Tom Løgstrup Andersen

Water-cooled non-thermal gliding arc for adhesion improvement of glass-fibre-reinforced polyester

A non-equilibrium quenched plasma is prepared using a gliding-arc discharge generated between diverging electrodes and extended by a gas flow. It can be operated at atmospheric pressure and applied to plasma surface treatment to improve adhesion properties of material surfaces. In this work, glass-fibre-reinforced polyester plates were treated using an atmospheric pressure gliding-arc discharge with air flow to improve adhesion with a vinylester adhesive. The electrodes were water-cooled so as to operate the gliding arc continually. The treatment improved wettability and increased the density of oxygen-containing polar functional groups on the surfaces. Double cantilever beam specimens were prepared for fracture mechanic characterization of the laminate adhesive interface. It was found that gliding-arc treatment significantly increases the fracture resistance in comparison with a standard peel-ply treatment.

Atmospheric pressure plasma surface modification of carbon fibres

Carbon fibres are continuously treated with dielectric barrier discharge plasma at atmospheric pressure in various gas conditions for adhesion improvement in mind. An x-ray photoelectron spectroscopic analysis indicated that oxygen is effectively introduced onto the carbon fibre surfaces by He, He/O2 and Ar plasma treatments, mainly attributed to an increase in the density of the C-O single bond at the carbon fibre surfaces. The O/C ratio increased to 0.182 after 1-s He plasma treatment, and remained approximately constant after longer treatment. After exposure in an ambient air at room temperature for a month the O/C ratio at the plasma treated surfaces decreased to 0.151, which is close to that of the untreated ones. It can be attributed to the adsorption of hydrocarbon contamination at the plasma treated surfaces.

Autoclave consolidation of fibre composites with a high temperature thermoplastic matrix

Abstract Process technology for the autoclave consolidation of fibre composites with a high-temperature thermoplastic matrix material has been developed and investigated. Five different types of carbon fibre/PEEK (PolyEtherEtherKetone) have been examined: APC-2 solid prepreg (pre-impregnated) tape from ICI; Quadrax 5 Harness Satin prepreg fabric from Quadrax; and unidirectional, 8 Harness Satin and 5 Harness Satin postpreg (post impregnated) fabrics of Filmix™ (a drapeable yarn spun from a blend of carbon and PEEK fibres) from Heltra Inc. The influence of autoclave pressure, pressure cycle and additional matrix material in the form of PEEK films on laminate quality and properties are reported. The laminates are characterised by microscopy, fibre content, porosity, inter-laminar shear strength (ILSS), bending strength and bending modulus. High-quality laminates with less than 1% porosity can be fabricated from APC-2 unidirectional tapes at a pressure of 0.3 MPa, whereas a woven fabric of Filmix™ requires a pressure 2.0 MPa in order to produce laminates which also have less than 1% porosity. By adding a small amount of extra matrix material in the form of PEEK films to the Filmix™ material, an autoclave pressure of only 0.7 MPa can produce laminates with a porosity of less than 1%. The ILSS is relative high (100–120 MPa) for all the laminates. It was expected that in general, a higher ILSS of the Filmix™ laminates would be found, since the nature of the yarn construction creates some fibre bridging between the different plies in the laminate, but the ILSS of the UD-laminates is 20% higher for the APC-2 laminates. This is caused by a very homogeneous fibre distribution with no matrix-rich areas in the APC-2 laminates, whereas thin matrix rich layers are observed by microscopy in the UD-Filmix™ laminates.

Adhesion Improvement of Glass-Fibre-Reinforced Polyester Composites by Gliding Arc Discharge Treatment

A gliding arc is a plasma that can be operated at atmospheric pressure and applied for plasma surface treatment for adhesion improvement. In the present work, glass-fibre-reinforced polyester plates were treated using an atmospheric pressure gliding arc discharge with an air flow to improve adhesion with a vinylester adhesive. The treatment improved wettability and increased the polar component of the surface energy and the density of oxygen-containing polar functional groups at the surfaces. Double cantilever beam specimens were prepared for fracture mechanics characterisation (fracture resistance as a function of nominal mode mixity) of the laminate adhesive interface. It was found that gliding arc treatment significantly increases the interfacial fracture energy and fracture resistance in comparison with a standard peel ply treatment, although the mixed mode fracture energy of the gliding arc treated specimen was not as high as that of the laminate itself.

Life cycle strain monitoring in glass fibre reinforced polymer laminates using embedded fibre Bragg grating sensors from manufacturing to failure

A holistic approach to strain monitoring in fibre-reinforced polymer composites is presented using embedded fibre Bragg grating sensors. Internal strains are monitored in unidirectional E-glass/epoxy laminate beams during vacuum infusion, curing, post-curing and subsequent loading in flexure until failure. The internal process-induced strain development is investigated through use of different cure schedules and tool/part interactions. The fibre Bragg grating sensors successfully monitor resin flow front progression during infusion, and strain development during curing, representative of the different cure temperatures and tool/part interfaces used. Substantial internal process-induced strains develop in the transverse fibre direction, which should be taken into consideration when designing fibre-reinforced polymer laminates. Flexure tests indicate no significant difference in the mechanical properties of the differently cured specimens, despite the large differences in measured residual strains. This indicates that conventional flexure testing may not reveal residual strain or stress effects at small specimen scale levels. The internal stresses are seen to influence the accuracy of the fibre Bragg gratings within the loading regime. This study confirms the effectiveness of composite life cycle strain monitoring for developing consistent manufacturing processes.

Influence of fiber type, fiber mat orientation, and process time on the properties of a wood fiber/polymer composite

A rapid press consolidation technique was used to produce composites from two types of air-laid wood fiber mat, incorporating either mechanically refined or bleached chemi-thermomechanically refined Norway Spruce [Picea abies (L.) Karst] and a bicomponent polymer fiber. The manufacturing technique involved pre-compression, contact heating to the process temperature under vacuum and then rapid transfer to the press for consolidation and cooling. Composites were tested to determine response to water or water vapor, porosity, fiber volume fraction and tensile properties. The composites absorbed water rapidly and showed changes in thickness with fluctuations in relative humidity. Porosity was higher in composites containing mechanically refined (MDF) fibers than in composites containing bleached chemi-thermomechanically refined (CTMP) fibers. Tensile test results suggessted that fiber wetting by the polymer matrix had been maximized within a five-minute heating time. Results also indicated that had been maximized within a five-minute heating time. Results also indicated that porosity was not the key determinant of tensile properties in the composites.

Effect of Polymer Form and its Consolidation on Mechanical Properties and Quality of Glass/PBT Composites

The aim of this study was to understand the role of the processing in determining the mechanical properties of glass fibre reinforced polybutylene terephthalate composites (Glass/PBT). Unidirectional (UD) composite laminates were manufactured by the vacuum consolidation technique using three different material systems included in this study; Glass/CBT (CBT160 powder based resin), Glass/PBT (prepreg tapes), and Glass/PBT (commingled yarns). The different types of thermoplastic polymer resin systems used for the manufacturing of the composite UD laminate dictate the differences in final mechanical properties which were evaluated by through compression, flexural and short beam transverse bending tests. Microscopy was used to evaluate the quality of the processed laminates, and fractography was used to characterize the observed failure modes. The study provides an improved understanding of the relationships between processing methods, resin characteristics, and mechanical performance of thermoplastic resin composite materials.

Mechanical Characterization and Fractography of Glass Fiber/Polyamide (PA6) Composites

The mechanical properties of the glass fiber reinforced Polyamide (PA6) composites made by prepreg tapes and commingled yarns were studied by in-plane compression, short-beam shear, and flexural tests. The composites were fabricated with different fiber volume contents (prepregs—47%, 55%, 60%, and commingled—48%, 48%, 49%, respectively) by using vacuum consolidation technique. To evaluate laminate quality in terms of fiber wet-out at filament level, homogeneity of fiber/matrix distribution, and matrix/fiber bonding standard microscopic methods like optical microscopy and scanning electron microscopy (SEM) were used. Both commingled and prepreg glass fiber/PA6 composites (with Vf ? 48%) give mechanical properties such as compression strength (530–570 MPa), inter-laminar shear strength (70–80 MPa), and transverse strength (80–90 MPa). By increasing small percentage in the fiber content show significant rise in compression strength, slight decrease in the ILSS and transverse strengths, whereas semipreg give very poor properties with the slight increase in fiber content. Overall comparison of mechanical properties indicates commingled glass fiber/PA6 composite shows much better performance compared with prepregs due to uniform distribution of fiber and matrix, better melt-impregnation while processing, perfect alignment of glass fibers in the composite. This study proves again that the presence of voids and poor interface bonding between matrix/fiber leads to decrease in the mechanical properties. Fractographic characterization of post-failure surfaces reveals information about the cause and sequence of failure

Plasma treatment of carbon fibres and glass-fibre-reinforced polyesters at atmospheric pressure for adhesion improvement

Atmospheric pressure plasma treatment is useful for adhesion improvement, because cleaning, roughening and addition of polar functional groups can be expected at the surfaces. Its possible applications in the wind energy industry include plasma treatment of fibres and fibre-reinforced polymer composites before assembling them to build wind turbine blades. In the present work, unsized carbon fibres are continuously treated using a dielectric barrier discharge plasma in helium at atmospheric pressure, and carbon fibre reinforced epoxy composite plates are manufactured for the mechanical test. The plasma treatment improved fracture toughness, indicating that adhesion between the fibres and the epoxy was enhanced by the treatment. In addition, glass-fibre-reinforced polyester plates are treated using a gliding arc and an ultrasound enhanced dielectric barrier discharge, improving the wettability and/or the adhesive strength with a vinylester resin.

Pin‐on‐disk apparatus for tribological studies of polymeric materials

Purpose – The purpose of this paper is to describe the construction of a custom‐built pin‐on‐disk (POD) apparatus based on a simple design and on important guidelines.Design/methodology/approach – The POD apparatus is built as a part of the main authors PhD project. The apparatus is built at a low cost and is suited for testing polymeric materials under dry‐sliding conditions. The different main parts of the apparatus are described in a way which partly explains the choice of construction and partly makes it possible to produce a similar apparatus. Furthermore, a limited amount of tribological data is presented mainly to exemplify the usefulness of the machine.Findings – The POD apparatus is successfully applied to measure coefficients of friction, wear rates and disk temperatures at an acceptable level of precision and accuracy. Tribological data obtained with this equipment show the effect of reinforcing an epoxy resin with a plain glass fiber weave.Research limitations/implications – The data presente...