Melt Flow Characteristics Research Articles

Recent advances of interfacial modifications toward carbon fiber‐reinforced thermoplastic polypropylene and polyamide composites

AbstractThe performance of carbon fiber‐reinforced thermoplastic composites (CFRTP) has been restricted by the performance of the interface. In general, the interfacial properties of CFRTP are determined by both the surface properties of the carbon fiber (CF) reinforcement and the infiltration properties of the thermoplastic matrices, which possess high melt viscosity and seem difficult to sufficiently infiltrate the fiber reinforcement. As a result, the melt flow characteristics of different matrices significantly influence the interfacial melt penetration and mechanical properties of CFRTP. In this paper, in order to explore the influence of melt flow characteristics of various thermoplastic resins toward CFRTP interfacial behaviors, high‐polarity polyamide (PA) and low‐polarity polypropylene (PP) resins are selected as representative resin matrices among commonly used resin systems. Specifically, the polarity differences and interface‐forming mechanisms of CFRTP are first established. Following a systematical discourse on the latest research progress of interfacial modifications in PP/PA‐based CFRTP are described, centering on the effects of various modification methods on improving the interlaminar/interfacial strength, toughness, impact strength, and bending strength of the composites. In addition, this paper also classifies the interfacial mechanisms of CFRTP in terms of interface bonding, interface strengthening, and interface failure. Finally, the shortcomings and future research directions are pointed out to achieve effective interfacial construction and innovative modification of CFRTP.Highlights An introduction of resin polarity differences of CFRTP is established. An introduction of interface‐forming mechanisms of CFRTP is established. State‐of‐art characterization techniques of CFRPs interface are provided. Effect of melt flow property on the interfacial behavior of CFRTP was explored. The interfacial mechanisms are systematically analyzed.

Unveiling mechanisms and onset threshold of humping in high-speed laser welding

The fabrication of fuel cells relies on a rapid laser welding process. However, challenges arise with the occurrence of humping when the welding speed surpasses a critical threshold, which poses difficulties in achieving a smooth surface finish and a consistent weld strength. This study aims to elucidate the humping mechanisms by analyzing the morphology of molten pool and the characteristics of melt flow at varying welding speeds via in situ synchrotron high-speed X-ray imaging and computational fluid dynamics simulations. Our findings indicate that the short keyhole rear wall, the high backward melt velocity, and the prolonged tail of molten pool are the primary factors contributing to the onset of humping. Furthermore, a dimensionless humping index (πh\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\\pi }_{h}$$\\end{document}) was introduced, which successfully captured the onset threshold of humping across different literatures. This index not only provides a quantitative description of the humping formation tendency but also serves as a valuable tool for optimizing the laser welding process.

Laser-directed energy deposition of low-carbon, low-temperature ultra-fine bainitic multi-physical modeling, microstructure and performance studies

An innovative iron-based alloy powder characterized by reduced carbon content and elevated Mn content was developed, leading to the fabrication of iron-based ultrafine bainitic steel with exceptional mechanical properties utilizing laser-directed energy deposition (L-DED). The layers' morphology, microstructure, phase composition, and elemental distribution were analyzed, indicating that the melting depth of the layer was deep and ultra-fine dendrite formed in the top region. A multi-physical powder and melt pool simulation was conducted to analyze the melt flow and pool solidification characteristics, showing that the strong downward flow inside the molten pool caused by the powder impingement increased the melting depth. The cooling rate G × R, where G was the temperature gradient and R was the solidification rate, was higher at the top pool boundary, facilitating the ultra-fine dendrite formation at this location. Following subsequent low-temperature isothermal heat treatment, a refined bainitic microstructure emerged within the deposited layer. The bainitic plates in the 573 K isothermally transformed bainite were interspersed with film-retained austenite (RA). Conversely, the bainitic plates formed at a lower temperature (523 K) exhibited a coalesced morphology stemming from the diminished stability of super-cooled austenite. The bainite plates underwent growth and coalescence, ultimately giving rise to the bainitic microstructure. The 523 K transformed coatings demonstrated superior hardness (509.2 HV), strength (1435 MPa), and elongation (11.5 %) compared to the 573 K transformed coatings (456.5 HV, 1241 MPa, 10.1 %). This research holds significant implications for advancing low-carbon bainitic materials with remarkable comprehensive mechanical properties in additive manufacturing applications.

Determination of beam oscillating pattern for tailoring melt flow and microstructural characteristics of laser welded Ti–6Al–4V alloy

The trajectory of beam is highly correlated to the heat distribution and fluid flow within the melting pool in laser welding, which has a great impact on improving the joint microstructure. This study employs fluid simulation techniques to investigate the temperature distribution and flow behavior of Ti–6Al–4V alloy under three laser oscillation welding patterns including none oscillation, sinusoidal oscillation, and circular oscillation, and the optimal oscillating pattern was determined through an analysis of microstructure characteristics. Temperature field simulation results indicate that the oscillation of the beam is efficaciously utilized to diminish the concentrated heat distribution on the base material. Moreover, a manifest difference in energy density and the area of laser action is produced, which leads to variations in the location and depth of the distribution of keyholes. Under circular oscillation, the flow behavior is more pronounced, with peak flow velocity increasing by approximately 80 % compared to none oscillation and new vortices were created in the horizontal section at the end of an oscillation period. Furthermore, compared to none oscillation and sinusoidal oscillation, the lower cooling rate under circular oscillating pattern contributes to the formation of equiaxed grains. The fine equiaxed grains are easy to move and form an ordered lattice structure, which favors the transformation of low-angle grain boundaries and the increase in the strength of the crystal texture. Therefore, with oscillation frequency and amplitude set at 80 Hz and 0.8 mm, respectively, the use of circular oscillating pattern in laser welding results in an improvement in weld seam microstructure.

Expanded Perlite Mineral As a Natural Additive Used In Polylactide-Based Biodegradable Composites

Polylactide (PLA) is a biodegradable polymer derived from natural resources used in various applications ranging from medical to packaging. In this study, biocomposites were developed by combining perlite mineral (PER), a natural filler material, with a biodegradable PLA matrix in incorporated contaminations of 2.5%, 5%, 10%, and 15%. The purpose of this work is to obtain composites having low production costs while retaining their main properties. Mixing force measurements, tensile, Shore hardness, impact tests, melt flow indices (MFI), and scanning electron microscopy (SEM) evaluations were carried out on composite samples to determine the processing, mechanical, melt flow, and morphological aspects of the developed composites. When the tensile test data were reviewed, minor decreases in the tensile strength and % elongation parameters were noticed with perlite loadings. The inclusion of perlite powder significantly reduced the impact strength value of PLA. Composites with high amounts of PER displayed elevated hardness values. While the MFI results were analyzed, it was deduced that the addition of PER increased the melt flow characteristics of the PLA polymer. At low PER quantities, SEM micrographs displayed that PER particles were homogeneously distributed in the PLA phase. The particle homogeneity in the composite morphology deteriorated as the PER loading ratio in the composites rose. According to the overall results, the highest performance among composites was achieved in the sample including 2.5% PER, and this sample was considered to be the most suitable option for applications regarding PLA-based biocomposite material purposes.

Investigations on melt flow index of nano bio fillers reinforced thermoplastic composites for fDM filament fabrication

Three-Dimensional (3D) printing, is a creative manufacturing technique. Well-known additive manufacturing technique Fused deposition modelling (FDM), has seen an increase in ppopularity over the recent years due to its capability to make complex geometries that conventional production ways are unable to. Typically used materials in the fused deposition modelling are polymer based, however they do not have certain attributes that would allow them for usage in more extensive applications. Nano materials are used in 3d printing to improve novel functionalities. In the current research, we investigated the melt flow characteristics of a novel material to produce filament wire for uutilization in 3d printing mainly FDM applications. Different weight percentages of orange peel powder (0%, 2%, 4%, 6%, 8%, 10%) were reinforced with PLA pellets to produce a composite, study the composite’s melt flow properties. Out of all weight percentages 2% shows the best result than the neat PLA. The MFI’s test result clearly indicates that the value of MFI of PLA varied significantly based on the weight percentages of filler used as reinforcement.

Influence of shielding gas on filler wire mixing at laser hybrid welding of thick high strength steels

The laser hybrid welding process offers many advantages during welding of thick-walled steels, such as the increased penetration depth and, thus, reduced number of layers, reduced heat input and decreased distortion compared to arc-based welding processes. Especially, when welding high-strength steels (HSS), the reduced heat input plays an essential role. However, a major challenge when laser hybrid welding of thick-walled steels is the limited filler wire mixing over the entire seam thickness, which can lead to changed mechanical properties over the depth. To overcome this issue, the add of oxygen into the shielding gas and its influence on the filler wire mixing and finally to the mechanical properties were investigated within this work. Therefore, 20 mm thick S690QL steels were laser hybrid welded in a single-pass. A contactless electromagnetic backing was used to avoid sagging. The admixture of oxygen was performed by a gas mixer, where the oxygen content was varied between 0 % and 7.2 %. The experiments were also accompanied by laser beam welding tests in steel/glass configuration, where the melt pool geometry as well as the melt flow characteristics were captured by a high-speed camera. It can be concluded, that adding of approx. 4 % oxygen into the shielding gas had a positive effect on the filler wire mixing, were up to a depth of 18 mm elements of the filler wire could be observed.

Analysis of Melt Flow Characteristics in Large Bottom-Blowing Furnace Strengthened by Oxygen Lance Jet at Different Positions

Analysis of Melt Flow Characteristics in Large Bottom-Blowing Furnace Strengthened by Oxygen Lance Jet at Different Positions

Additive Manufacture of Recycled Poly(Ethylene Terephthalate) Using Pyromellitic Dianhydride Targeted for FDM 3D-Printing Applications

The suitability of recycled poly(ethylene terephthalate) (R-PET) for 3D-printing applications was evaluated by studying the melt flow characteristics of the polymer. R-PET is known to experience significant deterioration in its mechanical properties when recycled due to molecular weight loss that results from reprocessing. Lower molecular weight hinders R-PET from being 3D-printable due to low viscosity and melt strength. The hypothesis was that R-PET can be modified with reasonable effort and resources to a 3D-printable thermoplastic if the low viscosity problem is tackled. Higher viscosity will enhance both the melt strength and the melt flow characteristic of the polymer, making it more suitable for processing and 3D printing. Reactive extrusion was selected as the method for modifying the polymer to achieve the objective via a coupling reaction with chain extender PMDA (pyromellitic dianhydride). A decrease in the melt flow index (MFI) from 90 to 1.2 (g/10 min) was recorded when PMDA was added at 0.75 wt% which lowered the MFI of modified R-PET to a comparable value to commercial 3D-printing filaments. Furthermore, FT-IR analysis was performed to investigate the chemical composition of the product. Finally, a 3D-printing filament was made from the modified R-PET by mimicking the main processing stations that exist in the filament-making process, which are the extrusion stage, water bath cooling stage and spooling stage. With 0.75 wt% PMDA, the melt strength was satisfactory for pulling the filament and, therefore, a filament with on-spec dimension was produced. Finally, a small object was successfully 3D-printed using the filament product at a minimum recommended temperature of 275 °C.

Numerical study of melt hydrodynamics in pulsed laser processing of nickel-based superalloy

Pulsed laser processing (PLP) of materials has wide-spread applications in the industry, yet the underlying complex material response to the incident laser pulse especially the melt flow mechanism is not fully understood. Knowledge of melt hydrodynamics can provide systematic theoretical guidance for the improvement of PLP quality. In this paper, a two-dimensional numerical model was built to simulate melt flow during PLP of nickel-based superalloy. The driving forces for melt hydrodynamics at different stages of laser pulse irradiation were studied comprehensively. Numerical results reveal that thermo-capillary stress drives radially-outward melt flow at the initial stage of laser pulse irradiation. At the middle stage, evaporation-induced recoil pressure is the dominant driving force for melt pool deformation, creating a depression at the center and a hump at the periphery. Thermo-capillary force has a minor effect on melt pool deformation but a large contribution to the flow velocity field. At the post-irradiation stage, the peripheral molten hump flows back rapidly and the melt pool experiences some gradually damping oscillations under the action of Young-Laplace stress. Moreover, it was demonstrated that laser power density plays an important role in deciding the melt flow characteristics and the relative contributions of different driving forces. The results in this study provide an unambiguous physical picture of the melt hydrodynamics in pulsed laser processing.

Spectrum and linear Lyapunov instability of a resting state for flows of an incompressible polymeric fluid

The Lyapunov linear instability of the state of rest for flows of an incompressible viscoelastic polymeric fluid in an infinite plane channel is proved. We use the Vinogradov-Pokrovski rheological model, which is well suited for describing the flow characteristics of linear polymer melts. The spectrum of the mixed problem is found and it is proved that the solution of a linearized mixed problem in the class of periodic perturbations with respect to a variable varying along the channel wall grows in time faster than any exponential function to a linear degree.

Highly Efficient and Solvent-Free Purification Technique and Model Study of Layer Melt Crystallization

Developing a green and sustainable technique seems necessary when facing an increase in the environmental burden. Layer melt crystallization (LMC) is recognized as an environmentally friendly separation technique because of its lower energy consumption and chemical waste emission. For the first time, this study applied LMC to prepare the high-purity isophthaloyl chloride (IPC), which is an important chemical intermediate in the synthesis of fibers. Under the optimal trajectory, the purity of IPC could improve from 97.811 to 99.381%, which reached the standard of subsequent production. Meanwhile, theoretical models were established and combined with the experimental results to visualize the crystallization and sweating processes. The fractal porosity model was used to describe the crystal layer structure, in which the pore structure could provide the adsorption sites for inclusion components and channels for the melt flow. Crystallization and sweating process kinetics models were established to explore the crystal layer growth and sweating melt flow characteristics. The distribution coefficient and the impurity removal rate were used to describe the separation efficiency. The interfacial solute distribution factor and the mass transfer coefficient were used to explore the solute and impurity distribution rules. The mechanisms of the mass flow were revealed. Finally, four different crystallizer structures were designed to intensify the heat and mass transfer, which significantly improved the separation efficiency.

In-line steady shear flow characteristics of polymer melt in rectangular slit cavities during thin-wall/micro injection molding

Both scale and temperature field effects have a considerable impact on polymer melt viscosity during thin-wall/micro injection molding. In this work, an in-line rheological test with similar dynamic test conditions to thin-wall/micro injection molding was adopted to further analyze the rheological properties and improve the simulation accuracy. An injection mold with rectangular slit cavity and storage region was designed to obtain a steady flow. The effects of factors such as the cavity size, viscous dissipation and melt temperature on polymer melt viscosity were studied. The results demonstrate that the injection molding conditions have a significant influence on the in-line rheological properties. When the cavity thickness (h) was 0.5 mm, the average percentage reductions of viscosity were 8.86 % (200 to 220 °C) and 4.07 % (220 to 240 °C) as the melt temperature rose. They were 57.13 % (200 to 220 °C) and 38.86 % (220 to 240 °C) when the cavity thickness was reduced to 0.2 mm. The test results show that the average prediction errors of pressure drop based on the capillary rheometer viscosity and in-line viscosity are 29.78 % (die: 5/0.2 mm) and 16.61 % (slit:h = 0.2 mm), respectively. In-line rheological viscosity shows potential for application in mold flow simulation.

Reinforced Composite as a Feeder for 3D Printing Application

Kenaf fibre has a low environmental impact because it is recyclable, light density and strong to be used as a product. Natural fibres, especially kenaf fibre, are undertilised and understudied in 3D printing technology. 3D technology is gaining traction to replace traditional methods because it saves cost and production time. This study focuses on producing kenaf composite materials that can be used as a feeder for 3D printing. This study used different fibre compositions (20,25,30) % mixed with polypropylene set at 190 ˚C temperature, 45 rpm speed, and 25 minutes. The material was left to cool to form clot to go through for the rheology process, and injection analysis was performed using Autodesk Moldflow Insight 2014. This study showed that a mixing temperature of 190 ˚C was suitable for forming a high shear mechanism. Kenaf fibre was treated in an alkaline solution of NaOH to 3 hours to prevent damage to the surface of the filler fibre in composites. Kenaf fibre at 6% of NaOH solution reaches a higher value for mechanical strength and roughness, resulting in better mechanical interlocking between the fibres and the matrix. In addition, analysis from Autodesk Moldflow Insight 2014 reveals that at 200 ˚C injection temperature pretend, the shear rate is higher creating smoother melt flow characteristics.

Numerical design of distributive mixing elements

This paper presents a novel shape-optimization technique for the design of mixing elements in single-screw extruders. Extruders enable the continuous production of constant-cross-section profiles. Equipped with one or several screw-shaped rotors, extruders transport polymer particles towards the outlet. Due to shear heating, melting is induced and a melt stream is created, which can be further processed. While many variants of multi-screw extruders exist, a significant share of all extrusion machines is made up of single-screw extruders due to their comparatively low operating costs and complexity. While the reduced complexity yields economic benefits, single-screw extruders' mixing capabilities, i.e., their ability to produce a melt with a homogeneous material and temperature distribution, suffer compared to multi-screw extruders. To compensate for this shortcoming, so-called mixing elements are added to the screw to enhance mixing by recurring flow reorientations. In view of the largely unintuitive flow characteristics of polymer melts, we present an optimization framework that allows designing these mixing elements numerically based on finite-element simulations of the melt flow. To reduce the computational demand required by shape optimization of a complete mixing section, we only focus on the shape optimization of a single mixing element. This paper presents advances in three aspects of numerical design: (1) A combination of free-form deformation and surface splines is presented, allowing to parameterize the mixing element's shape by very few variables. (2) The combination of this concept with a linear-elasticity-based mesh update method to deform the computational domain without the need for remeshing is demonstrated. (3) A simple yet robust and sensitive objective formulation to assess distributive mixing in laminar flows based on a measure for the interfacial area is proposed.

Mechanical, thermal, rheological assessment of polyamide-6 reinforced composites by addition of lamellar zirconium phosphate

The improvement of properties has been pursued through the addition of an immense variety of fillers in polymers. In this work we studied the effect of lamellar zirconium phosphate (ZrP) on the physico-mechanical properties of polyamide-6 (PA-6). The ZrP was synthesized and incorporated into PA-6 matrix at 1, 2 and 3 wt.%. Structural, thermal, relaxometric, tensile, melt flow and rheologic characteristics were assessed. Thermogravimetry indicated a low influence of the filler on thermal stability. The deconvolution of the melting peaks indicated transformation of the PA-6 α to γ phase and increase in crystallinity degree. Sample with 1 wt.% of ZrP showed an additional peak at higher relaxation time indicating restriction of polymer molecular mobility. By infrared, amine and carbonyl indices evaluation suggested ZrP interfered on the PA-6 hydrogen bonds. The elastic modulus increased slightly for all composition. Melt flow rate decreased with the amount of ZrP. The composite with 1 wt.% of ZrP exhibited the highest storage modulus and shear thinning effect noticed in the complex viscosity.

Novel, injection molded all-polyethylene composites for potential biomedical implant applications

This study aimed to create a self-reinforced composite material that can be processed by injection molding and other standard thermoplastic processing techniques and can be potentionally used as implant material. Self-reinforcement in biomaterials is desirable because it does not compromise biocompatibility and improves biofunctionality through improved mechanical performance. Self-reinforced composites can be currently processed by specialized, expensive and unproductive methods; hence we aimed to create a simpler processing alternative that works with biocompatible materials. We combined a high-density polyethylene matrix with high-performance polyethylene (Dyneema®) fibers. Before making the composite structure, the fibers were cross-linked by gamma irradiation to prevent their melting and maintain their structural integrity. The cross-linked fibers withstood the compounding by twin-screw extrusion and the subsequent injection molding. The effect of the irradiation dose on the processability, crystallinity, morphology, mechanical performance and cytotoxicity was investigated. We found that adding 20 m% of 200 kGy irradiated Dyneema® fibers increased the tensile modulus by 22.0%, the tensile strength by 71.1%, while both the composite and its constituents were all found to be biocompatible. The 41.1 MPa tensile strength, the 1.62 GPa tensile modulus, and the 64 Shore D hardness is quite similar to those of ultra-high molecular weight polyethylene, which is widely used in implants. Still, the material introduced in this paper shows no issues with the melt flow characteristics. These achievements are similar to other self-reinforcing methods, but the manufacturing method presented here can be economically realized on widely available processing technologies and machines.

Influence of an external applied AC magnetic field on the melt pool dynamics at high-power laser beam welding

The study deals with the determination of the influence of an externally applied oscillating magnetic field on the melt pool dynamics in high power laser beam and hybrid laser arc welding processes. An AC magnet was positioned under the workpiece which is generating an upward directed electromagnetic force to counteract the formation of the droplets. To visualise the melt flow characteristics, several experiments were carried out using a special technique with mild steel from S355J2 with a plate thickness of up to 20 mm and a quartz glass in butt configuration. The profile of the keyhole and the melt flow were recorded with a highspeed camera from the glass side. Additionally, the influence of the magnetic field orientation to the welding direction on the filler material dilution on laser hybrid welding was studied with variating oscillation frequency. The element distribution over the whole seam thickness was measured with X-ray fluorescence (XRF). The oscillation frequency demonstrated a great influence on the melt pool dynamics and the mixing of the elements of the filler wire. The highspeed recordings showed, under the influence of the magnetic field, that the melt is affected under strong vortex at the weld root, which also avoids the formation of droplets.

Coupled thermal-structural modelling and experimental validation of spiral mandrel die

The conventional theoretical method to calculate deformations and stress states is only limited to a few cases of simple extrusion dies due to a number of assumptions and simplifications. A coupled thermal-structural modelling framework incorporating finite element method is thus developed and implemented to determine the mechanical performances of the complicated spiral mandrel die, which has a complex geometrical feature of spiral grooves and is exposed to severe conditions of thermal load and high pressure. The steady-state thermal analysis is carried out by mapping the temperature load on the flow channel from previously simulated flow characteristics of polymer melt. The structural analysis takes inputs from both thermal analysis and previously simulated pressure on polymer melt. Both the temperature and pressure loads on flow channel are transferred via the Smart Bucket Surface mapping algorithm. The mechanical properties of the spiral mandrel die are evaluated by analysing the deformation and stress distribution. The experimental validation is conducted to demonstrate the effectiveness of the numerical model. The effects of both structure parameters of the spiral mandrel and processing parameters upon the maximum stress in the die body and the maximum pressure induced deformation at the die orifice are investigated.

Melt Rheology and Mechanical Characteristics of Poly(Lactic Acid)/Alkylated Graphene Oxide Nanocomposites.

Poly(lactic acid) (PLA) nanocomposites were synthesized by a solution blending and coagulation method using alkylated graphene oxide (AGO) as a reinforcing agent. Turbiscan confirmed that the alkylation of GO led to enhanced compatibility between the matrix and the filler. The improved dispersity of the filler resulted in superior interfacial adhesion between the PLA chains and AGO basal plane, leading to enhanced mechanical and rheological properties compared to neat PLA. The tensile strength and elongation at break, i.e., ductility, increased by 38% and 42%, respectively, at the same filler content nanocomposite (PLA/AGO 1 wt %) compared to nonfiller PLA. Rheological analysis of the nanocomposites in the molten state of the samples was performed to understand the filler network formed inside the matrix. The storage modulus increased significantly from PLA/AGO 0.5 wt % (9.6 Pa) to PLA/AGO 1.0 wt % (908 Pa). This indicates a percolation threshold between the two filler contents. A steady shear test was performed to examine the melt flow characteristics of PLA/AGO nanocomposites at 170 °C, and the viscosity was predicted using the Carreau−Yasuda model.