Extrusion Flow Research Articles

Effect of Wall Slip on the Extrusion Characteristics of 3D Printing of Cementitious Materials

AbstractThis paper investigates the impact of wall slip on the screw extrusion of cementitious materials. A wall slip extrusion model is developed based on the theory of infinite parallel plates. Then, the extrusion characteristics under different slip conditions of the screw and the cylinder wall are discussed. Finally, the Finite Element Method is used to verify the conclusions drawn from theoretical model analysis. The results show that when −1≤a←1/3 (where a is the ratio of pressure flow to the sum of drag flow and slip flow), slippage on either the screw wall or the cylinder wall can reduce the extrusion flow rate, and the number of flow recirculation planes is one. When −1/3≤a≤1, the number of flow recirculation planes increases to two, and screw wall slip is conducive to expanding the extrusion flow rate. Conversely, cylinder wall slip may reduce the extrusion flow rate. Moreover, the simulation results are consistent with those of the theoretical model, further verifying the rationality of the model.

ANALYSIS OF RHEOLOGICAL PROPERTIES IN PE FIBER-REINFORCED FLY ASH GEOPOLYMER FOR ADDITIVE MANUFACTURING

The leading edge of construction advancements is represented by 3D printing which creates durable and elaborate structures and minimizes resource wastage. As a viable substitute for regular cement materials highlights the ecological benefits and strong mechanical traits of fly ash geopolymers. This study investigates how the addition of polyethylene (PE) fibers alters these properties and how varying concentrations influence the flow behavior and capability of producing the composite material. The analysis of non-Newtonian behavior in these fiber-reinforced geopolymers is conducted using the Herschel-Bulkley model. By precisely measuring critical rheological factors such as viscosity and flow behavior researchers can evaluate how they influence 3D printing processes. This research reveals that adding PE fibers boosts the material’s strength and improves resistance against cracking while also elevating the viscosity and yield stress that can hinder its passage through the printer’s nozzle. An optimal blend of fiber content emerges from controlled tests that align increased durability with controllable extrusion flow and structure reliability. The results offer deep practical applications that reveal methods for producing geopolymers that can maintain strength while meeting the exacting requirements of 3D printing methods. Research deepens the grasp of how adding fibers alters the properties of geopolymers and enriches the overall dialogue on green building materials. It opens doors for subsequent analysis of complex fiber systems and creative additive practices to boost the effectiveness and resilience of construction materials in practical use.

Increased metamorphic conditions in the lower crust during oceanic transform fault evolution

Abstract. Oceanic transform faults connect the segments of active spreading ridges that slide past each other. In a classical view, transform faults are considered conservative, where no material is added or destroyed. Recent studies, however, suggest that the crust in the transform fault region is deformed during different episodes and is therefore non-conservative. We combine high-resolution 3D broadband seismic data with shipborne potential field data to study ancient oceanic fracture zones in Albian–Aptian aged oceanic crust in the eastern Gulf of Guinea offshore São Tomé and Príncipe. The crust in this region is characterized by a thin, high-reflective upper crust, underlain by a thick, almost seismically transparent lower crust. At the paleo-transform faults, the lower crust, however, comprises reflectors, which dip towards the transform fault and were previously interpreted as extrusive lava flows at an extensionally thinned inside corner. The lower crust therefore defines the target area for inversion and forward modeling of the potential field data. The chosen seismic horizons are used as geometrical boundaries of the crustal model. First, we perform a lateral parameter inversion for the lower crust, which provides vertical columns of density and magnetic susceptibility. Second, we sort the estimated values using a clustering approach and identify five groups with common parameter relationships. Third, we use the clustered lower-crustal domains to define a consistent 3D model of the study area that aligns with the seismic structure and geological concepts, which is preferred over the simple inversion of the first step. The final model generally shows anomalous low susceptibility and medium to high densities close to the buried fracture zones, which reflects increasing pressure and temperature as the transform faults evolved. This is accompanied by a change in metamorphic facies from prehnite-pumpellyite to greenschist. Our model indicates evolving extension and a second magmatic phase during juxtaposition against the trailing ridge segment. These results are in line with recent studies and strengthen the impressions of a widespread non-conservative character of transform faults.

Challenges on extrusion-based additive manufacturing of thermoplastic polyurethane

Fused filament fabrication (FFF) offers rapid production with user-friendly operation and cost-effectiveness, yet challenges in printing with thermoplastic polyurethane (TPU) persist. This study identifies causes of print defects in FFF-TPUs and their relation to process parameters, by visually analysing samples produced with various TPU materials. Extrusion temperature, printing speeds, filament cooling, overlap, and extrusion flow are subject to evaluation. Common issues include filament entanglements, under-extrusion, stringing, or geometric deviations. Among other approaches, results highlight the importance of slow, constant print speeds and careful optimization of extrusion temperature.

Magnetic alginate microrobots with dual-motion patterns through centrifugally driven flow control

Magnetic alginate microrobots with dual-motion patterns through centrifugally driven flow control

Heating patterns and temperature distribution of projectile surface in lunar regolith penetration

Heating patterns and temperature distribution of projectile surface in lunar regolith penetration

Reinforcing Efficiency of Recycled Carbon Fiber PLA Filament Suitable for Additive Manufacturing.

The use of 3D printing technology for manufacturing new products based on sustainable materials enables one to take advantage of secondary raw materials derived from recycling. This work investigates the structural performances of 3D printing composite filaments based on polylactic acid (PLA), as a matrix, reinforced by recycled carbon fiber (rCF). Carbon fibers were recovered from industrial scraps by a patented thermal process and used to produce thermoplastic composite filaments for additive manufacturing without any additional treatment and additives. The influence of the recovered carbon fiber (rCF) content on the thermal properties, mechanical properties and microstructure of the composites was studied in the range of 3-20 wt%. The recorded TGA curves exhibited a one-stage weight loss within the temperature range 290-380 °C for all samples and the residual rCF content was in good agreement with the theoretical fiber loading. The Young modulus of the extruded filaments strongly increased below a critical content (5 wt%), while at higher content the improvement was reduced. An increase in the storage modulus of 54% compared to neat PLA 3D printed sample resulted in a printed specimen with a higher rCF content. SEM images highlighted a strong rCF prevailing alignment in the direction of the extrusion flow, creating almost unidirectional reinforcement inside the filament. These findings suggest that homogeneous composite filaments reinforced with well-dispersed recycled CF without additional chemical modification and additives are suitable materials for additive manufacturing. The effect of rCF topological distribution within the material on the mechanical performances has been discussed, highlighting that the isolated fibers could efficiently transfer loads with respect to the percolated 3D network and have been correlated with the microstructure.

Toward a large-batch manufacturing process for silicon-stabilized lipid nanoparticles: A highly customizable RNA delivery platform

While lipid nanoparticles (LNPs) are a key enabling technology for RNA-based therapeutics, some outstanding challenges hinder their wider clinical translation and use, particularly in terms of RNA stability and limited shelf life. In response to these limitations, we developed silicon-stabilized hybrid lipid nanoparticles (sshLNPs) as a next-generation nanocarrier with improved physical and temperature stability, as well as the highly advantageous capacity for "post-hoc loading" of RNA. Nevertheless, previously reported sshLNP formulations were produced using lipid thin film hydration, making scale-up impractical. To realize the potential of this emerging delivery platform, a manufacturing process enabling multikilogram batch sizes was required for successful clinical translation and deployment at scale. This was achieved by developing a revised protocol based on solvent injection mixing and incorporating other process adjustments to enable in-flow extrusion of multiliter volumes, while ensuring sshLNPs with the desired characteristics. Optimized procedures for nanoparticle formation, extrusion, and tangential flow filtration (to remove residual organic solvent) currently enable production of 2kg finished batches. Importantly, sshLNPs produced via the modified large-scale workflow show equivalent physical and functional properties to those derived from the earlier small-scale methods, paving the way for GMP manufacturing protocols to enable vital translational clinical studies.

Environmentally-friendly solvent pulping and grafting strategies for better foamability of poly(lactic acid)/agricultural waste biocomposites

In this study, the foamability of poly (lactic acid) (PLA) through a continuous extrusion process was enhanced by using an agricultural waste, environmentally friendly pulping methods, and reactive compatibilization of the lignocellulosic filler with matrix in the extrusion flow field. Both applied solvent-pulping methods by using chemicals with low safety and toxicity risks were considerably successful in purifying the micron-sized cellulosic fibers of rice straw (RS). The interface of PLA matrix with RS pulp fibers was modified by applying reactive compatibilizers containing maleic anhydride (MA) and epoxy functional groups. Both compatibilizers had the ability to simultaneously react with the hydroxyl groups of RS pulp fibers and end groups of PLA chains during the melt-compounding process. As a result of RS pulping and PLA/RS pulp compatibilizing reactions, the processability of PLA in an extrusion foaming process was substantially enhanced, in a way that the void fraction and cell density of PLA foam increased more than seven and two times, respectively. The extruded lightweight all-green biocomposite foams can be applied in construction and packaging applications.

Compounding and Dispersion Technology for Nanocomposites and Polymer Blends by Using Extensional Flow in Twin-Screw Extruder

Compounding and Dispersion Technology for Nanocomposites and Polymer Blends by Using Extensional Flow in Twin-Screw Extruder

Material extrusion: A promising tool for processing CoCrMo alloy with excellent wear resistance for biomedical applications

Material extrusion: A promising tool for processing CoCrMo alloy with excellent wear resistance for biomedical applications

Microstructure and corrosion behaviour of Mg-1Sc alloy with different processing conditions

The microstructure and corrosion resistance of Mg-1Sc alloys in different processing conditions were investigated. The composition was examined by Inductively Coupled Plasma Atomic Emission Spectrometer, the microstructure was analyzed by metallographic microscope. The corrosion behaviour of the alloy was investigated by hydrogen evolution tests and electrochemical tests. The results showed that as-cast and rolled Mg-1Sc possess better corrosion resistance compared with extruded Mg-1Sc alloys, which is due to the fact that the extrusion flow lines and residual stresses caused by machining in extruded Mg-1Sc alloys can lead to easier corrosion. In addition, rolled Mg-1Sc alloy shows better corrosion resistance than as-cast alloy, which is attributed to the finer grain sizes and a denser corrosion product film.

Rheological Properties and 3D Printing Behavior of PCL and DMSO2 Composites for Bio-Scaffold.

The significance of rheology in the context of bio three-dimensional (3D) printing lies in its impact on the printing behavior, which shapes material flow and the layer-by-layer stacking process. The objective of this study is to evaluate the rheological and printing behaviors of polycaprolactone (PCL) and dimethyl sulfone (DMSO2) composites. The rheological properties were examined using a rotational rheometer, employing a frequency sweep test. Simultaneously, the printing behavior was investigated using a material extrusion 3D printer, encompassing varying printing temperatures and pressures. Across the temperature range of 120-140 °C, both PCL and PCL/DMSO2 composites demonstrated liquid-like behavior, with a higher loss modulus than storage modulus. This behavior exhibited shear-thinning characteristics. The addition of DMSO2 10, 20, and 30 wt% into the PCL matrix reduced a zero-shear viscosity of 33, 46, and 74% compared to PCL, respectively. The materials exhibited extrusion velocities spanning from 0.0850 to 6.58 mm/s, with velocity being governed by the reciprocal of viscosity. A significant alteration in viscosity by temperature change directly led to a pronounced fluctuation in extrusion velocity. Extrusion velocities below 0.21 mm/s led to the production of unstable printed lines. The presence of distinct viscosities altered extrusion velocity, flow rate, and strut diameter. This phenomenon allowed the categorization of pore shape into three zones: irregular, normal, and no-pore zones. It underscored the importance of comprehending the rheological aspects of biomaterials in enhancing the overall quality of bio-scaffolds during the 3D printing process.

Modelling supercritical CO2 flow in a co-rotating twin screw extruder using the level-set method

Modelling supercritical CO2 flow in a co-rotating twin screw extruder using the level-set method

Numerical simulation of 3D concrete printing derived from printer head and printing process

Numerical simulation of 3D concrete printing derived from printer head and printing process

Emplacement of shergottites in the Martian crust inferred from three‐dimensional petrofabric and crystal size distribution analyses

AbstractShergottites are mafic to ultramafic igneous rocks that represent the majority of known Martian meteorites. They are subdivided into gabbroic, poikilitic, basaltic, and olivine–phyric categories based on differences in mineralogy and textures. Their geologic contexts are unknown, so analyses of crystal sizes and preferred orientations have commonly been used to infer where shergottites solidified. Such environments range from subsurface cumulates to shallow intrusives to extrusive lava flows, which all have contrasting implications for interactions with crustal material, cooling histories, and potential in situ exposure at the surface. In this study, we present a novel three‐dimensional (3‐D) approach to better understand the solidification environments of these samples and improve our knowledge of shergottites' geologic contexts. Shape preferred orientations of most phases and crystal size distributions of late‐forming minerals were measured in 3‐D using X‐ray computed tomography (CT) on eight shergottites representing the gabbroic, poikilitic, basaltic, and olivine–phyric categories. Our analyses show that highly anisotropic, rod‐like pyroxene crystals are strongly foliated in the gabbroic samples but have a weaker foliation and a mild lineation in the basaltic sample, indicating a directional flow component in the latter. Star volume distribution analyses revealed that most phases (maskelynite, pyroxene, olivine, and oxides/sulfides) preserve a foliated texture with variable strengths, and that the phases within individual samples are strongly to moderately aligned with respect to one another. In combination with relative cooling rates during the final stages of crystallization determined from interstitial oxide/sulfide crystal size distribution analyses, these results indicate that the olivine–phyric samples were emplaced as shallow intrusives (e.g., dikes/sills) and that the gabbroic, poikilitic, and basaltic samples were emplaced in deeper subsurface environments.

A generalized method aiming at predicting the polymer melt flow field in the metering zone of large-scale single-screw extruders

Single-screw extruders (SSE) are commonly used in a wide variety of applications, ranging from polymer-extrusion to pellet additive manufacturing (PAM). Existing mathematical models focus on Newtonian and power-law rheologies to model melt flow in the last screw vanes. However, molten polymers usually follow more complex rheological patterns, and a generalized extrusion model is still lacking. Therefore, a semi-analytical model aiming at describing the flow of molten polymers in SSE is presented, to encompass a wide range of non-Newtonian fluids, including generalized non-Newtonian fluids (GNF). The aim is to evaluate the molten polymer flow field under the minimum set of dimensionless parameters. The effect of dimensionless extrusion temperature, flow rate, channel width, and height on the flow field has been investigated. A full factorial plane has been chosen, and it was found that the impact of dimensionless flow rate is the most prominent. The results were initially compared to numerical computations, revealing a strong agreement between the simulations and the proposed GNF method. However, significant deviations emerged when employing the traditional power-law model. This is particularly true at high values of flow rate and extrusion temperature: the mean error on overall flow speed is reduced from 12.91% (traditional power-law method) to 1.04% (proposed GNF method), while keeping a reasonable computational time (time reduction: 96.70%, if compared to fully numerical solutions). Then, the predicted pressure drop in the metering section was benchmarked against established literature data for industrial-scale extruders, to show the model’s accuracy and reliability. The relative errors of the traditional model range between 34.33 and 62%. The proposed method reduces this gap (errors ranging between 5.34% and 10.97%). The low computational time and high accuracy of the GNF method will pave the way for its integration in more complex mathematical models of large-scale additive manufacturing processes.

Flexible actuation with intrinsic sensing for ram extrusion 3D printing

Conventional actuation mechanisms used in liquid deposition modeling (LDM) technology limit the flow handling capability and the visibility of the printing materials’ properties. This work presents a flexible actuation system with intrinsic sensing for a ram extrusion printhead used in LDM technology. A mathematical model is used to design and simulate the printhead. The experimental results demonstrate the system’s ability to control the extrusion flow in two modes. The pressure control mode is favorable for the flow in a transient state such as flushing. The volumetric control mode provides a constant printed line width with less than 0.1-mm deviation between each tested material (biogel, chocolate fudge, and silicone sealant). A lower standard deviation for printed lines in the volumetric control mode indicates more precise line printing. The system also incorporates real-time monitoring of extrusion pressure and flow rate. The intrinsic capability to detect printing material properties is validated in both simulation and experiment. It provides valuable insights for further optimization of the printing process. The proposed system offers the advantage of improved pressure and flow control as well as the ability to monitor and respond to the properties of printing material.

Spatial distribution of mid-lower crustal flow in the SE Tibetan Plateau revealed by P-wave velocity and azimuthal anisotropy beneath the Lijiang–Xiaojinhe fault and its vicinity

SUMMARY The Lijiang–Xiaojinhe fault (LXF) and its vicinity are located in the transition zone among the Tibetan Plateau (TP), the South China block and the Indochina block. Researchers believe that this area has acted as a key tectonic zone during the evolution of the TP. Owing to the continuous growth and SE-ward expansion of the TP, the LXF and its vicinity have experienced intense deformation. Although different models, such as the rigid block extrusion and mid-lower crustal flow models, have been proposed to explain this intense deformation, a consensus has not yet been achieved. To better understand the deformation of the LXF and its vicinity, a high-resolution image of the subsurface structure must be constructed. In this study, we construct images of P-wave velocity and azimuthal anisotropy structures by using an eikonal equation-based traveltime tomography method. We collect high-quality seismic data from 276 broad-band seismic stations and manually pick a total of 48 037 first arrivals for the tomography study. Our tomographic results reveal a strong low-velocity body below the LXF and its vicinity. In addition, a strong azimuthal anisotropy structure with an N–S-oriented fast velocity direction is distributed along the low-velocity body. These features indicate the occurrence of mid-lower crustal flow, that penetrates across the LXF and extends to the Dianzhong block (DZB). In addition, we find obvious low-velocity perturbations in the mid-lower crust and uppermost mantle beneath the DZB. The low velocities may be attributed to the upwelling of hot materials from the upper mantle. We consider the limited distribution of mid-lower crustal flow on the margin of the SE TP, and mid-lower crustal flow may not play a significant role in the expansion of the TP.

Pressure drop non-linearities in material extrusion additive manufacturing: A novel approach for pressure monitoring and numerical modeling

Pressure drop non-linearities in material extrusion additive manufacturing: A novel approach for pressure monitoring and numerical modeling