Mechanical properties of single- and double-gated injection moulded short glass fibre reinforced PBT/PC composites

Tensile and flexural properties of single-gated (SG) and double-gated (DG) injection moulded blend of polybutylene terephthalate (PBT) and polycarbonate (PC) and its composites containing 15, 20 and 30 wt.% short glass fibres were investigated. In the DG mouldings, a weldline was formed by direct impingement of two opposing melt fronts (i.e. cold weld). It was found that tensile modulus was not affected by the weldline but flexural modulus decreased in the presence of weldline. For both specimen types, modulus increased linearly with volume fraction of fibres (ϕ _f), according to the rule-of-mixtures for moduli. The weldline integrity (WIF) factor for flexural modulus decreased linearly with increasing ϕ _f. Results showed that tensile and flexural strengths for SG mouldings increase with increasing ϕ _f in a linear manner according to the “rule-of-mixtures” for strengths. The presence of weldline affected both strengths in a significant way; WIF factor decreased linearly with increasing ϕ _f and was independent of loading mode. It was noted also, that the overall fibre efficiency parameter for tensile modulus was independent of specimen type but for flexural modulus it was lower in the case of DG mouldings. In all cases, efficiency parameter for strength was considerably lower than for the modulus. Impact strength and fracture toughness of SG mouldings were significantly greater than for DG mouldings. Although these properties for SG mouldings increased with increasing ϕ _f, they decreased significantly for DG mouldings. Results showed that WIF factor for impact strength and fracture toughness decreased linearly with increasing ϕ _f.     

A study on the characteristics of glass fibre reinforced thermoplastics by transfer moulding

Lately, the use of fibre reinforced thermoplastics (FRTP) has increased due to its increased mouldability compared to thermosetting FRP material.

FRTP includes stampable sheet, short and long fibre reinforced thermoplastic pellets, continuous fibre reinforced thermoplastics sheets, etc. The long fibre reinforced thermoplastic (LFRTP) pellet has better mechanical properties than short fibre reinforced pellets and better mouldability than stampable sheet. At present, injection moulding method is mainly used for moulding LFRTP pellets because of its high productivity.

However, the long fibre of LFRTP pellets, whose length is the same as pellet length, is degraded during processing if conventional injection moulding machines are used, and as a result, the mechanical properties are not improved as expected in many cases. Therefore, a new moulding process is required to make good use of LFRTP pellets.

For this study, a transfer moulding apparatus was designed and built to minimize fibre degradation of the moulded parts.

Firstly, the LFRTP pellets with fibre lengths of 3, 6, 9, 12.7 and 17 mm were prepared in order to clarify the difference of mechanical properties due to fibre length. The fibre ratio was 30% in weight for all cases and the same polypropylene was used. They were moulded to the shape of the test specimens. Tensile, bending and Izod impact strengths were measured by using these test specimens. Secondly, LFRTP pellets were moulded to the shape of test specimens by the transfer moulding apparatus and conventional injection moulding machine, and then mechanical properties were measured. At the same time, short fibre pellets were moulded to the smae shape of test specimens by the injection moulding machine, and mechanical properties were compared with those of LFRTP pellets.

With the long glass fibre reinforced polypropylene, good results of fibre preservation and mechanical properties were obtained by the transfer moulding apparatus which was built for this study. The impact strength was increased remarkably as the fibre length increased, and consequently the preservation of fibre length in the moulded parts was especially effective in improving the impact strength.     

Jetting and fibre degradation in injection moulding of glass-fibre reinforced polyamides

Injection-moulded glass fibre-reinforced polyamides with up to 50% by weight fibre content were examined for processing behaviour such as jetting and fibre degradation. Jetting was found to be a function of the ratio of the gate depth to mould-cavity depth, fibre length, fibre content and injection ram speed. Contrary to expectation, jetting occurred less frequently as the injection ram speed was increased. Major fibre degradation was experienced during the transport of the melt from the injection machine to the mould cavity. Further fibre degradation due to increases in injection back-pressure was comparatively small. Tensile strength was shown to be sensitive to variations in the fibre length distribution, whereas the elastic modulus remained unaffected.     

Mechanical properties of flax fibre/polypropylene composites. Influence of fibre/matrix modification and glass fibre hybridization

The effect of fibre treatments and matrix modification on mechanical properties of flax fibre bundle/polypropylene composites was investigated. Treatments using chemicals such as maleic anhydride, vinyltrimethoxy silane, maleic anhydride-polypropylene copolymer and also fibre alkalization were carried out in order to modify the interfacial bonding between fibre bundles and polymeric matrix. Composites were produced by employing two compounding ways: internal mixing and extrusion. Mechanical behaviour of both flax fibre bundle and hybrid glass/flax fibre bundle composites was studied. Fracture surfaces were investigated by scanning electron microscopy. Results suggest that matrix modification led to better mechanical performance than fibre surface modification. A relevant fact is that silanes or MA grafted onto PP matrix lead to mechanical properties of composites even better than those for MAPP modification, and close to those for glass fibre/PP.     

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.     

Mechanical and thermal expansion properties of glass fibers reinforced PEEK composites at cryogenic temperatures

Polyetheretherketone (PEEK) has been widely used as matrix material for high performance composites. In this work, 30% chopped glass fibers reinforced PEEK composites were prepared by injection molding, and then the tensile, flexural and impact properties were tested at different temperatures. The modulus, strength and specific elongation of glass fibers reinforced PEEK at room temperature, 77 K and 20 K have been compared. And the fracture morphologies of different samples were investigated by scanning electron microscopy (SEM). The results showed a dependence of mechanical properties of glass fibers reinforced PEEK composites on temperature. The coefficient of thermal expansion of unfilled PEEK and glass fibers reinforced PEEK were also investigated from 77 K to room temperature. The results indicated that the thermal expansion coefficient (CTE) of PEEK matrix was nearly a constant in this temperature region, and it can be significantly decreased by adding glass fibers.     

Mechanical behaviour of carbon and glass hybrid fibre reinforced polyester composites

Mechanical behaviour of carbon fibre/glass mat/polyester resin hybrid composites of sandwich construction is studied through tension, flexure, impact and post-impact tension tests. Tensile and flexural strength, modulus and failure strain values are compared to the calculated values. Total impact fracture energy and residual (after impact) tensile strength values of hybrid composites are analysed with regard to corresponding values of carbon/polyester composites. Failure of tested coupons was analysed by visual inspection and observation by scanning electron microscopy.     

The influence of fibre microstructure on fibre breakage and mechanical properties of natural fibre reinforced polypropylene

The aim of the study was to investigate the influence of fibre morphology of different natural fibres on the composites mechanical properties and on the fibre breakage due to extrusion process. The composite materials were manufactured using LTF (long fibre thermoplastic) extrusion and compression moulding and the used fibres were sisal, banana, jute and flax, and the matrix was a polypropylene. The results showed that sisal composites had the best impact properties and the longest fibres after the extrusion. Generally, the composites flexural stiffness was increased with increased fibre content for all fibres, being highest for flax composites. The flexural strength was not affected by the addition of fibres because of the low compatibility. The addition of 2 wt.% maleated polypropylene significantly improved the composites properties. Unlike the other three fibres, flax fibres were separated into individual elementary fibres during the process due to enzymatic retting and low lignin content.     

Mechanical properties of natural fibre reinforced polymer composites

During the last few years, natural fibres have received much more attention than ever before from the research community all over the world. These natural fibres offer a number of advantages over traditional synthetic fibres. In the present communication, a study on the synthesis and mechanical properties of new series of green composites involving Hibiscus sabdariffa fibre as a reinforcing material in urea-formaldehyde (UF) resin based polymer matrix has been reported. Static mechanical properties of randomly oriented intimately mixed Hibiscus sabdariffa fibre reinforced polymer composites such as tensile, compressive and wear properties were investigated as a function of fibre loading. Initially urea-formaldehyde resin prepared was subjected to evaluation of its optimum mechanical properties. Then reinforcing of the resin with Hibiscus sabdariffa fibre was accomplished in three different forms: particle size, short fibre and long fibre by employing optimized resin. Present work reveals that mechanical properties such as tensile strength, compressive strength and wear resistance etc of the urea-formaldehyde resin increases to considerable extent when reinforced with the fibre. Thermal (TGA/DTA/DTG) and morphological studies (SEM) of the resin and biocomposites have also been carried out.     

Mechanical properties of a degradable phosphate glass fibre reinforced polymer composite for internal fracture fixation

This paper reports on the mechanical properties and pH upon degradation of phosphate glass fibre reinforced methacrylate-modified oligolactide. Phosphate glass fibres of the composition 51.04 P₂O₅–21.42 CaO–25.51 Na₂O–2.03 SiO₂ (mol%) were produced by a crucible spinning technique. Fibres were embedded into a matrix of a degradable organic polymer network based on methacrylate-modified oligolactide; samples with and without addition of CaCO₃ for pH control were produced. pH during degradation in physiological NaCl solution could be increased to up to 6.5 by addition of 20 wt.% calcium carbonate to the fibre composites. pH in Tris buffer solution was about 7.11. Mechanical properties of dry specimens were investigated during 3-point bending tests and gave elastic moduli in the range of cortical bone (15 to 20 GPa). However, addition of calcium carbonate decreased tensile strength of the fibre composites and resulted in brittle fracture behaviour, while CaCO₃-free composites showed a fibrous fracture mode. Control of pH and degradation is a requirement for obtaining a fracture fixation device with degradation properties matching in vivo requirements. Results show that addition of CaCO₃ is suitable for controlling the pH during degradation of metaphosphate glass polymer composites.     

The mechanical properties of carbon fibre reinforced Pyrex glass

The mechanical properties of carbon fibre reinforced Pyrex glass are discussed in terms of the volume fraction of fibre, the orientation of the fibres, fibre damage during fabrication, matrix porosity, matrix critical strain, interface properties and the mode of failure in bend tests. The stress at which matrix cracking occurs increases with fibre concentration indicating that the critical strain of the matrix increases as the fibre separation decreases. The ultimate strength of the composite is considerably greater than the stress at which the matrix begins to crack. Preliminary stress cycling experiments at stresses above that at which matrix cracks are formed suggest that propagation of these cracks is inhibited by the fibres.     

Fabrication and mechanical properties of glass fibre–carbon fibre polypropylene functionally gradient materials

Hybrid fibre mat reinforced polypropylene (PP) composites with carbon(CF) and glass fibre (GF) were prepared and four kinds of functionally gradient materials (FGM) were fabricated by changing the spatial distribution of GF and CF. To measure the mechanical properties of FGMs and hybrid composites, flexural tests and instrumented impact tests were performed. The flexural strengths and the flexural moduli of hybrid composites increased following the rule of mixture as the relative volume content of CF increased. On the other hand, the total impact absorption energy of hybrid composites decreased with the increment of CF relative volume content. Compared with GF–CF PP isotropic hybrid composite, the composites with compositional gradient showed similar flexural strengths, but characteristic flexural moduli. Especially, sandwich-type FGMs with a CF-rich outer layer and a GF-rich inner layer exhibited higherflexural moduli than others. Total impact absorption energies of four FGMs were also similar, but the ratios of crack initiation energy,Ei, to crack propagation energy, Ep, or ductility index, were quite different.     

Carbon fibre reinforced glass matrix composite tension and flexure properties

Carbon fibre reinforced borosilicate glass matrix composites have been fabricated to determine their mechanical properties in tension and flexure. Composite tensile stress-strain properties, including elastic modulus, proportional limit and ultimate tensile strength, have been measured as a function of fibre content. Composite tensile properties were also obtained at temperatures of up to 625° C through the testing of 0/90 cross-plied specimens. Composite short-beam shear strength was found to depend on specimen orientation and also on the composition of the glass matrix. This compositional dependence was associated with an independent measurement of the fibre-matrix interfacial shear strength and was related to the degree of fibre-matrix reaction taking place during composite fabrication.     

Mechanical properties of chemically-treated hemp fibre reinforced sandwich composites

In this study, hemp fabrics were used as reinforcements with polyester resin to form composite skins while short hemp fibres with polyester as a core for making composite sandwich structures. To improve the fibre matrix adhesion properties, alkalisation, silane and acetylation treatments on the fibres surface were carried out. Examinations through fourier transform infrared (FTIR) spectroscopy, scanning electron microscope (SEM), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were conducted to investigate the physical and thermal properties of the fibres. Mechanical properties such as flexural and compressive strengths of the sandwich structures made by treated and untreated hemp fibres were studied. Based on the results obtained from the experiments, it was found that the fibre treated with alkalic solution and post-soaked by 8% NaOH exhibited better mechanical strength as compared with other treated and untreated fibre composite samples. Besides, DSC and TGA analysis showed that the thermal stability of all treated fibre was enhanced as compared with untreated samples.     

Mechanical properties of a self-healing fibre reinforced epoxy composites

Inspired by biological systems in which damage triggers an autonomic healing response, a polymer composite material that can heal itself when cracked has been developed. In this work, compression and tensile properties of a self-healed fibre reinforced epoxy composites were investigated. Microencapsulated epoxy and mercaptan healing agents were incorporated into a glass fibre reinforced epoxy matrix to produce a polymer composite capable of self-healing. The self-repair microcapsules in the epoxy resin would break as a result of microcrack expansion in the matrix, and letting out the strong repair agent to recover the mechanical strength with a relative healing efficiency of up to 140% which is a ratio of healed property value to initial property value or healing efficiency up to 119% if using the healed strength with the damaged strength.     

Failure characterisation of blast-loaded fibre–metal laminate panels based on aluminium and glass–fibre reinforced polypropylene

Previous work on the blast response of aluminium/glass–fibre reinforced polypropylene fibre–metal laminates (FMLs) presented observations and quantitative analysis on panels of varying thickness and stacking configuration. Diamond and cross-shaped back face damage was observed and dimensionless analysis showed that the front and back face displacement fell within one plate thickness of a linear trend line [Langdon GS, Lemanski SL, Nurick GN, Simmons MC, Cantwell WJ, Schleyer GK. Behaviour of fibre–metal laminates subjected to localised blast loading: Part I – experimental observations. Int J Impact Eng, in press; Lemanski SL, Nurick GN, Langdon GS, Simmons MC, Cantwell WJ, Schleyer GK. Behaviour of fibre–metal laminates subjected to localised blast loading: Part II – quantitative analysis. Int J Impact Eng, in press]. This paper presents failure characterisation of the blast-loaded square fibre–metal laminate panels, identifying trends and failure modes for each panel type. Multiple debonding, large plastic displacement, fibre fracture and matrix cracking are identified as damage mechanisms within the panels. Back face spalling, debonding failure and front face buckling are also discussed.     

Fabrication and mechanical properties of glass fibre reinforced thermoplastic elastomer composite

The paper investigates the effects of fabrication conditions on mechanical properties of glass fibre reinforced thermoplastic elastomer composites. The impregnation time was varied between 5 and 30 min and the cooling conditions were rapid and gradual cooling. Tensile testing was carried out on samples with different fibre orientations. Double Cantilever Beam (DCB) tests were carried out to evaluate the fracture toughness of the composites. The degree of crystallinity and morphology of the composite were studied by using differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). Impregnation of matrix resin into glass fibre was found to be complete before 30 min and tensile properties increased with increasing impregnation time. SEM micrographs of fractured surfaces revealed poor adhesion between the matrix and the reinforcing agent. Due to the flexible nature of the composite, the fracture toughness (G_IC) could not be determined because of the formation of ridges on the surface.     

Mechanical properties of polypropylene composites reinforced with chemically treated abaca

In the present study, abaca was chemically treated with benzene diazonium salt in order to improve in the mechanical properties of the abaca-PP composites. Both raw and treated abaca samples were utilized for the fabrication of the composites. The mechanical properties of the composites prepared from chemically treated abaca are found to increase substantially compared to those of untreated ones. Tensile strengths of the composites of both raw and chemically treated abaca-PP composites showed a decreasing trend with increasing filler content. However, the values for the chemically treated abaca-PP composites at all mixing ratios are found to be higher than that of neat PP. The surface morphologies of the fracture surfaces of the composites were recorded using scanning electron microscopy (SEM). The SEM micrographs reveal that interfacial bonding between the treated filler and the matrix has significantly improved, suggesting that better dispersion of the filler into the matrix has occurred upon treatment of abaca.