Glass Fiber Reinforced Epoxy Composites Research Articles

Dielectric and friction behaviour of unidirectional glass fibre reinforced epoxy (GFRE)

The aim of this paper is to confirm the role of the electric charges on the friction behaviour of non-conductive materials. This correlation is proven using tribo-tests and SEMME (Scanning Electron Microscope Mirror Effect) measurements carried out on the neat epoxy matrix and on two GFRE composites, which only differ by the sizing of the fibres. For the matrix, the influence of friction is only obvious inside the friction track but, for the composites, a modification of the properties of the whole composite (inside and outside the friction track) is observed after friction. Consequently, the glass fibre/matrix interfaces play the role of diffusion path and, then, allow the trapping of electric charges, inducing the formation of defects, as proved by the dielectric modification of material, outside the friction track. In addition, it will be noted that a diffusion of electric charges through the fibre–matrix interfaces permits a stabilization of the friction coefficient and a limitation of the wear, whereas a localised trapping of charges on the interfaces is a source of damage and wear. In this way, the choice of the sizing process permits to control the motion of the electric charges and, consequently, to optimize the mechanical and tribological properties of the composites.

Influences of amine‐terminated oligomers on glass fibre‐epoxy composite

PurposeThe purpose of this paper is to evaluate the mechanical properties of glass fibre reinforced epoxy composites modified with amine‐terminated poly (ethylene glycol) benzoate (ATPEGB) along with their thermal stability.Design/methodology/approachATPEGB prepared from poly (ethylene glycol) (PEG) of different molecular weights (200, 400, 600, 4,000 and 20,000) were used as modifiers for glass fibre epoxy composite here. For toughening, 12.5 parts per hundred grams (phr) of epoxy resin of each ATPEGB was added to epoxy and pre‐reacted with it. The impact, tensile and flexural strengths of modified and unmodified composite were characterised and compared for each ATPEGB.FindingsModified resin displayed a significant improvement in fracture toughness with glass fibre over unmodified epoxy. The modification caused the formation of oligomer domains having relatively round shapes in the matrix. These oligomer domains led to improved strength and toughness due mainly to the “rubber toughening” effect in the brittle epoxy matrix. The optimum results were obtained for composite modified with ATPEGB‐2 prepared from PEG of molecular weight 400.Research limitations/implicationsIn the present context, only 12.5 phr concentration of each ATPEGB was used to modify composite and the composites were made sing three layers of glass fibre. Besides, modification could also be done using other concentrations and more layers of glass fibre could also be used to make composite.Originality/valueThe method for enhancing toughness of epoxy glass fibre composite was novel and finds numerous applications as surface coatings, casting and adhesive onto an intricate structure, etc.

Interlaminar shear strength of glass fiber reinforced epoxy composites enhanced with multi-walled carbon nanotubes

In this study, we examine the interlaminar shear strength (ILSS) of traditional glass fiber reinforced epoxy composites enhanced by strategically injecting multi-walled carbon nanotube (MWNT)–epoxy suspensions into stationary glass fiber mats. The suspensions were prepared by combining the techniques of high-speed mechanical stirring, ultrasonic agitation and acid oxidation. Two types of process designs were introduced to fabricate the hybrid MWNT/glass/epoxy composites and their relative merits were discussed. Short beam shear (SBS) and compression shear tests (CST) were conducted on the manufactured components to characterize the influence of the process and the weight percentage of nanotubes on the ILSS. The results show that the introduction of MWNT into the composite increased the ILSS by up to 33%. The preferential orientation of the MWNTs in the thickness direction was found to contribute to the increase in the interlaminar shear properties.

The effect of OPWF filler on impact strength of glass-fiber reinforced epoxy composite

In the present study, oil palm wood flour (OPWF) particles with less than 250 μm sizes have been used as filler materials in the woven-glass-fiber reinforced epoxy composite. The hybrid composites were fabricated using a hand lay-up method and cured at room temperature under a compressive load of 196 N (20 kg). The OPWF of 2.5 to 10 parts per hundred (pph) by weight was used to evaluate its effect on impact strength of the hybrid composites at a range of temperature from −50 to 50 °C. The impact strength, evaluated using V-notch Charpy method, showed reduction with increasing filler content up to 5 pph and then the strength increment in those composites containing more than 5 pph OPWF. More severe damages were found in specimens with higher filler contents resulting higher energy absorption during impact. The composites with a large amount of OPWF particles deflected crack propagation paths or created obstacles at the crack tips and increased toughness of the composites. The impact strength was found to decrease when the samples fractured at subzero temperatures and this happened because of the reduction of the matrix ductility at lower temperatures.

Investigation on glass/epoxy composite surfaces machined by abrasive water jet machining

Experimental investigations were conducted to assess the influence of abrasive water jet machining (AWJM) process parameters on surface roughness (Ra) of glass fibre reinforced epoxy composites. The approach was based on Taguchi's method and analysis of variance (ANOVA) to optimize the AWJM process parameters for effective machining. It was found that the type of abrasive materials, hydraulic pressure, standoff distance and traverse rate were the significant control factors and the cutting orientation was the insignificant control factor in controlling the Ra. For noise factors effect, the forms of glass fibres and thickness of composite laminate showed the greatest influence on Ra. A Mathematical model was developed using piecewise linear regression analysis to predict the performance of Ra in terms of the cutting parameters of AWJM. The models successfully predicted the Ra of an AWJ machined glass/epoxy laminate within the limit of this study. Verification of the improvement in the quality characteristics has been made through confirmation test with respect to the chosen reference parameter setting. It was confirmed that the determined optimum combination of AWJM parameters satisfy the real need for machining of glass fibre reinforced epoxy composites in practice.

The effect of cutting tool geometry on thrust force and delamination when drilling glass fibre reinforced plastic composite

This work is focused on the investigation of the effect of the cutting tool geometry and material on the thrust force and delamination produced when drilling a glass fibre reinforced epoxy composite. Four drills with distinct geometries and composition were tested. Additionally, the influence of the cutting parameters was studied. Generally speaking, the results indicated that lower thrust force was observed using drill EDP27199, whereas drill A1167A (with three cutting edges) gave highest thrust force values. In contrast to other reports, a direct relationship between thrust force and delamination was not observed, i.e., the drill responsible for the highest thrust force was also responsible for the second smallest delaminated area. Finally, within the cutting range tested the damaged area increased considerably with feed rate and moderately with cutting speed.

The Effect of Curing Conditions on the Properties of Silica Modified Glass Fiber Reinforced Epoxy Composite

The effects of curing conditions on the mechanical properties of glass fiber reinforced epoxy composites under different fiber prestressing levels were quantitatively studied. The composite samples were prepared with silica particle modified continuous E-glass fibers, epoxy resin matrix, fiber prestressing and step curing processing. Room temperature cured and isothermal high temperature cured composite samples, with the same content and structure, were made to study the difference of three curing conditions on a quantitative level. Based on the test results of flexural, shear, and impact properties of the composite samples, it was found that the step curing procedure generates composite samples with up to 47% and 14% increased properties than room temperature cured and isothermal high temperature cured samples, respectively, when manufactured under the same fiber prestressing level. The possibility of generating an optimum residual stress within the samples during processing is proposed and discussed to explain the contribution of the step curing process to the composite properties.

Three-body abrasive wear behaviour of carbon and glass fiber reinforced epoxy composites

Three-body abrasive wear behaviour of carbon–epoxy (C–E) and glass–epoxy (G–E) composites has been investigated. The effect of abrading distance, viz., 270, 540, 810 and 1080 m and different loads of 22 and 32 N at 200 rpm have been studied. The wear volume loss and specific wear rate as a function of load and abrading distance were determined. The wear volume loss increases with increasing load/abrading distance. However, the specific wear rate decreases with increase in abrading distance and increases with the load. However, C–E composite showed better abrasion wear resistance compared to G–E composite. The worn surface features have been examined using scanning electron microscope (SEM). SEM micrographs of abraded composite specimens revealed the high percentage of broken glass fiber compared to carbon fiber and also better interfacial adhesion between epoxy and carbon fiber.

TERAHERTZ QUALITY CONTROL OF POLYMERIC PRODUCTS

We report on experiments that evaluate the potential of terahertz (THz) time-domain spectroscopy (TDS) for quality control of polymeric compounds. We investigate specimens out of a polyethylene compound with silver-coated titanium dioxide nanospheres and a glass-fiber reinforced epoxy composite. We further examine an industrial polymer product produced by injection molding. Our data demonstrates that THz imaging is a powerful tool for contactless quality control in the polymer industry.

On the Effect of Counterface Materials on Interface Temperature and Friction Coefficient of GFRE Composite Under Dry Sliding Contact

Nowadays, there is an increase interest in polymeric composite materials for high-performance in many industrial applications. In other words, the tribo-studies on polymeric materials are growing fast to enhance the polymeric products such as bearings, seals, ring and bushes. The current work presents an attempt to study the correlation between the type of counterface material and frictional heating at the interface surfaces for different, normal loads (23N, 49N and 72N), sliding velocities (0.18, 1.3 and 5.2 m s?1) and interval time (0-720 sec). Sliding friction experiments are performed on a pin-on-ring (POR) tribometer under dry contact condition. Interface temperature and friction force were measured simultaneously during sliding of glass fiber reinforced epoxy (GFRE) composite against three different counter face materials, hardened steel (HS), cast iron (CI) and Aluminum alloy (Al). Experimental results showed that the type of counterface material greatly influences both interface temperature and friction coefficient. Higher temperature and friction coefficient were evident when sliding took place against HS surface, compared to sliding against CI and Al under same condition. When sliding took place against HS, the friction coefficient of GFRE composite was about an order of magnitude higher than sliding the GFRE composite against the other counter face materials. Based on the optical microscope graphs, the friction and induced temperature results of GFRE composite are analyzed and discussed.

Flexural and Shear Properties of Silica Particle Modified Glass Fiber Reinforced Epoxy Composite

The objective of this study is to develop a new method of manufacturing glass fiber reinforced epoxy composites and to quantitatively show that the properties of such a new material are superior to that of a conventional fiber reinforced polymer composite of the same material base composition. To achieve this objective, the glass fiber (GF) reinforced epoxy composite samples are prepared in four different ways: Method A, using ‘clean’ GF as the reinforcement (i.e., with no modification or additional treatment to the as-received fiber); Method B, modifying the surface of the GF with silica particles before applying in the composite system; Method C, prestressing the clean GF during the curing procedure of the composite; and Method D, prestressing the silica modified GF during the curing procedure of the composite. Preparation by Method D is the newly developed method. The finished composite samples are tested by the three-point bend test and the short-beam shear test under ASTM standard conditions. The results indicate that the composites prepared by the new method, which include the GF surface modification and the GF prestressing preparation conditions, have an excellent combination of properties when compared to the specimens made by the other three methods.

Modelling the nonlinear shear stress–strain response of glass fibre-reinforced composites. Part II: Model development and finite element simulations

The ASTM D3518/D3518M-94(2001) Standard Test Method for “in-plane shear response of polymer matrix composite materials by tensile test of a ±45° laminate” is based on the uni-axial tensile stress–strain response of a ±45° composite laminate which is symmetrically laminated about the midplane. For long glass fibre-reinforced epoxy composites, the test shows a highly nonlinear shear stress–strain curve. This work is concerned with the development of a material model to predict this mechanical behaviour. Part I discusses the experimental program with tensile tests on [+45°/−45°]2s laminates and off-axis [10°]8 composites. Cyclic tensile tests have been performed to assess the amount of permanent shear strain and the residual shear modulus.Part II focuses on the development of the material model and the finite element implementation. Two state variables have been introduced to represent the shear modulus degradation and the accumulation of permanent shear strain. The model has also been applied to the simulation of a three-point bending test on a [+45°/−45°]2s laminate.

Modelling the nonlinear shear stress–strain response of glass fibre-reinforced composites. Part I: Experimental results

The ASTM D3518/D3518M-94(2001) Standard Test Method for “In-plane shear response of polymer matrix composite materials by tensile test of a ±45° laminate” is based on the uni-axial tensile stress–strain response of a ±45° composite laminate which is symmetrically laminated about the midplane. For long glass fibre-reinforced epoxy composites, the test shows a highly nonlinear shear stress–strain curve. This work is concerned with the development of a material model to predict this mechanical behaviour. Part I discusses the experimental program with tensile tests on [+45°/−45°]2s laminates and off-axis [10°]8 composites. Cyclic tensile tests have been performed to assess the amount of permanent shear strain and the residual shear modulus.Part II focuses on the development of the material model and the finite element implementation. Two state variables have been introduced to represent the shear modulus degradation and the accumulation of permanent shear strain. The model has also been applied to the simulation of a three-point bending test on a [+45°/−45°]2s laminate.

Production and Properties of Glass Fibre-Reinforced Polymer Composites with Nanoparticle Modified Epoxy Matrix

AbstractIncreasing the mechanical performance, e.g. strength, toughness and fatigue properties of composites is the objective of many ongoing research projects. Nanoparticles, e.g. carbon nanotubes (CNTs) and fumed silica provide a high potential for the reinforcement of polymers. Their size in the nanometre regime make them suitable candidates for the reinforcement of fibre reinforced polymers, as they may penetrate the reinforcing fibre-network without disturbing the fibre-arrangement.In this work, glass fibre-reinforced epoxy composites with nanoparticle modified matrix systems were produced and investigated. GFRPs containing different volume fractions of the nanofillers were produced via resin transfer moulding. Matrix dominated mechanical properties of the GFRP laminates could be improved by the incorporation of nanoparticles. The addition of only 0.3 wt.% CNTs to the epoxy matrix increased the interlaminar shear strength from 33.4 to 38.7 MPa (+16%). Furthermore, the application of electrically conductive nanoparticles enables the production of conductive nanocomposites. This offers a high potential for antistatic applications and the implementation of functional properties in the composite structures. The effects of different filler types and volume fractions on the electrical properties of the GFRPs were investigated. GFRPs containing 0.3 wt.% of CNTs, for example, exhibit an anisotropic electrical conductivity. Furthermore, an electrical field was applied to the composites during curing. The effects on the resulting electrical and mechanical properties are discussed.

Effects of crosshead velocity and sub-zero temperature on mechanical behaviour of hygrothermally conditioned glass fibre reinforced epoxy composites

Abstract Experimental studies have been carried out to study the effects of thermal and moist environments (hygrothermal) on mechanical behaviour of glass fibre/epoxy composites. The hygrothermal conditioning impairs the fibre/matrix interfacial and/or interphasial chemistry, which plays a predominantly important role in determining the mechanical properties, especially the matrix dominated one, of a polymer composite. The hygrothermallly conditioned laminated composites are further treated at −6 °C temperature to freeze the absorbed moisture in the composites. The inter-laminar shear strength (ILSS) is found to be affected by this conditioning and it is also noticed that the further degradation occurs in the frozen state. The present paper also investigates the effect of variation of loading speeds on the degradation behaviour of polymer composites. A change in loading rate may result in variation of failure modes. The lower value of ILSS at lower crosshead speed may be due to higher ductility or failure strain of the epoxy resin.

Mechanical characterization of new glass fiber reinforced epoxy composites

AbstractGlass fiber reinforced plastic (GFRP) composites were made using CTPEGA [carboxyl terminated poly(ethylene glycol) adipate] modified epoxy as a matrix and characterized for their flexural properties, impact strength and interlaminar shear stress (ILSS). The volume fraction of glass was about 0.45 for all the composites. The concentration of CTPEGA in the matrix was varied gradually from 0 to 40 phr (parts per hundred parts of resin), to investigate the effect of CTPEGA concentration on the mechanical properties of the composites. It was found that the flexural strength and ILSS gradually decreases with increase in CTPEGA concentration. However, the impact strength of the composites increases up to 20 phr of CTPEGA concentration and decreases thereafter. Scanning electron microscope (SEM) analysis of the fracture surface indicates massive plastic deformation in modified epoxy based composites. Polym. Compos. 25:165–171, 2004. © 2004 Society of Plastics Engineers.

Thermal shock on interfacial adhesion of thermally conditioned glass fiber/epoxy composites

The fiber/matrix adhesion is most likely to control the overall mechanical behavior of fiber-reinforced composites. An interfacial reaction may result in various morphological modifications to polymer matrix microstructure in proximity to the fiber surface. The interactions between fiber and polymer matrix during thermal conditioning and thermal shock are important phenomena. Thermal stresses were built-up in glass fiber-reinforced epoxy composites by upthermal shock cycles (negative to positive temperature exposure) for different durations and also by downthermal shock cycles (positive to negative temperature exposure). The concentration of thermal stresses often results in weaker fiber/matrix interface. A degradative effect was observed in both modes for short shock cycles and thereafter, an improvement in shear strength was measured. The effects were shown in two different crosshead speeds during short-beam shear (SBS) test.

Factors affecting the machinability of GFR/epoxy composites

Drilling is an essential operation in the assembly of the structural frames of automobiles and aircrafts. The life of the joint can be critically affected by the quality of the drilled holes. The main objective of the present paper is to investigate the influence of some parameters on the thrust force, torque and surface roughness in drilling processes of fiber-reinforced composite materials. These parameters include cutting speed, feed, drill size and fiber volume fraction. The quasi-isotropic composite materials were manufactured from randomly oriented glass fiber-reinforced epoxy, with various values of fiber volume fractions ( V f), using hand-lay-up technique. Two components drill dynamometer has been designed and manufactured to measure the thrust and torque during the drilling process. The dynamometer was connected with a data acquisition, which installed in a PC computer. This set-up enable to monitor and record the thrust force and torque with the aid of a computer program that designed using Lab View utilities. The results indicate that the start point of torque cycle is delayed by few seconds (depending on the value of feed) than the thrust force. This time is consumed to penetrate the specimen by chiseling edge. After the thrust force reached its maximum value it is gradually decreased during the full engagement of the drill and goes to zero when both the chisel edge and the cutting lips have exit of the laminate. In contrast the torque was gradually increased up to the end of the cycle and sudden jump to a value about 10 times the peak value. Cutting speed has insignificant effect on the thrust force and surface roughness of epoxy resin. For glass fiber-reinforced epoxy composites (GFREC) with V f=9.8–23.7% the thrust force and torque were decreased with increasing cutting speed. On contrast increasing feed, drill size and fiber volume fractions lead to increase the thrust force and torque. The drilled holes of GFREC with lower V f ratio at lower feed have greater roughness than that drilled at higher feed. Specimens with high V f ratio have a contrary behavior. Drill diameter combined with feed has a significant effect on surface roughness.

Flexibility improvement of short glass fiber reinforced epoxy by using a liquid elastomer

In certain applications of fiber reinforced polymer composites flexibility is required. The aim of this study was to improve flexibility of short glass fiber reinforced epoxy composites by using a liquid elastomer. For this purpose, diglycidyl ether of bisphenol-A (DGEBA) based epoxy matrix was modified with hydroxyl terminated polybutadiene (HTPB). A silane coupling agent (SCA) was also used to improve the interfacial adhesion between glass fibers and epoxy matrix. During specimen preparation, hardener and HTPB were premixed and left at room temperature for an hour before mixing with epoxy resin to allow possible reactions to occur. In order to compare flexibility of the specimens flexural tests were conducted and the data were evaluated numerically by using a derived relation. Test data and scanning electron microscope analysis indicated that surface treatment of glass fibers with SCA, and HTPB modification of epoxy matrix improved flexural properties especially due to the strong interaction between fibers, epoxy, and rubber. It was also observed that HTPB modification resulted in formation of relatively round rubber domains in the epoxy matrix leading to increased flexibility of the specimens.

The influence of matrix chemical structure on the mode I and II interlaminar fracture toughness of glass‐fiber/epoxy composites

AbstractThe present paper is concerned with Mode I and Mode II delamination tests performed on three different glass fiber reinforced epoxy composites, chosen to obtain different final structures. The effect of crosshead speed on the fracture resistance of the composites was also analyzed. It was found that Mode I propagation values (GIC) increase as the crosshead speed decreases, probably because of the increase of brittleness in the studied range. An Arrhenius type relation between GIC and the glass transition temperature of the epoxy resin/amine system (Tg) was found. Mode II initiation values (GIICinit) and apparent shear strength (SH) were found to increase with the decrease of Tg. The relation between matrix toughness and composite interlaminar fracture toughness was also considered. Finally, the GIC propagation values were compared to the data available in literature for similar materials.