Filament Cross-section Research Articles

Polyether Ketone Ketone (PEKK) matrix composites for material extrusion additive manufacturing

Despite the widespread use of fused filament fabrication (FFF) (an extrusion-based additive manufacturing process) to manufacture end-use parts for the aerospace industry, limited materials are available within this process that can be used for structural applications in the harsh space environment. Currently available high-performance polymers need to be improved by incorporating additives within the polymer matrix to achieve multi-functional properties. Additives such as graphene, graphene oxide, carbon nanotubes and boron carbide are known to improve mechanical and thermal properties and radiation shielding. This study aims to understand if these additives can be successfully incorporated into PEKK matrix to manufacture printable filaments for FFF. Graphene, graphene oxide (GO) and boron carbide (B4C) were compatibilised with PEKK matrix, and their mechanical, thermal and rheological properties were analysed and compared with commercially available carbon fibre and carbon nanotube-reinforced PEKK where appropriate. As rheological properties of the formulations confirmed that they were printable, filaments for FFF were then manufactured. Graphene–PEKK was the most printable filament followed by GO–PEKK while B4C–PEKK was not printable. TEM images of filament cross-section showed good dispersion of graphene and graphene oxide, while boron carbide formed large agglomerates; B4C also presented feeding issues due to its hardness which affected its printability. Dispersion of the additives was also confirmed by studying their X-ray diffraction (XRD) patterns, and chemical structures were assessed using FT-IR spectroscopy. Finally, parts were printed using selected composite filaments, and their porosity and surface roughness were compared with neat PEKK and commercial CNT-reinforced PEKK to develop an understanding of metrology and bulk material properties of the composites.

The structure and dynamics of massive high-z cosmic-web filaments: three radial zones in filament cross-sections

ABSTRACT We analyse the internal structure and dynamics of cosmic-web filaments connecting massive high-z haloes. Our analysis is based on a high-resolution arepo cosmological simulation zooming-in on three Mpc-scale filaments feeding three massive haloes of $\sim 10^{12}\, \text{M}_\odot$ at z ∼ 4, embedded in a large-scale sheet. Each filament is surrounded by a cylindrical accretion shock of radius $r_{\rm shock} \sim 50 \, {\rm kpc}$. The post-shock gas is in virial equilibrium within the potential well set by an isothermal dark-matter filament. The filament line-mass is $\sim 9\times 10^8\, \text{M}_\odot \, {\rm kpc}^{-1}$, the gas fraction within rshock is the universal baryon fraction, and the virial temperature is ∼7 × 105 K. These all match expectations from analytical models for filament properties as a function of halo mass and redshift. The filament cross-section has three radial zones. In the outer ‘thermal’ (T) zone, $r \ge 0.65 \, r_{\rm shock}$, inward gravity, and ram-pressure forces are overbalanced by outward thermal pressure forces, decelerating the inflowing gas and expanding the shock outwards. In the intermediate ‘vortex’ (V) zone, 0.25 ≤ r/rshock ≤ 0.65, the velocity field is dominated by a quadrupolar vortex structure due to offset inflow along the sheet through the post-shock gas. The outward force is dominated by centrifugal forces associated with these vortices, with additional contributions from global rotation and thermal pressure. Shear and turbulent forces associated with the vortices act inwards. The inner ‘stream’ (S) zone, $r \lt 0.25 \, r_{\rm shock}$, is a dense isothermal core, $T\sim 3 \times 10^4 \, {\rm K}$ and $n_{\rm H}\sim 0.01 \, {\rm cm^{-3}}$, defining the cold streams that feed galaxies. The core is formed by an isobaric cooling flow and is associated with a decrease in outward forces, though exhibiting both inflows and outflows.

Characterizing properties of scaffolds 3D printed with peptide-polymer conjugates

Three-dimensional (3D) printing is a popular biomaterials fabrication technique because it enables scaffold composition and architecture to be tuned for different applications. Modifying these properties can also alter mechanical properties, making it challenging to decouple biochemical and physical properties. In this study, inks containing peptide-poly(caprolactone) (PCL) conjugates were solvent-cast 3D printed to create peptide-functionalized scaffolds. We characterized how different concentrations of hyaluronic acid-binding (HAbind-PCL) or mineralizing (E3-PCL) conjugates influenced properties of the resulting 3D-printed constructs. The peptide sequences CGGGRYPISRPRKR (HAbind-PCL; positively charged) and CGGGAAAEEE (E3-PCL; negatively charged) enabled us to evaluate how conjugate chemistry, charge, and concentration affected 3D-printed architecture, conjugate location, and mechanical properties. For both HAbind-PCL and E3-PCL, conjugate addition did not affect ink viscosity, filament diameter, scaffold architecture, or scaffold compressive modulus. Increasing conjugate concentration in the ink prior to printing correlated with an increase in peptide concentration on the scaffold surface. Interestingly, conjugate type affected final conjugate location within the 3D-printed filament cross-section. HAbind-PCL conjugates remained within the filament bulk while E3-PCL conjugates were located closer to the filament surface. E3-PCL at all concentrations did not affect mechanical properties, but an intermediate HAbind-PCL concentration resulted in a moderate decrease in filament tensile modulus. These data suggest final conjugate location within the filament bulk may influence mechanical properties. However, no significant differences were observed between PCL filaments printed without conjugates and filaments printed with higher HAbind-PCL concentrations. These results demonstrate that this 3D printing platform can be used to functionalize the surface without significant changes to the physical properties of the scaffold. The downstream potential of this strategy will enable decoupling of biochemical and physical properties to fine-tune cellular responses and support functional tissue regeneration.

3D-Printable PLA/Mg Composite Filaments for Potential Bone Tissue Engineering Applications.

Magnesium (Mg) is a promising material for bone tissue engineering applications due to it having similar mechanical properties to bones, biocompatibility, and biodegradability. The primary goal of this study is to investigate the potential of using solvent-casted polylactic acid (PLA) loaded Mg (WE43) composites as filament feedstock for fused deposition modeling (FDM) 3D Printing. Four PLA/Magnesium (WE43) compositions (5, 10, 15, 20 wt%) are synthesized and produced into filaments, then used to print test samples on an FDM 3D printer. Assessments are made on how Mg incorporation affected PLA's thermal, physicochemical, and printability characteristics. The SEM study of the films shows that the Mg particles are uniformly distributed in all the compositions. The FTIR results indicate that the Mg particles blend well with the polymer matrix and there is no chemical reaction between the PLA and the Mg particles during the blending process. The thermal studies show that the addition of Mg leads to a small increase in the melting peak reaching a maximum of 172.8 °C for 20% Mg samples. However, there are no dramatic variations in the degree of crystallinity among the Mg-loaded samples. The filament cross-section images show that the distribution of Mg particles is uniform up to a concentration of 15% Mg. Beyond that, non-uniform distribution and an increase in pores in the vicinity of the Mg particles is shown to affect their printability. Overall, 5% and 10% Mg composite filaments were printable and have the potential to be used as composite biomaterials for 3D-printed bone implants.

Numerical Simulation and Experimental Study the Effects of Process Parameters on Filament Morphology and Mechanical Properties of FDM 3D Printed PLA/GNPs Nanocomposite.

The selection of optimal process parameters has a decisive effect on the quality of 3D printing. In this work, the numerical and experimental methods were employed to investigate the FDM printing deposition process of PLA/GNPs nanocomposite. The effect of process parameters on cross-sectional morphology and dimension of the deposited filament, as well as the mechanical property of the FDM printed specimens were studied. The extrusion and the deposition process of the molten PLA/GNPs nanocomposite was simulated as a fluid flow by the paradigm of CFD, the effects of printing temperature and shear rate on thermal-physical properties, such as viscosity and surface tension, were considered in models. Under the assumptions of non-Newtonian fluid and creep laminar flow, the deposition flow was controlled by two key parameters: the nozzle temperature and the nozzle velocity. The numerical model was verified by experiments from four aspects of thickness, width, area, and compactness of the deposited PLA/GNPs nanocomposite filament cross-section. Both the numerical simulation and experiment results show that with the increase of nozzle temperature and nozzle velocity, the thickness, area, and compactness of the deposited filament decreases. While the width of deposited filament increased with the increase of nozzle temperature and decrease of nozzle velocity. The decrease in thickness and the increase in width caused by the change of process parameters reached 10.5% and 24.7%, respectively. The tensile strength of the printed PLA/GNPs specimen was about 61.8 MPa under the higher nozzle temperatures and velocity condition, an improvement of 18.6% compared to specimen with the tensile strength of 52.1 MPa under the lower nozzle temperatures and velocity condition. In addition, the experimental results indicated that under the low nozzle velocity and nozzle temperature condition, dimensional standard deviation of the printed specimens decreased by 52.2%, 62.7%, and 68.3% in X, Y, and Z direction, respectively.

Suppression of Filament Defects in Embedded 3D Printing

Embedded 3D printing enables the manufacture of soft, intricate structures. In the technique, a nozzle is embedded into a viscoelastic support bath and extrudes filaments or droplets. While embedded 3D printing expands the printable materials space to low-viscosity fluids, it also presents new challenges. Filament cross-sections can be tall and narrow, have sharp edges, and have rough surfaces. Filaments can also rupture or contract due to capillarity, harming print fidelity. Through digital image analysis of in situ videos of the printing process and images of filaments just after printing, we probe the effects of ink and support rheology, print speeds, and interfacial tension on defects in individual filaments. Using model materials, we determine that if both the ink and support are water-based, the local viscosity ratio near the nozzle controls the filament shape. If the ink is slightly more viscous than the support, a round, smooth filament is produced. If the ink is oil-based and the support is water-based, the capillary number, or the product of the ink speed and support viscosity divided by the interfacial tension, controls the filament shape. To suppress contraction and rupture, the capillary number should be high, even though this leads to trade-offs in roughness and roundness. Still, inks at nonzero interfacial tension can be advantageous, since they lead to much rounder and smoother filaments than inks at zero interfacial tension with equivalent viscosity ratios.

Multi-Scale Modelling of the Bound Metal Deposition Manufacturing of Ti6Al4V

Nonlinear shrinkage of the metal part during manufacturing by bound metal deposition, both on the ground and under microgravity, is considered. A multi-scale physics-based approach is developed to address the problem. It spans timescales from atomistic dynamics on the order of nanoseconds to full-part shrinkage on the order of hours. This approach enables estimation of the key parameters of the problem, including the widths of grain boundaries, the coefficient of surface diffusion, the initial redistribution of particles during the debinding stage, the evolution of the microstructure from round particles to densely-packed grains, the corresponding changes in the total and chemical free energies, and the sintering stress. The method has been used to predict shrinkage at the levels of two particles, of the filament cross-section, of the sub-model, and of the whole green, brown, and metal parts.

Environmental impact of extrusion-based additive manufacturing: generic model, power measurements and influence of printing resolution

We focus in this paper on the embodied and operational contribution to climate change of a concrete-printing robotic cell. We first propose, in the case of extrusion-based additive manufacturing, a simple functional unit that relates a volume-based material impact and a time-based process impact through the printing head velocity and the filament cross section. We then compute, for two robotic arms/bi-component case studies, the embodied impact related to the production of the printing cells themselves and measure their hourly electrical power consumptions. Our results and analysis suggest that the relative contribution to climate change of the printing process alone depends mostly on its spatial resolution. This suggests finally the existence of an optimal printing resolution that may allow for the highest material saving while minimizing the process-related climate change impact.

Microstructural examination of carbonated 3D-printed concrete.

The recent interest in 3D printing with concrete has generated great interest on how inhomogeneities arise and affect performance parameters, in particular strength and durability. With respect to durability, of particular interest is how 3D‐printed layer interfaces can impact transport of species of interest, such as moisture, chlorides or carbon dioxide in carbonation processes. This is of particular interest considering that the primary use case of 3D‐printed concrete has been as a lost formwork for a cast structural concrete, and thus it is of interest to determine the carbonation resistance. This study consists of a preliminary look at the microstructure after accelerated carbonation of a 3D‐printed concrete used as a lost formwork. Preferential carbonation is observed in the layer interfaces compared to the bulk of the printed filaments, possibly related to porosity from air voids or a locally high capillary porosity corresponding to the lubrication layer.

High-resolution 2D Raman mapping of mono- and bicomponent filament cross-sections

A high-resolution Raman mapping method has been developed in order to obtain 2D information about structural anisotropies (crystallinity, molecular alignment) in thin filament cross-sections (diameters between 27 μm and 79 μm). Cross-sections of melt-spun, hot-drawn poly (ethylene terephthalate) (PET) filaments and bicomponent core-sheath PET-polyamide 6 (PA6) filaments have been scanned through a laser beam (spatial resolution <1 μm). Raman spectra were analyzed with a specifically developed peak fitting method to obtain Raman maps, e.g., mapped peak height ratios across the face of the fibers. These maps reveal microscopic interconnected networks of crystalline strands within a low crystalline matrix. Radial gradients in PET crystallinity, as well as average and surface crystallinities, were determined. The presented Raman mapping method to visualize variations in the PET crystallinity across such fine filament cross-sections, and the findings thereof, open a new pathway to better understand how fiber processing parameters affect radial fiber structures.

Novel hole-pillar spacer design for improved hydrodynamics and biofouling mitigation in membrane filtration

Feed spacers are the critical components of any spiral-wound filtration module, dictating the filtration performance. Three spacer designs, namely a non-woven commercial spacer (varying filament cross-section), a symmetric pillar spacer, and a novel hole-pillar spacer (constant filament diameter) were studied using Direct Numerical Simulations (DNS), 3-D printed and subsequently experimentally tested in a lab-scale ultrafiltration set-up with high biofouling potential feed water at various feed pressures. Independent of the applied pressure, the novel hole-pillar spacer showed initially the lowest feed channel pressure drop, the lowest shear stress, and the highest permeate flux compared to the commercial and pillar spacers. Furthermore, less biofilm thickness development on membrane surface was visualized by Optical Coherent Tomography (OCT) imaging for the proposed hole-pillar spacer. At higher feed pressure, a thicker biofilm developed on membrane surface for all spacer designs explaining the stronger decrease in permeate flux at high pressure. The findings systematically demonstrated the role of various spacer designs and applied pressure on the performance of pre-treatment process, while identifying specific shear stress distribution guidelines for engineering a new spacer design in different filtration techniques.

Water/moisture vapor permeabilities and thermal wear comfort of the Coolmax®/bamboo/tencel included PET and PP composite yarns and their woven fabrics

This study examined the water and moisture vapor permeabilities and the heat retention rate related to the wear comfort of the woven fabrics made from different types of composite yarn, the sheath/core composite yarn structure and non-circular cross-section of the constituent filaments (Coolmax®) in the core region played a very important role with high fabric porosity by including a capillary absorption in the wicking property. The fabric structures with high porosity composed of Coolmax® sheath/core yarns, and spun yarns with non-circular cross-sectional fibers (Coolmax®) affected strongly the fast drying rate due to moisture vapor diffusion of composite yarn fabrics. The moisture vapor permeability of the composite yarn fabrics was highly dependent on the porosity in the sheath/core yarn structures, In addition, the heat retention rate of the composite yarn fabric was strongly influenced by the high porosity due to the sheath/core and bulky staple yarn structures as well as the low thermal conductivity of the constituent fibers.

Improving end use potential of denim fabric in cold climates by chenille yarn

Some thermal comfort parameters of denim fabrics including chenille weft yarns that have different pile materials (polyester (PET-polyethylene terephthalate) filaments, polyester/viloft, acrylic) were investigated. Besides objective measurements, subjective forearm test was carried out on 30 subjects. Weave of the fabric was selected as not to show the pile material from outer surface of the fabric not to destroy denim look, but to enhance thermal contact and insulation characteristics. Results show that thermal feelings are not related to surface friction characteristics when materials are used in pile form, but although acrylic pile created smoother surface, it was evaluated as warmer than the other fabrics. Permeability (air and water vapor) results decreased with rougher and bulkier pile materials as expected. Thermal resistance, one of the parameters that was aimed to be enhanced in this study, was also affected from the number of filaments in cross section but not affected from other features such as non-circular cross section and crimped structure enabling more air trapped within the structure as in normal woven fabrics.

Quick measurement of all filaments' diameters in E-glass yarn by Image-Pro Plus

At present, there are many methods to measure the diameters of filaments in E-glass yarn, but only the average diameter is reported, which cannot reflect all the filaments in the yarn. The methods based on physical principle are not intuitive, the data based on the longitudinal fiber diameter image measurement method are not comprehensive, the observation on the cross-section image of yarn based on slice-making is time-consuming and labor-intensive, and requires manual measurement or self-developed software application. In this article, Keyence VK-X110 3D laser morphometry microscope was used to quickly obtain the cross-section image of glass filament yarn without making a slice of E-glass yarn, and Image-Pro Plus was used to measure all the filaments' diameters in the yarn automatically. The measurement data and analysis show that under the condition of completely processing all the filaments' image, minor axis of filament cross-section is approximate to the filament diameter. This method is not only able to verify whether glass filament yarn meets the quality criteria of ASTM D578-00, but also provides the diameter distribution of all the filaments in an E-glass yarn. In addition, the data support more comprehensive evaluation standard for the quality of glass filament spinning.

Molecular-dynamics study of the carbon nanotube mechanical metahelix

Hierarchical helical structures extensively exist in both natural and artificial systems and hold remarkable mechanical properties. Here, tensile mechanical properties of metahelix designed by twisting multiply twisted helical carbon nanotube ropes are investigated by coarse-grained molecular dynamic simulations. One-level metahelix are slightly mechanically strengthened with increasing twist angle α. However, two-level ones are more sensitive to the twist operation angles α and β, with maximum reduction in strength and Young's modulus by 64% and 87%, respectively. Three distinct failure modes are identified, although all metahelix show brittle failure under tension. For type I fracture mode, regardless the twist angle in metahelix, stress is uniformly distributed, resulting in simultaneous breakage of bonds at a cross-section. The type II and III failure modes are featured by stepwise localized failures, resulting from non-uniform stress distribution along each filament and identical cross-section of metahelix. This work provides molecular insights into optimal mechanical performance of CNT-based hierarchical helical yarns.

Visualization of the grain structure in the filament cross sections of uniaxially textured high J c Bi-2223 tapes

In this study, we extensively used electron backscatter diffraction orientation imaging microscopy to visualize the grain structure in the flat-rolled (Bi,Pb)2Sr2Ca2Cu3O x (Bi-2223) tapes. The thermomechanical process made the grains’ c-axes oriented normal to the tape surface. The 24% difference in critical current density J c was caused by the ∼5° difference in the degree of out-of-plane texture. Although the in-plane orientations are not controlled, the Bi-2223 grains can form the domains, each of which consists of the grains with similar in-plane orientation. Controlling the domain formation could be the next protocol to raise the J c of Bi-2223 tapes.

Point contact spectroscopy of superconductors via nanometer scale point contacts formed by resistive switching

Point contact spectroscopy is commonly used to investigate electronic properties of superconductors. Here we show that nanometer scale point contacts, which enable to study the superconductor properties locally, can be created by means of the resistive switching phenomenon. Our experiments were performed on sandwiched MgB2/Al/TiO2/Pt structures, where multiple bipolar resistive switching cycles were conducted. The differential conductance as a function of voltage was measured at temperatures below the critical temperature of the MgB2 superconductor. In the low-resistance state the MgB2 and Pt electrodes are connected by an ultrathin metallic filament which creates at the MgB2 electrode the Sharvin point contact with diameter below 10 nm. In this case the differential conductance data demonstrate the Andreev reflections due to the carrier transport between the superconducting MgB2 electrode and filament. From these data the two-gap superconductivity of MgB2 is clearly visible which also confirms the fit by the Blonder-Tinkham-Klapwijk model. If the bottom electrode is made of a superconductor with known gap, our approach allows us to estimate from the Andreev reflection spectrum the resistance of both the filament and point contact. We can then determine from the Sharvin formula the cross-section size of the point contact and thus also the filament cross-section size. In the high resistance state when the filament is ruptured, the differential conductance data demonstrate the spectrum typical for tunneling between two normal metals, with a zero-bias anomaly due to the Altshuler-Aronov effect. This suggests that the filament is not ruptured at the superconducting MgB2 electrode but elsewhere.

New Image Analysis Method for Determination of the Inter-Fibre Pore Size Intensity of Polyester Woven Barrier Fabrics

Porosity is an important characteristic of a filter textile, which affects permeability and retention properties. Determination of the inter-yarn and inter-fibre pore sizes of barrier textiles is also required to assess the filter behaviour of these textiles. In this study, a software tool was developed to detect the inter-fibre pore size distribution and pore size intensity of multifilament woven barrier fabrics using cross-section images. Fabrics were chosen according to their fabric construction parameters, such as the fabric index, weft yarn filament fineness and weft yarn structure (flat or textured). Microscopic cross-section images of weft yarns were taken, processed to binary images, and analysed with respect to the pore size distribution, number of pore lengths and pore intensity. It was also analysed how the fabric index, filament cross-section and filament fineness affect the inter-fibre pore lengths and separation level proposed. It was found that weft yarns with wider lengths and lower height showed wider inter-fibre pores. Inter-fibre pores decreased with a decrease in filament fineness. Moreover the separation level proposed deviated from the 90% level depending on the fabric index. This deviation was very small in samples with reduced filament fineness and textured samples. The separation level proposed will be useful to understand the effect of fabric construction parameters to obtain targeted properties regarding inter-fibre and inter-yarn pore size.

Cross section of gill filaments in histological preparations helps better identification of the location of myxosporean plasmodia in gill tissues

Location and tissue preference of filamental-type myxosporean plasmodia in histological slides of the gills can be properly identified only in cross sections of the gill filaments. The authors selected three myxosporeans (Myxobolus rutili, M. dispar and Henneguya psorospermica, parasites of the roach, the common carp and the pike, respectively) for studying the problem. The plasmodia of these species studied in longitudinal sections were earlier regarded as developing inside the filamental arteries. Cross sections of the filaments showed that all the three species developed plasmodia in the dense connective tissue constituting the adventitia of gill arteries and covering the cartilaginous gill rays. Myxobolus rutili started its development close to the afferent branchial artery but attached to the cartilaginous gill ray. More developed plasmodia of this species surrounded the rays. Plasmodia of M. dispar were formed on the inner side of the afferent branchial artery, while those of H. psorospermica were located at the external side of the efferent branchial artery.

Microtubules soften due to cross-sectional flattening.

We use optical trapping to continuously bend an isolated microtubule while simultaneously measuring the applied force and the resulting filament strain, thus allowing us to determine its elastic properties over a wide range of applied strains. We find that, while in the low-strain regime, microtubules may be quantitatively described in terms of the classical Euler-Bernoulli elastic filament, above a critical strain they deviate from this simple elastic model, showing a softening response with increasingdeformations. A three-dimensional thin-shell model, in which the increased mechanical compliance is caused by flattening and eventual buckling of the filament cross-section, captures this softening effect in the high strain regime and yields quantitative values of the effective mechanical properties of microtubules. Our results demonstrate that properties of microtubules are highly dependent on the magnitude of the applied strain and offer a new interpretation for the large variety in microtubule mechanical data measured by different methods.