High Friction Force Research Articles

Laser-Assisted Surface Modification of TRIP Steels: Chemical and Microstructural Evolution, Residual Stresses, and Micromechanical Properties

AbstractThe use of new lightweight design strategies is implemented in the automotive industry, for applications where high friction forces are present and lubrication systems need to be implemented. Micro-topography modification through laser texturing is an advantageous manufacturing technique that is currently being used by the industry. Combining both ideas, this manuscript aims to analyze the effect of surface modification laser-texturing process on a TRansformation-Induced Plasticity steel. Residual stresses, superficial chemistry, microstructure, and mechanical properties at the submicrometric length scale are investigated. Results show that the intensity and the number of pulses strongly modify the pattern geometry. Also, the pattern distance affects the residual stress state, changing from tensile to compressive stresses for distances higher than 20 µm. Chemical and microstructural changes at the vicinity of the laser may be associated to the fast cooling of the sublimated material around the pattern induced during the laser-assisted surface modification thermal process. Furthermore, the hardness remains stable, and no changes are evident in the bulk material. However, a hardness reduction of around 95 pct in the austenitic value is evident in the pile-up zone around the laser pattern due to (1) the microporosity and defects confined inside the pile-up region and (2) due to the residual chemical composition created during the solidification process, which is rich in iron, chromium, nickel, and manganese and poor in oxygen.

Influence of enhanced Laves phase shape and distribution on atomic-scale frictional wear mechanisms in nickel-based single crystal alloys

This study aims to simulate the influence of different shapes and distribution states of Laves phases on the friction-wear behavior of nickel-based alloys using molecular dynamics (MD). The investigation systematically examined the mechanical properties, friction coefficient, number of worn atoms, dislocations, temperature, and other micro-deformation behaviors of materials incorporating horizontally and vertically distributed short rod-shaped, spherical, and short strip-shaped Laves phases. The presence of the Laves phase significantly impedes temperature transfer, defect motion, and atomic displacement in the workpiece, resulting in reduced dislocation glide rate and shorter average dislocation lengths. High dislocation densities accumulate at the Laves/γ phase interface, enhancing surface wear resistance. The short rod-shaped Laves phase, due to its large surface area at the Laves/γ interface, impedes defect motion more effectively than spherical and short strip-shaped phases. dislocation tangle, higher friction force, fewer worn atoms, a higher friction coefficient, and improved wear resistance. However, vertically distributed short strip-shaped and short rod-shaped Laves phases exhibit less effective defect interaction, resulting in increased wear and significant deformation. The spherical Laves phase, with its geometric symmetry, shows consistent wear resistance regardless of distribution state. Short rod-shaped Laves phase provides the best reinforcement due to its effective defect motion impedance, while the spherical Laves phase offers stable performance across different distribution states, making it the most suitable shape for Laves phase reinforcement.

Clinical efficiency of new generation elastomeric ligatures over conventional: An in-vivo study

Friction being an imperative element in clinical orthodontics affects all stages of treatment and high frictional forces can affect the treatment duration and outcome in a deleterious manner. This study was done to appraise frictional resistance of non-conventional elastomeric modules in comparison with conventional elastomeric modules, during the retraction of teeth. The study sample size includes 30 patients (11 males and 19 females) undergoing orthodontic treatment. They were grouped into 3, namely, Group A- Slide nonconventional elastomeric ligatures Group B- super slick nonconventional elastomeric ligatures, and Group C- the conventional ligature. The study models were obtained to assess canine retraction rate, anchor loss, canine rotation, and molar rotations at different time intervals and subjected to statistical analysis. : The canine retraction rate(maxilla) for Group A, B and C was 1.674+/-0.092, 1.187+/-0.156, and 1.147+/-0.113,(mandible)1.765+0.099, 1.300+0.099 and 1.270+0.111 respectively. Mean anchorage loss(maxilla) group A- 1.054mm, group B- 1.080mm, group C -1.715mm (mandible) 1.024mm, 0.952mm and 1.664mm respectively. Canine rotation(maxilla) of Group A, B and C is 8.550+/-1.506, 5.300+/-1.386, 6.100+/-1.315and(mandible) 8.930/-+1.474, 5.830+/-1.096, 6.880+/-1.813 respectively. Mean molar rotation (maxilla) 2.580+0.735, 2.210+0.549 and 2.210+0.700 (mandible)2.900+0.541, 2.650+0.639 and 2.780+0.604 in group A, B and C respectively. Mean anchor loss was lesser in non-conventional modules, canine retraction rate was higher with Slide ligature, canine rotations were least in superslick more in Slide ligature, and rotation of molar was apparent for all the groups.

Role of gravity magnitude on flowability and powder spreading in the powder bed fusion additive manufacturing process: Towards additive manufacturing in space

Understanding powder spreading under low gravity conditions is essential for optimizing final products using additive manufacturing in space. In this study, we investigated the role of gravity on flowability and spreading mechanisms through combined experimental and discrete element method (DEM) studies. Three powders with different theoretical densities were used to reenact low compressive conditions resembling those in a low-gravity environment. The influence of low compressive conditions on flowability and spreading behavior was examined using the Hall flowmeter, rotating drum, and spreading experiments. In the experimental result, the static flowability was primarily affected by the presence of elongated particles rather than the compressive conditions. The dynamic AoR of TD_4 powder increased compared to that of TD_8 powder, despite the presence of spherical particles with a smooth surface finish. A DEM simulation study was conducted using TD_8 powder to investigate the impact of different gravity levels on dynamic flowability. The DEM studies revealed that the dynamic flowability under rotation was decreased under low gravity owing to the promoted cohesive interactions. The powder spreading experiment was performed using the three powders with different theoretical densities. The in-situ observation with particle image velocimetry analysis revealed that kinetic energy dissipation in the spreading process was accelerated in the TD_8 powder pile, despite its high interparticle friction and cohesive force. The powder spreading simulation was conducted using TD_8 powder to clarify the effect of low gravity on the powder spreading process. In TD_8 powder under 1 G, particle supply was facilitated by a synergistic effect of free-falling and deposited particles. However, increased cohesive interactions under 0.5 G and 0.16 G restricted particle supply via free-falling, consequently reducing the powder bed density by about 2 % and 6.2 %, respectively. These findings prove that the cohesive force predominantly controls dynamic flowability and powder bed quality in the spreading process under low gravity conditions.

Transportation of Objects on an Inclined Plane Oscillating in the Longitudinal Direction Applying Dynamic Dry Friction Manipulations

A transportation system requires an asymmetry to achieve objects’ motion on an oscillating surface. Transportation methods based on vibrational techniques usually employ different types of asymmetries, such as temporal (time) asymmetry, kinematic asymmetry, wave asymmetry or power asymmetry. However, transporting an object on an inclined angle requires a relatively high net frictional force over each period of vibrational cycles due to the gravitational potential energy exerted on the object. This paper investigates the transportation of an object upward on an inclined plane that harmonically oscillates in its longitudinal direction. The novelty of this research is attributed to the upward motion of the object on the inclined plane, which is achieved by creating an additional asymmetry of the system through dry friction dynamic manipulations. For this reason, periodic dynamic dry friction manipulations have been employed to create the asymmetry of frictional conditions, resulting in a net frictional force that outweighs the gravitational force. A mathematical model has been developed using the Lagrange method, which describes the moving object’s motion. Moreover, the theoretical findings and results confirmed that the object’s velocity and direction can be controlled by dynamic dry friction manipulations. To demonstrate the technical feasibility of the proposed method, an experimental investigation was carried out where the results demonstrated that the control parameters significantly influence the characteristics of the directional motion of the moving object. This transportation method is beneficial for various modern industries engaged in transportation and manipulation tasks with objects spanning a broad range of sizes, including those operating at small scales for applications in lab-on-a-chip technology, micro-assembly lines, micro-feeder systems and other delicate component manipulation systems. The presented research advances the classical theories of vibrational transportation on inclined surfaces.

Temperature dependence of the dynamics and interfacial width in nanoconfined polymers via atomistic simulations.

We present a detailed computational study on the temperature effect of the dynamics and the interfacial width of unentangled cis-1,4 polybutadiene linear chains confined between strongly attractive alumina layers via long, several μs, atomistic molecular dynamics simulations for a wide range of temperatures (143-473 K). We examine the spatial gradient of the translational segmental dynamics and of an effective local glass temperature (TgL). The latter is found to be much higher than the bulk Tg for the adsorbed layer. It gradually reduces to the bulk Tg at about 2nm away from the substrate. For distant regions (more than ≈1.2nm), a bulk-like behavior is observed; relaxation times follow a typical Vogel-Fulcher-Tammann dependence for temperatures higher than Tg and an Arrhenius dependence for temperatures below the bulk Tg. On the contrary, the polymer chains at the vicinity of the substrate follow piecewise Arrhenius processes. For temperatures below about the adsorbed layer's TgL, the translational dynamics follows a bulk-like (same activation energy) Arrhenius process. At higher temperatures, there is a low activation energy Arrhenius process, caused by high interfacial friction forces. Finally, we compute the interfacial width, based on both structural and dynamical definitions, as a function of temperature. The absolute value of the interfacial width depends on the actual definition, but, regardless, the qualitative behavior is consistent. The interfacial width peaks around the bulk Tg and contracts for lower and higher temperatures. At bulk Tg, the estimated length of the interfacial width, computed via the various definitions, ranges between 1.0 and 2.7nm.

Friction Blisters of the Feet: A New Paradigm to Explain Causation.

Friction blisters on the feet commonly occur when individuals engage in active pursuits such as running, hiking, and military training. The high prevalence of blisters in active individuals underscores the fact that the pathomechanics of this condition are not fully understood. The traditional blister causation paradigm revolves around heat, moisture, and friction. In reality, foot friction blisters are caused by repetitive shear deformation. The 3 fundamental elements of blister-inducing shear deformation are (1) motion of bone, (2) high friction force, and (3) repetition of the resulting shear events. Rubbing at the skin surface is not a mechanism for friction blister formation. To that end, prevention of the friction blister continues to be an elusive quest for both the patient and the treating clinician. In this article, we aimed to highlight the limitations of the long-held blister-causation paradigm and offer a new explanation.

A case study on heat transport of electrically conducting water based-[formula omitted] ferrofluid flow over the disc with various nanoparticle shapes and highly oscillating magnetic field

The objective of the current paper is to explore the unsteady electrically conducting ferro-nanofluid flow over the stretchable rotating porous disc with the presence of Hall effect and viscous dissipation. Various shapes of Cobalt-Ferrite(CoFe2O4) nanoparticles(Blade, Brick and Platelet) are considered and dispersed in the base fluid as water(H2O) to make the ferro-nanofluid. Among different magnetic nanoparticles, Cobalt-Ferrite(CoFe2O4) nanoparticles are very interesting due to their high chemical stability, good reactivity, high surface area, excellent semiconductivity, easy synthesis, high catalytic performance, and superior magnetic properties. The Darcy-Forchheimer fluid model and highly oscillating magnetic field is employed to develop the ferrofluid flow system and Newtonian heating has been incorporated in the boundary condition. By employing the suitable similarity transformation the set of partial governing transport equations are modified into the set of highly nonlinear ordinary differential equations and solved via Runge–Kutta-Fehlberg method along with shooting technique. The present results are compared with earlier published results, and it has an excellent agreement. Key heat transfer parameters, such as Nusselt number, temperature profiles, fluid velocity distributions are analyzed and compared across different nanoparticle shapes and magnetic field strengths. The results demonstrate that the nanoparticle shape significantly influences the heat transfer rate and temperature distribution within the ferrofluid. Moreover, the skin friction force is significantly affected 2.18% by increasing the high field frequency(1≤ω0τB≤3) and skin friction force increased 0.6% by adjusting the electrical parameter(0.2≤E1≤0.4). The heat transfer rate is enhanced 0.5% due to rising the high field frequency. In addition, this work is developed to multiply the rate of energy transference and increasing the execution as well as effectiveness of energy delivering in industrial field. This model considers the Hall effect, since it helps in achieving energy circulation in numerous devices like refrigerators and in other heating applications. Especially using the magnetized nanofluid helps in improved energy transmission in biomedical imaging.

Mechanisms controlling friction and material transfer in sliding contacts between cemented carbide and aluminum during metal forming

Cold forming of aluminum alloys is frequently associated with problems related to severe adhesion and material transfer onto the forming tools which results in high friction forces and negatively affects the surface quality of the formed parts, a phenomenon frequently named galling. In the present study, well controlled laboratory tests using a scratch testing equipment have been performed to evaluate the friction characteristics and investigate the mechanisms controlling the initial transfer of aluminum in dry sliding contact with five different cemented carbide grades. In the tests, an aluminum pin (representing the work material) with a conical tip slides against a flat, fine-polished, cemented carbide surface (representing the tool). During sliding, the mechanical contact results in plastic deformation and flattening of the work material against the tool surface, thus simulating a metal forming contact. The small scale and well-defined tribo contact in combination with post-test surface characterization using optical surface profilometry, high resolution SEM and EDS makes it possible to evaluate the influence of material transfer on the friction characteristics.The results show that sub-μm surface irregularities in the cemented carbide surface trigger mechanical interaction with the softer aluminum surface which promotes aluminum transfer to the cemented carbide surface resulting in high friction. Common surface irregularities, promoting aluminum transfer, are sharp edges of slightly protruding carbide grains, surface steps in connection to binder phase pockets, surface steps in connection to surface pores, etc. It should be noted that even very small surface steps, < 20 nm in height, constitute efficient cutting edges able to effectively cut off the passing aluminum material and thus have a very strong impact on material transfer. In contrast, the effect of carbide composition, e.g. the presence of cubic carbides of different composition, seems to be of minor importance to reduce the adhesion and the tendency to material transfer.

The heating effect on tribological behaviour in the hot rolling process using TiO2 oil-in-water emulsion - A comparative study

The tribological investigations were performed at various nanoparticle concentrations (TiO2 wt%) of 0.05, 0.1, 0.3, 0.5, and 1.0 in oil-water (O/W) emulsions. The materials used for the pin and disc are IS 2062 E250 and 2% chromium-forged steel respectively. IS 2062 E250 is used for good mechanical properties, excellent resistance to corrosion at elevated temperatures, and superior tensile strength and hardness. The tribological tests were performed at the optimised concentration (0.1%) from normal temperature to 150 °C. Excellent tribological efficacy and surface characteristics were observed for optimised concentration. Relatively high friction, wear, and surface roughness were observed at a high temperature. The high-temperature test showed 40% higher frictional force than the low-temperature test. The Wear Scar Diameter increased to 2.76 mm from 2.28 mm. Surface roughness of 0.246 μm from 0.212 μm was detected from low to high-temperature tests. Hence, the nano-additive O/W emulsion could substitute O/W emulsions in the near future for high-temperature applications.

Influence of Nitrile Butadiene Rubber (NBR) Shore Hardness and Polytetrafluoroethylene (PTFE) Elastic Modulus on the Sealing Characteristics of Step Rod Seals

The influence of NBR Shore hardness and PTFE elastic modulus on the sealing characteristics of step rod seals is analyzed in this paper based on the developed mixed elastohydrodynamic lubrication (EHL) model. The optimized selection studies of NBR Shore hardness and PTFE elastic modulus under different operating conditions are carried out based on the principle of minimizing net leakage and friction power loss. Results show that the Shore hardness of the NBR O-ring and, in particular, the elastic modulus of the PTFE ring has a significant effect on the sealing characteristics. Although the high values of these parameters result in high friction forces, they are beneficial for leakage control. To achieve both low leakage and low friction, it is recommended that high hardness and low modulus are selected for moderate-low pressure or high speed conditions, but low hardness and high modulus are selected for high pressure or low speed conditions.

Molecular dynamics simulation of frictional properties of Pt cluster on graphite under load

Structural lubricity, characterized by nearly frictionless behavior at solid incommensurate interfaces with weak interactions, holds significant technological importance. However, various factors can lead to the breakdown of structural lubricity, such as spontaneous reorientation to a commensurate state, applied load, edge effects, deformations, and wear. To overcome these challenges, clusters can be employed at interfaces. With their high Young’s modulus and stiffness, clusters can withstand high loads and tolerate elastic deformations. Therefore, Pt cluster, which inherently possess incommensurate contact with graphite surface, are expected to exhibit structural superlubric behavior, even under high loads, as long as they can sustain incommensurate contact. Our molecular dynamics (MD) simulations, however, have revealed that a Pt cluster on graphite can undergo metastable transitions from the incommensurate state to a commensurate state, resulting in subsequent stick-slip behavior. In the absence of any external load, the Pt cluster has demonstrated the ability to maintain incommensurate contact with almost zero friction force, primarily attributed to its weak interaction with graphite. However, the presence of an applied load force leads to the loss of the initial incommensurate contact between the Pt cluster and graphite, resulting in the emergence of high friction forces and the breakdown of structural lubricity with a similar stick-slip behavior to that observed in the comparative simulations conducted for the commensurate state. It becomes evident that the maintenance of incommensurate contact is crucial for achieving superlubric behavior in Pt cluster-graphite systems, while the presence of an applied load force can disrupt this behavior and lead to higher friction forces.

Valorization potential of pine needle waste biomass: recent trends and future perspectives.

Pines play a significant role in forest biodiversity globally and generate huge forest litter. Dry pine needles due to low ignition temperature and high frictional force with the ground catch fire quickly. Annual forest fires in the northern states of India greatly impact the Indian economy besides causing huge loss to biodiversity, livelihood, and environment. Pine needles are also considered unfit for fodder consumption due to presence of tannins. Although the presence of softwood lignin in pine needles makes it difficult to degrade easily, the presence of holocellulose (68.5%) containing 45-51% cellulose makes this biomass a potential substrate to be used in pulp-making industries for low-grade paper sheets. The good fiber length of pine needles (1.3-1.4mm) with a diameter of 30-32μm, maybe considered important property for paper making. The use of pine needles in the pharmaceutical and food industries are due to the presence of secondary metabolites (α-pinene, β-pinene, caryophyllene etc.). The various other potential applications of pine needles are for producing bio-ethanol (yield, 3.98%; purity, 94%), biogas (yield, 23.1 L kg-1), smokeless briquettes (calorific value, 18.77MJkg-1), biochar (calorific value, 25.6MJkg-1), bio-composites (tensile strength, 21-60MPa), and bio-pesticides. This paper comprehensively reviews the current applications of pine needles along with its future prospective applications that can have the dual advantage of providing employment opportunities to the people along with environmental protection.

Effect of fiber layer formation on mechanical and wear properties of natural fiber filled epoxy hybrid composites

Natural fiber-reinforced polymer matrix composites are gathering significance in future trend applications such as automotive, aerospace, sport, and other engineering applications due to their superior enhanced mechanical, wear, and thermal properties. Compared to synthetic fiber, natural fiber is low adhesive and flexural strength properties. The research aims to synthesize the epoxy hybrid composites by utilizing the silane (pH = 4) treated Kenaf (KF) and sisal fiber (SF) as layering by uni, bi, and multi-unidirectional via hand layup techniques. Thirteen composite samples have been prepared by three-layer formation adopted with different weight ratios of E/KF/SF such as 100E/0KF/0SF, 70E/30KF/0SF, 70E/0KF/30SF, 70E/20KF/10SF, and 70E/10KF/20SF respectively. The effect of layer formation on the tensile, flexural, and impact strength of composites is studied by ASTM D638, D790, and D256 standards. The unidirectional fiber layer formed (sample 5) 70E/10KF/20SF composite is found maximum tensile and flexural strength of 57.9 ± 1.2 MPa and 78.65 ± 1.8 MPa. This composite is subjected to wear studies by pin-on-disc wear apparatus configured with a hardened grey cast-iron plate under an applied load of 10, 20, 30, and 40 N at different sliding velocities of 0.1, 0.3, 0.5, and 0.7 m/s. The wear rate of the sample progressively increases with increasing load and sliding speed of the composite. The minimum wear rate of 0.012 mg/min (sample 4) is found on 7.6 N frictional force at 0.1 m/s sliding speed. Moreover, sample 4 at a high velocity of 0.7 m/s with a low load (10 N) shows a wear rate of 0.034 mg/min. The wear-worn surface is examined and found adhesive and abrasive wear on a high frictional force of 18.54 N at 0.7 m/s. The enhanced mechanical and wear behavior of sample 5 is recommended for automotive seat frame applications.

Development of a flexible high-friction pressure sensor with structural colors for soft gripper fingers

For energy-efficient and lightweight sensor applications, structural colors were utilized to sense the pressure applied to the surface. However, conventional structural color sensors have been usually fabricated with nanoscale features focusing on high pressure sensitivity with small load limits. In this study, a flexible surface with high frictional force and wide pressure-sensing capability was fabricated by ultra-precision machining for soft gripper applications. Friction and grip detection are very important for gripping performance and sensors for soft grippers are required to cope with loads of over 1 kg. Here, microscale three-dimensional trapezoidal patterns were fabricated and transferred to a polymer to increase the contact area for higher friction and improve structural color expression. The effects of pattern geometry on structural color changes due to the varying loads were analyzed using the hue, saturation, and brightness (HSB) model. The hues of the patterned surfaces decreased with loads. Clear color changes were apparent as the pattern width and depth varied; patterns with blue colors (hue of ~240) at no-load status sensed pressure most effectively. Based on the experimental results, a sensor was designed to have a clear color change in terms of pressure and then was applied to soft gripper fingers. Significant color changes were evident as the pressure changed during gripping even under large loads of up to 1200 g; the high friction (compared to that of a plain surface) also improved gripping performances. The sensor provides intuitive information detectable by the naked eye, and there is no need for any power source, wire, or data acquisition system. This research can contribute to the development of multi-functional, lightweight energy-efficient systems.

C60 filling-enabled tribological improvement of graphene in conformal contact with a rough substrate

Graphene has great potential in the field of solid lubricity due to its superlow friction and high wear resistance. However, the excellent tribological performance of graphene is degraded when it conformally contacts with a rough substrate. This work proposes a novel method to improve the tribological performance of graphene on a rough Si/SiO2 substrate by filling grooves on the substrate surface with C60 molecules. When C60 filling is not performed, the friction force on the graphene surface increases rapidly at the groove edges where graphene presents large out-of-plane deformation due to its conformal contact with the substrate. Inspiringly, such high friction force is reduced by one order of magnitude when C60 filling is introduced to provide out-of-plane support to graphene for preventing its conformal contact with the substrate. Meanwhile, the high mechanical strength of C60 molecules enables a greater than 5-fold strengthening of the load-carrying capacity of graphene, which greatly improves its wear resistance on the rough substrate. These observations are helpful in promoting the tribological application of graphene by diminishing its conformal contact with the rough substrate.

Friction Optimization of Talc Powder-Reinforced Elastomers for Prosthetic Foot Application

Patients with lower limb amputation usually use prosthetic feet. Elastomeric material is an important part of prosthetic feet since it can determine their safety and lifetime. The elastomeric material should have high friction for safety, and at the same time it should have low wear for a longer lifetime. This research is aimed to study the optimum formulation of talc-powder-reinforced silicone elastomer to obtain high friction during sliding contact. The Taguchi orthogonal array L9 formula is used to achieve the aforementioned goal. The experiments use multiple parameters, namely, the type of silicone, the type of surface texture, the amount of catalyst, and the amount of talc powder. The results show that the combination of RTV 683, a smooth texture, 4% of catalyst, and 60% of talc powder is the most optimum composition to obtain the highest frictional force. It has a higher friction force in comparison with the imported products, and, at the same time, it has comparable wear with the imported products. The hardness of the optimized materials is comparable with the imported products. However, the tensile and tear strengths of the optimized materials need to be improved.

Molecular dynamics simulation on friction performance of collision sliding contacts of soft metals in vibration environment

Soft metals are often used for space mechanism lubrication because of their low shear strength. In outer space, the vibration of spatial mechanism will occur when there is a small disturbance due to the effects of microgravity environment. Studies on the friction properties of soft metals in vibration environment could contribute to the application of space lubrication materials. Taking a clearance joint as an example, the relative motion between the shaft and the bearing is simplified to a sliding contact between a cylinder and two smooth contact bodies. A molecular dynamics model of the collision sliding contact between a rigid cylindrical indenter and an elastic substrate is established. The effects of sliding velocity, collision velocity and indenter radius on the friction properties of soft metals are studied. The results show that the Ag substrate and Au substrate present strong adhesion to the Fe indenter. The indenter and the substrate are always in a state of adhesive sliding contact. The larger the initial collision velocity of the indenter, the higher the friction force. The friction force shows great values as the sliding velocity increases. As the increase of indenter radius, the contact area is enlarged, which results in a high friction force. The adhesion of the Cu substrate to the Fe indenter is weak, so the friction force shows a low value, and the friction performance of Cu is the best, while the friction performance of Au is the worst.

A Homogeneous Flow Model for nitrogen cooling in the aluminum-alloy extrusion process

Extrusion of aluminum alloys has become extensively employed as a process to manufacture a variety of products. However, heat generated by the high deformation energy and the high friction forces imposed during the process may cause defects in the extrudate, as well as reduce tool life. So, effective die cooling is key in achieving high product quality and production rate. Nitrogen has recently been identified as a promising coolant; however, current modeling does not take the presence of two phases into account, only including either the liquid or the gas phase within cooling channels, which often results in poorly designed cooling systems. The present research was aimed at exploring the homogenous-flow approach as a simple, yet representative method to account for the liquid and the gas phase, as they both occur during the cooling subprocess. Ten AA6060 billets were extruded in an industrial production line, varying nitrogen flow rate and monitoring temperature trend at various locations of interest. A Finite Element model was then developed in a multiphysics environment, into which the simulation of both the extrusion process and the nitrogen flow were integrated, with the latter being represented as a homogeneous flow. Validation was performed against the experimental dataset through steady-state and transient analysis. This work proved the homogeneous-flow approach remarkably successful in capturing the involved physics and assessing the provided cooling effect quantitatively.

Application of poly (vinyl alcohol)-cryogels to immobilizing nitrifiers: Enhanced tolerance to shear stress-induced destruction and viability control

The hardness of poly (vinyl alcohol)-cryogels (PVA-CGs) was improved under three parameter conditions: 7.5 %–12.5 % PVA, 1–5 freezing–thawing cycles (FTCs), and the addition of 0 %–10 % glycerol as a cryoprotectant. This study investigated the effects of shear stress-induced destruction (SSID) on mechanical strength by inducing rapid erosion with a high frictional force. Tolerance to SSID (Tol-SSID) exhibited different sensitivities and trends depending on the above three fabrication parameters. The measured Tol-SSID exhibited consistent and inconsistent trends with tensile strength and swelling, respectively. Tol-SSID evaluation provides new insights into the practically meaningful mechanical strength of PVA-CGs against strong friction, which simulates extreme shear stress in a bioreactor. A PVA-CG with a PVA concentration of 10 % and in two FTCs resulted in Tol-SSID and tensile strength of 88.3 % and 0.59 kPa, respectively. Here, 5 % glycerol was added to maintain the bacterial respiration activity of immobilized nitrifiers of 0.097 mg-O2/g-VSS·min and survival of 88.6 %. The continuous mode of nitrification using the optimized PVA-CG for 10 days resulted in an ammonia removal rate of 0.2173 kg-N/m3·d, which is an improvement over cases without glycerol addition: 0.1426 and 0.1472 kg-N/m3·d for PVA-CGs in two and three FTCs, respectively.