The wear resistance of glass fibre reinforced epoxy composites

Polymers are usually characterized by low moduli and strength. Epoxy, as a thermoset material, has a low wear resistance. Additions of glass fibres improve the elastic modulus and tensile strength and can improve the wear resistance. The composites were prepared by pultrusion of the glass fibres after saturation of epoxy. The fibre volume fraction was varied up to 50%. Tensile and wear tests were carried out to examine the improvement in the composite properties. A small deviation of the tensile strength and the elastic modulus from the calculated values using the rule of mixture was observed due to the existence of porosities. The wear resistance increases with increasing the sliding velocity, with decreasing the applied contact pressure and with selecting the most favourable glass fibre volume fraction.     

Stress corrosion crack propagation in glass fibre reinforced/thermoplastic PET

This study covers results of stress rupture tests obtained with compact tension specimens of a glass fibre/thermoplastic matrix composite in chemical environments at room temperature. The corrosive media used were various acidic solutions. All the tests indicate a deterioration of the crack resistances of the materials to a greater or lesser extent, under environmental attack, i.e. cracks can propagate faster than in water or air. This particular behaviour is also influenced by microstructural parameters, i.e. fibre fraction and the local orientation of fibres to the propagating crack. In all cases, most attack occurs at the fibre-matrix interfaces and at the fibres, while the matrix is insensitive to the aggressive medium. The results are discussed in terms of crack growth rate, da/dt, and threshold fracture toughness value,K _SCC, below which statically loaded structural components are expected to have infinite life when subjected to a particular test environment.This work was carried out by the author during a research stay at the Centre for Composite Materials, University of Delaware, Newark, Del. 19711, USA.     

A study of skin-core adhesion in glass fibre reinforced sandwich materials

A test technique for measuring skin-core adhesion in fibre reinforced sandwich structures has been developed and applied. The test enables the interfacial fracture energy to be measured for most standard sandwich constructions. The technique has been subsequently employed to investigate skin-core adhesion in a number of sandwich structures similar to those currently used in the marine industry. It has been shown that the interfacial fracture toughness of a GFRP-crosslinked PVC sandwich structure can be as high as 2700 J/m²; however, sandwich constructions based on balsa cores offered considerably lower values of interfacial fracture energy. Here it was found that pre-treating the balsa core prior to bonding of the composite skins has a deleterious effect on the measured fracture toughness. Finally, the results of these tests have been correlated with data obtained from conventional climbing drum and short beam shear tests.     

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.     

Polymer-modified glass fibre reinforced gypsum

Glass fibre reinforced gypsum, modified by addition of specially selected and developed thermosetting polymers, is the basis of a new composite material, called PGRG. An investigation has been performed into its mechanical properties such as bending strength, tensile strength and long-term performance under constant load and fatigue load. The influence of moisture and temperature on mechanical properties has been determined. The equilibrium moisture content at various relative humidities, the moisture content under natural weathering conditions, the coefficient of linear expansion and the microstructure have been studied. Furthermore, the durability has been investigated under accelerated ageing conditions and outdoor exposure. The results have shown that the polymer-modified glass fibre reinforced gypsum has good mechanical properties under tension and, unlike unmodified gypsum, is resistant to the Western European climate. A variety of new outdoor applications for gypsum are likely to be possible now: The material has already been used successfully for outdoor applications in the UK, the Middle East and The Netherlands.

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Resume Le platre renforcé de fibres de verre, modifié par l'addition de polymère thermodurcissable spécialement sélectionné et fabriqué, forme la base d'un nouveau matériau composite appelé PGRG, dont on a examiné certaines propriétés mécaniques: résistance à la flexion, à la traction et performance à long terme sous charge constante et charge de fatigue. On a déterminé l'influence de l'humidité et de la température sur les propriétés mécaniques. On a également étudié l'équilibre de la teneur en eau à différentes humidités relatives, la teneur en eau en exposition naturelle, le coefficient d'expansion linéaire et la microstructure. On a aussi examiné la durabilité dans des conditions de vieillissement accéléré et l'exposition à l'atmosphère. Les résultats ont montré que les propriétés mécaniques du composite sont bonnes et que, à la différence du platre non traité, il peut résister au climat d'Europe Occidentale. Ceci permet d'envisager maintenant pour le platre diverses applications en ouvrages extérieurs. Le matériau a déjà été utilisé avec succès pour ce type d'applications en Grande-Bretagne, aux Pays-Bas et au Moyen-Orient.

     

Carbon fibre and glass fibre hybrid reinforced plastics

A review of the literature on carbon fibre and glass fibre hybrid reinforced plastics is presented. There are indications that the incorporation of both fibres into a single matrix sometimes leads to better properties than would be expected from consideration of the rule of mixtures. The incorporation of glass fibres in cfrp appears to improve impact properties and to increase the strain to failure of the carbon fibre in tension. The addition of carbon fibres to the surface of grp beams markedly increases the flexural modulus. A system of nomenclature for the diverse types of hybrid composite lay up is proposed.     

Acid corrosion analysis of fibre glass

The scanning electron microscope and the energy dispersive X-ray based analytical techniques have been used to study the sulphuric acid corrosion resistance of standard “E” fibre glass and PPG developed and patented 1201 [1], an “ECR” acid-resistant fibre glass. While it is well agreed by the experts in the field that direct exposure of fibre glass to 0.5 m sulphuric acid is much too severe a condition to simulate service conditions of most filament wound fibre glass products, nevertheless, the above corrosive environment was used to demonstrate a significant superiority of PPG 1201 glass in acid resistance over the standard “E” glass regardless of the source of its origin. It is also demonstrated that not only boron oxide leached out during acid exposure but a significant amout of calcium, aluminium, and magnesium oxides also were depleted from the “E” glass composition during acid treatment. It is also demonstrated that heat treatment of “E” glass products reduced the rate of acid attack. It did not, however, eliminate it completely. Heat treatment affects the strength properties of this fibre glass adversely.     

Fretting of glass fibre reinforced composites

Favourable specific mechanical properties of polymer matrix composites make them an attractive material for application in many engineering structures for which they offer substantial improvements over metals. The paper deals with fretting behaviour of unidirectional glass epoxy composites/metal contacts. Fretting is a plague for many industries: failures, loss of matter, loss of function can be induced by fretting. It occurs in all quasi-static contacts and appears as a complex wear phenomenon where a lot of parameters have been studied. From the interface tribology concept, the velocity accommodation mechanisms are discussed for different fibre orientations versus the contact surface of the glass fibre reinforced epoxy material. Results were analysed in two steps. From friction logs, Running Conditions Fretting Maps (RCFM) were first plotted in order to give an analysis of contact conditions and determine the associated material responses. The tribological degradations were then analysed. Differences between the different fibre orientations are mainly discussed on the basis of the stiffness of the anisotropic material and the velocity accommodation in the contact.     

A novel bogie design made of glass fibre reinforced plastic

This paper presents a completely new design of a bogie-frame made of glass fibre reinforced composites and its performance under various loading conditions predicted by finite element analysis. The bogie consists of two frames, with one placed on top of the other, and two axle ties connecting the axles. Each frame consists of two side arms and a transom between. The top frame is thinner and more compliant and has a higher curvature compared with the bottom frame. Variable vertical stiffness can be achieved before and after the contact between the two frames at the central section of the bogie to cope with different load levels. Finite element analysis played a very important role in the design of this structure. Stiffness and stress levels of the full scale bogie presented in this paper under various loading conditions have been predicted by using Marc provided by MSC Software. In order to verify the finite element analysis (FEA) models, a fifth scale prototype of the bogie has been made and tested under quasi-static loading conditions. Results of testing on the fifth scale bogie have been used to fine tune details like contact and friction in the fifth scale FEA models. These conditions were then applied to the full scale models. Finite element analysis results show that the stress levels in all directions are low compared with material strengths.     

Low temperature transitions in fibre reinforced polymers

The results of an investigation into the effect of absorbed moisture on the low temperature transitions of several polymer composite systems are reported. The longitudinal shear modulus and loss factor were measured over a range of temperature, from −150 to +20°C, both before and after conditioning in a hot, wet environment. In all cases, the presence of absorbed water had a plasticising effect, lowering the temperature at which the transition took place and increasing the peak loss factor. Even allowing for differences in measurement frequencies, the transition temperatures of the composites were found to be greater than those of the corresponding matrix resins. This suggests that the resin in the composite did not necessarily have the same properties as the bulk unreinforced resin.     

Statistical changes during the corrosion of glass fibre bundles

The mechanical properties of E-glass fibre bundles have been measured after corrosive attack by hydrochloric acid of various concentrations for various times. The effective stiffness of the fibre bundles is seen to be proportional to the effective cross-sectional area of the fibres as identified with the characteristic core-sheath geometry found in fibres exposed to long-term acid attack. However, the strength of the fibre bundles is not simply related to the effective area of the fibres and the statistics of fibre strength vary considerably with time. In particular the Weibull shape parameter is seen to increase rapidly at short times, before core-sheath formation is observed, and then fall slowly with core-sheath formation. Hence we have a shortterm narrowing of the strength distribution followed by a long-term broadening.     

Poisson's ratios in glass fibre reinforced plastics

The characterisation of the mechanical properties of an orthotropic composite material generally requires nine interdependent elastic constants: three Young's moduli, three shear moduli and three Poisson's ratios. In most papers it is the practice to quote only two orthogonal axial moduli, a shear modulus and a Poisson's ratio in the plane of the laminate. However, the value of Poisson's ratio is a function of the orientation of the loading axis relative to the principal axis of the reinforcement fibres, both in and through the plane of the laminate. In an earlier paper, the correlation of experimental and theoretically predicted Poisson's ratios was reported around the angles in the plane of the laminate. Both unidirectional and woven roving fibreglass panels were tested. Accurate prediction of Poisson's ratio was shown to be critically dependent on the value of shear modulus used. This paper reports an extension of the previous work to consider the through-plane properties and will examine the results in the context of the Lempriere constraints.     

Electrically conductive glass fibre reinforced epoxy resin

 The research on an industrially manufactured, electrically conductive glass fibre reinforced epoxy prepreg for aviation applications is reported. In a co-operative effort between Technical University Hamburg-Harburg (TUHH) and Daimler-Benz Aerospace Airbus (DASA) a new glass-epoxy composite with both electrical and good mechanical properties was successfully developed. The electrical conductivity was achieved adding carbon black as a conductive filler into the epoxy matrix and this at a very low level of content. The range of possible applications for this new material is not only limited to aviation. It can also be used in other transport systems or in electric and electronic devices. Received: 21 July 1998 / Accepted: 28 August 1998     

Novel basalt fibre reinforced glass matrix composites

A novel hot-pressing technique for the manufacturing of basalt fibre reinforced glass matrix composites was investigated. Two-dimensional (2D) fibre mats were sandwiched between borosilicate glass powder layers, thus configuring a much simpler processing route than that commonly employed for the production of fibre-reinforced glasses. Besides economic benefits, the use of fibre mats may lead to technologic advantages due to the possibility of readily coating the fibres with a suitable material (e.g. titanium oxide) by means of the sol-gel method. The coating of basalt fibre mats with TiO₂ is proposed for preventing the fibres from an excessive adhesion to the glass matrix. The developed composites containing 15 vol% of 2D-fibre reinforcement exhibited promising bending strength (∼90 MPa) and desirable “graceful” fracture behaviour without catastrophic failure. Thus the present study represents a convenient approach for production of advanced low-cost fibre reinforced glass matrix composites for structural applications.     

A static fatigue model for the durability of glass fibre reinforced cement

This paper presents a model for predicting service lives for glass-fibre reinforced cement (grc) components using hot-water accelerated ageing. It improves on previous models, being derived from consideration of a specific proposed micro-mechanical strength loss mechanism based on static fatigue principles and can be applied from time = 0. The model fitted well to all available strength vs. time data pertaining to various grc formulations. The activation energies thus derived for the strength loss process (80–90 kJ mol^–1) were consistent with those derived previously and those proposed for general glass dissolution mechanisms. Updated acceleration factors for predicting service lives for grc are advanced. The model was also applied to grc made with modified cement matrices. For metakaolin modified matrices, the activation energy appeared similar to that for OPC-grc, thus the use of similar acceleration factors appears justified. There is some evidence that calcium sulphoaluminate modified grc degrades according to a different activation energy. More data are required for modified matrix grcs if the model is to be applied thereto with confidence.     

Fatigue behaviour of continuous glass fibre reinforced composites

A study has been undertaken of fatigue in glass fibre reinforced composites. Two matrix resins were tested: a standard polyester and a polyurethane-vinyl-ester, which was designed to have a higher toughness. Three different types of glass fibre fabrics were used for reinforcement: a conventional woven roving and two stitch-bonded cloths. The glass cloths were combined into various lay-ups, in order to consider the effects of matrix, cloth and lay-up on the fatigue strength. Additionally, a study was undertaken to evaluate the micromechanisms that occurred during fatigue and how damage accumulated throughout the sample lifetime. This involved measuring stiffness changes during fatigue cycling, followed by microscopic study of the samples. It was found that similar damage micromechanisms occurred in each lay-up regardless of resin and cloth type, and these included matrix cracking, delamination and fibre breakage. However, differences were observed in the extent, location and rate of damage, and these were consistent with the variations seen in the fatigue strengths.     

Fatigue endurance of aged glass fibre reinforced cement

The resistance to flexural fatigue of glass fibre reinforced cement (GRC) stored in water for six years, has been studied. Peak stresses of between 6.0 and 18.2 MN m^–2 were used. At stresses of 10.0 and 18.2 MN m^–2 the median times before failure were 1.95×10⁵ and 2.0×10³ cycles, respectively. At a stress of 8.1 MN m^–2, six out of sixteen samples tested survived 4.65×10⁶ cycles. At a stress of 6 MN m^–2, all of the samples survived 1.75×10⁶ cycles. An unreinforced mortar specimen was also studied and its fatigue endurance showed greater scatter than the GRC samples.     

Characterization of the interphase in glass sphere reinforced polymers

In this study glass spheres were treated with an aminoalkyl-functional silane to promote adhesion, a methyltrimethoxysilane to reduce adhesion, and an amine terminated butadiene-acrylonitrile rubber to alter the interphase properties, and then embedded in an epoxy matrix. Tensile testing, optical microscopy, finite element, and micromechanics analysis were used to compare the effect of the different surface conditions on local elastic fields around a spherical glass inclusion imbedded in an epoxy matrix. It was observed that the angle, which a shear band makes with the direction of applied load is approximately 45° but in this case initiated at a polar angle of approximately 27°. Thus failure is not purely due to shear. These observations agree with the analytical observations presented in this paper. The location and direction of the point of where the maximum shear stress is located with respect to the direction of the applied load varies with the level of adhesion. This study showed that the best adhesion promoter for the ‘soda-lime glass’ solid spheres in the epoxy/mPDA system is aminoalkyl-functional silane. The alkyl silane can be used to totally eliminate adhesion.