Glass bead filled Polyetherketone (PEK) composite by High Temperature Laser Sintering (HT-LS)

Copyright © 2015 Elsevier. NOTICE: this is the author’s version of a work that was accepted for publication in Materials and Design. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Materials and Design, Vol. 83 (2015). DOI: 10.1016/j.matdes.2015.06.005Thermal expansion behaviour and mechanical performance of high temperature laser sintered PEK (LS-PEK) and glass bead filled PEK composite (LS-GB/PEK) are reported and discussed for the first time. The laser sintered PEK and its composite show anisotropic thermal expansion properties related with their multilayer structure created by the laser sintering method. Compared with the PEK manufactured by conventional injection moulding (IM-PEK), LS-PEK has a 10% lower tensile strength but a higher hardness due to its greater crystallinity. Addition of glass bead to PEK increases the hardness of PEK without affecting the ultimate tensile strength and also improves the thermal stability of laser sintered parts. The rule of mixtures is applied to simulate the coefficient of thermal expansion (CTE) of the LS-GB/PEK composite structures and compare with experimental results. The measured CTE values match the calculated results below Tg and deviate slightly from the simulated trend line above Tg

Morphology of polymeric powders in Laser Sintering (LS): from polyamide to new PEEK powders

In an attempt to expand the range of engineering polymers used for laser sintering, this paper examines the morphology, flowability and interparticle interactions of two commercially available Poly (ether ether) ketone (PEEK) powders, not yet optimised for the LS process, by comparison with the LS optimised Polyamide (PA) and Polyetherketone (PEK) powdered polymers. The effect of incorporating fillers and additives on the flow behaviour is also analysed. The Particle Size Distribution (PSD) results alone do not allow ranking the powder materials in relation to the flow behaviour. The particle morphology has a stronger influence on the flow characteristics for materials with similar PSDs. The work also provides additional characterisation parameters to be considered when analysing LS powders

The fabrication and mechanical properties of a novel 3-component auxetic structure for composites

Copyright © 2015 Elsevier. NOTICE: this is the author’s version of a work that was accepted for publication in Composites Science and Technology. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Composites Science and Technology (2015), DOI: 10.1016/j.compscitech.2015.06.012Functional auxetic composite materials can be fabricated from conventional or from auxetic components. The helical auxetic yarn (HAY) is a very recently invented auxetic reinforcing component for composite materials. This paper investigates the Poisson’s ratio behaviour of a further development of the HAY, needed for many practical applications. The 3-component auxetic yarn is based on a stiff wrap fibre (the first component) helically wound around an elastomeric core fibre (the second component) coated by a sheath (the third component). The resultant structure can overcome problems such as slippage of the wrap and changes in wrapping angles previously encountered during the manufacture and utilisation of the two-component HAY. The mechanical performance of conventional and novel systems is investigated; with emphasis on the differences between the engineering and true Poisson’s ratio. The importance of the utilisation of a true tensile modulus and a true Poisson’s ratio is demonstrated. This is the first time reported in the literature that an experimental auxetic effect analysis of HAYs was carried out by comparing true and engineering Poisson’s ratio. We show that depending on the coating thickness of the third component, the 3-component auxetic system can demonstrate auxetic behaviour, and the coating thickness can be employed as a new design parameter to tailor both the Poisson’s ratio and modulus of this novel composite reinforcement for a wide range of applications.Engineering and Physical Science Research Council (EPSRC

The manufacture and mechanical properties of a novel negative Poisson’s ratio 3-component composite

This paper was presented at the ICCM 20 Conference - 20th International Conference on Composite Materials in Copenhagen, 19-24 July 2015. Full conference proceedings are available via the link in this recordMaterials with a negative Poisson’s ratio known also as auxetic materials [1] exhibit unusual property of getting thicker when stretched and thinner when compressed. The helical auxetic yarn (HAY) is a recently invented auxetic reinforcing structure for composites [2]. A helical auxetic yarn (HAY) consists of two fibres: a low modulus elastomeric core and a high modulus wrap fibre in a double helix structure. When a tensile load is applied the core of the HAY becomes wider as the wrap straightens out, resulting in a lateral expansion of the core, and therefore a large negative Poisson’ ratio behaviour. The auxetic behaviour of the HAY can be tailored by altering fibre properties, the initial geometry and also the applied strain to comply with specific applications, such as composites [3, 4], blast mitigation, and filtration [5]. This paper introduces a further development to the current HAY by addition of a third component (a sheath). The presence of the sheath is expected to overcome problems such as slippage of the wrap and inconsistency in the initial wrap angle previously encountered during the manufacture of the HAY. The auxetic performance of conventional and novel systems is investigated and Poisson’s ratio data are presented.Engineering and Physical Sciences Research Council (EPSRC

A study of interface adhesion between polyamide 6 (PA6) and nitrile rubber (NBR)

This is the peer reviewed version of the following article: Wang Y., Ghita O., Kavanagh D., and Chandler D. (2014), A study of interface adhesion between polyamide 6 (PA6) and nitrile rubber (NBR), Surf. Interface Anal., 10-11, pages 1000–1004, which has been published in final form at 10.1002/sia.5488. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving: http://olabout.wiley.com/WileyCDA/Section/id-820227.html#termsThe mechanism of interface bonding of a selected nitrile rubber compound vulcanized on polyamide 6 was studied using transmission electron microscopy. The two types of interfaces identified were formed through mechanical clamping and enhanced by hydrogen bonding between polyamide 6 and silane coupling agent in nitrile rubber compoun

Powder characteristics, microstructure and properties of graphite platelet reinforced Poly Ether Ether Ketone composites in High Temperature Laser Sintering (HT-LS)

This is the author's accepted manuscript. The final published article is avilable from the publisher via DOI: 10.1016/j.matdes.2015.09.094Copyright © 2015 Elsevier Ltd. All rights reserved.The properties of graphite platelet reinforced Poly Ether Ether Ketone (PEEK/GP) composites from powder to laser sintered parts were investigated in this study. The flowability, particle size and laser absorption characteristics of PEEK/GP powders with various graphite loadings were studied. It was found that the addition of graphite improved laser absorption; however, the flowability of powder was reduced. Micro-CT scanning was used to study the distribution, dispersion and the orientation of graphite platelets as well as the porosity and maximum pore size of laser sintered PEEK/GP composites. The graphite platelets were observed to be distributed evenly in the structure without significant agglomeration. Most of the graphite had their in-plane surface orientated in the X-Y plane of fabrication, which increased the tensile strength of the composites incorporating 5. wt.% graphite. The investigation also demonstrated that the porosity and maximum pore size increased with increasing amounts of graphite. A significant increase in porosity and pore size was found in PEEK/GP composites with 7.5. wt.% graphite, and it is believed to be responsible for the drop in tensile strength. DMA analysis showed no reduction of the damping properties in the composites incorporating up to 5. wt.% graphite, whereas the composites with 7.5. wt.% graphite showed increased stiffness

Enhanced Ductility of PEEK thin film with self-assembled fibre-like crystals

This is the author accepted manuscript. The final version is available from the publisher via the DOI in this record.Poly Ether Ether Ketone (PEEK) is a high temperature polymer material known for its excellent chemical resistance, high strength and toughness. As a semi-crystalline polymer, PEEK can become very brittle during long crystallisation times and temperatures helped as well by its high content of rigid benzene rings within its chemical structure. This paper presents a simple quench crystallization method for preparation of PEEK thin films with the formation of a novel fibre-like crystal structure on the surface of the films. These quenched crystallised films show higher elongation at break when compared with conventional melt crystallised thin films incorporating spherulitic crystals, while the tensile strength of both types of films (quenched crystallised and conventional melt) remained the same. The fracture analysis carried out using microscopy revealed an interesting microstructure which evolves as a function of annealing time. Based on these results, a crystal growth mechanism describing the development of the fibre-like crystals on the surface of the quenched crystallised films is proposed.This work is supported by the UK Engineering and Physical Science Research Council (EPSRC Grant No EP/L017318/1-Particle Shape and Flow behaviour in Laser Sintering: from modelling to experimental validation)

Polymer viscosity, particle coalescence and mechanical performance in high-temperature laser sintering

The final publication is available at Springer via http://dx.doi.org/10.1007/s10853-016-9761-6High-temperature laser sintering (HT-LS) is an additive manufacturing technology whose potential could be limited by the restricted number of materials optimised for the process. Poly ether ether ketone (PEEK) with different melt viscosity values, PEEK 150PF and PEEK 450PF, have been used in parallel with the commercial grade, poly ether ketone (PEK) HP3, to investigate the role of material viscosity on particle coalescence, structure and mechanical performance of components manufactured in HT-LS. The material with lower viscosity, PEEK 150PF, was found to exhibit faster coalescence and lower tensile strength than the grades with higher viscosities, PEEK 450PF and PEK HP3

Control and modelling of capillary flow of epoxy resin in aligned carbon nanotube forests

This paper examines the mechanism of infiltration by capillary flow of epoxy resin into vertically-aligned carbon nanotube forests. The resin viscosity during curing was characterized by rheometry. Carbon nanotube forests were brought into contact with resin at a range of times during curing, therefore at a range of viscosities. The penetration of the resin into the forests was measured using electron microscopy, X-ray micro-computed tomography and energy-dispersive X-ray spectroscopy, the latter relying on a chromium-complex dye additive which acts as a marker for the presence of resin. Experimental results were compared to a simulation based on the Implicit Lucas–Washburn equation for capillary flow. It was found that prior to the resin gel point, the resin penetrates through the full height of the forest. Close to the gel point, the flow into the forest ceases, leaving unwetted regions of nanotubes. Understanding the relationship between resin flow in nanotube structures and the resin viscosity and curing has important application in the fabrication of nanocomposite materials. This “partial wetting” effect is a key requirement for a previously proposed method for the fabrication of carbon nanotube composites by additive manufacture (AM) which would provide strong interlayer reinforcement combined with the versatility of AM.Airbus Corp. Ltd. (Airbus Group)University of Exete

Fabrication of Three Dimensional Layered Vertically Aligned Carbon Nanotube Structures and their Potential Applications

This paper proposes a new technique for fabrication of vertically aligned carbon nanotube (VACNT) structures, controlled in shape, height and functionality, through continuous successive growth of VACNT layers by chemical vapour deposition (CVD) combined with patterning strategies. This was achieved by vacuum deposition of additional catalyst material onto the original VACNT “forest” layer. A second forest layer is then observed to grow underneath the first by CVD. It is proposed that the new catalyst material diffuses through the porous nanotube forest to coat the growth substrate underneath. The enhanced height, coating, and vertical alignment of the nanotube forests were verified by electron microscope observation. By repeating this process, aligned nanotube bi-layers and tri-layers were grown, producing a “stack” of nanotube layers. By using a “shadow mask” patterning technique to screen areas of the original forest from catalyst deposition, the growth can be confined to specific areas of the substrate. Potentially, these multilayer nanotube structures would have diverse applications as long composite reinforcements, p–n junctions for electronic devices, or to allow the production of near net shape complex multilayer nanotube structures