Random Short Fiber Research Articles

Implementation of eco-sustainable biocomposite materials reinforced by optimized agave fibers

Although several works have recently been published in literature about biocomposites, i.e. about composites with polymeric matrix reinforced by natural fibers, only a few articles have been devoted to the implementation of high performance biocomposites for structural and semi-structural applications. The present study aims to give a contribution by considering biocomposites obtained by using an eco-friendly partially bio-based epoxy (green epoxy) and sisal (agave sisalana fibers) obtained by a proper optimization process.Through a systematic experimental analysis, three different types of biocomposites obtained with a suitable manufacturing process, such as random short fiber biocomposites, random discontinuous fibers biocomposite obtained through the preliminary manufacture of MAT fabrics, and unidirectional long fibers biocomposites obtained through the preliminary manufacture of unidirectional “stitched” fabrics, have been studied.

Failure of a sag water pipe triggered by aging of the GFRP composite relining

Abstract A sag water pipe failed 12 years after it had been reinforced with a composite relining. The chronological sequence and the failure mode indicated that both the advanced aging of the glass fibre reinforced polymer pipe made in a centrifugal casting process and the increased local loading of the pipe shell due to an incomplete backfilling with injection mortar must have induced the failure. The investigations focussed on a detailed mechanical analysis of the pipe's composite shell in order to assess the progress of aging in the GFRP material which was in some layers reinforced with chopped random short glass fibres and in other layers with silica sand. Structural tests on entire ring segments complemented the experimental study. The results of the mechanical tests indicated a loss of 20% in stiffness and up to 40% in strength after the mentioned 12 years of operation, though only a few reference values of the initial state were available from test certificates of new pipes. The measured strength and stiffness values were used in a nonlinear finite element model to recalculate the strength analysis in the current situation, and to suggest a retrofit procedure. The investigation led to the conclusion that aging had progressed significantly in the centrifuged GFRP pipes. However, this alone would not have precipitated the failure. The partially incomplete backfilling between the composite relining and the original steel pipe had locally increased the stresses in the composite shell considerably due to hoop bending stresses. Hence, only the combination of both effects with a reduction of the composite shell strength due to aging and additional local loads could explain the delayed failure of the pipe after 12 years of operation.

Influence of Chemical Treatment on the Flexural Properties of Sisal Fiber Reinforced Resin Composites

Environmental awareness and an increasing concern with sustainable development have stimulated many industries including ground engineering to replace the conventional synthetic fibers. In this work, flexural strength and flexural modulus of chemically treated random short sisal fiber reinforced polypropylene and unsaturated polyester composites were investigated over a range of fiber content. Flexural strength of the composites was found to decrease with increased fiber content; however, flexural modulus increased with increased fiber content. The reason for this decrease in flexural strength was found to be due to fiber defects which could induce stress concentration points in the composites during flexural test, accordingly flexural strength decreased. Alkali and silane fiber treatments were found to improve flexural strength and flexural modulus which could be due to enhanced fiber/matrix adhesion.

Plant fibre-reinforced polymers: where do we stand in terms of tensile properties?

ABSTRACTThis article reviews the tensile properties of various plant fibre-reinforced polymers reported in literature. We critically discuss the use of plant fibres as reinforcement for the production of bio-based, renewable or green polymer composites. The tensile properties of these composites are compared against various (non-)renewable engineering/commodity polymers and commercially available randomly oriented glass fibre-reinforced polymers (GFRP). Composites containing random short plant fibres possess similar properties to randomly oriented GFRP at a lower overall part weight. Unidirectional plant fibre-reinforced polymers offer better performance than randomly oriented GFRP and have the potential to be adapted in applications requiring better mechanical performance, especially in applications where the use of costly synthetic fibres might be less attractive. Plant fibres can also be regarded as fillers to replace the more expensive polymers and improve the green credentials of the final composite parts. These features may motivate the industry to move towards plant fibre-based products.

Replacement of glass particles by multidirectional short glass fibers in experimental composites: Effects on degree of conversion, mechanical properties and polymerization shrinkage

ObjectiveTo test the null hypothesis that the replacement of a small fraction of glass particles with random short glass fibers does not affect degree of conversion (DC), flexural strength (FS), fracture toughness (FT) and post-gel polymerization shrinkage (PS) of experimental composites. MethodsFour experimental photocurable composites containing 1 BisGMA:1 TEGDMA (by weight) and 60vol% of fillers were prepared. The reinforcing phase was constituted by barium glass particles (2μm) and 0%, 2.5%, 5.0% or 7.5% of silanated glass fibers (1.4mm in length, 7–13μm in diameter). DC (n=4) was obtained using near-FTIR. FS (n=10) was calculated via biaxial flexural test and FT (n=10) used the “single edge notched beam” method. PS at 5min (n=8) was determined using the strain gage method. Data were analyzed by ANOVA/Tukey test (DC, FS, PS) or Kruskal–Wallis/Dunn's test (FT, alpha: 5% for both tests). ResultsDC was similar among groups (p>0.05). Only the composite containing 5.0% of fibers presented lower FS than the control (p<0.001). FT increased significantly between the control (1.3±0.17MPam0.5) and the composites containing either 5.0% (2.7±0.6MPam0.5) or 7.5% of fibers (2.8±0.6MPam0.5, p<0.001). PS in relation to control was significantly reduced at 2.5% fibers (from 0.81±0.13% to 0.57±0.13%) and further reduced between 5.0% and 7.5% (from 0.42±0.12% to 0.23±0.07%, p<0.001). SignificanceThe replacement of a small fraction of filler particles with glass fibers significantly increased fracture toughness and reduced post-gel shrinkage of experimental composites.

Polymerization stress of experimental composites containing random short glass fibers

ObjectiveTo test the null hypotheses that (1) the replacement of particles by short fibers does not affect polymerization stress (PS), flexural modulus (FM) or volumetric shrinkage (VS) of experimental composites and (2) PS is not affected by specimen thickness. MethodsThree experimental composites were prepared, each containing similar mass fractions of BisGMA and TEGDMA and 60 vol% of fillers, being 0%, 3% or 6% constituted by 1.6-mm long glass fibers and the remaining by 1μm glass particles. PS (n=5) was tested in a high compliance system, using two specimen heights (1.5mm and 4.0mm). VS and maximum shrinkage rate were obtained in a mercury dilatometer (n=3). FM was tested in three-point bending (n=10). As an additional control, a commercial composite (Filtek Z250, 3M ESPE) was tested. Data were recorded 10min after the onset of photoactivation and analyzed by ANOVA/Tukey test (FM only) and Kruskal–Wallis (alpha: 5%). ResultsAt both specimen heights, the composite with 3% of fibers presented significantly higher PS than the controls (which showed similar PS values). Replacing 6% of particles by fibers did not increase PS significantly. FM was reduced in the presence of fibers, and 6% of fibers led to a decrease in VS. Shrinkage rate was not affected by the fibers. SignificanceReplacing 3vol% of particles by fibers resulted in significantly higher PS, which was associated to a decrease in FM compared to the control. PS was not affected by specimen height for any of the tested materials.

The role of reinforcement orientation on the damage evolution of AlSi12CuMgNi + 15% Al2O3 under compression

Internal damage of an AlSi12CuMgNi alloy reinforced with planar random short fibres has been investigated after compression. This damage strongly influences the load partition between matrix and reinforcement. For fibres perpendicular to the applied load, breakage and interconnected cracks appear in significantly higher volume fraction than with fibres parallel to load.

Tensile and Flexural Strength of Untreated Napier Grass Fibre/Polyester Composites

This paper describes the experimental investigation of the tensile and flexural strength of untreated Napier grass fibre reinforced polyester composites. Napier grass fibres were extracted trough conventional water retting process and used as reinforcing materials in the polyester composite laminates. Tensile tests were then conducted for the composite specimens from the laminates at 25% fibre loading using the electronic extensometer setup to obtain the tensile properties. The results show significant differences in tensile strength between random short fibres laminates and random long fibrelaminates with the long fibres yield over 30 % higher in strength.Both the short and long fibre composites exhibits similar strength with short fibres having slightly higher flexural strength to long fibres The laminate also shows higher maximum strength compared to other commonly available natural fibre composites with almost 75 % improved in the maximum strength compared to the short kenaf fibre reinforced composites.

Tensile Strength of Untreated Napier Grass Fibre Reinforced Unsaturated Polyester Composites

This paper describes the experimental investigation of the tensile strength of untreated Napier grass fibre reinforced polyester composites. Napier grass fibres were extracted trough conventional water retting process and used as reinforcing materials in the polyester composite laminates. Tensile tests were then conducted for the composite specimens from the laminates at 25% fibre loading using the electronic extensometer setup to obtain the tensile properties. The results show significant differences in tensile strength between random short fibres laminates and random long fibre laminates with the long fibres yield almost 45 % higher in the strength. The laminates also show higher maximum strength compared to other commonly available natural fibre composites with over 70 % increase in the maximum strength compared to the short kenaf fibre reinforced composites.

A Computational Approach for Prediction of the Damage Evolution and Mechanical Characteristics of Random Fiber Composites

In this study we developed a computational approach by implementing the damage models proposed by authors for simulating the damage evolution and mechanical properties of random short fiber composites according to the respective characteristics of the matrix, the reinforcement and the volume fraction. Material damage induced by fiber de-bonding is considered. A comparison between the different existing models of homogenization was performed to determine the model that best reflects the response of our study material. And furthermore a range of simulations was carried out to study the influence of various parameters of the composite for predicting the response of the material and damage evolution.

The importance of the mesostructure in toughening cellulosic short fibre composites

In tonnage terms the commercial production of engineering composites is dominated by glass reinforced systems, this is particularly the case in the automotive industry. Natural fibres have long been regarded as a viable lightweight replacement for glass, however the various shortcomings of natural/cellulosic fibres have so far, inhibited exploitation, where resistance to fast fracture during impact is a major failing. Composite mesostructure describes mid-scale structures in composites, such as fibre alignment patterns, bundling effects, and fibre end synchronisation. The mesostructure can dramatically affect final properties in some random short fibre systems where flow is involved, such as sheet moulding compounds (SMC), and can be the determining factor in, for example, the success of one fibre system over another. This study seeks to manipulate the fibre mesostructure in moulding compounds reinforced with natural/cellulosic fibres, where it is shown that by arranging mechanically inferior fibres in bundles, composite impact energy absorption can be substantially improved, where the reasons behind the toughening mechanism at work, is discussed and optimum bundle dimensions for several fibre systems are identified. Fibre bundling seems to be a highly interesting method for toughening composites made from mechanically inferior natural/cellulosic fibres, however no work in the area has been reported until now.

An Experimental and Numerical Hybrid Technique for Analysis the Fracture Behaviors in Natural Fiber Reinforced Composites

Natural fiber reinforced composites have become excellent candidates for automotive applications and civil engineering facilities. The design procedures will require precisely evaluating the toughness of the materials, which demand accurate measurements of strain or displacement that are difficult to obtain for ductile materials. The primary objectives of this paper were to develop reliable experimental approaches which can effectively evaluate the fracture behaviors of random short natural fiber reinforced polypropylene (PP) composites. The digital image correlation method (DICM) was applied to compute the deformation fields around the crack tip of a compact-tension specimen in a process of loading. An experimental and numerical hybrid method was used to describe the fracture behaviors of the composites. The relationship between the micro-structure of random fibers and the macroscopic mechanical properties of the composites can also be understood.

Influence of morphological parameters of a 2D random short fibre composite on its effective elastic properties

The paper deals with the assessment of the influence of morphological parameters of a 2D random short fibre composite on its effective elastic properties. A double-scale 2D finite element approach is used and periodic representative volume elements are generated according to the model with an n -order approximate geometry. This one is a recent and powerful tool to generate meshes in the context of complex microstructures such as random fibre composites. Impact of three morphological features namely, aspect ratio, tortuosity of fibres and width of the interphase area, is investigated. Numerical results are provided for several contrasts of properties and volume fractions of fibres.

Numerical Simulation of Tensile Behaviors for Random Spruce Short Fiber Reinforced Composites

Natural short fiber reinforced composite is promising in motor industry, it is meaningful to study the tensile property of spruce short fiber reinforced polypropylene (PP) composite. In this paper, the finite element model is developed with the consideration of the fiber random orientation, random distribution, fiber volume content and interphase effect, especially the cohesive zone model to simulate the interphase property. The tensile behaviors of the short spruce/PP composite with kinds of fiber volume content are predicted. The results show that both strength or stiffness and experimental data are well identical.

Heterogeneities Measurements of Crack Tip Deformation Fields in Random Short Spruce/PP Composites

The random spruce short fiber reinforced polypropylene composites is a type of thermoplastic bio-composites. It is considered as homogeneous, isotropic in macro-scale of its specimen, in fiber scale about 500μm, the composite material appears heterogeneity, anisotropy due to the influence of microstructures of random short fibers. The heterogeneous deformations near the crack tip of the compact tension (CT) specimen which made from spruce/PP composites were measured by means of the digital image correlation method (DICM) with high resolutions digital image. The crack tip fields of heterogeneous displacement and strain for spruce/PP composites with fiber volume content 49% were obtained. The effects of random fiber microstructures on macroscopic deformations were discussed.

PENGARUHORIENTASI DANFRAKSI VOLUME SERAT DAUN NANAS (ANANAS COMOSUS)TERHADAP KEKUATAN TARIK KOMPOSIT POLYESTERTAK JENUH(UP)

Composite manufacturing is done by hand lay-up method with a fiber volume fraction 10%, 20%, 30%, and 40% with unidirectional and random short fiber orientation of pineapple leaves. Specimen testing is performed with a standard tensile strength test ASTM D3039. As a results is known that the tensile strength of composites increased with increasing fiber volume fraction for unidirectional fiber orientation, but rather to the random orientation of short fibers. Meanwhile, the composite tensile strain increases withincreasingfibervolume fractionfor both theorientation of thefibersof pineappleleaves.

Flexural properties of hemp fibre reinforced polylactide and unsaturated polyester composites

In this work, flexural strength and flexural modulus of chemically treated random short and aligned long hemp fibre reinforced polylactide and unsaturated polyester composites were investigated over a range of fibre content (0–50wt%). Flexural strength of the composites was found to decrease with increased fibre content; however, flexural modulus increased with increased fibre content. The reason for this decrease in flexural strength was found to be due to fibre defects (i.e. kinks) which could induce stress concentration points in the composites during flexural test, accordingly flexural strength decreased. Alkali and silane fibre treatments were found to improve flexural strength and flexural modulus which could be due to enhanced fibre/matrix adhesion.

Tensile Properties of Random Distribution Short SMA Fiber Reinforced Composites

Shape memory alloy (SMA) reinforced composites have been widely used in aerospace engineering fields. In this paper, four basic assumptions were presented to simply the research model based on the Eshelby’s equivalent inclusion method and Mori-Tanaka scheme. Based on the three-phase equivalent system and two-step equivalent process, the effective elastic modulus and thermal expansion coefficient of unidirectional random distribution short SMA fiber reinforced composites were derived. The tensile mechanical properties of composites with fiber volume fraction (15%), size (L=3, D=1; L=5, D=1), and number (N= 30, 50), were simulated using software ANSYS12.0, and discussed the failure mode of the composites.

Influence of loading rate, alkali fibre treatment and crystallinity on fracture toughness of random short hemp fibre reinforced polylactide bio-composites

Plane-strain fracture toughness ( K Ic ) of random short hemp fibre reinforced polylactide (PLA) bio-composites was investigated along with the effect of loading rate, fibre treatment and PLA crystallinity. Fracture toughness testing was carried out at loading rates varying from 0.5 to 20 mm/min using single-edge-notched bending specimens with 0 to 30 wt.% fibre. K Q (trial K Ic ) of composites decreased as loading rate increased, until stabilising to give K Ic values at a loading rate of 10 mm/min and higher. The reduction of crazing and stress whitening, as well as a more direct crack path observed in PLA samples combined with reduced plastic deformation observed in composites provided explanation for this reduction. K Ic of composites was found to decrease with increased fibre content and fibre treatment with sodium hydroxide. Studies controlling the degree of PLA crystallinity by heat treatment or “annealing” showed that reduction of K Ic can be attributed to increased crystallinity.

Improvement of mechanical performance of industrial hemp fibre reinforced polylactide biocomposites

In this work, mechanical properties of chemically treated random short fibre and aligned long hemp fibre reinforced PLA composites were investigated over a range of fibre content (0–40 wt.%). It was found that tensile strength, Young’s modulus and impact strength of short hemp fibre reinforced PLA composites increased with increased fibre content. Alkali and silane fibre treatments were found to improve tensile and impact properties which appears to be due to good fibre/matrix adhesion and increased matrix crystallinity. A 30 wt.% alkali treated fibre reinforced PLA composite (PLA/ALK) with a tensile strength of 75.5 MPa, Young’s modulus of 8.18 GPa and impact strength of 2.64 kJ/m 2 was found to be the best. However, plane-strain fracture toughness and strain energy release rate decreased with increased fibre content. The mechanical properties of the PLA/ALK composites were increased further due to alignment of long fibres.