Elastostatics of star-polygon tile-based architectured planar lattices

We showed a panoptic view of architectured planar lattices based on star-polygon tilings. Four star-polygon-based lattice sub-families were investigated numerically and experimentally. Finite element-based homogenization allowed computation of Poisson's ratio, elastic modulus, shear modulus, and planar bulk modulus. A comprehensive understanding of the range of properties and micromechanical deformation mechanisms was developed. By adjusting the star angle from $0^\circ$ to the uniqueness limit ($120^\circ$ to $150^\circ$), our results showed an over 250-fold range in elastic modulus, over a 10-fold range in density, and a range of $-0.919$ to $+0.988$ for Poisson's ratio. Additively manufactured lattices showed good agreement in properties. The additive manufacturing procedure for each lattice is available on www.fullcontrol.xyz/#/models/1d3528. Three of the four sub-families exhibited in-plane elastic isotropy. One showed high stiffness with auxeticity at low density with a primarily axial deformation mode as opposed to bending deformation for the other three lattices. The range of achievable properties, demonstrated with property maps, proves the extension of the conventional material-property space. Lattice metamaterials with Triangle-Triangle, Kagome, Hexagonal, Square, Truncated Archimedean, Triangular, and Truncated Hexagonal topologies have been studied in the literature individually. We show that all these structures belong to the presented overarching lattices

Carbon fibre reinforced material extrusion additive manufacturing: fibre orientation and mechanical properties

Material extrusion additive manufacturing (MEAM) of short-fibre-reinforced polymer composites (SFRPCs) has received increased research interest in recent years due to their potential to improve mechanical properties compared to pure polymers. Discrepancies and contradictions regarding the mechanical properties were found in the literature, due to a lack of a microscale fibre morphology and meso-scale geometric characterisation. In addition, true load-bearing areas were rarely measured due to complex specimen configuration and printing defects (inter-filament voids and non-uniform filament orientation). Single-filament-wide specimens not only overcome unnecessary complexity and common defects but also enable reliable properties along the direction of printed filaments and normal to interlayer direction (F and Z directions respectively). These are representative of the upper bound and lower bound of properties of 3D printed SFRPCs. To fully understand the mechanics of 3D printed SFRPCs, fibre orientation and fibre reinforcing effects were studied experimentally and theoretically. Short-fibre orientation in 3D printed SFRPCs was parametrically studied in 2D and 3D experimentally. This unveiled the effects of printing parameters, non-uniform spatial distribution, and fibre length on fibre orientation. Four polymers and their short-carbon-fibre composites were 3D printed into single-filament-wide tensile-testing specimens. Tensile properties were analysed in terms of fibre reinforcement effects, mechanical anisotropy, and printing parameters. Despite widely varying properties of polymers, fibre reinforcements caused greater strength and stiffness anisotropy but lower strain-at-break anisotropy compared to pure polymers. In addition, critical effects of extrusion width on tensile strength, ductility, and stiffness were found for all materials. A brittle-to-ductile fracture transition was achieved by varying extrusion width in all materials. Compared to extrusion width, nozzle temperature and layer height showed limited and inconsistent effects on mechanical properties since they did not affect filament geometry significantly. Finally, theoretical prediction of strength and modulus was implemented via seventeen classical fibre models to test model validity and identify important factors to consider. Effective reinforcing effects of carbon fibre were validated experimentally and theoretically (strength by up to 60% and stiffness by up to 124%). Meanwhile, short fibres did not cause great change in mechanical anisotropy, even less anisotropic for strain-at-break. By controlling extrusion width, mechanical anisotropy could be further reduced across all tested SFRPCs. This was achieved based on understanding of underlying factors for short fibre orientation and parameter inter-correlations. This reveals possibly the simplest way to control or reduce mechanical anisotropy – by increasing the extrusion width. This thesis provides new understanding of the processing-structure-property relationship for extrusion additive manufacturing of SFRPCs, which may enlighten future research and industrial practice in process control, property control, theoretical prediction, and computational simulation of 3D printed fibre composites.</p

3D short fibre orientation for universal structures and geometries in material extrusion additive manufacturing

Fibre orientation critically affects properties in material extrusion additive manufacturing. This study developed new understanding of 3D short-fibre orientation in representative structures intended to capture most features of typical tool-paths. The parametric representative structures included straight paths, curved paths, corners, a range of intersection types, and the start/end of paths. Fibre orientation tensors were used to quantify 3D fibre alignment along the direction of printed filaments (F-alignment), lateral to the in-plane filament direction (F-lat alignment), and normal to the print-platform (Z-alignment). Overall, fibres were highly aligned along the filament direction in both straight paths and curved paths but less aligned at corners and intersections. However, recovery of fibre orientation was found after corners and intersections. To assess fibre orientation uniformity throughout the layer thickness, specimens were sectioned normal to the print platform in seven planes throughout the thickness of a single extruded filament. High fibre orientation (F-alignment) was found intra-filament, but it gradually decreased from upper section to bottom section. Interlayer region showed both high F-alignment and Z-alignment. In addition, extruded-filament width and height critically affected fibre orientation: increasing extrusion width and layer height led to decreased F-alignment. Case studies showed the results are translatable to more complicated structures and a different polymer material. This study provides new understanding of 3D fibre orientation in additive manufacturing and will allow more informed design, analysis and optimisation of short-fibre-reinforced structures to improve performance

Single-filament-wide tensile-testing specimens reveal material-independent fibre-induced anisotropy for fibre-reinforced material extrusion additive manufacturing

Purpose: This study/paper aims to develop fundamental understanding of mechanical properties for multiple fibre-reinforced materials by using a single-filament-wide tensile-testing approach.  Design/methodology/approach: In this study, recently validated single-filament-wide tensile-testing specimens were used for four polymers with and without short-fibre reinforcement. Critically, this specimen construct facilitates filament orientation control, for representative longitudinal and transverse composite directions, and enables measurement of interlayer bonded area, which is impossible with “slicing” software but essential in effective property measurement. Tensile properties were studied along the direction of extruded filaments (F) and normal to the interlayer bond (Z) both experimentally and theoretically via the Kelly–Tyson model, bridging model and Halpin–Tsai model.  Findings: Even though the four matrix-material properties varied hugely (1,440% difference in ductility), consistent material-independent trends were identified when adding fibres: ductility reduced in both F- and Z-directions; stiffness and strength increased in F but decreased or remained similar in Z; Z:F strength anisotropy and stiffness anisotropy ratios increased. Z:F strain-at-break anisotropy ratio decreased; stiffness and strain-at-break anisotropy were most affected by changes to F properties, whereas strength anisotropy was most affected by changes to Z properties.  Originality/value: To the best of the authors’ knowledge, this is the first study to assess interlayer bond strength of composite materials based on measured interlayer bond areas, and consistent fibre-induced properties and anisotropy were found. The results demonstrate the critical influence of mesostructure and microstructure for three-dimensional printed composites. The authors encourage future studies to use specimens with a similar level of control to eliminate structural defects (inter-filament voids and non-uniform filament orientation).</p

Supplemental information files for Are classical fibre composite models appropriate for material extrusion additive manufacturing? A thorough evaluation of analytical models

  Supplementary files for article Are classical fibre composite models appropriate for material extrusion additive manufacturing? A thorough evaluation of analytical models To improve mechanical properties, fibre reinforcement has been used in material extrusion additive manufacturing (MEAM). However, there are few reports about fibre composite mechanics and property prediction in MEAM. This study evaluated seventeen classical composite numerical models to assess their prediction capabilities and applicability in MEAM. Four carbon fibre reinforced polymer composites (PLA, ABS, PA, and PETG) were used. Longitudinal strength and modulus were predicted via the rule of mixtures (RoM), modified rule of mixtures (MRoM), Kelly model, Cox shear lag model, and modified Cox models. Transverse strength was predicted via the RoM transverse model and bridging model. Transverse modulus was predicted via the RoM transverse model, Halpin-Tsai, and modified Halpin-Tsai models. These models are widely accepted in the composite field but have not been assessed for MEAM. The predicted strengths and moduli were normalised by experimental values. For all materials, all models overestimated the longitudinal strength. The best predictions were found for the Kelly model, Cox-Krenchel model, and modified Cox model (with porosity) for longitudinal strength: normalised strengths were 2.02, 1.54, 1.63, respectively, averaged for all materials, compared to 2.46–8.82 for other models. Longitudinal modulus was well-predicted by the Kelly model and Cox-based models (normalised modulus of 0.87–2.05). The RoM transverse model and bridging model accurately predicted transverse modulus and strength, respectively (normalised strength 0.99 and normalised modulus 1.14). Additionally, model efficiency also varied between materials. PA was more predictable for longitudinal strength than PLA, PETG, and ABS (normalised strengths: 3.19, 3.98, 4.56, and 4.81, respectively) and in modulus (normalised moduli: 2.64, 3.01, 2.84, and 2.99), but less predictable in transverse strength (1.74, 2.02, 1.29, and 1.64) and transverse modulus (1.90, 2.02, 0.92, and 1.13). Fractography evidenced non-uniform fibre length, non-uniform fibre orientation, and weak fibre-matrix interface, which likely caused the discrepancies between theoretical and experimental properties. Potential revisions to improve model accuracy were discussed. Factors including fibre orientation, fibre length, fibre clustering, porosity, and fibre-matrix interface were highlighted for better prediction, which facilitates better understanding in mechanics and modelling of 3D printing fibre composites. </p

Are classical fibre composite models appropriate for material extrusion additive manufacturing? A thorough evaluation of analytical models

To improve mechanical properties, fibre reinforcement has been used in material extrusion additive manufacturing (MEAM). However, there are few reports about fibre composite mechanics and property prediction in MEAM. This study evaluated seventeen classical composite numerical models to assess their prediction capabilities and applicability in MEAM. Four carbon fibre reinforced polymer composites (PLA, ABS, PA, and PETG) were used. Longitudinal strength and modulus were predicted via the rule of mixtures (RoM), modified rule of mixtures (MRoM), Kelly model, Cox shear lag model, and modified Cox models. Transverse strength was predicted via the RoM transverse model and bridging model. Transverse modulus was predicted via the RoM transverse model, Halpin-Tsai, and modified Halpin-Tsai models. These models are widely accepted in the composite field but have not been assessed for MEAM. The predicted strengths and moduli were normalised by experimental values. For all materials, all models overestimated the longitudinal strength. The best predictions were found for the Kelly model, Cox-Krenchel model, and modified Cox model (with porosity) for longitudinal strength: normalised strengths were 2.02, 1.54, 1.63, respectively, averaged for all materials, compared to 2.46–8.82 for other models. Longitudinal modulus was well-predicted by the Kelly model and Cox-based models (normalised modulus of 0.87–2.05). The RoM transverse model and bridging model accurately predicted transverse modulus and strength, respectively (normalised strength 0.99 and normalised modulus 1.14). Additionally, model efficiency also varied between materials. PA was more predictable for longitudinal strength than PLA, PETG, and ABS (normalised strengths: 3.19, 3.98, 4.56, and 4.81, respectively) and in modulus (normalised moduli: 2.64, 3.01, 2.84, and 2.99), but less predictable in transverse strength (1.74, 2.02, 1.29, and 1.64) and transverse modulus (1.90, 2.02, 0.92, and 1.13). Fractography evidenced non-uniform fibre length, non-uniform fibre orientation, and weak fibre-matrix interface, which likely caused the discrepancies between theoretical and experimental properties. Potential revisions to improve model accuracy were discussed. Factors including fibre orientation, fibre length, fibre clustering, porosity, and fibre-matrix interface were highlighted for better prediction, which facilitates better understanding in mechanics and modelling of 3D printing fibre composites

Supplementary information files for 3D short fibre orientation for universal structures and geometries in material extrusion additive manufacturing

© the authors, CC-BY 4.0 Supplementary files for article 3D short fibre orientation for universal structures and geometries in material extrusion additive manufacturing Fibre orientation critically affects properties in material extrusion additive manufacturing. This study developed new understanding of 3D short-fibre orientation in representative structures intended to capture most features of typical tool-paths. The parametric representative structures included straight paths, curved paths, corners, a range of intersection types, and the start/end of paths. Fibre orientation tensors were used to quantify 3D fibre alignment along the direction of printed filaments (F-alignment), lateral to the in-plane filament direction (F-lat alignment), and normal to the print-platform (Z-alignment). Overall, fibres were highly aligned along the filament direction in both straight paths and curved paths but less aligned at corners and intersections. However, recovery of fibre orientation was found after corners and intersections. To assess fibre orientation uniformity throughout the layer thickness, specimens were sectioned normal to the print platform in seven planes throughout the thickness of a single extruded filament. High fibre orientation (F-alignment) was found intra-filament, but it gradually decreased from upper section to bottom section. Interlayer region showed both high F-alignment and Z-alignment. In addition, extruded-filament width and height critically affected fibre orientation: increasing extrusion width and layer height led to decreased F-alignment. Case studies showed the results are translatable to more complicated structures and a different polymer material. This study provides new understanding of 3D fibre orientation in additive manufacturing and will allow more informed design, analysis and optimisation of short-fibre-reinforced structures to improve performance.</p

Elastostatics of star-polygon tile-based architectured planar lattices

A panoptic view of architectured planar lattices based on star-polygon tilings was developed. Four star-polygon-based lattice sub-families, formed of systematically arranged triangles, squares, or hexagons, were investigated numerically and experimentally. Finite-element-based homogenization allowed computation of Poisson's ratio, elastic modulus, shear modulus, and planar bulk modulus. A comprehensive understanding of the range of properties and micromechanical deformation mechanisms was developed. Adjusting the star-polygon angle achieved an over 250-fold range in elastic modulus, over a 10-fold range in density, and a range of -0.919 to +0.988 for Poisson's ratio. Additively manufactured lattices, achieved by novel printing strategies, showed good agreement in properties. Parametric additive manufacturing procedures for all lattices are available on www.fullcontrol.xyz/#/models/1d3528. Three of the four sub-families exhibited in-plane elastic isotropy. One showed high stiffness with auxeticity at low density and a primarily axial deformation mode as opposed to bending deformation for the other three lattices. The range of achievable properties, demonstrated with property maps, proves the extension of the conventional material-property space. Lattice metamaterials with Triangle-Triangle, Kagome, Hexagonal, Square, Truncated Archimedean, Triangular, and Truncated Hexagonal topologies have been studied in the literature individually. Here, it is shown that these structures belong to the presented overarching lattice family

Extrusion width critically affects fibre orientation in short fibre reinforced material extrusion additive manufacturing

This study develops new understanding of fibre orientation distribution in material extrusion additive manufacturing of short fibre reinforced polymer composites. Short carbon fibre reinforced polylactic acid was 3D printed at several nozzle temperatures (Tn), printing speeds (V), and extrusion widths set in the GCode (Wset), to identify the effects of these parameters on fibre orientation. Microscopic characterisation of the top surface of 3D printed filaments allowed detailed analysis of fibre orientation including dependencies on extruded filament width and printing parameters. The printing parameters directly affected measured width of extruded filaments and a wider extrusion resulted from increased Tn, increased Wset, and decreased V. An assumption of normal distribution appropriately represented the planar fibre orientation distribution. A direct relationship was found between fibre orientation and extrusion width: fibres were more highly oriented along the printing direction when the extruded filament was narrower. This is logical because when extruded material spreads laterally to the printing direction - to achieve wider extrusions - the polymer-fibre-composite melt flow is less aligned to the printing direction. A consistent relationship between fibre orientation and extrusion width was found even when printing conditions varied several-fold (4-fold change in V; 2-fold change in Wset; 20 °C change in Tn), highlighting the dominant influence of the extruded-filament geometry. This relationship also existed for considerably different 3D printing hardware and a different polymer (acrylonitrile butadiene styrene). A case study for tensile modulus of three different short-carbon-fibre-reinforced polymers, each with three different extrusion widths, showed how the findings related to fibre orientation can explain variation in mechanical properties for multiple materials. The results of this study allow more in-depth understanding and analysis of processing-structure-property correlations. They also highlight the crucial role of extrusion width and fibre orientation as well as the importance of characterising both direct and indirect effects of printing parameters

Development of combi-pills using the coupling of semi-solid syringe extrusion 3D printing with fused deposition modelling

Three-dimensional (3D) printing allows for the design and printing of more complex designs than traditional manufacturing processes. For the manufacture of personalised medicines, such an advantage could enable the production of personalised drug products on demand. In this study, two types of extrusion-based 3D printing techniques, semi-solid syringe extrusion 3D printing and fused deposition modelling, were used to fabricate a combi-layer construct (combi-pill). Two model drugs, tranexamic acid (water soluble, rapid release) and indomethacin (poorly water-soluble, extended release), were printed with different geometries and materials compositions. Fourier transform infrared spectroscopy results showed that there were no interactions detected between drug-drug and drug-polymers. The printed combi-pills demonstrated excellent abrasion resisting properties in friability tests. The use of different functional excipients demonstrated significant impact on in vitro drug release of the model drugs incorporated in two 3D printed layers. Tranexamic acid and indomethacin were successfully 3D printed as a combi-pill with immediate-release and sustained-release profiles, respectively, to target quick anti-bleeding and prolonged anti-inflammation functions. For the first time, this paper systematically demonstrates the feasibility of coupling syringe-based extrusion 3D printing and fused deposition modelling as an innovative platform for various drug therapy productions, facilitating a new era of personalised combi-pills development