Polymer Flow Research Articles

Towards fast relaxation rates and creep resistance in disulfide vitrimer-like materials

Reaching a delicate balance between polymer flow for reprocessing and mechanical robustness at service temperatures remains a challenge in designing dynamic polymer networks. The demand for creep-resistant materials with fast relaxation rates at relatively low temperatures is a crucial research topic in the academic world. In this study, we present the preparation of a series of disulfide vitrimeric materials by curing two commercially available aromatic and aliphatic epoxy resins and cystamine. Through careful variation of the proportions between the epoxy resins, the properties of the final materials can be properly tailored. The completion of the curing was confirmed using FTIR spectrometry, and the thermal stability of all materials was evaluated by TGA. The thermomechanical properties were investigated using DMA analysis, obtaining glass transition temperatures (Tgs) above 60 °C and high rigidity in the glassy state depending on the proportion of the aromatic resin.Extensive stress relaxation tests unveiled remarkable vitrimeric behavior, with all materials capable of relaxing 63% of the initial stress in less than 2 min at 140 °C. The in-depth creep experiments not only allowed for determining material viscosity at high temperatures and the topology freezing temperatures (Tvs) but also offered control over dynamic stability at room temperature, depending on the initial formulation composition. Dilatometry and tensile tests provided further insights into the materials' characteristics.The self-healing and self-welding behavior enabled by the disulfide metathesis exchange reactions were also evaluated, revealing a total self-healing recovery process with short times and comparable tensile modulus in the welded samples. The facile preparation, commercial availability of monomers, and excellent thermosetting and vitrimeric properties highlight the immense potential of this series of materials.

A comprehensive review of viscoelastic polymer flooding in sandstone and carbonate rocks

Polymer flooding is a proven chemical Enhanced Oil Recovery (cEOR) method that boosts oil production beyond waterflooding. Thorough theoretical and practical knowledge has been obtained for this technique through numerous experimental, simulation, and field works. According to the conventional belief, this technique improves macroscopic sweep efficiency due to high polymer viscosity by producing moveable oil that remains unswept after secondary recovery. However, recent studies show that in addition to viscosity, polymer viscoelasticity can be effectively utilized to increase oil recovery by mobilizing residual oil and improving microscopic displacement efficiency in addition to macroscopic sweep efficiency. The polymer flooding is frequently implemented in sandstones with limited application in carbonates. This limitation is associated with extreme reservoir conditions, such as high concentrations of monovalent and divalent ions in the formation brine and ultimate reservoir temperatures. Other complications include the high heterogeneity of tight carbonates and their mixed-to-oil wettability. To overcome the challenges related to severe reservoir conditions, novel polymers have been introduced. These new polymers have unique monomers protecting them from chemical and thermal degradations. Monomers, such as NVP (N-vinylpyrrolidone) and ATBS (2-acrylamido-2-methylpropane sulfonic acid), enhance the chemical resistance of polymers against hydrolysis, mitigating the risk of viscosity reduction or precipitation in challenging reservoir conditions. However, the viscoelasticity of these novel polymers and their corresponding impact on microscopic displacement efficiency are not well established and require further investigation in this area. In this study, we comprehensively review recent works on viscoelastic polymer flow under various reservoir conditions, including carbonates and sandstones. In addition, the paper defines various mechanisms underlying incremental oil recovery by viscoelastic polymers and extensively describes the means of controlling and improving their viscoelasticity. Furthermore, the polymer screening studies for harsh reservoir conditions are also included. Finally, the impact of viscoelastic synthetic polymers on oil mobilization, the difficulties faced during this cEOR process, and the list of field applications in carbonates and sandstones can also be found in our work. This paper may serve as a guide for commencing or performing laboratory- and field-scale projects related to viscoelastic polymer flooding.

Numerical and experimental studies on design of multi-lumen tube extruded with drawing and air flow

This study represents the design and optimization procedure of a multi-lumen tube used for endoscopic retrograde cholangiopancreatography (ERCP) catheter. The geometry of tip and die for the multi-lumen tube is designed based on numerical analysis of molten polymer and air flow. In particular, this numerical study consider the interaction between the molten polymer and the air flow in the lumen which is the main process variable of extrusion, and analyze the heat transfer and pressure distribution through the air flow for the first time. In addition, to reflect the reality of the multi-lumen extrusion process, the velocity is controlled at the end of the tube ejected to the free surface in consideration of the extrusion process, which is drawn by the puller downstream of the extruder. The shear rate and temperature dependent viscosity of PEBAX 7233 SA01 MED is measured for non-isothermal numerical simulations. The extrusion process for multi-lumen tubes with drawing is simulated using ANSYS Polyflow. The profile of extrudate is numerically predicted with the initial design of the tip and die with the manufacturing parameter is optimized. The predicted profile of extrudate is compared to the target profile with dimensional requirements. The design of the tip and die is modified based on numerical results following the design procedure. To suppress the die swell phenomena, the flow area of molten polymer is increased, and the velocity difference is reduced. Finally, the multi-lumen tube with the optimized tip and die is experimentally extruded and compared to the target profile of the extrudate. It has a good agreement with the target profile and satisfies the dimensional requirements. This design procedure and numerical analysis help achieve the desired target profile of extrudate.

60 years of the Kaye–Bernstein, Kearsley, Zapas rheological constitutive law for polymers

The K–BKZ (Kaye–Bernstein, Kearsley, Zapas) rheological constitutive model is now 60 years old. The paper reviews the connections of the model and its variants with continuum mechanics and experimental evidence in polymer melt flow, presenting an up-to-date recap of research and major findings in the open literature. In the Introduction, an historical perspective is given on developments in the last 60 years of the K–BKZ model. Then, a section on mathematical modeling of polymer flows follows, including the governing equations of flow, the rheological constitutive equations (with emphasis on the viscoelastic integral constitutive equations of the K–BKZ type), dimensionless numbers controlling the flow, and relevant boundary conditions. The “Method of Solution” section reviews the major developments of numerical techniques for particle tracking and integral evaluation for the viscoelastic stresses. Finally, selected examples of successful application of the K–BKZ model in polymer flows are presented including considerations of wall slip and non-isothermal flows.

Structural Optimization Design of Throttle Valve Core for Intelligent Layered Polymer Injection String Controlled By Cable

Optimization Design of Throttling Valve Core Structure for Wired Intelligent Layered Polymer Injection String : Wired intelligent layered polymer in-jection technology can improve the coverage of polymer flooding, alleviate inter-layer conflicts in reservoir development, and improve crude oil recovery. It is an important component of tertiary oil recovery. However, the layered polymer in-jection technology currently used in most domestic oilfields is still the method of fishing and changing the injection nozzle for testing and adjustment. The alloca-tion efficiency of injection volume testing for each layer is slow, with large er-rors, and it is impossible to monitor polymer injection parameters throughout the process. To this end, research has been carried out on the cable controlled intelli-gent layered polymer injection string. By optimizing a highly efficient and low viscosity loss streamlined layered polymer injection throttling device with contin-uously adjustable gaps, the adjustment stroke is shorter and the measurement and adjustment efficiency is higher. Using finite element simulation, the low shear throttle control unit was studied and optimized. By moving the polymer core up and down slightly in the axial direction, the relative gap between the polymer core and the working cylinder was changed to achieve flow adjustment. At the same time, it is necessary to complete the direct reading measurement and adjustment process to form a single pipe layered polymer injection measurement and adjust-ment integration technology. The cable controlled intelligent layered polymer in-jection matching technology connects with the ground intelligent control system through cables to achieve realtime monitoring and online control of polymer flow, pressure, temperature, and other parameters, improving monitoring accura-cy and efficiency, and providing technical support for the construction of the “Digital Intelligence Oilfield”.

MODELLING AND TESTING OF SYNCHRONOUS MOTORS WITH PERMANENT MAGNETS

Applying a layer of polymer material to the fabric gives new characteristics to the base fabric. The resulting coated material may have functional properties such as resistance to dirt, liquid penetration, etc., or the finished leather products may have a completely different aesthetic appeal. The choice of the coating method depends on several factors: the type of substrate, the polymer formula and its viscosity for coating, the desired final product and the accuracy of the coating, the economy of the process. In the conditions of modern enterprises, it is advisable to use the spray application method for the application of polymer coatings due to the fact that the roller and brush methods do not provide the opportunity to operate with different forms of parts, and volumetric application is not always economically feasible. Jet application of the material is similar to spraying, but for polymer coatings, the temperature value is important, which in this case is difficult to control. Therefore, it is advisable to use the spraying method for applying polymer coatings The paper presents the results of preliminary research on the breakdown of polymers into droplets. The shape of the flow coming out of the nozzle was determined, and based on this, a model describing this process was developed. It is shown that for a sheet of polymer flow, its thickness is inversely proportional to the distance from the nozzle and K=2sx, calculated knowing the thickness of the sheet at some distance x from the nozzle. For a “hollow cone” spray nozzle with taper angle, θ and orifice diameter, δ and sheet thickness h, at the nozzle exit, an equation for the flow length break was derived. The obtained results of the calculations of the dependence of the droplet diameter on the flow rate. A spray test was carried out in different modes. The ratio of the length of the jet to the length of the gap L serves as the beginning of the decay mode. It was determined that the ratio of the length of the jet to the length of the gap of the canvas when reaching 1 can be a reasonable criterion for evaluating the determination of the limits of the spraying mode. For a good spraying (for example, tearing of the web), small values of the ratio of the length of the jet to the length of the tearing of the web are necessary. This is achieved due to low surface tension, high gas density, high injection pressure (velocity) and large nozzle exit angles. The obtained results can be used for the design of sprayers and their modes of operation.

Controlling anisotropy and brittle-to-ductile transitions by varying extrusion width in short fibre reinforced additive manufacturing

PurposeExtrusion width, the width of printed filaments, affects multiple critical aspects in mechanical properties in material extrusion additive manufacturing: filament geometry, interlayer load-bearing bonded area and fibre orientation for fibre-reinforced composites. However, this study aims to understand the effects of extrusion width on 3D printed composites, which has never been studied systematically.Design/methodology/approachFour polymers with and without short-fibre reinforcement were 3D printed into single-filament-wide specimens. Tensile properties, mechanical anisotropy and fracture mechanisms were evaluated along the direction of extruded filaments (F) and normal to the interlayer bond (Z). Extrusion width, nozzle temperature and layer height were studied separately via single-variable control. The extrusion width was controlled by adjusting polymer flow in the manufacturing procedure (gcode), where optimisation can be achieved with software/structure design as opposed to hardware.FindingsIncreasing extrusion width caused a transition from brittle to ductile fracture, and greatly reduced directional anisotropy for strength and ductility. For all short fibre composites, increasing width led to an increase in strain-at-break and decreased strength and stiffness in the F direction. In the Z direction, increasing width led to increased strength and strain-at-break, and stiffness decreased for less ductile materials but increased for more ductile materials.Originality/valueThe transformable fracture reveals the important role of extrusion width in processing-structure-property correlation. This study reveals a new direction for future research and industrial practice in controlling anisotropy in additive manufacturing. Increasing extrusion width may be the simplest way to reduce anisotropy while improving printing time and quality in additive manufacturing.

Assessing the environmental impacts of flow and batch syntheses of hypercrosslinked polymers for low-pressure CO2 adsorption

The microporosity of hypercrosslinked polymers (HCPs) renders such materials ideal adsorbents for carbon capture. We recently showed that the CO2/N2 selectivity of HCPs synthesised by internal crosslinking of poly-α,α′-dichloro-p-xylene (p-DCX) in continuous flow synthesis was 850 % higher than those produced in batch reactions. We hypothesised that this could potentially reduce the amount of HCP adsorbents required for delivering the same carbon capture performances, hence improving the environmental impacts of carbon capture. This was evaluated here where we analysed the environmental impacts of using both batch- and flow-synthesised HCPs for adsorbing 40 mg of CO2 with the life-cycle assessment method. We also deployed this approach to evaluate HCPs synthesised via post-crosslinking of polystyrene crosslinked with DCX (p-PS-DCX) and externally crosslinking of polystyrene with formaldehyde dimethyl acetal (FDA) crosslinker (p-PS-FDA). Amongst all HCPs studied in this work, the changes in environmental impact of deploying internally crosslinked HCPs for carbon capture were the worst. This was mostly attributed to its low product yield (7 %), which had a larger influence on the environmental impacts than its adsorption performance as verified by sensitivity analysis. To offset the adverse effects of low product yield, the product yield from flow synthesis of HCPs should ideally reach 25 %. By identifying that product yield is key for promoting environmental sustainability in carbon capture using flow-derived HCPs, future work should focus on optimising continuous flow synthesis to deliver ideal product yield. Hypercrosslinked polymers (HCPs) can be deployed adsorbents for carbon capture. Here we hypothesise that one can use HCPs with better CO2/N2 selectivity to deliver the same carbon capture performances, hence improving the environmental impacts of carbon capture. This was evaluated here using batch- and flow-synthesised HCPsvia internal, external and post-crosslinking strategies with the life cycle assessment method. The environmental impacts of internally crosslinked HCPs were worst due to a low product yield of 7 % Sensitivity analyses indicated that this limitation can be overcome when HCP yield from flow synthesis reach 25 %. Future work should focus on optimising continuous flow synthesis to deliver ideal product yield for minimising environmental impacts of deploying HCPs in carbon capture.

Modeling and Simulation of a Multizone Circulating Reactor for Polyethylene Production with Internal Cooling.

Polyolefins play a role in industries and are typically manufactured using two types of reactors: high-pressure tubular reactors and fluidized bed reactors. An innovative technology called the Multizone Circulating reactor (MZCR) has emerged, which introduces an innovative approach with interconnected polymerization zones creating a continuous loop of polymer flow. This study focuses on modeling and simulating ethylene gas phase polymerization within the MZCR in the presence of internal cooling to gain insights into its behavior. To achieve this, a comprehensive computational fluid dynamics (CFD) simulation was developed. It considered momentum, material, and energy balance aspects. The model equations were solved using the finite difference method in COMSOL Multiphysics version 6.1. The investigation primarily focused on studying the impact of incorporating a cooler into the riser section on the temperature profile within the reactor and ethylene conversion. The presence of this cooler resulted in a reduction in temperature change along the riser from approximately 8.0 °C to 4.0 °C. Moreover, it led to an increase of 7%, in ethylene single-pass conversion.

Tuning Molecular Orientation Responses of Microfluidic Liquid Crystal Dispersions to Colloid and Polymer Flows.

An important approach to molecular diagnostics is integrating organized substances that provide complex molecular level responses to introduced chemical and biological agents with conditions that optimize and distinguish such responses. In this respect, liquid crystal dispersions are attractive components of molecular diagnostic tools. This paper analyzes a colloid system, containing a nematic liquid crystal as a dispersed phase, and aqueous surfactant and polymer solutions as the continuous phases. We applied a microfluidic approach for tuning orientation of liquid crystal molecules in picoliter droplets immobilized on microchannel walls. Introduction of surfactant to the aqueous phase was found to proportionally increase the order parameter of liquid crystal molecules in microdroplets. Infusion of polymer solutions into surfactant-mediated microfluidic liquid crystal dispersions increased the order parameter at much lower surfactant concentrations, while further infusion of surfactant solutions randomized the orientation of liquid crystal molecules. These effects were correlated with the adsorption of surfactant molecules on surfaces of microdroplets, stabilizing the effect of a polymer matrix on bound surfactant ions and the formation of insoluble polymer-colloid aggregates, respectively. The revealed molecular behavior of liquid crystal dispersions may contribute to optimized synthesis of responsive liquid crystal dispersions for in-flow molecular diagnostics of polymers and colloids, and the development of functional laboratory-on-chip prototypes.

Melting Heat Transfer Rheology in Bioconvection Cross Nanofluid Flow Confined by a Symmetrical Cylindrical Channel with Thermal Conductivity and Swimming Microbes

Nonlinear thermal transport of non-Newtonian polymer flows is an increasingly important area in materials engineering. Motivated by new developments in this area which entail more refined and more mathematical frameworks, the present analysis investigates the boundary-layer approximation and heat transfer persuaded by a symmetrical cylindrical surface positioned horizontally. To simulate thermal relaxation impacts, the bioconvection Cross nanofluid flow Buongiorno model is deployed. The study examines the magnetic field effect applied to the nanofluid using the heat generated, as well as the melting phenomenon. The nonlinear effect of thermosolutal buoyant forces is incorporated into the proposed model. The novel mathematical equations include thermophoresis and Brownian diffusion effects. Via robust transformation techniques, the primitive resulting partial equations for momentum, energy, concentration, and motile living microorganisms are rendered into nonlinear ordinary equations with convective boundary postulates. An explicit and efficient numerical solver procedure in the Mathematica 11.0 programming platform is developed to engage the nonlinear equations. The effects of multiple governing parameters on dimensionless fluid profiles is examined using plotted visuals and tables. Finally, outcomes related to the surface drag force, heat, and mass transfer coefficients for different influential parameters are presented using 3D visuals.

Numerical simulation of “sand-like” polymer flow during rotational moulding using smoothed particle hydrodynamics method

Rotational moulding is a versatile polymer shaping process used to create enclosed parts from powdered precursors using heat and multi-axis rotation. Controlling the heating process and mould motion is critical to producing high-quality parts, and failures due to incorrect mould coverage or variable wall thickness are common. To date, limited simulation tools exist to predict the motion of the powder within the mould, and operators rely on unreliable prior experience to avoid defects. This paper presents an SPH simulation framework to predict particle flow patterns and powder contact time within a rotating mould. The powder-to-wall contact time was derived from the transient rigid body force (RBF) of different sensors on the mould. The method was compared with the results of DEM simulation and validated by the particle flow pattern of two experimental results. Results showed that the SPH method was capable of simulating particle flow macroscopic properties. The great computing efficiency of SPH compared to DEM simulation was also demonstrated.

Flow Disturbance Characterization of Highly Filled Thermoset Injection Molding Compounds behind an Obstacle and in a Spiral Flow Part.

In the injection molding process, weld line regions occur when a molten polymer flow front is first separated and then rejoined. The position, length, and angle of weld lines are dependent on the gate location, injection speed, injection pressure, mold temperature, and, especially, the direction and degree of the polymer melt velocity in the mold-filling process. However, the wall surface velocity of the thermoset melt in the mold-filling process is not zero, which is not found for thermoplastic injection molding. The main reason leading to this difference is the slip phenomenon in the filling phase between the thermoset melt and the wall surface, which is directly affected by the filler content. In this study, commercial thermoset phenolic injection molding compounds with different amounts of filler were employed to investigate not only the mechanism of weld line formation and development behind an obstacle in the injection molding process but also the flow disturbance of the thermoset melt in the spiral flow part. In addition, the effect of the wall slip phenomenon on the flow disturbance characterization and the mechanism of weld lines of selected thermoset materials was carefully considered in this research. Furthermore, the generated material data sheet with the optimal developed reactive viscosity and curing kinetics model was imported into a commercial injection molding tool to predict the weld line formation as well as the mold-filling behavior of selected thermoset injection molding compounds, such as the flow length, cavity pressure profile, temperature distribution, and viscosity variation. The results obtained in this paper provide important academic knowledge about the flow disturbance behavior as well as its influence on the mechanism of weld line formation in the process of thermoset injection molding. Furthermore, the simulated results were compared with the experimental results, which helps provide an overview of the ability of computer simulation in the field of the reactive injection molding process.

Effects of Electrode Design on the Melt Electrowriting of Sinusoidal Structures

Melt electrowriting is a microscale manufacturing technique that uses polymer‐based melts to create fibrous structures. An electric field is used to stabilize a continuous molten jet, which is then written onto a substrate as a microscale fiber. Herein, it is investigated how different electrode designs affect the electric field's spatial distribution and intensity. Experiments show that the electrode design affects the temperature of the poly(ε‐caprolactone) melt in the nozzle and plays a crucial role in the formation of jet, its speed, and consequent deposition. A concave electrode design is observed to directly impact the temperature of the polymer being extruded, where it is found to be 10 and 8 °C lower than the flat and convex electrode, respectively. This lowering in temperature impacts the polymer flow and the critical translation speed directly, impacting the fidelity of prints using a sinusoidal toolpath, showing a reduction of 65% in the programmed value of amplitude. Sinusoid patterns with different amplitudes and wavelengths are designed and printed, providing a library of structures with preprogrammed mechanics for scaffold creation. A high level of control is demonstrated by designing complex alternating amplitude structures displaying dual elastic regions and step‐based mechanical properties.

Efekty lepkosprężyste w warunkach nawadniania kolektora szczelinowo-porowego cieczą wodno-polimerową

The work is devoted to the numerical simulation of the flow of simple and viscoelastic (polymer solution) fluids through a fracture by using polymer solutions for enhanced oil recovery from a reservoir. Polymer solutions have viscoelastic properties. Therefore, when polymer solution flows through the slot, we use the well-known Maxwell’s fluid model with the Jaumann derivative to evaluate deformation characteristics of the flow (stream functions, distributions of the longitudinal velocity gradient and normal stress) resulting in the manifestation of abnormal (compared with the behaviour of the ordinary fluid) effects. The case of slow flow is considered. In this case, the inertial terms can be neglected, the velocities, stresses, and stream functions can be written as the decomposition by Weisenberg number, and we can assume that the Weissenberg number is less than one. The determined regularities of viscoelastic (polymer solution) liquid behaviour with longitudinal velocity gradient and the elastic deformations effects manifested in this case have a decisive meaning in understanding the mechanism of anomalously high oil recovery capacity of a reservoir by using water-polymer flooding of the fractured-porous reservoir. Understanding the nature of the effects of elastic deformations under the conditions of water-polymer flooding of the fractured-porous reservoir enables hydrodynamic calculations of the optimal flow of the polymer solution. One of the main issues that need to be solved when developing the technology for increasing oil recovery from formations using polymer solutions is to determine the optimal flow regime in the fractured-porous reservoir. The calculation results verify the ideas obtained from the experimental solution of this problem concerning the strain-stress state of polymer macromolecules (liquid elements) during polymer flow in the inlet area of the fracture in the oil reservoir and confirm the possibility of using numerical analysis of convergent polymer flow for calculating longitudinal velocity gradients in the inlet area of the fracture and can also serve as additional substantiation of the proposed earlier mechanism for increasing oil recovery from reservoirs by using polymer solutions.

Submicrometer analyses of the polymer flow modifier effects on metal–polymer direct joining

Polymer modification is a promising approach to improve the joining performance of injection molded direct joining (IMDJ) technology. However, the factors contributing to the improved joining strength of submicron scale surface pattern joints have not been fully elucidated. In this study, we investigated the mechanism for improving the joining performance of polyamide 6 (PA6)/aluminum alloy A5052 joints with Blast + hot water treated metal structure using a flow modifier (OSGOL MF-11). Enhanced mechanical polymer infiltration at the submicron scale was confirmed, and the hydrogen bond generation at the joint interface was characterized. These findings elucidate the reason for the joining performance improvement caused by the flow modifier in the submicron scale.

A Decade of Melt Electrowriting.

Over the past decade, melt electrowriting (MEW) has established the fundamental understanding of processing (and printer) requirements. Iterative work on parametric development and dissemination of this recent additive manufacturing technology has been performed across many systems and polymers (mainly poly-(ε-caprolactone)), showing similarities and trends. However, the software and hardware ecosystems of MEW are not mature. Further, due to its multi-parametric nature, MEW can be challenging for laboratories to master. This review intends to provide a unique perspective on the dynamic relationship between MEW processing parameters. Such parameters can be divided into 1) those that affect the polymer flow rate to or 2) from the nozzle, and 3) environmental conditions. The most influential parameters for high-quality printing are applied voltage, applied pressure, collector speed, polymer temperature, nozzle diameter, and the conditions that lead to charge buildup (e.g., relative humidity). Other factors such as ambient temperature, nozzle size, and protrusion, collector temperature and conductivity, and collector distance can all affect the process. Success for MEW printing means fibers fall onto the collector according to their pre-programmed path with predicted fiber diameter. Here, the authors elucidate how the dynamic relationship between these parameters can converge into ideal printing conditions to produce scaffolds.

Statistical continuum damage healing mechanics (SCDHM)

Damage healing mechanics has been under tremendous development during the past decade in which many constitutive models for different classes of materials have been proposed in the literature. However, to bridge the gap between the physics of healing and the theoretical framework, the statistical nature of the damage healing mechanics must be considered. The statistical nature of the crack nucleation and propagation processes is well-known, and the healing mechanisms follow similar probabilistic processes. In general, the healing process consists of two steps: (I) sealing, in which the free crack surfaces are brought in contact with the help of external forces, and then, (ii) healing, which may include a variety of techniques including the flow of molten polymers or liquid healing agents into the crack free surface areas and solidifying. Both sealing and healing processes can be considered within statistical mechanics to include multiple uncertainties involved in the healing process. This work proposes a framework to integrate statistical mechanics into the continuum of damage healing mechanics. The proposed statistical damage healing mechanics may help designers and scientists to perform more realistic simulations for components under complex damage and healing cycles. The key outputs of the proposed statistical framework are (I) healing method choice, and (II) healing parameter optimization.

Experimental and numerical investigation of extrudate swell of polylactic acid via extrusion-based additive manufacturing process

Extrudate swell is a rheological phenomenon of polymers that occurs after the extrusion die exit due to relaxation of the residual molecular stress. This phenomenon is essential to ensure the accuracy and stability of components manufactured by Extrusion-based additive manufacturing (EAM) process. Extrudate swell can be affected by multiple factors including material properties and processing parameters that can be coupled and it is difficult to fully understand their effects, especially in absence of accurate online measurement devices. In this study, the extrudate swell was investigated experimentally as a function of the extrusion rate, melt temperature and nozzle diameter for polylactic acid (PLA) material. The Computational fluid dynamics (CFD) and level set method (LS) in COMSOL Multiphysics were used to simulate the polymer flow out of the extrusion nozzle. The simulation results matched well with experimental results and showed that the swell rate decreases with increasing temperature and nozzle diameter and decreasing extrusion rate. These results can be used to optimize the parameters of EAM processes.

Pore-scale experiments reveal distinct flow field of polymer flooding with viscoelasticity loss by high salinity

It has been confirmed that high salinity significantly reduces the oil recovery from polymer flooding, which is generally considered to be due to the loss of polymer viscoelasticity. However, how the lost viscoelasticity affects the polymer flow field remains unclear. Therefore, the micro-PIV technique and rheological experiments were utilized in this study to investigate the pore-scale flow field of polyacrylamide (HPAM) under different salinities (NaCl). The results showed that as the salinity increased from 0 g/L to 10 g/L, the storage modulus and loss modulus of HPAM decreased by 84.5%− 97.9% and 87.3%− 98.3%, respectively. Regarding the pore-scale flow field, the average velocity of HPAM under low (0 g/L) and high (10 g/L) salinities was 33.4% lower and 19.5% higher than that of water flooding, respectively. Besides, high salinity resulted a higher velocity ratio between main stream and margin regions (11.8) than that of water flooding (2.0), which suggested a greater heterogeneity and a lower sweep efficiency of the flow field in pore networks. Thus, the lower sweep efficiency with high salinity is one of the dominant causes for the reduction in oil recovery. Furthermore, the breaching in main stream and the plugging in margin regions indicated that the shear resistance stability of polymer solution was diminished under high salinity. Consequently, the flow velocity in the main stream with a higher shear rate increased, whereas the margin region with a lower shear rate was plugged, which reduced the sweep efficiency. This study provides a further understanding of the porous media flow mechanisms in polymer applications.