Thermo-mechanical behaviour of composite moulding compounds at elevated temperatures

This is the author accepted manuscript. The final version is available from Elsevier via the DOI in this record.The use of fibre-reinforced polymer composites as a lightweight metal replacement for automotive componentry is constantly expanding into new and more challenging application areas (e.g. whole range of under-bonnet, exhaust applications and other automotive components), where service temperatures are not expected to go beyond 150°C. This study seeks to provide some useful baseline data on the bending stiffness performance of a large range of commercially available composite moulding compounds, in order to provide guidance in selecting appropriate materials for various applications requiring higher operating temperatures, where retention of bending stiffness is a key parameter. Whilst glass transition data can give some indication, this study seeks to go further. Three point bending flexural tests and Dynamic Mechanical Analysis were used to investigate and compare properties both at ambient and 150°C comparing various composite systems, particularly phenolics, one of the fastest-growing systems in the thermoset moulding compounds market.Innovate U

Mechanical property variance amongst vertical fused filament fabricated specimens via four different printing methods

This is the final version. Available on open access from Wiley via the DOI in this recordAmongst additive manufacturing processes, fused filament fabrication (FFF) is one of the most affordable and cost efficient technologies that can produce complex shaped components with an increasing number of printable polymers such as the polyaryletherketone (PAEK) family, polyetherimide (PEI), and polyphenylene sulfide (PPS). Despite the gain in popularity, there is a lack of standardization in specimen's preparation and mechanical testing of FFF samples. This study investigates the effect of different methods of printing vertical tensile specimens on the mechanical properties whilst the material and the printing parameters are fixed. A slow crystallising polyetheretherketone (PEKK) grade was selected as the printing material to exclude the effect of crystallisation on the interlayer bonding strength, leaving the temperature‐dependent amorphous molecular diffusion across the layers as the governing mechanism. Vertical tensile specimens made by four printing methods: individually printed, machined, and connected (based on ISO 527‐2‐1A and ISO 527‐2‐1BA) were assessed. Individually printed vertical specimens were found to have the highest mean tensile strength, owing to the high level of diffusion induced by the very short layer time. The strengths of specimens printed via the other three methods are less sensitive to the effect of layer time, due to the rate of change during cooling and its relationship with the local temperature at the interlayer surface. This study highlights the importance of the disclosure of FFF printing methods along with any reported mechanical data

Slow and fast crystallising poly aryl ether ketones (PAEKs) in 3D printing: crystallisation kinetics, morphology, and mechanical properties

This is the author accepted manuscript. The final version is available from Elsevier via the DOI in this recordPoly aryl ether ketone (PAEK) polymers are gaining interest in 3D printing for their good mechanical properties and high service temperatures. The aim of this study was to compare the crystallisation kinetics, morphology, and mechanical properties of two different PAEK polymers used in fused filament fabrication (FFF), i.e. the fast crystallising PEEK151 (poly ether ether ketone) grade originally designed for injection moulding and the slow crystallising AM 200 grade tailored specifically for FFF. The crystallisation kinetics of both grades were examined across a wide temperature range. A method to select annealing temperatures and annealing times based on the intrinsic crystallisation behaviour of each polymer was proposed. The dual-Avrami model highlighted a different crystallite growth for AM 200 in comparison with PEEK151 with a higher rate of secondary crystallisation. Lamellar thicknesses were measured by SAXS and calculated via the Thomson-Gibbs equation. The lamellar thicknesses of primary and secondary crystallisation for AM 200 showed a stronger temperature dependence with steeper slopes when increasing the isothermal temperature. The benefit of using a slow crystallising PAEK polymer over the conventional fast crystallising grades is evidenced by the improvement of Z strength which enhances the overall isotropy of printed parts

Powder Bed Fusion Versus Material Extrusion: A Comparative Case Study on Polyether-Ether-Ketone Cranial Implants

This is the final version. Available on open access from Mary Ann Liebert via the DOI in this recordAs the choice of additive manufacturing (AM) technologies is becoming wider with reliable processes and a wider range of materials, the selection of the right technology to fabricate a certain product is becoming increasingly difficult from a technical and cost perspective. In this study polyether-ether-ketone cranial implants were manufactured by two AM techniques: powder bed fusion (PBF) and fused filament fabrication (FFF) and their dimensional accuracy, compression performance, and drop tower impact behavior were evaluated and compared. The results showed that both types of specimens differed from the original computer-aided design; although the origin of the deviation was different, the PBF samples were slightly inaccurate owing to the printing process where the accuracy of the FFF samples was influenced by postprocessing and removal of the scaffolds. The cranial implants fabricated using the FFF method absorbed more energy during the compression and impact tests in comparison with the PBF process. The failure mechanisms revealed that FFF samples have a higher ability to deform and a more consistent failure mechanisms, with the damage localized around the puncture head region. The brittle nature of the PBF samples, a feature observed with other polymers as well, led to complete failure of the cranial implants into several pieces.Engineering and Physical Sciences Research Council (EPSRC

Multiscale Porous Poly (Ether-Ether-Ketone) Structures Manufactured by Powder Bed Fusion Process

This is the final version. Available on open access from Mary Ann Liebert via the DOI in this recordThe aim of the study is to create a multiscale highly porous poly (ether-ether-ketone) (PEEK) structure while maintaining mechanical performance; the distribution of pores being generated by the manufacturing process combined with a porogen leaching operation. Salt at 70 wt% concentration was used as a porogen in a dry blend with PEEK powder sintered in the powder bed fusion process. The printed porous PEEK structures were examined and evaluated by scanning electron microscopy, microcomputed tomography, and mechanical testing. The PEEK structures incorporating 70 wt% salt achieved 79–86% porosity, a compressive yield strength of 4.1 MPa, and a yield strain of ∼60%. Due to the salt leaching process, the PEEK porous frameworks were fabricated without the need to drastically reduce the process parameters (defined by the energy density [ED]), hence maintaining the structural integrity and good mechanical performance. The compression results highlighted that the performance is influenced by the printing orientation, level of the PEEK particle coalescence (controlled here by the ED), pore/cell wall thickness, and subsequently, the overall porosity framework. The porous printed PEEK structures could find potential uses in a wide range of applications from tissue engineering, filtration and separation to catalysts, drug release, and gas storage