prepared via co-extrusion. The use of the relatively less-stiff pure HDPE with high linear coefficients of thermal expansion (LCTEs) lowered the general thermal stability and modulus of the wood polymer composites (WPCs). Flexural and thermal expansion properties were improved for the GF-filled HDPE shells in comparison to the unmodified material, enabling a well-balanced performance of this novel core–shell material. Implementation of GF-modified HDPE or unmodified HDPE layers as a shell for WPC core remarkably improved the impact resistance of the co-extruded WPCs. In comparison with composites possessing unmodified HDPE shell, the flame resistance performance of the shell layer was slightly improved in case that the GF content was below 25 wt%. A slight decrease in composite general heat release and rate was discovered in case that the GF content was greater than 25 wt%.

Time-dependent degradation behaviour of phosphate glass fibre reinforced composites with different fibre architecture

In this study, biodegradable Polylactic acid (PLA) composites reinforced with phosphate glass fibres (PGF) using different fibre architecture (UUU, CCC, UCU and CUC) were prepared via compression moulding process. The maximum initial flexural strength and modulus were observed for unidirectional (UD) fibre reinforced composites (UUU), whereas CCC composites with thoroughly chopped fibre reinforcement exhibited the lowest values. The sandwich structure of UCU composite with 50% UD reinforcement in the skin and 50% chopped fibre in core exhibited similar flexural properties in comparison to UUU composites, meeting the flexural property requirements of cortical bone. Furthermore, the degradation behaviour and mechanical performance of composites with different fibre architecture were analysed during the degradation process for 28 days. The UUU composites showed the most rapid degradation of the flexural performance. Meanwhile, a lower reduction of flexural properties was observed for UCU composites due to less susceptibility to wicking in discontinuous fibres. As such, the UCU composite could provide near flexural performance with better retention of properties during the degradation.

Tensile strength and thermal behavior of jute fibre reinforced polypropylene laminate composite

In the current era, sustainability and biodegradability are two necessary terms, which are related to the composite materials. Due to environmental sustainability use of the natural fibres as reinforcement is increased in composites for various applications as compared to glass fibre. In this research work, jute fibres are used as reinforcement due to the low cost and Polypropylene (PP) as matrix due to its ease of availability. The novelty of the work is to study the effect of plying of PP sheets on the tensile strength and thermal behavior of PP-Jute laminate composites by using simple hot press machine. Effect of polymer degradation due to repeated thermal processing on the mechanical performance of composite is also investigated. In this work the effect of the fibre cut length (3 cm, 6 cm and 9 cm), number of plies (1, 2 and 4) and fibre loading (0%, 5% and 10%) is studied. The structural, thermal and mechanical properties of the composites are investigated using X-Ray diffraction, tensile test, DSC and dynamic mechanical analysis. It is observed that the mechanical properties of composite improved up to 2 plies and deteriorate thereafter. Best results are obtained for 2-plied composites at all levels of fibre loading. Crystallinity percentage is reduced while crystallite size is increased in case of composites as compared to neat PP sheet. Jute-PP composites could be used for various applications in automobile industries, building components such as partitioning panels and similar applications.

Characterization of Mechanical Performance of Composites Fabricated Using Innovative Carbon Fiber Wet Laid Process

Recent innovation in production of optimized nonwoven wet laid (WL) carbon fiber (CF) mats raised the question of optimal translation of the performance and isotropy into composites formed through these dry preforms. This work explores the mechanical behavior of composites produced from WL-CF mats in conjunction with the microstructure predicted through Object Oriented Finite Element Analysis (OOF). The mats used for the composites were prepared in two dispersion regimes using 25.4 mm long CF. The mixing regimes discussed in the author’s previous work, are identified as Method 1 for the traditional processing regime and Method 2 for the innovative regime that provided optimal nonwoven WL-CF mats. Composite panels from Method 2 mats showed a normalized tensile strength increase of 52% over those from Method 1 panels. Reproducibility analysis of composites made from Method 2 mats demonstrated a standard deviation of 2% in fiber weight content, 2% in tensile modulus and 9% in tensile strength, while composites made from Method 1 mats demonstrated a standard deviation of 5% in fiber weight content, 5% in tensile modulus and 17% in tensile strength. Systematic study of the microstructure and its analysis through OOF confirmed the isotropy translation of mats produced through method 2 to the composites. This study validated the hypothesis that optimal nonwoven mats lead to a well-balanced composite with optimal performance and that non-optimal nonwoven mats do not pack into a well-balanced composite.

Rapid electrothermal-triggered flooded thermoset curing for scalable carbon/polymer composite manufacturing

Carbon-based (e.g. carbon fibers or carbon nanotube (CNT)) polymer composite materials, due to the high specific strength, and good chemical stability features, is a promising structural material for energy-efficient applications in aerospace and civil infrastructures. However, the difficulty of viscosity-related infusing and curing of polymer limits composite mechanical performance and manufacturing efficiency. Here we overcome these difficulties and report an electrothermal-triggered flooded thermoset curing to enable rapid and energy-efficient manufacturing of carbon/polymer composite. The underlying concept is based on the two-step localized in-situ infusion and curing in flooded polymer by Joule heating of carbon-based materials to facilitate the flow of polymer into the microstructure in low current, followed by curing of polymer resin in high current. The viscosity adjustment and defoaming process in the infusing process and the curing properties (degree of cure and strength) of the composites were used to prove the effectiveness of this curing strategy in composite fabrication. This electrothermal-triggered curing approach provides a rapid, energy-efficient, scalable, and volumetric composite manufacturing technique.

Characterization of poly-hydroxybutyrate/luffa fibers composite material

Luffa fibers were evaluated as a reinforcement material in poly-hydroxy-butyrate matrix composites. The treatments consisted of varying the incorporation percentage of mercerized and non-mercerized luffa fibers in a poly-hydroxybutyrate (PHB) matrix (5%, 10%, and 20% w/v). Composites made with PHB and reinforced with luffa fibers (treated and non-treated) were mechanically evaluated (tensile strength, Young’s modulus, and percentage of elongation at break), the surface morphology was described by using scanning electronic microscopy, and the degradability behavior of composites was obtained. According to the results, mechanical properties decreased when the percentage of fibers increased and no significant effects were observed when compared with mercerized fiber composites. Degradability tests demonstrated that the weight loss increased with increased fiber content in composites, independent of the applied pretreatments. Microscopy images exhibited that mercerization improved the fiber incorporation into the polymeric matrix, diminishing the “pull out” effect; the above-mentioned result was supported by using the Fourier-transform infrared spectroscopy technique, observing the reduction of lignin and hemicellulose peaks in mercerized fibers. Based on the composite mechanical performance and degradability behavior, it was concluded that this material could be used in the packaging sector as biodegradable secondary packaging material.

Tribological characterization of LM26/SiC/Ni.-Gr. Hybrid aluminium matrix composites (HAMCs) for high temperature applications

In this study, tribological characteristics of the hybrid composite material LM26/ SiC / Ni.-Gr. were studied under different temperature conditions. The LM26 aluminum alloy was reinforced with silicon carbide (SiC) with various weight fractions (0%, 10% and 20%) by keeping nickel-coated graphite (Ni.-Gr.) constant at 2%. Using stir casting setup wear test samples were prepared. Pin on disk equipment was used to assess the tribological performance of both pure aluminum alloy and hybrid composites on the basis of wear loss and friction coefficient. Further, the plan order for performing trials was developed with design of experiments (DOE) and analysis of variance (ANOVA) tools. It was found that the composite's tribological and mechanical performance under high temperature sliding wear conditions was improved because of the hybridization of hard and soft reinforcements. Experimental results revealed that load and temperature primarily affect both pure aluminum alloys and hybrid composites performance. Also low wear loss and friction coefficient were obtained during high-temperature wear tests. The LM26 + 20% SiC + 2%Ni.-Gr.hybrid composite showed the highest improvement in tribological performance. Worn surface analysis using SEM technique showed that hybrid reinforcement significantly increases wear resistance in hybrid aluminum composites. These findings indicate that the proposed hybrid aluminum composites can be considered as an alternative material in which wear-resistant and high-strength components are of primary importance in the automotive industry.

Failure simulation and design optimization of bioinspired heterogeneous interfaces by Floquet-based bar-spring model

Interface plays a critical role in the mechanical performance of composites. Lack of a suitable interface design has long been a bottleneck impeding the full exploitation of the mechanical strengths of many superior reinforcement phases such as the high-performance carbon fibers and carbon nanotubes. Here a Floquet-based bar-spring model is developed to simulate the elastic and failure behaviors of three topological designs of heterogeneous interface inspired by the load-bearing biological materials in nature: end-concentrated, center-concentrated, and uniform pattern. Through comparative analyses, the advantages and disadvantages of every topological design are presented, and the guidelines of design optimization are summarized. The newly developed method is convenient and computationally economical for studying the mechanical behaviors of fiber/platelet reinforced composites. The study on the bioinspired design of interfaces not only shed lights on the interface strengthening and toughening mechanisms in natural materials but also give valuable guidelines for artificial interface designs.

Enhancing Mechanical Performance of Bagasse Fiber-Epoxy Composite by Surface Treatment

Surface treatment is one of the method used to enhance the mechanical performance of natural fiber composite by improving the compatibility of fiber and matrix. Nevertheless, no proof can be shown on which surface treatment is the absolute solution in improving the mechanical properties of natural fiber composite. Different surface treatments might have needed for different kinds of natural fiber composites. In this research work, water, alkaline, permanganate, bleaching and acetylation treatment on bagasse fiber are evaluated and the effect of soaking temperature as well as the effect of fiber loading are investigated. The mechanical performance of bagasse fiber-epoxy composite was studied by carrying out three-point bending test and optical microscopy test. Among 0w/w% and 5w/w% fiber loading, composite with 1w/w% and 2w/w% fiber loading possessed the highest flexural strength and modulus respectively. However, poor wettability between fiber and matrix was observed at higher fiber loading. Water, bleaching, permanganate and acetylation treatment have minor positive effect on the mechanical performance of the composite, yet a great increment in flexural properties of alkali treated fiber composite was noticed such that 21.48% and 23.95% of improvement was made on flexural strength and flexural modulus respectively. Optical microscopy test indicated that alkali treatment is responsible for roughening the fiber surface, and improving the fiber wettability and dispersion. Depend on the surface treatment, effect of soaking temperature may vary. In some treatments, hotter soaking temperature led to faster rate of reaction, which resulted in greater surface roughening and greater cleansing effect. Despite of that, over reaction can be happened in some cases, which will result in lower flexural properties due to over damaged fiber. Hence, it was concluded that the alkaline treatment at room temperature could be the most effective surface treatment to enhance the mechanical performance of bagasse fiber-epoxy composite.

TiO2 reinforced high-performance epoxy-co-polyamide composite coatings

Epoxy-based protective coatings for outdoor and marine applications are commonly used to protect metals and alloys, and architectural elements against the environmental impact. An epoxy-co-polyamide (EP-PA) polymer is synthesized by reacting pre-polymers: epoxy and polyamide resins. TiO2 nanoparticles of different sizes are embedded into EP-PA copolymer to form composite coatings on the Teflon substrate, referred to as EP-PA/TiO2. TiO2 content is varied from 0.1 to 1.0 wt.% and the electrical, thermal, and mechanical performance of composites is analyzed. Both EP-PA polymer and EP-PA/TiO2 composite coatings are characterized by FTIR spectroscopy and electron microscopy. EP-PA/TiO2 composites exhibit a uniform distribution of individual TiO2 nanoparticles in the EP-PA matrix at low TiO2 content, while some aggregates are observed at the higher TiO2 content. The size effect of TiO2 nanoparticles is also demonstrated by clear differences in the surface topography, size distribution, extent of agglomeration, and surface roughness of the EP-PA/TiO2 composites. TiO2 nanoparticles have lower surface energy and therefore, increase the hydrophobic character of the composite coatings that is revealed by the increasing water droplet contact angle. The surface resistivity of EP-PA/TiO2 composites decreased with the increasing TiO2 content, while thermal degradation temperatures are improved by 100 K (15.7 %) compared to neat EP-PA polymer. The mechanical properties such as yield strength and Young’s modulus are also enhanced by 56.9 % and 32.7 %, respectively at 1.0 wt.% TiO2 loading, while the toughness of EP-PA/TiO2 composites is comparable to the neat polymer. The remarkable enhancement in the hydrophobic character, electrical conductivity, thermal stability, and mechanical performance of EP-PA/TiO2 composites at low TiO2 content (1.0 wt.%) is achieved by the small size, high surface area, and excellent dispersion of nanoparticles in the polymeric matrix. The simultaneous improvement in properties suggests EP-PA/TiO2 composites useful as protective coatings for a variety of applications in the harsh environment.

Ligno-Cellulosic Fibre Sized with Nucleating Agents Promoting Transcrystallinity in Isotactic Polypropylene Composites.

The mechanical performance of composites made from isotactic polypropylene reinforced with natural fibres depends on the interface between fibre and matrix, as well as matrix crystallinity. Sizing the fibre surface with nucleating agents to promote transcrystallinity is a potential route to improve the mechanical properties. The sizing of thermo-mechanical pulp and regenerated cellulose (Tencel™) fibres with α- and β-nucleating agents, to improve tensile strength and impact strength respectively, was assessed in this study. Polarised microscopy, electron microscopy and differential scanning calorimetry (DSC) showed that transcrystallinity was achieved and that the bulk crystallinity of the matrix was affected during processing (compounding and injection moulding). However, despite substantial changes in crystal structure in the final composite, the sizing method used did not lead to significant changes regarding the overall composite mechanical performance.

Mechanical properties obtained by nanoindentation of sintered zircon–glass matrix composites

This study was undertaken to determine the effect of zircon content and firing temperature on the hardness and indentation modulus of zircon–glass composites obtained by sintering. A standard non-devitrified borosilicate glass (SRM 717a) powder and an industrial micrometric zircon powder were used to prepare mixtures with a zircon volume/solids volume between 0 and 0.63, by the wet method. The values of these mechanical properties were determined by nanoindentation and related to the most important microstructural characteristics of the composites, such as porosity, zircon volume fraction, glass volume fraction, and average zircon grain size. Composite mechanical performance was interpreted and determined by statistically analysing the results of a large number of indentations using two maximum loads. An empirical model was developed that describes the effect of these microstructural characteristics on composite hardness and modulus of indentation. Composites of high hardness (11.3 ± 2.5 GPa) and low porosity (ε = 0.07) were obtained at 1100 °C from a mixture with a zircon volume/solids volume of 0.43.