A review of the tensile and fatigue responses of cellulosic fibre-reinforced polymer composites

ABSTRACT

The use of polymer-based composites has been gaining popularity in the industry over the last few decades. Their high strength to weight ratio and high fatigue resistance make these composites the preferred materials for a wide variety of applications. The current trend has inclined towards hybrid fibre reinforced composites owing to their outstanding characteristics compared to non-hybrid composites. Numerous research works have been conducted to study the fatigue life behaviour of such composite materials. This study addressed the monotonic and dynamic performance of non-hybrid and hybrid natural fibre based composite materials, and the factors that influence their fatigue performance, along with the stiffness decay of each composite material. Most studies have shown the superior potential of using natural fibres in place of synthetic fibres in those critical applications that involve tensile and cyclic loading.     

Recycled carbon fibre-reinforced polypropylene thermoplastic composites

Comingled carbon fibre (CF)/polypropylene (PP) yarns were produced from chopped recycled carbon fibres (reCF) (20 mm in length, 7-8 μm diameter) blended with matrix polypropylene staple fibres (60 mm in length, 28 μm diameter) using a modified carding and wrap spinning process. Microscopic analysis showed that more than 90% of the reCF were aligned along the yarn axis. Thermoplastic composite test specimens fabricated from the wrap-spun yarns had 15-27.7% reCF volume content. Similar to the yarn, greater than 90% of the reCF comprising each composite sample made, showed a parallel alignment with the axis of the test specimens. The average values obtained for tensile, and flexural strengths were 160 MPa and 154 MPa, respectively for composite specimens containing 27.7% reCF by volume. It was concluded that with such mechanical properties, thermoplastic composites made from recycled CF could be used as low cost materials for many non-structural applications.     

The utilization of bamboo charcoal enhances wood plastic composites with excellent mechanical and thermal properties

In order to enhance the mechanical properties and thermal properties of wood plastic composites (WPCs), bamboo charcoal (BC) was used as reinforcing filler of WPC, and a series of BC-WPC composites were prepared. The effect of BC and water treatment on water absorptions, morphologies, mechanical properties, the effect of water treatment on mechanical properties and thermal properties of the composites were investigated. The results showed that BC could have strong interfacial interaction in the WPC. The water resistance, flexural properties, tensile properties and thermal properties of BC-WPC were higher than WPC. The flexural and tensile properties were reduced and the impact strength was increased after water treatment. The presence of BC resists the influence of water absorption on composites mechanical properties.     

The mechanical properties of oxyfluorinated hybrids of glass fibre and polypropylene fibre

The mechanical properties of a low-cost system comprising orthophthalic polyester resin reinforced with hybrids of glass and polypropylene fibres were investigated. The fibres were oxyfluorinated to overcome the poor surface adhesion properties of polypropylene. Interlaminar shear tests, Izod-type impact tests and tensile tests were considered. It would be expected that increasing polypropylene fibre content corresponds with a decrease in mechanical properties due to the poor properties of polypropylene. Oxyfluorinated laminates containing approximately 25% and 50% polypropylene in the warp direction were, however, found to exhibit significant improvements in interlaminar shear strength, in peak shear stress under impact loading as well as in impact resistance over untreated glass fibre laminates. Scanning electron microscope images show that the reason for this improvement is that the interfacial bond between the polypropylene fibres and the resin is strengthened to such an extent that failure occurs within the polypropylene fibres rather than at the interface.     

Influence of moisture uptake on the static,cyclic and dynamic behaviour of unidirectional flax fibre-reinforced epoxy laminates

This papers aims to characterize the influence of moisture uptake on the mechanical behaviour of unidirectional flax fibre-reinforced epoxy laminates. Monotonic and cyclic tensile tests and free vibration characterization are carried out. Results show that UD flax-epoxy composites, when exposed to hygrothermal conditioning at 70 °C and 85% RH, exhibit a diffusion kinetic which follows a one dimensional Fickian behaviour. The mass uptake at equilibrium is approximately 3.3% and the diffusion coefficient 6.5 × 10⁻⁶ m² s⁻¹. Water vapour sorption is shown to induce a significant change in the shape of the tensile stress-strain curve, a decrease in the dynamic elastic modulus of about 20% and a 50% increase in the damping ratio. Contrary to all expectations, water saturation does not degrade the monotonic tensile strength of such a flax-epoxy composites and leads to an increase in the fatigue strength for a high number of cycles.     

Effect of Bonder at Skin/Core Interface on the Mechanical Performances of Sandwich Structures Used in Marine Industry

The present work is aimed to extend the knowledge of mechanical properties of sandwich structures used for marine applications focusing on the possibility to increase the performances of such structures by adding a bonder at the skin/core interface. Therefore, three sandwich structures that are utilised in different structural components of a yacht were realised by manual lay-up. The mechanical characterisation was performed by flatwise compressive, edgewise compressive and three point flexural tests. The tests execution has allowed both to determine the mechanical performances and to understand the fracture mechanisms that take place when the bonder is added in the stacking sequence of the samples.     

Natural fibre-reinforced composites for bioengineering and environmental engineering applications

Recently, the mankind has realized that unless environment is protected, he himself will be threatened by the over consumption of natural resource as well as substantial reduction of fresh air produced in the world. Conservation of forests and optimal utilization of agricultural and other renewable resources like solar and wind energies, and recently, tidal energy have become important topics worldwide. In such concern, the use of renewable resources such as plant and animal based fibre-reinforce polymeric composites, has been becoming an important design criterion for designing and manufacturing components for all industrial products. Research on biodegradable polymeric composites, can contribute for green and safe environment to some extent. In the biomedical and bioengineered field, the use of natural fibre mixed with biodegradable and bioresorbable polymers can produce joints and bone fixtures to alleviate pain for patients. In this paper, a comprehensive review on different kinds of natural fibre composites will be given. Their potential in future development of different kinds of engineering and domestic products will also be discussed in detail.     

Can thermally degraded glass fibre be regenerated for closed-loop recycling of thermosetting composites?

Commercially manufactured E-glass fibres were heat-conditioned to mimic the effects of thermal recycling of glass fibre thermosetting composites. Degradation in the strength and surface functionality of heat-treated fibres was identified as a key barrier to reusing the fibres as valuable reinforcement in composite applications. A chemical approach has been developed to address these issues and this included two individual chemical treatments, namely chemical etching and post-silanisation. The effectiveness of the treatments was evaluated for both thermal degraded fibres and corresponding composites. Drastic reduction was observed in the properties of the composites with the heat-conditioned preforms indicating thermally degraded glass fibres have no value for second-life reinforcement without further fibre regeneration. However, significant regeneration to the above properties was successfully obtained through the approach developed in this work and the results strongly demonstrated the feasibility of regeneration of thermally degraded glass fibres for potential closed-loop recycling of thermosetting composites.     

Effect of surface treatment on performance of pineapple leaf fiber–polycarbonate composites

This research is to study the properties of pineapple leaf fiber reinforced polycarbonate composites (PC/PALF). Surface of pineapple leaf fiber (PALF) was pre-treated with sodium hydroxide (PALF/NaOH) and modified with two different functionalities such as γ-aminopropyl trimethoxy silane (PALF/Z-6011) and γ-methacryloxy propyl trimethoxy silane (PALF/Z-6030). The effects of PALF content and chemical treatment were investigated by Fourier transform infrared spectroscopy, scanning electron microscopy and mechanical testing. The modified pineapple leaf fibers composite also produces enhanced mechanical properties. Young’s modulus is the highest in the case of the PALF/NaOH composites. The PALF/Z-6011 composites showed the highest tensile strength and impact strength. In thermal property, the results from thermogravimetric analysis showed that thermal stability of the composites is lower than that of neat polycarbonate resin and thermal stability decreased with increasing pineapple leaf fiber content.     

Fabrication of toughened Cf/SiC whisker composites and their mechanical properties

In this paper, dense short carbon fiber reinforced silicon carbide matrix composites had been fabricated by hot-pressed (HP) sintering using Al₂O₃ and La₂O₃ as sintering additives. The results showed that the combination of Al₂O₃ and La₂O₃ system was effective to promote densification of short cut carbon fiber reinforced silicon carbide composites (Cf/SiC). The whisker structure of silicon carbide was formed during the annealed treatment at 2023 K for 1 h. However, it was noted that this structure was not observed in the as-received HP material. The mechanism of forming whisker structure was not clear, but this kind of whisker structure was helpful to improve mechanical properties. The combination of grain bridging, crack deflection and whisker debonding would improve the fracture toughness of the Cf/SiC composites.     

A comparative study of fatigue behaviour of flax/epoxy and glass/epoxy composites

Experimental investigations on flax and glass fabrics reinforced epoxy specimens, i.e. FFRE and GFRE, submitted to fatigue tests are presented in this paper. Samples having [0/90]_3S and [±45]_3S stacking sequences, with similar fibre volume fractions have been tested under tension–tension fatigue loading. The specific stress-number of cycles to failure (S–N) curves, show that for the [0/90]_3S specimens, FFRE have lower fatigue endurance than GFRE, but the [±45]_3S FFRE specimens offer better specific fatigue endurance than similar GFRE, in the studied life range (<2 × 10⁶). Overall, the three-stage stiffness degradation is observed in all cases except for [0/90]_3S FFRE specimens, which present a stiffening phenomenon of around 2–3% which could be related to the straightening of the microfibrils.     

Microstructure and room temperature fracture toughness of cast Nbss/silicides composites alloyed with Hf

The effect of Hf addition on microstructure and room temperature fracture toughness of cast Nb-16Si alloy was investigated. The Hf addition changes significantly the microstructural morphology of Nb-16Si alloys, which includes microstructure refinement and disappearance of eutectic colonies. Fracture toughness of the alloys improves with increasing Hf content. The improvement in fracture toughness is mainly attributed to the microstructural change by Hf addition. The Hf addition leads to a transition of Nb solid solution fracture manner from brittle cleavage to plastic stretching.     

The effect of molecular weight on the interfacial properties of GF/PP injection molded composites

It is well established that the molecular weight of recycled PP decreases significantly as compared to the virgin material. Hence this study involved 2 PP grades of different molecular weights in order to simulate the recycling process. The effect of weight–average molecular weight on interfacial adhesion between GF and PP was investigated. Tensile test was done and the fiber length distribution around the fracture zone in both composites was compared with the distributions from similar locations of unstressed composites. The effect of PP-grafted maleic anhydride coupling agent was also studied. It was found that a decrease in weight–average molecular weight of PP improved interfacial adhesive strength between GF/PP. The lower molecular weight matrix has a lower viscosity that enables its molecules to penetrate easily into the silane interphase. In that case, the interfacial area that is available for coupling is higher, leading to a more effective coupling. The higher interfacial shear strength between the glass fiber and the lower molecular weight matrix induced more breakage of the glass fiber during tensile test.     

Macro and micromechanics analysis of short fiber composites stiffness: The case of old newspaper fibers–polypropylene composites

Stiffness is one of the most relevant characteristics of composite materials. Natural wood fibers have demonstrated their ability to increase the Young’s moduli of composite materials, and old newspapers are a potential source of reinforcing fibers for composite materials. There are some micromechanic models to predict the Young’s modulus of composite materials, and one of the input data is the intrinsic modulus of their fibers. This intrinsic modulus is a value which is difficult or impossible to measure in the case of wood fibers, due to their measures. This paper evaluates the stiffening abilities of old newspaper fibers and the possibility to back calculate the value of the intrinsic Young’s modulus by means of micromechanic models. Different percentages of old newspaper fibers were compounded with polypropylene (PP). Micromechanics of the fibers were obtained using Hirsch model, Cox–Krenchel’s model, Tsai–Pagano model and Halpin–Tsai equations. The most important results were the average intrinsic Young’s modulus of the fibers, the mean orientation angle and the mean modulus efficiency factor.     

Evaluation of creep compliances of unidirectional fibre-reinforced composites

In this paper, a method is proposed for the determination of the viscoelastic behaviour of unidirectional fibre-reinforced composites. The method is based on the model of Laws and McLaughlin. The interface problem is taken into account by using anisotropic elastic coefficients for the fibre. The non-linearity of the matrix is also considered and integrated in the model. Comparisons with experimental data are performed on glass/epoxy materials.     

Compressive failure of hybrid multidirectional fibre-reinforced composites

In this paper, the hybridisation of multidirectional carbon fibre-reinforced composites as a means of improving the compressive performance is studied. The aim is to thoroughly investigate how hybridisation influences the laminate behaviour under different compression conditions and thus provide an explanation of the “hybrid effect”. The chosen approach was to compare the compressive performance of two monolithic carbon fibre/epoxy systems, CYTEC HTS/MTM44-1 and IMS/MTM44-1, with that of their respective hybrids. This was done by keeping the same layup throughout ((0/90/45/−45)_2S) while replacing the angle plies in one case or the orthogonal plies in the other case with the second material, thus producing two hybrid systems. To investigate the compressive performance of these configurations, compact and plain compression test methods were employed which also allowed studying the sensitivity of compressive failure to specimen geometry and loading conditions. The experimental results and the subsequent fractographic analysis revealed that the hybridisation of selective ply interfaces influenced the location and severity of the failure mechanisms. Finally, in light of this knowledge, an update of the generic sequence of events, previously suggested by the authors, which lead to global fracture in multidirectional fibre-reinforced composites under compression is presented.     

Thermal conductivity and thermal diffusivity analyses of low-density polyethylene composites reinforced with sisal, glass and intimately mixed sisal/glass fibres

The thermal conductivity and thermal diffusivity of sisal-reinforced polyethylene (SRP), glass-reinforced polyethylene (GRP) and sisal/glass hybrid fibre-reinforced polyethylene (GSRP) has been evaluated at cryogenic to high temperature (120–350 K). It has been observed that the variation of thermal conductivity with temperature is almost the same for LDPE and SRP containing perpendicularly oriented sisal fibres. The difference between the values of thermal conductivity shown by LDPE and GRP is greater than that of SRP and LDPE. The enhanced thermal conductivity of glass fibre is due to the presence of Fe²⁺ ions in the glass fibres. The linear variation in thermal conductivity with fibre loading is explained with the help of a model suggested by Agari. The difference between the thermal conductivity properties in directions parallel and perpendicular to the applied flux is a maximum for SRP owing to the anisotropic nature of sisal fibre. The difference is marginal for GRP on account of its isotropic nature. The position of GSRP is found to be intermediate. It can been observed that the variation of thermal diffusivity with temperature is just opposite to that of thermal conductivity. This may be due to a reduction in the mean free path of phonons. An empirical equation is derived to explain the variation in thermal conductivity and thermal diffusivity with temperature.     

Electro-mechanical moduli of three-phase fiber composites

Analytical expressions of effective properties for three-phase piezoelectric unidirectional composites are reported. Using Asymptotic Homogenization scheme for periodic media, very simple effective moduli are determined. The model includes one interphase separating the reinforcement inclusion phase from the host matrix. It can be used to have a better control of the composite properties and to improve sensor applications.     

Processing of Al/B4C composites by cross-roll accumulative roll bonding

In the present study, Al/B₄C composites were successfully produced in the form of sheets, through accumulative roll bonding (ARB) and cross-roll accumulative roll bonding (CRARB) processes. The CRARB process was performed in two steps. In the first step, the strips were roll-bonded with a draft percentage of 66% reduction, while in the second step the strips were roll-bonded with a draft percentage of 50%. The results indicated that the dispersion of the B₄C particles in the CRARB process is more homogeneous than the ARB process. In addition, the tensile strength of the CRARBed composite is higher than that of the ARBed composite.     

Solvent exfoliated graphene for reinforcement of PMMA composites prepared by in situ polymerization

Graphene (GP)-based polymer nanocomposites have attracted considerable scientific attention due to its pronounced improvement in mechanical, thermal and electrical properties compared with pure polymers. However, the preparation of well-dispersed and high-quality GP reinforced polymer composites remains a challenge. In this paper, a simple and facile approach for preparation of poly(methyl methacrylate) (PMMA) functionalized GP (GPMMA) via in situ free radical polymerization is reported. Fourier transform infrared (FTIR), X-ray photoelectron spectra (XPS), Raman, transmission electron microscope (TEM) and thermogravimetric analysis (TGA) are used to confirm the successful grafting of PMMA chains onto the GP sheets. Composite films are prepared by incorporating different amounts of GPMMA into the PMMA matrix through solution-casting method. Compared with pure PMMA, PMMA/GPMMA composites show simultaneously improved Young's modulus, tensile stress, elongation at break and thermal stability by addition of only 0.5 wt% GPMMA. The excellent reinforcement is attributed to good dispersion of high-quality GPMMA and strong interfacial adhesion between GPMMA and PMMA matrix as evidenced by scanning electron microscope (SEM) images of the fracture surfaces. Consequently, this simple protocol has great potential in the preparation of various high-performance polymer composites.