Corner Gap Research Articles

Flow simulation around square cylinder with inclined corner gap at low Reynolds number

In this paper, an investigation of the effects of inclined corner gaps of varying widths and lengths on the static aerodynamic force coefficients and flow features of a square cylinder at low Reynolds number (Re of 100) by comparing with an unmodified square cylinder is discussed. The width of the corner gap (x/D) was varied between 0.02 and 0.24, with two different lengths of it (l/D), namely, 0.05 and 0.11. The open-source code OpenFOAM was used as a solver. A second-order accuracy level was ensured for both time and space during the numerical set up of the model. Validation and verification studies were conducted to ensure the authenticity of the results. The mean and rms values of the static force coefficients of these cylinders were compared and important flow features were explored. Even at a low Re, the proposed corner modification was found to be effective in improving the static aerodynamic performance. For different gap widths, the static force parameters evidenced some patterns, with an optimum width for which the mean drag value reached the minimum value identified. Furthermore, the mean and fluctuating pressure and velocity contour were analyzed to understand the underlying flow mechanism.

Impact design of die parameters on Severe plastic deformation during Equal channel angular pressing: An overview

Equal channel angular pressing causes less uniform deformation than simple shear, even though its not as obvious as with other metal forming procedures. Investigation is done into how internal and external factors affect the deformity inhomogeneity through Equal .channel angular pressing. Finite element analysis of plastic deformity are integrated with die corner angle and the strain harden ability of metallic workpiece. The material characteristics are significantly influenced by the type of plastic shear deformation that occurs through Equal channel angular pressing and this is primarily impacted by the die geometry, the properties of the material and the process factors. Segmenting the workpiece into a front transient zone, end transient zone, outer less sheared zone and the remaining shear deforming zone allowed researchers to examine the uneven strain distribution throughout the workpiece. The deformed geometry for the non-hardening and it was assumed that rate-insensitive materials would be largely homogeneous. In materials that are strain-rate sensitive, gaps between the upper and lower channels developed, whereas strain-hardening materials experienced the corner gap. The strain hardening and implications of strain-rate sensitivity exponent had a considerable impact on the deformation inhomogeneity. Metals having an ultrafine grain microstructure can be created by severe plastic deformation. The FE models were used to affect the process and they all took as inputs the material properties, load variation, Different velocity and boundary conditioned. For the purpose of evaluating the impact of the channel angle on the AA5083 sample, The FE analysis produced the value of strain distribution. When the channel angle was 1200, there was less strain overall, but there was also less concentrated stress in the channel corner area.

Equal channel angular pressing die design through finite element analysis method for non-strain hardening material

ABSTRACT The present research aimed to optimise process parameters such as outer corner angle (ψ = 0°–36°), frictional coefficient (μ = 0–0.05), inner corner angle (ω = 0°–8°) and die channel angle (φ = 90°–120°) for the equal channel angular pressing (ECAP) die design considering a non-strain hardening material Al6061-T6 alloy using ABAQUS finite element analysis software in terms material flowability, corner gap formation, surface gap formation, induced strain intensity and strain distribution. The ECAP die having 100° φ, 24° ψ, 0.02 μ and 8° ω provide better material flowability, (no corner gap formation and surface gap formation), moderate induced strain intensity and homogeneous distribution. The ECAP processing on the designed die effectively modifies the microstructure morphology of as-cast Al6061 alloy. The α-Al grain size decreases and roundness increases and the thicker grain boundary is altered into the thinner boundary, as an effect of this, hardness and tensile strength improved by 28.3% and 32.7%, respectively.

A novel broadband monopole coplanar antenna configuration with circular polarization

In this paper, a novel construction of a wideband slotted monopole antenna supplied by a single coplanar waveguide (CPW) with circular polarization (CP) characteristic for the small wireless device is proposed and discussed. The circular polarized CPW antenna is intended for the Industrial Scientific Medical (ISM) band spanning at 2.45 GHz. It consists of a monopole-shaped patch with two oppositely facing corner gaps extending from the CPW signal strip into the middle of a square metal frame serving as the ground, incorporates a couple of L-shaped grounding strips surrounding two oppositely facing corners of the ground, and an L slot in the topside of the ground plane. The bandwidth of the antenna’s input impedance is widened through reconfiguring the necessary parameters of the reversed L-shaped grounding strips. The circularly polarization can be significantly achieved through cutting an upturned L-slot mostly in the topmost half of the ground. The proposed antenna has a size of 60600.74mm3. Two electromagnetic solvers have been used to examine and to optimize the proposed circuit. The final circuit of the circularly polarized CPW monopole antenna is fabricated and validated by measurements. The measured bandwidth concerning the return loss at -10 dB is about 1.30 GHz and for the axial ratio at 3 dB, it’s about 500 MHz.

Numerical Investigation of Plastic Strain Homogeneity during Equal-Channel Angular Pressing of a Cu-Zr Alloy

A three-dimensional finite element method (3D FEM) simulation was carried out using ABAQUS/Explicit software to simulate multi-pass processing by equal-channel angular pressing (ECAP) of a circular cross-sectional workpiece of a Cu-Zr alloy. The effective plastic strain distribution, the strain homogeneity and the occurrence of a steady-state zone in the workpiece were investigated during ECAP processing for up to eight passes. The simulation results show that a strain inhomogeneity was developed in ECAP after one pass due to the formation of a corner gap in the outer corner of the die. The calculations show that the average effective plastic strain and the degree of homogeneity both increase with the number of ECAP passes. Based on the coefficient of variance, a steady-state zone was identified in the middle section of the ECAP workpiece, and this was numerically evaluated as extending over a length of approximately 40 mm along the longitudinal axis for the Cu-Zr alloy.

Finite element analysis of the Non-Equal Channel Angular Pressing (NECAP) with different die geometries

The Non Equal Channel Angular Pressing is one of the promising severe plastic deformation techniques which is used to produce ultra-fine grained and nanostructured materials. In the present investigation, the deformation behavior of Al1100 alloy during non-equal channel angular pressing was studied using two dimensional finite element simulation. Results showed when the ratio of the width of output to input channel is higher than 0.7, the corner gap is formed in the outer side of the intersecting area of two channels and the amount of plastic strain decreases in the lower part of the sample. In contrast, when the amount of this ratio is lower than 0.7, the dead metal zone is formed in the outer region of the intersecting area and the amount of strain is increased in the lower side of sample. It is also observed that the uniformity of the applied plastic strain is decreased with the formation of dead metal zone. In addition, the amount of damage factor is increased with increasing the ratio of the width of output to input channel and the region with higher amounts of damage factor is shifted from the lower side to the middle region of deformed sample. Finally, the results of FEM simulation showed that the amount of pressing force is decreased with increasing the width of output channel.

Effect of Die Design parameters on materials processed by Equal Channel Angular Pressing

Equal Channel Angular Pressing technique is used for grain refinement in bulk materials, where the material is passed through the die in which the two channels intersect at some angle, that result in finer grains. There are number of die design parameters which affects the production of ultra-fine grains. This paper presents the effect of die design parameters such as channel angle, corner angle, several passes and route followed for processing of the material for grain refinement. The results of different parameters are compared, and it was observed that the optimum values for producing maximum shear strain is for channel angle 90° and it reduces with the increase in channel angle. About 20° corner angles is found to suitable for filling the corner gap, around 4 to 6 passes, and route Bc leads to the ultrafine grained structure of homogeneous equiaxed grains separated by high angle grain boundaries in the materials. The sample of Al-TiO2 was prepared and its microstructure and mechanical properties were tested after equal channel angular pressing.

Formation Mechanism of a Wide-Face Longitudinal Off-Corner Depression During Thick Slab Continuous Casting

In practical continuous casting, consecutive longitudinal depressions often occur in the off-corner areas of slab wide faces, which may cause surface cracks in the depression areas and subsurface cracks beneath the depressions. To investigate the formation mechanism of the longitudinal depression, a 3D transient thermomechanical-coupled model was developed in the present work with consideration of the heat transfer in steel strand, thermal shrinkage of solidifying shell, ferrostatic pressure, contact with mold and guiding rolls, etc. Based on the model, evolution of the longitudinal off-corner depression and the associated thermal, distortion, and strain behaviors of steel slab were studied partly or fully throughout the continuous casting process. The results showed that the shell shrinkage in mold leads to an obvious shell-mold interfacial gap in the corner and off-corner areas. At the mold exit, the continuous expansion of corner gap at the wide-face side results in a thin spot forming at approximately 50 mm off the corner. When the shell moves out of the lateral strand guide rolls, narrow face of the shell bulges outward and rotates the corner, during which the thin spot in the wide-face off-corner area bends inward and shapes a longitudinal depression. As the shell moves down, the longitudinal depression deepens and widens in zones 2 to 4, and becomes stable in the subsequent cooling zones. When the shell moves through the soft reduction segments, depth and width of the longitudinal depression decrease as the marginal areas of the depressions are flattened. The model in this work is supposed to reveal an insight into the formation of consecutive longitudinal off-corner depressions at the wide face of slab during continuous casting.

Numerical studies on swirling of internal fire whirls with experimental justifications

Numerical studies on internal fire whirls (IFW) generated in a vertical shaft model with a single corner gap were reported in this paper. The generation of IFW, burning rate of fuel and temperature were studied experimentally first. Numerical simulations on medium-scale IFW were carried out using a fully-coupled large eddy simulation incorporating subgrid scale turbulence and a fire source with heat release rates compiled from experimental results. Typical transient flame shape was studied and then simulated numerically by using temperature. The dynamic phenomena of generation and development of IFW were simulated and then compared with experimental results. The predicted results were validated by comparing with experimental data, which demonstrated that an IFW can be simulated by Computational Fluid Dynamics. Numerical results for flame surface, temperature, and flame length agreed well with the experimental results. The IFW flame region and intermittent region were longer than those for an ordinary pool fire. The modified empirical formula for centerline temperature was derived. Variations of vertical and tangential velocity in axial and radial directions were also shown. The vortex core radius was found to be determined by the fuel bed size. Velocity field was not measured extensively due to resources limitation. Comparing measured temperature distribution with predictions is acceptable because temperature is related to the heat release rate, air flow and pressure gradient.

Experimental Cyclic Test of Reduced Damage Detailed Drywall Partition Walls Integrated with a Timber Rocking Wall

ABSTRACT Bidirectional quasi-static cyclic loading was applied to a subassembly of drywall partition walls integrated with cross-laminated timber rocking walls. Details aimed to reduce seismic damage to the partition walls were investigated, such as slip connections of partition walls to the diaphragm and gap detailing for the wall intersections. Telescoping detailing eliminated damage to the framing at the wall ends compared to traditional slip-track detailing. The distributed gap wall delayed the damage to about 1% inter-story drift. In the corner gap wall, the sacrificial corner bead opened up at low drifts (0.43%), but the wall was damage-free until more than a 2% drift.

Observation on a fire whirl in a vertical shaft using high-speed camera and associated correlation derived

The fire whirl generated by burning a pool fire in a vertical shaft with a single corner gap of appropriate width was studied using a high-speed camera. A 7 cm diameter pool propanol fire with heat release rate 1.6 kW in free space was burnt inside a 145 cm tall vertical shaft model with gap widths lying between 2 cm and 16 cm. The flame height was between 0.25 m and 0.85 m for different gap widths. Photographs taken using a high-speed camera at critical times of swirling motion development were used to compare with those taken using a normal camera. From the experimental observations on flame swirling by a high-speed camera, stages for generating the fire whirl were identified much more accurately. Two flame vortex tubes moving over the horizontal burning surface of the liquid pool were observed. Based on these observations a set of more detailed schematic diagrams on the swirling motion was constructed. From the observed flame heights under different gap widths and using three assumptions on the variation of air entrainment velocity with height, an empirical expression relating the burning rate with flame height and the corner gap width was derived from the observation with high-speed camera. The correlation expression of the burning rate of the pool fire obtained would be useful in fire safety design in vertical shafts of tall buildings.

Severe plastic deformation of AA 5083 and copper bimetallic metal

The purpose of the present study is to investigate the effect of Cu casing and wall thickness of the drilled copper bars on uniform distribution of imposed stain in terms of structural homogeneity and distribution of micro-hardness in the severely deformed AA 5083 after equal channel angular extrusion (ECAE). In this study, AA 5083 cylindrical inserts of 6 mm, 8 mm and 10 mm diameter with 100 mm length are tightly inserted in the 16 mm square copper bars having the respective diameter holes. The square cross sectioned AA 5083 billets of 16 mm × 16 mm and 100 mm length are also considered as feedstock. The longitudinal surfaces of the bimetallic metals are polished and annealed at 530 °C for 1 h and then processed by ECAE up to four passes in route A (same sense after every pass without any rotation) at room temperature using a die with square cross-sectioned channels having channel intersection angle (ϕ) 105° and outer corner angle (Ψ) 30°. The initial grain size of 60 µm has been greatly refined and the ultrafine grains of the sizes in the range of 400–700 nm are formed in the extruded AA 5083 inserts after the four passes. The microhardness of extruded AA 5083 significantly increased from 69 to 134 VHN, 132, 176 and 157 respectively for the square billets without Cu casing and cylindrical inserts with the diameters of 6, 8 and 10 mm covered with Cu casing after the four passes. The variations in the microhardness measurements at different regions on the sectioned surfaces are also investigated in this study. The requirement of pressing force is very significantly reduced by using copper casing which is having more ductile nature and the frictional forces between the copper and steel die are very less as compared to the Aluminium and steel. The chances of formation of dead metal zone are avoided by filling the corner gap by cooper metal during the ECAE process. The uniform distribution of strain imposed on the severely deformed billets develops the homogeneous ultrafine grain structure and significantly improves the micro-hardness of the processed material.

Analysis of plastic deformation behavior of ultrafine-grained aluminum processed by the newly developed ultrasonic vibration enhanced ECAP: Simulation and experiments

In this research, plastic deformation behavior of the commercially aluminum AA-1050 processed by using a newly developed ultrasonic vibration enhanced equal channel angular pressing (UV-ECAP) method has been investigated. A finite element model, including constitutive equations describing the acoustic softening effect, is developed to study the effect of applying high-intensity vibration in the ECAP process. Experiments are carried out to validate model predictions and to characterize microstructure and hardness of processed specimens. The experimental results suggested that the developed FE model is capable of predicting the deformation behavior of aluminum reasonably well under various process parameters. The results showed that applying ultrasonic vibration in frequency 20 kHz and amplitude 15 μm in the UV-ECAP process exhibits 31% reduction in the required load, eliminates the folding defect during ECAP, increases the effective length with reducing the corner gap. The predicted maximum and average equivalent plastic strains of the UV-ECAPed samples exhibited an increase of 33% and 58% comparing conventional ECAP. More uniform Misses stress distribution with lower longitudinal strain inhomogeneity factor were achieved in this process. The microhardness exhibited an increase by a factor of about 2.1 after first pass of UV-ECAP on aluminum. The average grain size of specimens was measured about 2.6 μm and 1.7 μm after one and two passes of UV-ECAP process respectively. It is found that a greater ultrasonic energy is required to maintain the efficiency of the UV-ECAP method in higher passes due to enhanced work-hardening caused by ultrasonic vibration in the specimen.

Development of homogeneity in a Cu-Mg-Ca alloy processed by equal channel angular pressing

A Cu-0.41Mg-0.06Ca (wt.%) alloy was processed by equal channel angular pressing (ECAP) for up to 12 passes via Bc route at room temperature, and its homogeneity was evaluated from three aspects of hardness, microstructure and crystallographic texture. The hardness was measured in detail on the whole transverse planes, and the microstructure and the crystallographic texture in the central and bottom regions on the transverse planes were investigated by electron backscatter diffraction (EBSD) technique. After 1 ECAP pass, the hardness in the central region was 9.4% higher than that in the bottom region; the microstructure in the central region consisted of the elongated grains, while that in the bottom region was composed of the slightly distorted grains; the crystallographic texture in the central region followed the ideal orientations of the ECAP crystallographic texture, nevertheless the crystallographic texture in the bottom region obviously deviated from any ideal orientation of the ECAP crystallographic texture. Then, with the increase of ECAP passes, the hardness and microstructure differences between in the two regions gradually weakened, and the deviation of the crystallographic texture in the bottom region gradually decreased. After 8 ECAP passes, the both regions showed the same hardness, the similar ultrafine-grained microstructure and the similar crystallographic texture. The difference formation should be attributed to the non-uniform strain caused by the friction between the sample and the die wall, rather than caused by the corner gap. The difference weakening should be attributed to the strain hardening behavior of metals. The strength calculation showed that the Cu-Mg-Ca alloy after 8 ECAP passes had almost the same yield strengths where 593 MPa for the central region and 583 MPa for the bottom region, showing only 1.7% difference.

Finite Element Analysis of Aluminum Alloy at Many Die Channel Angles using DEFORM-3D

Equal channel angular pressing (ECAP) is a technique used to impose strain in material which helps to increase the mechanical properties of a material. It is generally used to refine grain size of the material by passing sample through equal channel. In this study, analysis on frictional effect in equal channel angular pressing using aluminum 1100 has been done by using FEM software DEFORM-3D version 10.1. Dies with different channel angle were designed with the help CATIA. This study shows the effect of friction with different die channel angle. It has been found that with the increase in friction, reduction in corner gap is found (dead zone), which may cause material damage and improve strain distribution homogeneity. The result obtained with FEM simulation are compared to those obtained theoretically, thus it is found that the current study is in good agreement to the theoretically result.

Non-equal Channel Multi-Angular Extrusion (NECMAE): A Design for Severe Plastic Deformation—Proof of Concept

Equal channel angular pressing (ECAP) is currently the most widely used severe plastic deformation (SPD) process. The current work presents a validated finite element modelling for a new SPD process named “non-equal channel multi-angular extrusion (NECMAE)”. NECMAE is combined of two stages; the first stage is a standard ECAP, while the second stage experiences a reduction in cross-sectional area. The effects of different reduction in area—in NECMAE—on material plastic deformation, corner gap, stress distribution and required load were examined. In addition, a mathematical model was developed in order to trace the shear strains imposed on the material at different stages. Cases with higher reduction in area were found to have smaller corner gap, higher and uniform plastic deformation, as well as higher loads. The magnitude of maximum stresses was unaffected by different designs; the shape and size of the highly stressed material varied with die design. The current results were explained in terms of; (1) back pressure; (2) strain hardening; (3) shear angle of the second stage; and (4) shear strain history.

Experimental studies on characteristics of fire whirl in a vertical shaft

SummaryAn internal fire whirl can be generated readily in a tall shaft model with appropriate gap width at one corner. Experimental study was carried out to investigate the relationship between the characteristics of an IFW and the corner gap width in a 9‐m‐tall vertical shaft model. The vertical shaft had a 2.1 m by 2.1 m square section with gasoline pool fire of different diameters burning inside. The gap width was varied to investigate its impact on fire whirl characteristics, such as flame development, swirling intensity, flame height, flame temperature, and heat release rate of the gasoline pool fire. Vigorous flame swirling motions were generated when the ratio of the gap width to the shaft section perimeter was within the range 0.16 to 0.21. From the flame streamline angle, it was observed that the swirling component was much stronger than buoyancy component near the bottom of burning region. The swirling component decreased and became roughly the same as buoyancy near the middle. Finally, it diminished to being much weaker than buoyancy near the top of the fire. These observations suggest that the Froude number Fr decreased from a large number to 1, and then continued to decrease to 0.

Effect of Strain Rate Sensitivity and Strain Hardening Exponent of Materials on Plastic Strain Distribution and Damage Accumulation During Equal Channel Angular Pressing

Flow pattern and plastic strain distribution inside deformed sample are two important factors governing the microstructural uniformity of equal channel angular pressing (ECAP) processed materials. In the present study, the effects of strain hardening exponent (n) and strain rate sensitivity (m) on the characteristics of the ECAP process were investigated by the aid of finite element simulation. Investigated parameters are plastic strain distribution and accumulated damage. In addition, contour maps were generated to demonstrate mutual effects of n and m coefficients on the uniformity of plastic strain and maximum damage developed on ECAPed samples. Results showed that the effect of m and n values on plastic strain is more pronounced at downside regions of sample compared with upper regions. Also, at a constant strain rate sensitivity, the plastic strain is increased with decreasing strain hardening exponent due to the small corner gap formed in outer region of the intersecting area of two channels. Increasing strain rate sensitivity at constant strain hardening rate is accompanied by the formation of severely deformed area near downside of sample which leads to non-uniform strain distribution.

Circumferential twisting during route B equal-channel angular pressing

Equal-channel angular pressing (ECAP) is a representative severe plastic deformation process to fabricate bulk nanostructured materials by repetitive passes. Typically, there are four basic processing routes for the repetitive passes: route B is the most beneficial for grain refinement and homogenization of microstructure. In this work, investigation on deformation during route B in ECAP was conducted using the finite element analysis. It was found that the route B could lead to the inhomogeneous equivalent strain along the longitudinal direction of the workpiece by an unusual phenomenon called “circumferential twisting”. The circumferential twisting is primarily attributed to the deformation inhomogeneity for the cross-section induced during the 1 st pass of ECAP. This phenomenon occurs remarkably for the large-scale ECAP process because the twisting angle per unit length is almost constant. In addition, the higher the strain hardening exponent of the material, the greater the sample twisting during ECAP by the corner gap effect.

The analysis of friction effect on equal channel angular pressing (ECAP) process on Aluminium 5052 to homogeneity of strain distribution

In the current study, the effect of friction coefficient on strain distribution and deformation was investigated with the computer simulation providing a better understanding of the material flow mechanism and deformation behavior in the ECAP. The 10×10 mm and 50 mm-long rectangular billet was used as the geometry of aluminum material. The geometry of dies is 105° channel angle, 0 mm inner fillet radius, and 5 mm outer fillet radius. The dies were modeled as rigid bodies, and the specimen was assumed as a bilinear hardening model. The effect of friction was investigated with the three-level variation coefficient of friction (0.01; 0.025 and 0.05). Based on the result, it can be shown that the friction affects the strain distribution condition. The friction of 0.05 produced more uniform strain distribution, better homogeneity, and smaller corner gap. The experimental study of modeling results was done with MoS2 lubricant while the strain distribution was verified by the microhardness test. The microhardness distribution test result was similar to strain distribution from modeling.