Optimal configuration of blast furnace slag runner to reduce fluid flow stresses at wall using mathematical modelling

Abstract

A three-dimensional mathematical model was developed to predict the wall shear stresses due to flow of liquid slag in slag runner of 'G' blast furnace of Tata Steel under different conditions. The liquid slag flow in the slag runner was considered to be turbulent and incompressible. The model was developed for single phase, steady state and isothermal conditions. To this end, the Navier Stokes equations along with continuity and turbulence equations (standard k–? model) were simultaneously solved with appropriate boundary conditions at the associated physical boundaries of the calculation domain. Several configurations were numerically assessed with respect to reduced shear stresses on the wall of the slag runner to select the best one. Due to accelerating flow the operating heights of liquid slag (density 2800 kg m^–3 at 1500°C) within the slag runner for different configurations were estimated with the help of Bernoulli's and continuity equations and fixed before the computation. The different configurations comprised of three segments with different parameters of either elevation or radius of curvature. Relatively high shear stresses were numerically predicted at the joint area of second and third segments of the slag runner for all the configurations. The radius of curvature was found as the dominant factor to reduce the shear stress at the joint region.     

33—THE SNARLING OF HIGHLY TWISTED MONOFILAMENTS. PART II: CYLINDRICAL SNARLING

An account is given of an experimental investigation of the cylindrical snarling of highly twisted monofilaments.

The theory underlying cylindrical snarling is set out, and an expression is derived for calculating the critical twist level at which normal snarling will be replaced by cylindrical snarling. Experiments on rubber filaments are described, and it is shown that there is good agreement between the theoretical and experimental results. Further experiments, in which the specimen was allowed to contract freely or forced into other forms, are also described.

It is shown from these experiments that it is difficult to establish the true equilibrium behaviour, since the situation appears to be dominated by frictional effects or by direct barriers to relative movement.     

Investigation of the relationship between statistical characteristics of substrate surface roughness and the strength of adhesive joints

The relationship between statistical characteristics of butadiene styrene rubber (BSR) surface roughness and shear strength of adhesive joints has been investigated. The assumption of stationary normal distribution of coordinates of surface points was made to determine the statistical characteristics of surface roughness. The profile length above the selected level l ₁ (u) was introduced as a new surface roughness parameter to characterize adhesive penetration depth. The validity of simulated l ₁ (u) value was verified experimentally. A good correlation between experimental and calculated results was found. A relationship between adhesive penetration depth and the bonding pressure during adhesive joint preparation was also obtained. The dependences among lap shear joint strength, bonding pressure and roughness characteristic l ₁ (u) were determined.     

32—THE SNARLING OF HIGHLY TWISTED MONOFILAMENTS. PART I: THE LOAD–ELONGATION BEHAVIOUR WITH NORMAL SNARLING

An account is given of an experimental investigation of the normal snarling of highly twisted monofilaments, those used being vulcanized rubber and nylon.

An earlier theoretical analysis is corrected, and the experimental results show that, after this correction, the theory put forward for the mechanical properties of the snarling mechanism holds reasonably well for elastic filaments. Although, as would be expected, there are larger deviations from the theory for viscoelastic filaments, the theory still gives a good indication of the behaviour of these filaments under torsion.     

Performance of Dowel-Welded T-Joints for Wood Furniture

Comparison of two types of furniture joints namely step butt T-joints and mortise and tennon T-joints held together either by one or two welded or glued dowels showed that the shear strength results of welded dowel and glued dowel joints were comparable. For mortise and tennon T-joints there is, in general, no difference if the dowel is inserted at a 45° or 90° angle. Also there is no significant difference between welded and glued dowel joints stiffness values in both step butt and mortise and tennon T-joints of the same geometry. Also, there is no significant difference between dowels inserted at 45° or 90° for mortise and tennon T-joints. Glued dowel and welded dowel step butt T-joints behave quite differently from linear joints. Thus, in step butt T-joints a higher shear strength is obtained if a single dowel is inserted at 45° for both glued and welded dowels. Both shear strength and stiffness increase as the number of dowels increases, namely from one to two. The application of the welded joint technique to joints where the number of dowels is limited by the limited space in which they can be inserted, such as in furniture, can give shear strength results comparable to those obtained by gluing the same dowels. This is particularly the case for mortise and tennon T-joints.     

Peak force as function of the embedded length in pull-out and microbond tests: effect of specimen geometry

We have derived the equations which explicitly express the peak force, F _max, and the apparent interfacial shear strength, τ _app, measured in the pull-out and microbond tests, as functions of the embedded length. Three types of test geometries were considered: (1) a fiber embedded in a cylindrical block of the matrix material; (2) microbond test with spherical matrix droplets; and (3) pull-out test in which the matrix droplet had the shape of a hemisphere. Our equations include the local interfacial shear strength (IFSS), τ _d, and the frictional interfacial stress, τ _f, as parameters; the effect of specimen geometry appeared in the form of dependency of the effective fiber volume fraction on the embedded length. The values of τ _d and τ _f were determined by fitting our theoretical curves to experimental F _max (l _e) plots by using the least squares method. Our analysis showed how the local IFSS and the frictional interfacial stress affected the measured F _max and τ _app values. In particular, it was revealed that intervals of embedded lengths could exist in which frictional interfacial stress had no effect on F _max and τ _app, even if the τ _f value was high. We also derived an equation relating the scatter in the interfacial strength parameters (τ _d and τ _f) to the scatter in τ _app, which is experimentally measurable, and proposed a procedure to determine the standard deviations of τ _d and τ _f from experimental pull-out and/or microbond test data.     

Modified shear lag model for fibers and fillers with irregular cross-sectional shapes

For fibers with irregular cross sections such as ultrahigh modulus polyethylene (UHMPE) fibers and ribbon-like carbon fibers, the original shear lag model would not provide accurate calculations for interfacial shear stress because it assumes a circular fiber cross section. In this study, a modified shear lag model is proposed to calculate the interfacial shear stress that reflects the change of fiber cross-sectional shape. Microbond test on a UHMPE fiber/epoxy system was used for verification of the model. The difference between the interfacial shear strength (IFSS) calculated using the modified model and that using the original model assuming an equivalent fiber diameter was found to be as high as 15% and it linearly increased as the irregularity of the cross-sectional shape increased. When the irregularity constant exceeds 1.12, the error in IFSS involved in using the original shear lag model and an equivalent fiber diameter is greater than 10%.     

Experimental study of joint performance in spot friction welding of 6111-T4 aluminium alloy

Abstract

The effect of process parameters (cycle time, tool speed and axial force) on the specimen temperature measured 2 mm away from the weld in spot friction welding (SFW) of Al 6111-T4 is investigated. The temperatures were correlated to the lap shear load. Results revealed that, to achieve a good joint strength with the maximum lap shear load >2˙5 kN, temperatures should be greater than a threshold value, which is 350°C at a location close to the SFW joint in this study. By studying the specimen macrographs, two internal weld geometric features based on the cross-section area were identified and correlated to the shear and mixed failure modes of the lap shear tested specimens. A model was developed and validated using experimental data of the cross section area of SFW joint with either shear or mixed mode fracture. The model predicts that the SFW joint strength is maximised at the transition region between the shear and mixed mode fracture.     

Thixotropy of Systems with Shear Thinning and Plastic Flow Behavior

The definition of the thixotropy is a decrease in viscosity with time in shear and a subsequent recovery of viscosity after the shear deformation is removed.We ...     

Morphology of adiabatic shear bands in cylindrical specimens of AISI 4340 steel impacted by Hopkinson pressure bar

Abstract

Cylindrical specimens of AISI 4340 steel, which were heat treated by quenching in oil followed by tempering at either 315 or 425°C, were impacted in a Hopkinson pressure bar at different impacting speeds. It was found that when strain and strain rate reached certain values, adiabatic shear bands (or plastic deformation zones) were formed in the specimens. The adiabatic shear bands appeared either in a circle on the transverse section, a hyperbola on different longitudinal sections without the central axis of the cylinder, and a triangle on the longitudinal section through the central axis of the cylinder. From these observations, it can be concluded that the plastic deformation localisation zone is limited in a thin conical shell in three dimensions. It was further confirmed that the adiabatic shear bands initiated along the maximum shear stress directions. In addition, the adiabatic shear bands in the specimens tempered at 315°C appeared white, while those in specimens tempered at 425°C had deformation characteristics. This indicates that the appearance of adiabatic shear bands is related to the hardness and microstructure of the tested steel.