Epoxy Matrix Material Research Articles

Co-curing of thermoset composites on metal structures with reduced cycle times for high-volume car applications

By locally reinforcing metal parts with fibre reinforced plastics, the mechanical behaviour can be increased significantly while adding only a minimum of weight. This technology has the potential for the introduction into high-volume car production due to i.e. the possibility to use conventional joining techniques of current car-manufacturing processes. Still the cycle time of this reinforcement process has to be decreased below 1 min to principally enable a further consideration in future car serial projects. This paper illustrates the evaluation of the reaction speed of an expedient epoxy matrix material and its mathematical description. The bonding strength of a unidirectional fibre reinforced semi-finished product, pre-impregnated with this matrix material onto a metallic surface is then evaluated by single-lap shear tests. The potential of this technology is validated using a locally reinforced metal hat profile, loaded under 3-point-bending. To evaluate the increase of performance, the energy absorption of these tested parts is calculated and compared with unreinforced metal profiles. Furthermore, the influence of compression time and pressure on the energy absorption was investigated. All the experiments are furthermore realized with two adhesives to demonstrates the influence of this additional material on the cycle times and the mechanical performance.

The flexural behavior of the epoxy and polyester based composite sandwich structures at subzero temperatures

The present work aims at characterizing the 3D woven spacer composites with carbon fiber reinforced polymer face-sheets under the 3-point flexural test at subzero temperature conditions. For this purpose, sandwich composite panels are manufactured using vacuum assisted resin infusion method for epoxy and polyester matrix materials with 2, 3, and 4 layered face-sheets. The 3-point flexural test was performed for warp and weft direction on liquid nitrogen temperature (−40 °C). Macroscopic fracture morphology was examined to understand the deformation and failure mechanism. The results show that the flexural properties were significantly affected by the number of face-sheets and then from matrix material and finally from the composite direction at subzero temperatures.

A comparative study on epoxy based composites filled with pineapple/areca/ramie hybridized with industrial tea leaf wastes/GFRP

Human beings have been strongly aware of environmental degradation, noise pollution and its human health implications as a result of the unprecedented use of synthetic fibres. The search is to develop a new class of material using eco-friendly fibers extracted from the environmental and industrial wastage which is to be better alternative for existing green composites. In this work, an industrial tea waste has been considered as filler materials due to its excellent sound absorbing properties. In addition to achieve a comprehensive characterization, sound absorbing properties are also to be potentially tested. In this context, three combinations of three different natural fibers (pineapple, areca and ramie) are hybridized with waste tea (powder form) and GFRP were fabricated by a compression molding process with the combinations of 40% reinforcement and 60% epoxy matrix material in a constant proportion. A hydrophilic content present in natural fibers are transformed to hydrophobic by 5% of alkyl treatment for enhancement of bonding between fiber and matrix phase. Mechanical, chemical, morphological, acoustical, humidity absorption and chemical examinations are done for laminates fabricated. The results are evaluated and compared to establish the possibility of using it as a new material for engineering applications especially in under-floor protection, engine decorative cover for passenger cars, wheel housing and inner door panel in automobiles.

Experimental investigation of fish scale reinforced polymer composite

Abstract Nowadays various biowaste materials are used as filler material in polymer composites. In this paper, the fish scale which is obtained from the outermost part of fish skin is utilized as filler material. Seven different volume fraction of fish scale were taken with epoxy matrix material to prepare composite plate. The composite specimens were fabricated by hand lay up method. The mechanical properties such as tensile, flexural and impact tests were evaluated as per ASTM standards. The addition of fish scale filler to reinforce the epoxy composite has considerably increased the mechanical properties of the composites. This investigation suggested the possibility of introducing fish scale obtained from the skin of the fish in polymer matrix composites.

Analysis of mechanical and tribological behavior of wood flour filled glass fiber reinforced epoxy composite

The present paper deals with the examination of mechanical and tribological behavior of glass fiber reinforced epoxy composite. Wood flour (WF) is added as filler in glass fiber (GF) and epoxy matrix material for the fabrication of composites. The Percentage of WF is varied from 2.5 wt% to 10 wt% keeping the glass fiber constant. The mechanical properties, water absorption and tribological behavior of fabricated composites evaluated. It was found that water uptake increases as the percentage of WF in the composite increases i.e. from 2.5 wt% to 10 wt% and it was least for neat GF reinforced epoxy composite. The composite of WF wt% of 7.5, absorb maximum energy and exhibited maximum strength. Moreover the wear rate increases as the percentage of WF in the composite increases. Present investigation also deals with the design of experiment (DOE). The DOE was carried out with the help of TOPSIS for the qualitative analysis and the ranking was done according to the order of preference.

A technique for in-situ detection of random failure in composite structures under cyclic loading

A technique to detect the random failure in composite structures is presented. The epoxy matrix material is made conductive by the incorporation of carbon nanotubes. The modified matrix is used to fabricate glass fiber/epoxy/carbon nanotubes composite panels. Conductive grid points made from silver-epoxy paste are attached on the surface of the composite panels, so that electrical resistances in the regions between the grid points can be measured. The increase in electrical resistance between grid points is used to determine the increase in deformation (and possibly cracks) at the region between the grid points. It is found that the location of maximum increase in electrical resistance jumps from point to point as the number of cycles during fatigue loading is increased. This shows the random nature of the development of damage in the composites. The technique can detect the occurrence of early failure, usually in the matrix materials. The result of this work brings out the random nature of the early failure in composites. This also sheds light into whether the concept of crack initiation in composites is valid, since the early cracks jump around. When the paths of the final cracks reach stability, there is rapid crack propagation leading to fast final failure.

Spall Characterization of EPON 828 Epoxy with Embedded Carbon Nanotubes

The increasing use of polymer nanocomposites in armor applications requires an understanding of how these materials behave at strain-rates relevant to ballistic impacts. Of particular interest is the role of the microstructure on the failure of these materials under dynamic tensile loading. In the present study, plate impact experiments were conducted in order to measure the spall strength of a neat epoxy (EPON 828) and an epoxy–carbon nanotube composite. The addition of pristine carbon nanotubes (CNTs) to the epoxy resulted in a composite material with a lower spall strength than the neat epoxy matrix material. Recovered composite fragments were imaged with a scanning electron microscope. Instances of nanotube pull-out were identified on internal fracture surfaces. The lower spall threshold of the epoxy–CNT composite was attributed to the comparatively weak epoxy–CNT interface, which provides potential sites from which spall failure can favorably nucleate.

Modeling compressive response of 3D woven textile composites accounting for microscale geometric uncertainties

The compressive response of 3D woven textile composites (3DWTC), that consist of glass fiber tows and an epoxy matrix material, is studied using a finite element (FE)-based mechanics model. A parametric Representative Unit Cell (RUC) model is developed in a fully three-dimensional setting with geometry and textile architecture for modeling the textile microstructure. The RUC model accounts for the nonlinear behavior of the fiber tows and matrix. The computational model is utilized to predict the compressive strength of 3DWTC and its dependence on various geometrical and material parameters. The finite element model is coupled with a probabilistic analysis tool to provide probabilistic estimates for 3DWTC compressive strength. The reported results are found to be in good agreement with experimental data.

Thermal conductivity of pillared graphene-epoxy nanocomposites using molecular dynamics

Thermal conductivity in a pillared graphene-epoxy nanocomposite (PGEN) is studied using equilibrium molecular dynamics simulations. PGEN is a proposed material for advanced thermal management applications because it combines high in-plane conductivity of graphene with high axial conductivity of a nanotube to significantly enhance the overall conductivity of the epoxy matrix material. Anisotropic conductivity of PGEN has been compared with that of pristine and functionalized carbon nanotube-epoxy nanocomposites, showcasing the advantages of the unique hierarchical structure of PGEN. Compared to pure carbon allotropes, embedding the epoxy matrix also promotes a weaker dependence of conductivity on thermal variations. These features make this an attractive material for thermal management applications.

Effect of carbon fiber winding layer on torsional characteristics of filament wound composite shafts

Composite materials are promising candidates as structural materials and substituting metals in extensive applications. Shafts are used in aerospace and automotive structures and hence replacing conventional shafts with composite material shafts is a viable option. Hollow shafts can be manufactured using filament winding technology employing hoop and helix winding layers. Filament winding technology offers several advantages such as continuous filaments through structure and capability for continuous manufacturing. Previously researchers have investigated composite shafts; however, this research elaborates the significance of type of winding layer on torsional characteristics. This paper reports the effects of carbon fiber winding layer on torsional characteristics of filament wound composite hollow shafts. Shafts were manufactured using filament winding technology with continuous carbon fiber roving and epoxy matrix material and tested using the torsional testing machine. The finite element (FE) simulations have been carried out with a general purpose commercial FE code, ABAQUS, to demonstrate shafts in torsional loading. The results revealed that values from torsional test correlate with developed finite element model. It was concluded that helix winding layer offers high hardness and more resistance to torsional forces as compared to hoop winding layer in filament wound composite shafts.

Synergistically effects of copolymer and core-shell particles for toughening epoxy

Simultaneously improving toughness and strength without sacrificing thermal resistance and maintaining the viscosity of an epoxy resin for application in Liquid Composite Molding (LCM) process has been challenging. This paper reported such a high performance epoxy system modified by a hybrid of toughening agents, block copolymer particle (BCP) and core-shell particle (CSP), was successfully prepared via a two-step processing method. The viscosity, thermal stability and mechanical property of the resulting modified epoxy, BCP∖CSP∖epoxy, were studied. The results showed that the BCP∖CSP∖epoxy maintained the viscosity and thermal stability of the epoxy resin, while its flexural strength and fracture toughness (KIC) were significantly increased in comparison with the neat epoxy, BCP∖epoxy and CSP∖epoxy. Based on the morphology analysis, a “ladybug” mechanism responsible for these impressive synergistic enhancement effects was proposed. It is believed that this study provides a new pathway for the toughening of epoxy matrix materials for making advanced LCM composites.

The synthesis and mechanical characterisation of laminated hybrid-epoxy matrix composites

High-performance and lightweight laminated hybrid composites were fabricated by using epoxy-impregnated carbon, Kevlar and hybrid fabrics. Carbon–Kevlar, carbon–hybrid, carbon–Kevlar–hybrid, and Kevlar–hybrid fabric epoxy matrix composites with 12 layers were synthesised using vacuum bag method. Tensile and three-point bending tests were used to determine the modulus of elasticity, % elongation, tensile strength, bending moment and bending strength of hybrid composites. The highest tensile strength, bending strength and bending moment were observed from carbon–Kevlar–epoxy matrix composite, while the lowest values were observed from the carbon–hybrid–epoxy matrix composite.

The effects of pile-up, viscoelasticity and hydrostatic stress on polymer matrix nanoindentation

It is well known that a clear disparity exists between the elastic modulus determined using macroscopic tensile testing of polymers and those determined using nanoindentation, with indentation moduli generally overestimating the elastic modulus significantly. The effects of pile-up, viscoelasticity and hydrostatic stress on the indentation modulus of an epoxy matrix material are investigated. An analysis of residual impressions using scanning probe microscopy indicates that material pile-up is insignificant. Viscous effects are negated by increasing the time on the sample during the loading/hold segment phases of the indentation test, and by calculating the contact stiffness at a drift-insensitive point of the unloading curve. Removing the effects of viscous deformation reduces the modulus by 10–13%, while also significantly improving the non-liner curve fitting procedure of the Oliver and Pharr method. The effect of hydrostatic stress on the indentation modulus is characterised using relations from literature, reducing the measured property by 16%. Once viscous and hydrostatic stress effects are accounted for, the indentation modulus of the material compares very well with the bulk tensile modulus, and modifications to standard indentation protocols for polymers are proposed.

A comparative study on the mechanical properties of carbon and glass fibre-reinforced epoxy, polyester and vinyl ester-based composites

In this paper, the effects of reinforcing and matrix material on the mechanical properties of composites were investigated. Carbon fibre (CF) and glass fibre (GF) are the most useful reinforcement materials in polymer-based composites, their major use being the manufacture of components in the aerospace, automotive and leisure industries. In this study, epoxy, polyester and vinyl ester-based matrix materials reinforced by CFs and GFs were manufactured by hand lay-up method. Mechanical properties were investigated by tensile and flexural testing methods. Composites with polyester-based and CF-reinforced composites exhibited the highest mechanical properties, whereas the epoxy-based and GF-reinforced composites showed lower mechanical properties.

Physico-Chemical Characterization of Novel Epoxy Matrix System Reinforced with Recycled Short Milled Carbon Fibre

As received recycled short milled carbon fiber (SMCF) reinforced diglycidal ether of bisphenol-A (DGEBA) epoxy matrix materials have been developed by ultra-sonication mixing of SMCF in epoxy then curing at room temperature for nine days. The SMCF with mean diameter 7.5 μm, and length 100 - 300 μm, was used at different loadings i.e. 1, 2, 3, 5 and 10 wt%. Elemental analysis, surface chemistry and crystallography of SMCF were examined using X-ray fluorescence, X-ray photoelectron spectroscopy and X-ray diffraction. Fourier Transform IR spectroscopy confirmed that both in unmodified and SMCF-modified epoxies, 99% curing was achieved. Surface microhardness study showed a slight increase with 5% and 10% SMCF addition. Raman study confirms no structural change in SMCF after incorporation in epoxy. Also, a numerical modelling is implemented to correlate the density of the modified epoxy and SMCF volume fraction/distribution uniformity.

TO DEVELOP AND EVALUATE IMPACT BEHAVIOR OF JUTE FIBRE REINFORCED COMPOSITE

The objective of this study is to investigate the impact behaviors of composites, metals and water absorption of composite. The Water absorption test is used to determine the amount of water absorbed under specified conditions .These composites (JRFC) are made of natural fibre (Jute) by volume 10% reinforcing in Epoxy (Matrix) Material. The Izod impact conditions have been considered .The result shows the specific impact energy of fibre composite is higher than the other materials.

Mechanical performance of epoxy/carbon fiber laminated composites

The objective of this research work was to gain a better understanding of the mechanical properties of epoxy resin composites reinforced with carbon fiber. For this purpose, the effects of fiber orientations, resin types, and number of laminates on mechanical properties of laminated composites have been investigated. In the sample preparation, composites were manufactured by hand lay-up process, using a fiber-to-resin ratio of 40:60 (w:w). To investigate the effect of fiber orientation, angles of 0°, 35°, 45°, and 90° were selected. Results show that the mechanical properties, in terms of tensile, flexural and impact strengths, were mainly dependent on the fiber orientations followed by the number of laminates. At a similar fiber orientation, the composites made with EM500 epoxy resin showed the highest mechanical properties (such as tensile and flexural and impact strengths) compared to other evaluated composites. However, the differences were not highly significant. The results indicated that the mechanical properties of composites made with five-ply were generally slightly greater than three-ply composites. It may be due to the bondline defects, which adversely influence the mechanical properties. Scanning micrographs of the composites showed that the epoxy matrix material was fully adhered to the fibers, indicating a strong interface. It can be concluded that the order of increment parameters in the mechanical properties of the composites is fiber orientation > number of laminates > resin type. In addition, the tensile and flexural properties were superior in case of ±35° fiber orientations.

Two-photon-induced thiol-ene polymerization as a fabrication tool for flexible optical waveguides

In this contribution, we present two flexible thiol-ene-based hybrid materials based on epoxy and acetoxy polysiloxane matrix materials. The latter cross-linking mechanisms allow for orthogonal curing of the matrix in the presence of thiol-ene monomers enabling fast one-step access to two-photon-polymerization (2PP) curable substrates for waveguide fabrication. Another time-saving feature of our concept is the straightforward UV-flood-curing after 2PP, which is also a progress compared to previous works with elaborate postprocessing. Optimization of the ratio of thiol/ene moieties with respect to reactivity and analyses of the thermal stability of the materials, which is required for the industrial process, were carried out. Besides investigations regarding the refractive index of the materials, the proof of principle for successful waveguiding will be given. Flexible optical waveguides were successfully fabricated inside a low refractive polysiloxane matrix material.

In-plane shear response of unidirectional fiber reinforced and fabric reinforced carbon/epoxy composites

The nonlinear in-plane shear properties of unidirectional fiber reinforced composites and fabric reinforced composites were compared by ±45° tension tests based on ASTM standard D3518. A set of epoxy matrix materials reinforced by unidirectional carbon tapes as well as satin and twill carbon woven fabrics were prepared. The experimental results revealed that fabric reinforced composite showed more ductile-like response in the pre-yield phase and better load bearing ability in the post-yield phase compared to the unidirectional fiber reinforced composite. There was no obvious damage on the surfaces of fabric reinforced composites prior to failure, whereas for unidirectional laminates obvious cracks and delaminations initiated from the free edges on the surface and propagated along the fibers. Finally, analysis of the Poisson's ratio fluctuations of the unidirectional composites separated the two contributors to the structural nonlinearity, the continuous micro changes and macro damage in laminae.

Effect of thermal treatment temperatures on the reinforcing and interfacial properties of recycled carbon fiber–phenolic composites

Carbon fiber reinforced plastic (CFRP) chips were thermally treated to clean their surfaces and their use as reinforcing materials in composites explored. The interfacial properties were dependent on the thermal treatment temperature. Electrical resistance measurements, by the 4-probe method, were used to evaluate the state of dispersion of the recycled carbon fibers (RCFs) in the RCF–phenolic composites. FE-SEM and AFM were used to study the surfaces of the recycled carbon fibers and the fracture surfaces of the RCF–phenolic composites, for the different treatment temperatures (200–600°C). There were differences in the nature and amount of residual epoxy resin on the surface of recycle CF subsequent to different thermal treatments. Mechanical and thermal properties of RCF–phenolic composites were affected by the presence of residual epoxy resin. SEM and AFM investigations indicated that the optimal treatment temperature was approximately 400°C, where the surface was clean of the residual epoxy matrix material and still relatively free of thermal damage. The decrease in diameter as well as damage to the fibers at the higher temperatures was accompanied by a decrease in the mechanical properties for composites manufactured with the recycled chips. The interfacial properties of the CFRP chips were generally improved by the appropriate thermal treatment, resulting in better interfacial adhesion between the recycled fibers and the phenolic resin.