Quantifying variability within glass fibre reinforcements using an automated optical method

This paper presents a novel optical technique to quantify in-plane geometric variations within dry glass fibre reinforcement materials. Samples of up to 290 × 450 mm can be examined. Three different reinforcement structures have been studied; a random mat, a plain weave and a stitched bi-axial fabric. Using an empirically derived function, reinforcement areal weight has been predicted locally from a single reinforcement photograph. It was found that areal weight predictions were typically within 5% of experimentally obtained values for 25.4 mm square samples. For periodically structured (woven or stitched) reinforcements, local information describing the tow orientation and geometry has been collected automatically. Manual verification of the reinforcement geometry showed good agreement with the automated technique. 3D textile models have been created within a textile modelling software that include the measured variability.     

High performance hybrid PP and PLA biocomposites reinforced with short man-made cellulose fibres and softwood flour

This paper presents the research on hybrid thermoplastic biocomposites reinforced with a combination of short man-made cellulose fibres and softwood flour. The introduced short fibre composites are meant to be processed with injection moulding and may be an alternative to glass-fibre reinforced thermoplastics on account of their comparable specific strengths. The occurring positive hybrid effect enables to substitute up to half the weight of short fibre cellulose reinforcement with softwood flour without a significant reduction of material flexural strength. The flexural modulus of investigated hybrid biocomposites remained approximately at the same level, while impact strength was reduced with increasing softwood flour content. The proposed hybridisation leads to establishing biocomposites of suitable performance with competitive density, price and recycling possibilities in comparison to standard glass fibre reinforced counterparts. Moreover, the application of biobased polymers like polylactide as biocomposite matrix, contributes to the development of so called “green” high performance materials.     

Regenerating the strength of thermally recycled glass fibres using hot sodium hydroxide

Results are presented from the ReCoVeR project on the regeneration of the strength of thermally conditioned glass fibres. Thermal recycling of end-of-life glass fibre reinforced composites or composite manufacturing waste delivers fibres with virtually no residual strength or value. Composites produced from such fibres also have extremely poor mechanical performance. Data is presented showing that a short hot sodium hydroxide solution treatment of such recycled fibres can more than triple their strength and restore their ability to act as an effective reinforcement in second life composite materials. The implications of these results for real materials reuse of recycled glass fibres as replacement for pristine reinforcement fibres are discussed.     

Flax fibre and its composites – A review

In recent years, the use of flax fibres as reinforcement in composites has gained popularity due to an increasing requirement for developing sustainable materials. Flax fibres are cost-effective and offer specific mechanical properties comparable to those of glass fibres. Composites made of flax fibres with thermoplastic, thermoset, and biodegradable matrices have exhibited good mechanical properties. This review presents a summary of recent developments of flax fibre and its composites. Firstly, the fibre structure, mechanical properties, cost, the effect of various parameters (i.e. relative humidity, various physical/chemical treatments, gauge length, fibre diameter, fibre location in a stem, oleaginous, mechanical defects such as kink bands) on tensile properties of flax fibre have been reviewed. Secondly, the effect of fibre configuration (i.e. in forms of fabric, mat, yarn, roving and monofilament), manufacturing processes, fibre volume, and fibre/matrix interface parameters on the mechanical properties of flax fibre reinforced composites have been reviewed. Next, the studies of life cycle assessment and durability investigation of flax fibre reinforced composites have been reviewed.     

Morphology, dynamic mechanical and thermal studies on poly(styrene-co-acrylonitrile) modified epoxy resin/glass fibre composites

Poly(styrene-co-acrylonitrile) (SAN) was used to modify diglycidyl ether of bisphenol-A (DGEBA) type epoxy resin cured with diamino diphenyl sulfone (DDS) and the modified epoxy resin was used as the matrix for fibre reinforced composites (FRPs) in order to get improved mechanical and thermal properties. E-glass fibre was used as the fibre reinforcement. The morphology, dynamic mechanical and thermal characteristics of the systems were analyzed. Morphological analysis revealed heterogeneous dispersed morphology. There was good adhesion between the matrix polymer and the glass fibre. The dynamic moduli, mechanical loss and damping behaviour as a function of temperature of the systems were studied using dynamic mechanical analysis (DMA). DMA studies showed that DDS cured epoxy resin/SAN/glass fibre composite systems have two T_gs corresponding to epoxy rich and SAN rich phases. The effect of thermoplastic modification and fibre loading on the dynamic mechanical properties of the composites were also analyzed. Thermogravimetric analysis (TGA) revealed the superior thermal stability of composite system.     

Hyperelastic modelling for mesoscopic analyses of composite reinforcements

A hyperelastic constitutive law is proposed to describe the mechanical behaviour of fibre bundles of woven composite reinforcements. The objective of this model is to compute the 3D geometry of the deformed woven unit cell. This geometry is important for permeability calculations and for the mechanical behaviour of the composite into service. The finite element models of a woven unit cell can also be used as virtual mechanical tests. The highlight of four deformation modes of the fibre bundle leads to definition of a strain energy potential from four specific invariants. The parameters of the hyperelastic constitutive law are identified in the case of a glass plain weave reinforcement thanks to uniaxial and equibiaxial tensile tests on the fibre bundle and on the whole reinforcement. This constitutive law is then validated in comparison to biaxial tension and in-plane shear tests.     

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.     

Compression moulding of glass and polypropylene composites for optimised macro- and micro- mechanical properties-1 commingled glass and polypropylene

The continuing desire in the automotive industry to reduce cost and weight while increasing safety requires innovative materials and processing routes. Glass-mat-reinforced thermoplastics have been used to produce semi-structural components but a higher and aligned glass fibre content is required in moulding materials for structural applications. Experimental design was used to investigate the non-isothermal processing of commingled fabrics which were woven from yarns of intimately mingled glass and polypropylene fibres. Processing models were generated by regression techniques to predict laminate properties over a range of processing conditions. Void contents were measured by image analysis techniques. Preheat temperature had the greatest effect on laminate flexural properties and porosity. A compaction time of 54 s was required to consolidate, cool and reduce the void content in laminates. A two-fold increase in stiffness was found compared with equivalent glass-mat-reinforced thermoplastic laminates. The intimate distribution of matrix and reinforcement reduced moulding pressures by a factor of 10.     

Experimental and theoretical studies on the properties of injection moulded glass fibre reinforced mixed plastics composites

Recycled mixed post-consumer and post-industrial plastic wastes consisting of HDPE, LDPE and PP were injection moulded with short glass fibre (10–30% by weight) to produce a new generation composite materials. Intensive experimental studies were then performed to characterise the tensile, compression and flexural properties of glass fibre reinforced mixed plastics composites. With the addition of 30 wt.% of glass fibre, the strength properties and elastic modulus increased by as much as 141% and 357%, respectively. The best improvement is seen in the flexural properties due to the better orientation of the glass fibres in the longitudinal direction at the outer layers. The randomness and length of the glass fibre were accounted to modify the existing rule of mixture and fibre model analysis to reliably predict the elastic and strength properties of glass fibre reinforced mixed plastics composites.     

Effect of the stochastic nature of the constituents parameters on the predictability of the elastic properties of fibrous nano-composites

The stochastic nature and the variability of the constituents of nano-composites materials affect the predictability of their properties. The few studies that dealt with the probabilistic nature of the micromechanics of fibrous nano-composites, focused on the effect of statistical variation of individual parameters. This study presents a systematic analysis of the influence of parameter randomness on the theoretical predictions of the elastic properties of nano-composites. To this end, Monte-Carlo simulations are performed using a modified version of the Mori–Tanaka Mean-Field theory under different combinations of parameter randomness. The results indicate that the randomness in interface imperfection, fibre orientation and length, and fibre stiffness have a significant influence on the variability of the composite properties. The analysis provided an insight into the sensitivity of the predictions of the elastic tensor to the probabilistic variations of the aforementioned parameters. A probabilistic model for the effective properties is called for in place of deterministic models.     

A short review on basalt fiber reinforced polymer composites

A recent increase in the use of ecofriendly, natural fibers as reinforcement for the fabrication of lightweight, low cost polymer composites can be seen globally. One such material of interest currently being extensively used is basalt fiber, which is cost-effective and offers exceptional properties over glass fibers. The prominent advantages of these composites include high specific mechano-physico-chemical properties, biodegradability, and non-abrasive qualities to name a few. This article presents a short review on basalt fibers used as a reinforcement material for composites and discusses them as an alternative to the use of glass fibers. The paper also discusses the basics of basalt chemistry and its classification. Apart from this, an attempt to showcase the increasing trend in research publications and activity in the area of basalt fibers is also covered. Further sections discuss the improvement in mechanical, thermal and chemical resistant properties achieved for applications in specific industries.     

Deformation micromechanics of a model cellulose/glass fibre hybrid composite

Interfacial stress transfer in a model hybrid composite has been investigated. An Sm³⁺ doped glass fibre and a high-modulus regenerated cellulose fibre were embedded in close proximity to each other in an epoxy resin matrix dumbbell-shaped model composite. This model composite was then deformed until the glass fibre fragmented. Shifts of the absolute positions of a Raman band from the cellulose fibre, located at 1095 cm⁻¹, and a luminescence band from a doped glass fibre, located at 648 nm, were recorded simultaneously. A calibration of these shifts, for both fibres deformed in air, was used to determine the point-to-point distribution of strain in the fibres around the breaks in the glass fibre. Each break that occurred in the glass fibre during fragmentation was shown to generate a local stress concentration in the cellulose fibre, which was quantified using Raman spectroscopy. Using theoretical model fits to the data it is shown that the interfacial shear stress between both fibres and the resin can be determined. A stress concentration factor (SCF) was also determined for the regenerated cellulose fibre, showing how the presence of debonding reduces this factor. This study offers a new approach for following the micromechanics of the interfaces within hybrid composite materials, in particular where plant fibres are used to replace glass fibres.     

Hybrid effects in thin ply carbon/glass unidirectional laminates: Accurate experimental determination and prediction

Experimental results are presented which allow the hybrid effect to be evaluated accurately for thin ply carbon/epoxy–glass/epoxy interlayer hybrid composites. It is shown that there is an enhancement in strain at failure of up to 20% for very thin plies, but no significant effect for thicker plies. Hybrid specimens with thick carbon plies can therefore be used to measure the reference carbon/epoxy failure strain. The latter is significantly higher than the strain from all-carbon specimens in which there is an effect due to stress concentrations at the load introduction. Models are presented which illustrate the mechanisms responsible for the hybrid effect due to the constraint on failure at both the fibre and ply level. These results give a good understanding of how variability in the carbon fibre strengths can translate into hybrid effects in composite laminates.     

The effect of mechanical defects on the strength distribution of elementary flax fibres

Flax fibres are finding non-traditional applications as reinforcement of composite materials. The mechanical properties of fibres are affected by the natural variability in plant as well as the damage accumulated during processing, and thus have considerable variability that necessitates statistical treatment of fibre characteristics. The strength distribution of elementary flax fibres has been determined at several fibre lengths by standard tensile tests, and the amount of kink bands in the fibres evaluated by optical microscopy. Strength distribution function, based on the assumption that the presence of kink bands limits fibre strength, is derived and found to provide reasonable agreement with test results.     

Analysis of knitted fabric reinforced composites: Part II. Stiffness and strength

The influence of the knit structure on the stiffness and strength in tensile and in share loading of glass warp knitted fabric epoxy composites is studied. The average strength depends on the fibre content and on the linear density of the yarn. The anisotropy in tensile and shear properties is related to the orientation tensor components a₁₁₁₁ and a₁₁₂₂, respectively. By making use of these relationships, a knit structure can be evaluated with regard to the mechanical properties of its composite with only two measurements: (1) measurement of the achievable fibre content; and (2) measurement of the fibre orientations.     

Nanoparticles with various surface modifications as functionalized cross-linking agents for composite resin materials

The performance of epoxy resins used for carbon fibre reinforced plastics can be significantly improved by the incorporation of nanoparticles. It is well known that the effect of material altering depends on many factors as filler material, particle distribution, particle size and shape. This paper investigates the hypothesis that particle surface modifications lead to a further improvement of the mechanical properties. Results of nanocomposites filled with four different surface modified boehmite particles are presented. The material was tested with different filler contents and analysed for chemical bonding, viscosity, thermal properties and bending performance. Surprising results show a strong influence of the surface modification on the viscosity, but no significant changes in the other material characteristics. The change of filler content in contrast has an influence on all tested performances of the nanocomposites. The results show a contrary effect of network interruption due to sterical hindrance by the particles and reinforcement due to the stiff ceramic fillers. For different filler contents these two effects have a varying influence on the material characteristics. From these results a model for the mechanism of the particle reinforcement in thermosets is concluded, which helps to understand the effectiveness of nanoparticles as reinforcement of epoxy resins.     

Impact and post-impact damage characterisation of hybrid composite laminates based on basalt fibres in combination with flax,hemp and glass fibres manufactured by vacuum infusion

The impact and flexural post-impact behaviour of ternary hybrid composites based on epoxy resin reinforced with different types of fibres, basalt (B), flax (F), hemp (H) and glass (G) in textile form, namely FHB, GHB and GFB, has been investigated. The reinforcement volume employed was in the order of 21–23% throughout. Laminates based exclusively on basalt, hemp and flax fibres were also fabricated for comparison. Hybrid laminates showed an intermediate performance between basalt fibre reinforced laminates on the high side, and flax and hemp fibre reinforced laminates on the low side. As for impact performance, GHB appears to be the worst performing hybrid laminate and FHB slightly overperforms GFB. In general, an increased rigidity can be attributed to all hybrids with respect to flax and hemp fibre composites. The morphological study of fracture by SEM indicated the variability of mode of fracture of flax and hemp fibre laminates and of the hybrid configuration (FHB) containing both of them. Acoustic emission monitoring during post-impact flexural tests confirmed the proneness to delamination of FHB hybrids, whilst they were able to better withstand impact damage than the other hybrids.     

Interfacial properties of phosphate glass fibres/PLA composites: Effect of the end functionalities of oligomeric PLA coupling agents

Polylactic acid (PLA) oligomers as coupling agents have shown higher interfacial shear strength in phosphate based glass fibres/PLA composites. To influence bonding on the glass fibre surface, short chain PLA oligomers with different end groups were used as coupling agents. The low molecular weight PLA with a sodium salt terminal group, a carboxylic acid end group and also with one, two and five hydroxyl groups were produced and applied on the fibre surface through a condensation reaction. Mechanical properties of the sized fibres/PLA composites were found to be increased. XPS and TG analyses showed the presence of the coupling agents on the fibres surface. SEM analysis further confirms the presence of the agents.     

Effect of areal weight and chemical treatment on the mechanical properties of bidirectional flax fabrics reinforced composites

In this paper several bidirectional flax fibers, usually used to made curtains, were employed as reinforcement of an epoxy matrix. Four different laminates were made by a vacuum bagging process, with varying both the areal weight and the treatment of the fabric.     

Thermal and dynamic mechanical analysis of polystyrene composites reinforced with short sisal fibres

The thermal behaviour of polystyrene composites reinforced with short sisal fibres was studied by means of thermogravimetric and dynamic mechanical thermal analysis. The thermal stability of the composites was found to be higher than that of sisal fibre and the PS matrix. The effects of fibre loading, fibre length, fibre orientation and fibre modification on the dynamic mechanical properties of the composites were evaluated. Fibre modifications were carried out by benzoylation, polystyrene maleic anhydride coating and acetylation of the fibre and the treatments improved the fibre-matrix adhesion. PS/sisal composites are thermally more stable than unreinforced PS and sisal fibre. The addition of 10% fibre considerably increases the modulus but the increase is found to level off at higher fibre loadings. The T_g values of the composites are lower than that of unreinforced PS and may be attributed to the presence of some residual solvents in the composites entrapped during the composite preparation. The treated-fibre composites show better properties than those of untreated-fibre composites. The Arrhenius relationship has been used to calculate the activation energy of the glass transition of the composites. A master curve is constructed based on time-temperature superposition principle.