Material Flow Behavior Research Articles

Variations of the Herschel–Bulkley exponent reflecting contributions of the viscous continuous phase to the shear rate-dependent stress of soft glassy materials

We explore the flow behavior of concentrated emulsions for which the viscosity of the continuous phase can be significantly varied by changing the temperature. The exponents obtained by fitting the shear rate-dependent stress with the popular Herschel–Bulkley (HB) model display a systematic dependence on the viscosity of the continuous phase, revealing that viscous dissipation via the suspending fluid cannot be neglected in the description of the flow behavior of soft glassy systems. We thus propose a simple constitutive equation that accounts for three distinct dissipation mechanisms: elastic, plastic, and viscous dissipation. This three component model describes the flow behavior of soft glassy materials as accurately as the HB model, albeit maintaining a clear physical insight into the dissipation processes at work.

A novel friction stir diffusion bonding process using convex-vortex pin tools

In this work, a novel friction stir diffusion bonding (FSDB) method was proposed to eliminate hook when joining thin sheets. Three tools, with several convex-vortex pins were innovatively designed to improve the diffusion bonding effect of the lap interface. Results showed that sound joints, excellently bonded at the lap interface and without hook, were obtained. The lap interfaces on the joints welded using the T-tool and F-tool almost remained intact, thereby indicating that they were formed by diffusion bonding. The material flow behavior was also simulated by FLUENT software and the results showed that the material flow along thickness was significantly enhanced by increasing the pin number. The joint welded by the T-tool showed shear fracture mode. Sound bonding was formed at the lap interface when using the F-tool and thus the joint showed tensile fracture.

Shape stability and flow behaviour of a phase change material based slurry in coupled fluid-thermo-electrical fields for electronic device cooling

The suitable phase transition temperature range and low electrical conductivity make fatty acid-based Phase Change Material (PCM) slurries an attractive heat transfer fluid for cooling of High–Voltage Direct Current (HVDC) electronic devices. However, their shape instability induced by external electrical field may alter their effective thermophysical properties and hence the heat transfer performance. In this work, the shape stability and flow behavior of a fatty acid droplet under a coupled fluid-thermo-electric coupled field are numerically investigated. The effects of droplet size, fluid velocity and temperature, and electrical field on the shape and energy of the droplet are evaluated. The results show that the droplet size is the major influencing factor for the shape stability. Given other conditions, the deformation ratio and the internal pressure difference of a 1 μm droplet are respectively 8 times higher and 5 times larger than a 7 μm droplet. An increase in the slurry velocity only slightly increases the particle interior pressure; given other conditions, an increase in the velocity from 0.22 m/s to 1.1 m/s only leads to an internal pressure increase by 25.77%. The electrical stress across the surface tends to squeeze the droplet into a prolate shape, offsetting the shape deformation by the shear stress and hence stabilizing the PCM slurry. The presence of the electrical field slows down the energy evolution and reduces the pressure difference inside the droplet.

Effect of ultrasonic vibration on thermal and material flow behavior, microstructure and mechanical properties of friction stir welded Al/Cu joints

Al/Cu dissimilar joint has been widely produced by using friction stir welding (FSW), but the weld quality remains limited. A recently developed ultrasonic vibration-assisted FSW (UVaFSW) technology has shown potential of enhancing the material flow and mechanical properties of Al/Cu joint. In this paper, a systematic study is presented to investigate the effect of ultrasonic energy on FSW Al/Cu joints with an optimized tool shoulder diameter of 16 mm and welding speed of 60 mm/min. It is found that the thermal effect of ultrasonic on the FSW process could be deemed negligible, which is distinguishing with other transmission method of ultrasonic energy. Correspondingly, the mechanical effect of ultrasonic is evident because of the dramatically decreased welding loads, the more intense intermixing between Al and Cu, and the more uniformly distributed micro-hardness in the stirring zone of UVaFSW Al/Cu joints. Moreover, the ultrasonic energy reveals a positive influence on the weld quality of Al/Cu joint; the maximum tensile strength by UVaFSW is achieved at the rotation speed of 500 rpm; and the value reaches 162.8 MPa, which improves by 60.7% compared with that by FSW. It is elucidated that the ultrasonic vibration effectively reduces the activation energy and flow stress of the material, stimulates stable plastic deformation in the vicinity of the tool, and is beneficial for the homogeneous of FSW Al/Cu joint.

Effects of tool shoulder size on the thermal process and material flow behaviors in ultrasonic vibration enhanced friction stir welding

To improve the joint quality and lower the welding loads, ultrasonic vibration enhanced friction stir welding (UVeFSW) had been developed and had shown several benefits. The most important geometric parameter in UVeFSW tool design is the shoulder diameter, but its effect on the thermal process and plastic material flow behaviors has not been quantitatively analyzed. To elucidate these effects, an integrated computational fluid dynamics (CFD) model was adopted to quantitatively study the effects of tool shoulder diameter on the thermal process and plastic material flow behaviors in UVeFSW. It is found that UVeFSW process can have significant effects in enhancing plastic material flow and reducing the welding loads without increasing the process temperature when compared to that in FSW by using larger tool shoulder to enhance the plastic material flow. It revealed that the maximum width of the shear zone at the top surface of the workpiece was highly dependent on the shoulder diameter. However, the minimum width of the shear zone at the bottom surface of the workpiece was insensitive to the shoulder diameter. Based on the combination of the integrated CFD model with the theory of maximum traction of the tool torque on the plastic material, the optimum shoulder diameter at various welding parameters had been systematically studied. It was found that the optimum shoulder diameter decreases with an increase of the tool rotation speed, while it increases with an increase of the welding speed. This model provides a reasonable method for optimum the shoulder diameter in UVeFSW process. The integrated CFD model is validated by a comparison of the predicted and measured thermal cycles and welding loads.

Constitutive modelling of hot deformation behaviour of a CoCrFeMnNi high-entropy alloy

ABSTRACT Models describing the constitutive flow behaviour of a metallic material are desired for appropriate process design and realization of defect-free components. In this study, constitutive equations based on the hyperbolic-sinusoidal Arrhenius-type model have been developed to define the hot deformation characteristics of a CoCrFeMnNi high-entropy alloy. The experimental true stress-true strain data were generated over a wide temperature (1023–1423 K) and strain rates (10−3–10 s−1) ranges. The impact of strain rate and temperature on deformation behaviour was further characterized through a temperature compensated strain rate parameter, i.e. Zener-Hollomon parameter. Additionally, a mathematical relation was employed to express the influence of various material constants on true-strain ranging from 0.2 to 0.75. Typical third order polynomial relations were found to be appropriate to fit the true-strain dependency of these material constants. The accuracy of the developed constitutive equations was evaluated by using the average absolute relative error (AARE) and correlation coefficient (R); the obtained values were 7.63% and 0.9858, respectively, suggesting reasonable predictions. These results demonstrate that the developed constitutive equations can predict the flow stress behaviour of the alloy with a good accuracy over a wide range of temperature and strain rate conditions and for large strains.

Influences of shape of the new interfaces and morphology of the intermetallics on mechanical properties of aluminum AA2024–pure copper joints by friction stir welding

Friction stir welding (FSW) joints are inevitably accompanied with the change in shape of the abutting surfaces due to the tool movement. Further, the formation of brittle intermetallics (during dissimilar welding) is also unavoidable. Therefore, the current work is focused to study the role of the shape of the new interface in properties of the joints and to control the morphology of intermetallics subsequently. FSW experiments were carried out between aluminum AA2024 and pure copper for different tool offset positions (on either side of the interface), plate positions (copper in advancing or retreating side), and tool geometry (plain and threaded). The microstructure observation showed noticeable changes in the shape of the new interface with respect to the selected parameters. Tensile tests highlighted that the weld which has continuous and smooth new interface gave better properties than the welds which had an irregular discontinuous interface. Also, this kind of interfaces had formed with a continuous thin intermetallic layer, and it was a desirable morphology of the intermetallics. The weld with this thin intermetallic layer (metallurgical bonding) alone has the maximum strength, whereas the welds that also had fine steps at the interface (mechanical bonding from interlocking effect) have maximum ductility. The mechanism behind this was explained in detail with the help of material flow behavior study for the selected conditions. This concluded that to achieve better properties, the shape of the new interface and the bonding along this interface are mainly important to be considered.

Digital Image Correlation Based Internal Friction Characterization in Granular Materials

Based on the realization that Newtonian fluids have the unique property to redirect the forces applied to them in a perpendicular direction, a new apparatus, called the Granular Friction Analyzer (GFA), and the related GFA index, were proposed for characterizing the internal friction and related flow behavior of granular materials under uniaxial compression loading. The calculation of the GFA index is based on the integration of the internal pressure distribution along the cylinder wall, within which the granular material is being uniaxially compressed by a piston. In this paper an optical granular friction analyzer (O-GFA) is presented, where a digital image correlation (DIC) method is utilized to assess the cylinder strains used to calculate the internal pressure distribution. The main advantage of using the DIC method is that the starting point (piston–powder contact point) and the length of the integration considering the edge effects can be defined. By using the DIC full-field, instead of a few points strain measurements, a 2% improvement of the GFA index’s accuracy has been achieved and its robustness with respect to the number of points has been demonstrated. Using the parametric error analysis it has been shown that most of the observed total error (7.5%) arises from the DIC-method-based measurements of the strains, which can be improved by higher-resolution cameras and DIC algorithms for the strain evaluation. Additionally, it was shown that the GFA index can be used for determining the well-known Janssen model parameters. The latter was demonstrated experimentally, by testing three SS 316 L granular material samples with different mean particle sizes. The results confirm that the mean particle size regulates the internal friction of granular materials.

Prediction of the Weld Pool Stability by Material Flow Behavior of the Perforated Weld Pool.

This article presents the application of a computational fluid dynamics (CFD) finite volume method (FVM) model for a thermo-mechanical coupling simulation of the weld pool used in variable polarity plasma arc welding (VPPAW). Based on the mechanism of the additional pressure produced through self-magnetic arc compression and the jet generated from mechanical plasma arc compression, and considering the influence of arc height and keyhole secondary compression on arc pressure, a three-dimensional transient model of variable polarity plasma arc (VPPA) arc pressure was established. The material flow behaviors of the perforated weld pools were studied. The results show that three kinds of flow behavior existed in the perforation weld pools and it is feasible to predict the weld pool stability by the material flow behaviors of the perforated weld pools. The weld pools can exist stably if the material flow in the bottom of the perforated weld pools can form confluences with moderate flow velocities of 0.45 m/s, 0.55 m/s and 0.60 m/s. The weld pools were cut when the material flowed downward and outward with the maximum velocity of 0.70 m/s, 0.80 m/s. When the maximum material flow velocity was 0.40 m/s, the weld pool collapsed downward under the action of larger gravity. The thermo-mechanical coupling model was verified by the comparison of the simulation and experimental results.

Quantitative earthquake-like statistical properties of the flow of soft materials below yield stress

The flow behavior of soft materials below the yield stress can be rich and is not fully understood. Here, we report shear-stress-induced reorganization of three-dimensional solid-like soft materials formed by closely packed nematic domains of surfactant micelles and a repulsive Wigner glass formed by anisotropic clay nano-discs having ionic interactions. The creep response of both the systems below the yield stress results in angular velocity fluctuations of the shearing plate showing large temporal burst-like events that resemble seismic foreshocks-aftershocks data measuring the ground motion during earthquake avalanches. We find that the statistical properties of the quake events inside such a burst map on to the scaling relations for magnitude and frequency distribution of earthquakes, given by Gutenberg-Richter and Omori laws, and follow a power-law distribution of the inter-occurrence waiting time. In situ polarized optical microscopy reveals that during these events the system self-organizes to a much stronger solid-like state.

Friction stir lap welding of AA2024-T4 with drastically different thickness

Friction stir lap welding is a promising technology to obtain high-strength joints of Al alloys in aviation and aerospace industries. Despite extensive studies performed on thin-wall structures, few works were conducted to join the plates with drastically different thickness, such as the joining of aircraft skins and panels. In this paper, 2.5-mm and 25-mm-thick AA2024-T4 plates were joined with a circumferential notches shape pin. The influence of pin length on joint features and mechanical properties was investigated. The pin improved the material flow behavior and stirred the materials violently, which were beneficial to reducing the interface migration and facilitating the joining of interfaces. The hook defects were eliminated. The failure load firstly increased with the pin length from 2.6 mm to 2.7 mm and then decreased when the pin length increased from 2.7 mm to 3.1 mm. The failure load reached 7.97 kN due to sufficient material intermixing with strong mechanical joining and large bearing area with metallurgical bonding. The selection of pin length should consider the deformation of thick plates, which acted as backing plates with lower elasticity modulus than typical backing plates made of steel.

Investigation of material flow behaviour and microstructure during differential velocity sideway extrusion

Differential velocity sideway extrusion (DVSE) process is a cutting-edge technology to manufacture curved profiles with solid or hollow cross-sections. Extrusion welding is inevitable to form hollow cross-section profiles during DVSE. In the present work, two billets (AA1070) were welded into a bar in the chamber of an extrusion die through DVSE. The material flow behaviour, grain structure and its development in the extruded bar were studied. Based on material flow behaviour, the flow plane of material in the chamber of extrusion die can be divided into metal dead zone (MDZ), shearing intensive zone (SIZ), and metal flow zone (MFZ, including the welding zone). A sound weld without any bonding interface can be obtained by DVSE welding at 500 ℃ and 0.1 mm/s. Before material arrives at the exit of extrusion die, banded structures form along the metal flow direction with the increase of deformation and the mean grain size continually decreases due to dynamic recrystallisation (DRX). Grains significantly grow after exiting from the extrusion die.

Microstructure and texture of friction stir welds in low carbon steel using prior austenite reconstruction method

Friction stir welding (FSW) was performed on thick plates of high-strength low-alloy (HSLA) steel with polycrystalline cubic boron nitride (PCBN) tools. To investigate the mechanism of microstructure formation in the stir zone (SZ), the prior austenite structure undergone through a thermo-mechanical history during the FSW process was investigated. The prior austenite structure was reconstructed by the local crystal orientations of prior austenite calculated from the bainite orientations by using the Kurdjumov–Sachs orientation relationship between the prior austenite and bainite. The reconstructed austenite revealed a heterogeneity in the SZ. The austenite grain size in the advancing side (AS) of SZ was larger than that of the retreating side (RS). Thus, a reheated temperature of AS was considered to be higher than that of RS. The textures of reconstructed austenite were also different in SZ. The rolling texture was observed in RS, but the shear texture was observed in the center and AS. The heterogeneous microstructure and texture in SZ was considered to be caused by the material flow behavior in FSW process.

Effects of processing parameters on mechanical, material flow and wear behaviour of friction stir welded 6101-T6 and 7075-T651 aluminium alloys

Dissimilar friction stir welding (FSW) between 6101-T6 and 7075-T651 aluminium alloys was conducted. Three different parameters each were investigated for rotational speed and travel speed, and the effects of these parameters on the tensile behaviour, hardness and wear were evaluated. The results indicate that the ultimate tensile strength increases with an increase in the feed rate. However, the increase in rotational speed decreases the ultimate tensile values. The fractured analysis of the tensile samples shows similarities in the fractured pattern as all the samples failed at heat affected zone close to the 6101-T6 alloy. The hardness varies across the heat affected zones and nugget zone both at constant rotational speed and welding speeds. The highest resistance to wear occurred at 65 mm min−1 and 1850 rpm welding speed and rotational speed respectively while better material mixing was achieved at the nugget zone of the welds at 1250 rpm and 110 mm/min.

Effect of Vane Shape on Fertilizer Distribution for a Dual-Disc Spinner Spreader

Abstract.Spinner-disc spreaders are commonly used for application of granular fertilizers with components (divider, spinner-discs, and vanes) influencing material flow behavior and distribution. Fertilizer ricocheting off these components is an uncontrolled aspect of material flow that negatively impacts spread uniformity. Therefore, an investigation using potash (KCl) was conducted to understand the impact of vane shape on fertilizer flow, ricocheting and distribution for a dual-disc spinner spreader. Four different vane shapes were used in this study. The first two vanes (Vanes 1 and 2) were common to this type of spinner spreader with a tapered and open-faced design. However, Vane 1 had a forward tapered top edge at an angle of 32° while Vane 2 had a top edge that was tapered backwards at 15°. Vanes 3 and 4 both had C-channel cross sections with Vane 3 tapered from inside out but Vane 4 had a constant height. Treatments included application rates of 220 and 440 kg/ha using three spinner disc speeds (600, 700, and 800 rpm). Stationary tests were conducted using a collection device that mounted around the spinner discs and vanes in order to estimate fertilizer particle exit points off the vanes. Standard pan tests were conducted to characterize resulting spread patterns, effective spread width, and spread uniformity. Results indicated that the level of ricocheting was significantly impacted by top edge design of a vane and increased with disc speed. The forward, upward facing top edge of Vane 1 caused on average, 26% of the material flow to be ricocheted by the vanes thereby inducing an uncontrolled nature of spread. However, the rearward facing top edge of Vane 2 reduced ricocheting by 13% plus generated a backward particle rotation for those contacting it. The majority of ricocheting occurred when particles contacted the vanes compared to the spinner discs. Ricocheting generated an uncontrollable aspect of the spread pattern with these particles applied along the centerline of the spreader. The effective spread width increased with disc speed. All four vane shapes generated equal effective spread widths of 18.3 and 21.3 m at 600 and 700 rpm, respectively. However, at 800 rpm, Vane 4 generated the greatest effective spread width of 24.4 m compared to 22.9 m for the other three vanes. The wider spread width for Vane 4 was contributed to the rectangular U cross-section maximizing the horizontal velocity of potash particles when exiting the vanes compared to the other three, more open faced vanes. Finally, the spread uniformity varied by vane shape with Vane 2 consistently generating the lowest CVs. Keywords: Distribution, Ricocheting, Vane Design, Spread uniformity, pattern.

Cross effect between temperature and consolidation on the flow behavior of granular materials in thermal energy storage systems

Calcium looping (CaL) process offers a promising option to boost the energy efficiency and dispatchability in concentrated solar power (CSP) plants. Backed by ample experience on lime and cement industry, the CaL integration in CSP plants could be not only a feasible and reliable technology for energy storage but also a low-cost choice based on the abundance and cheap price of limestone (CaCO3). However, to date, there is no deep fundamental understanding about how different conditions through the pipes and in storage silos affect the flowability of the granular medium. This is a critical issue, therefore, concerning the ease with which the granular medium is transported, fluidized or stored. Our present work challenges the status quo on the granular-based energy storage systems in which many central questions about powder dynamics through the circuit have been dodged. To deeply explore and figure out optimal settings, we have investigated the potential side effects that changes in temperature and consolidations can induce in the powder flowability. In so doing, we analyze the variation of the tensile strength of the powder while it is being fluidized in a wide range of temperatures and consolidations. The powder, CaCO3 with a particle size around 50 μm, was chosen to mimic the actual conditions in CaL-CSP pilot plants (currently under development). The results show a severe impact on cohesion when the CaCO3 granular medium is exposed at different temperatures ranging from ambient to 500 °C, and consolidation stresses up to 2 kPa. With cohesion increasing up until an order of magnitude in this range of relatively low consolidations, it is a foregone conclusion that those changes uncover a scenario that has not been brought up so far.

Regional material flow behaviors of agro‐food processing craft villages in Red River Delta, Vietnam

The economic reform “Đổi Mới” in 1986 has rapidly increased the number of craft villages in Vietnam, especially in the Red River Delta (RRD) leading to environmental degradation. This article presents an assessment of environmental and resource issues of agro‐Food Processing Craft Villages (FPCVs) in RRD using a refined approach to material flow analysis focusing on consistent quantification of uncertainty with particular attention to secondary and empirical data that are often faced in material flow analyses in transition economies. Material flows of agro‐Food Processing including eight types of production were examined and linked to activities of private Households, Rice Cultivation, and Pig Farming in a model called Red River Delta. Materials investigated were Goods (i.e., total materials), organic carbon (org.C), nitrogen (N), and phosphorus (P). The findings reveal material cycles are almost entirely open, that is, the materials used in FPCVs do not recycle within the region. From ∼10.5 million tons/year of imported Goods used for agro‐Food Processing, final products and utilized materials account for minor fractions (∼5%, by weight). Conversely, the majority (88%) is directly discharged. Materials accumulated as stocks represent 1% of Goods (100,000 tons/year), 21% of org.C (∼34,000 tons/year), 42% of N (∼1,300 tons/year), and 57% of P (∼300 tons/year), whose substance concentrations vastly exceed natural resilience capacities. Although agro‐Food Processing accounts for negligible material shares in Red River Delta, FPCVs pollution is severe at local levels due to the location of home‐based production. Several options for closing material loops at various system scales are recommended for environmental and resource management of FPCVs. The material flow analysis results provide a database that may be used as a decision support tool for production establishments in craft villages and relevant authorities in setting priorities on environmental planning and resource management. This article met the requirements for a gold – silver JIE data openness badge described at http://jie.click/badges.

Effects of ultrasonic assisted friction stir welding on flow behavior, microstructure and mechanical properties of 7N01-T4 aluminum alloy joints

Conventional friction stir welding (FSW) and ultrasonic assisted friction stir welding (UAFSW) were employed to weld 6-mm thick 7N01-T4 aluminum alloy plates. Weld forming characteristics and material flow behavior in these two different welding processes were studied and compared. Ultrasonic vibration was applied directly on the weld in axial direction through the welding tool. Metal flow behavior, microstructure characteristics in the nugget zone (NZ) and evolution of the mechanical properties of naturally aged joints were studied. Results show that the ultrasonic vibration can significantly increase the welding speed of defect-free welded joint. At the rotation speed of 1200 rpm, the UAFSW can produce defect-free welded joints at a welding speed that is 50% higher than that of the conventional FSW. Ultrasonic vibrations can also improve surface quality of the joints and reduce axial force by 9%. Moreover, ultrasonic vibrations significantly increase the volume of the pin-driven zone (PDZ) and decrease the thickness of the transition zone (TZ). The number of subgrains and deformed grains resulting from the UAFSW is higher than that from the FSW. By increase the strain level and strain gradient in the NZ, the ultrasonic vibrations can refine the grains. Ultrasonic energy is the most at the top of the NZ, and gradually reduces along the thickness of the plate. The difference in strengths between the FSW and the UAFSW joints after post-weld natural aging (PWNA) is small. However, the elongation of the UAFSW is 8.8% higher than that of the FSW (PWNA for 4320 h). Fracture surface observation demonstrates that all the specimens fail by ductile fracture, and the fracture position of the UAFSW joint changes from HAZ (PWNA for 120 h) to NZ (PWNA for 720 and 4320 h).

10.36910 ДОСЛІДЖЕННЯ ПАРАМЕТРІВ ВЗАЄМОДІЇ ЗЕРНОВОГО МАТЕРІАЛУ ІЗ ПОВЕРХНЕЮ ЕЛАСТИЧНОЇ СЕКЦІЇ ШНЕКА

У статті запропоновано нову конструкцію шнека з секційною еластичною поверхнею, яка призначена для зменшення ступеня пошкодження зернового матеріалу при його транспортуванні. Проведено теоретичний розрахунок взаємодії зернини з еластичною секцією шнека. Наведено результати експериментальних досліджень.

Rheology analysis of sago processing wastewater with variable starch content

Rheology properties are considered to be essential for designing a bioreactor to understand the flow behavior of materials inside the reactor. In this regard, rheological measurements of sago processing wastewater with different starch concentrations ranged 10, 20, 30, 40, 50, 60, 70, and 80 g L-1 were evaluated. The sago wastewater with a starch concentration of 10 and 20 g L-1 indicated a non- Newtonian behavior, showing yield stress and shear thinning. Based on the results, it is concded that sago wastewater with starch concentrations up to 20 g L-1 could be well suited for airlift bioreactors used for the microbial lipid production process.