Continuous Bar Research Articles

Microstructure of Zn–Pb immiscible alloys obtained by a rheomixing process

A rheomixing process has been developed for processing immiscible metallic liquids. In this paper, a binary Zn–Pb system is used to demonstrate the rheomixing process. During the rheomixing process, liquid Zn and Pb are premixed in the miscibility gap using a propeller mixer to achieve coarse dispersion of Pb liquid droplets in Zn liquid matrix. The coarse mixture is then transferred into a twin-screw rheomixer, where it is continuously cooled down to a temperature below the monotectic temperature to form a semi-solid slurry under the intensive shear mixing action of the twin-screw rheomixer. The semi-solid slurry is finally extruded through a cylindrical extrusion die to form a continuous bar. The microstructure of immiscible alloys produced by this method is characterised by a fine dispersion of Pb particles distributed uniformly throughout a Zn matrix. The effects of rheomixing temperature and alloy composition on the resultant microstructure have been investigated. It has been found that the average size of Pb particles increases linearly with increasing rheomixing temperature and with increasing Pb concentration in the Zn–Pb alloys.

Modifications of cascade structures in computer aided design of mechanical continuous vibration bar systems represented by graphs and structural numbers

The dynamical flexibility of continuous free systems with definite frequency spectrum and with cascade structure has the alternating: pole, zero, pole, zero, etc. The frequency with the zero value is always a pole. On the other hand, in the case of systems with cascade structure but fixed at one side, the dynamical flexibility has the alternating: zero, pole, zero, pole, etc. respectively. The frequency with the zero value is always a zero. In this paper the method distribution of characteristics into partial fraction and recurrent cascade method represented by graphs were applied in order to structural modification of the vibrating mechanical system with cascade structure.

Seismic performance of external reinforced concrete beam-column joints

Four external beam-column sub-assemblies were tested to investigate the influence of different details on the performance of the Joint zone. All the details conformed to the current New Zealand structural concrete standard (NZS3101-1995). It is shown that anchoring beam reinforcement in external beam- column joints short of the outer column bars results in a reduction in the flexural strength of the column. In tests premature yielding of the longitudinal bars on the inside of the column occurred when bars were anchored at a distance of 1⁄4 of the column depth from the outside face of the column, as permitted by the structural concrete Standard. This yielding had an adverse effect on the performance of the joint zone. A way of detailing external joint zones to compensate for this loss in strength is described. Elongation of plastic hinges in the beams of ductile frames induces unidirectional plastic hinges in the external columns at the first floor level. While this has a strong influence on the distribution of moments and shears in the columns tests indicated that it does not adversely affect the structural performance of the joint zone. The use of continuous bars bent in the form of a U provides a simple detail that worked very effectively. There was little difference in joint behaviour between beams with main bars uniformly distributed over the beam depth to conventionally reinforced beams with their main bars positioned near the top and bottom edges.

Macrocell Activity in Slightly Chloride-Contaminated Concrete Induced by Reinforcement Primers

Abstract Patch repair systems are usually composed of a primer (or paint) for the reinforcement, a bond bridge, and a repair mortar to restore the initial geometry. This system is said to induce an enhancement of the corrosion activity of the adjacent nonrepaired zones if they still contain a certain amount of chlorides. In the present paper, the action of the steel primers on the galvanic effect toward unrepaired zones was studied. Four protection mechanisms were selected: repassivation, inhibition, barrier, and cathodic protection. Small beams were fabricated with an embedded, continuous bar in the top part and a segmented one that enabled the monitoring of the corrosion potential and the corrosion rate of each segment when disconnected, and the macrocell or galvanic activity between segments in repaired interfaces and nonrepaired zones. The results after submitting the beams to different humidity conditions show that the primers were mainly effective in the first month after repair and sometimes they m...

Mechanical Properties of Hot-forged al 6061-T6

The effect of forging parameters, including different forging stock, strain rate and strain, on the mechanical properties of hot-forged Al 6061-T6 was investigated. The forging was conducted using either hydraulic press, crank press or hammer press, respectively, at a forging temperature of <TEX>$400^{\circ}C$</TEX>. When using an extruded bar as a forging stock, the tensile strength was lower for the specimens prepared by hammer forging than those by crank press forging. It was found that the coarsening of recrystallized grain was responsible for the decrease in tensile strength with hammer forging. Systematic studies on the effects of strain and strain rate on the tensile properties of hot-forged Al 6061-T6 products using extruded bar as a forging stock further suggested that the coarsening of recrystallized grains and<TEX>$ Mg_2$</TEX>Si precipitates complexed the observed trends in the tensile behavior. In case of hot forging with continuous cast bar as a forging stock, on the other hand, the mechanical properties of the specimen were largely improved with hammer press compared to those with crank press, which appeared to be due to the homogenization of microstructure.

Assessment of a spectral energy formulation based on driving point structural mobilities or impedances

To determine the contributions of parallel paths or interactions between structural components at any frequency, dynamic kinetic and potential energies are needed. However, an exact method to characterize an arbitrarily damped system in kinetic and potential energy forms is currently not available. One approximate characterization method examines time-averaged dynamic energies of subsystem(s) via the driving point transfer functions [J. Sound Vib. 217, 351–386 and 247, 683–702]. This concept, based on a real-valued energy formulation, is critically examined here. Linear time-invariant (LTI) system is assumed and harmonic excitation is applied to the system. Finite continuous (bar and beam) structures along with discrete system examples are utilized to illustrate concepts. Predictions show that the energy estimates deviate from the exact values, especially at higher frequencies and with higher damping. Further, the results from the impedance formulation differ from the ones from the mobility representation. The cause of discrepancies is explained by interpreting the transfer functions involved.

Connections of CHS concrete-filled diagonals of X-bracings

Abstract The scope of the present paper is the numerical investigation of the behaviour of concrete-filled CHS bars used as X-bracings diagonals. The weak point for an X-brace is the point where the two diagonals intersect where, in order that the two bars remain co-planar, one of them is usually interrupted. In this case, a usual practice is to connect the interrupted bar to the continuous one by means of two gusset plates each one welded along a generatrix of the continuous bar. The result is, that the axial load is transferred as an inside-the-cross-section loading situation of the continuous bar thus causing a prohibitively excessive ovalisation of the cylindrical shell of the CHS. The in-plane transfer mechanism of the forces causes an increase of the axial flexibility of the interrupted bar by a factor of 50–300 thus making this type of connection too flexible and therefore unsuitable for use in X-braces. Filling the tubular braces with concrete is already known as a promising technique against local buckling: the subject of the present work is the assessment the effect of this technique to the axial flexibility of the interrupted bar. From the numerical simulation point-of-view, the problem is formulated as a unilateral contact problem between the concrete in-fill and the steel shell and a parametric analysis is made to elucidate flexibility and strength aspects of this connection for the most frequently used CHS profiles.

Validation of a CHS connection used in X-bracing diagonals

The present paper investigates the behaviour of a connection widely used at the co-planar intersection of circular hollow sections (CHS), a case very common in X-bracings. The performance of this type of connection is validated by means of finite element modelling. Our connection is made up of two separate gusset plates, welded externally along the generatrices of the cylindrical surface of a CHS (in an ear-like manner), so as to accommodate the terminal gusset plates of the interrupted CHS: in this way the two bars intersect and remain on the same plane. Shell elements are used to model the CHS bar connection along several diameters on either side of the gusset plates (ears). The stiffness of the cylindrical shell that is called upon to undertake the axial force of the interrupted bar, drew our attention as it affects the structural behaviour of the X-brace well before local strength phenomena assume any importance. The actual result of this paper is that the stiffness of the interrupted length of the CHS bar is significantly less than that of the continuous bar: the interrupted bar of the X-bracing cannot develop any stresses whenever this type of connection is used, as any strain applied to its end will be cumulated in the connection zone. This effectively causes our X-brace to function with only one of its diagonals, i.e. the continuous one. Ending-up with a single-diagonal bracing can be dangerous even in the absence of material non-linearities or large displacement effects, not to mention an earthquake situation. These results are also compared with a formula derived by plane stress considerations and are found in good agreement. A total of 117 variants of this connection are examined for the purpose of this analysis and the stiffness reduction results are presented in a schematic form.

528 3ロール多パス連続圧延における炭素鋼オーステナイト組織の変化(OS 加工による材料の機能創製)

Change in austenite grain size after continuous bar rolling of S45C steel with 3-roll mill is investigated. From the double hot compression test with large plastic strain, when dynamic recrystallization takes place, it becomes clear that final austenite grain size is dominated only by the final deformation, even if inter-pass time is quite short. This proves that the size of final austenite grains, such as coarsened grains,,is affected not by the amount of plastic deformation but by the final forming condition, when the dynamic recrystllization takes place. This is confirmed by experimental results obtained by continuous rolling with 7-stands.

Longitudinal vibration of a continuous cracked bar

A continuous cracked bar vibration theory is developed for longitudinal vibration of rods with an edge crack. The Hu–Washizu–Barr variational formulation was used to develop the differential equation and the boundary conditions of the cracked bar as a one-dimensional continuum. The crack was modelled as a continuous flexibility using the displacement field in the vicinity of the crack found with fracture mechanics methods. The results of three independent evaluations of the lowest natural frequency of longitudinal vibrations of a bar with a single edge crack are presented: the continuous cracked bar vibration theory, the lumped crack bar vibration analysis, and experimental results obtained on aluminum bars with fatigue cracks. Experimental results fall between the values predicted by the two analytical methods. Moreover, the continuous bar theory agrees better with the experimental results than the lumped crack flexibility theory for small cracks. For larger cracks, a/ h>0.4, experimentation was difficult due to the co-existence of several coupled modes and no reliable results could be obtained.

Vibration of a Cracked Cantilever Beam

A continuous cracked bar vibration model is developed for the lateral vibration of a cracked Euler-Bernoulli cantilevered beam with an edge crack. The Hu-Washizu-Barr variational formulation was used to develop the differential equation and the boundary conditions for the cracked beam as an one-dimensional continuum. The crack was modelled as a continuous flexibility using the displacement field in the vicinity of the crack found with fracture mechanics methods. The results of three independent evaluations of the lowest natural frequency of lateral vibrations of an aluminum cantilever beam with a single-edge crack are presented: the continuous cracked beam vibration model, the lumped crack model vibration analysis, and experimental results. Experimental results fall very close to the values predicted by the continuous crack formulation. Moreover, the continuous cracked beam theory agrees better with the experimental results than the lumped crack flexibility theory.

Numerical simulation of continuous induction steel bar end heating with material properties depending on temperature and magnetic field

Continuous induction steel bar end heating is investigated by means of numerical calculations. A numerical model is used for the calculation of the three-dimensional eddy current and the heating process. The differential equations describing the electromagnetic field are integrated as an A-/spl phi/ formulation. For the calculation of the temperature fields, Fourier's heat-conduction equation is used. On principle, the finite element method is used for the numerical solution. The effect of material properties depending on temperature and magnetic field are taken into consideration in an iterative manner. The results of simulation correspond well to experimental data and give good transparency of the process. The computing time, however, is too long for an effective realization of optimization processes.

Thermal stress evolution in continuously quenched circular bars

This paper presents a finite element method for studying continuous quenching processes with emphasis on thermal and stress analyses of axisymmetric problems. Both the thermal and stress problems involved in the quenching process are formulated in the Eulerian frame. The heat transfer problem is solved with the Petrov-Galerkin method due to the convetion-diffusion nature of the governing equation. For the thermal stress problem, since the acceleration term in the equation of motion is small, it is neglected and the equilibrium equation is solved. The inelastic deformation associated with the quenching process is modeled with the visco-plastic type of constitutive laws. To determine the inelastic deformation of the quenched body, the inelastic strain rates are integrated along the quenched body with the Petrov-Galerkin formulation applied to the material derivatives of the inelastic strain rates. An example problem for a continuous bar quenching process is studied with the method presented in this paper. With the present method, computational time needed is significantly less than that with Lagrangian approaches.

Effects of Cr addition on the microstructure and mechanical behavior of 6061-T6 continuously cast and rolled redraw rod

Chromium additions to 6061 aluminum alloy can form α-Al 12(Fe, Cr) 3Si dispersoids during homogenization. Continuous cast bar does not receive a homogenization step and is rolled directly after casting, therefore, it is of interest to determine the effect of Cr addition on the microstructure and mechanical properties of continuous cast 6061-T6 rod. Microstructural examination of 0.5 inch diameter continuous cast and rolled 6061 w/Cr T6 rod revealed that the rod had a fully recrystallized microstructure with pancake-shaped grains indicative of aluminum alloys containing dispersoids. Examination of TEM samples confirmed the existence of α-Al 12(Fe, Cr) 3Si dispersoids in the T6 rod microstructure. X-ray diffraction (Guinier techiique) revealed that the 6061 w/Cr T6 rod contained α-Al 12Fe 3Si and α-Al 12(Fe, Cr) 3Si constituent phases whereas the 6061-T6 rod without Cr contained only β-Al 9Fe 2Si 2. Tensile test results showed that Cr addition to 6061-T6 rod substantially improved the ductility of the rod.

A CONSISTENT CRACKED BAR VIBRATION THEORY

A consistent continuous cracked bar vibration theory is developed. The stress and displacement field about the crack was used to modify the stress and displacement field throughout the bar, and reduction to one spatial dimension was achieved by integrating the stress and displacement fields throughout the bar cross-sections so that the total displacement would be exact. The resulting linear differential equation with variable coefficients has the modified displacement field due to the crack imbedded in it. Any number of cracks can be introduced into the differential equation as modifications of the displacement field. A numerical solution and a first order perturbation solution are presented for the prediction of changes in longitudinal vibration natural frequencies of a fixed-free bar with a single open-edge transverse crack. To assess the validity of the assumptions made experiments on aluminium bars with fatigue cracks were performed. The analytical results correlate very closely with experimental results with better correlation than the local flexibility solution.

The Improvement of Surface Quality of Continuous Rheocast Bars of Steel and High Melting Point Alloys.

A new continuous rheocasting process for steels and high temperature alloys has been developed by Inland Steel incorporating a dual chamber casting machine utilizing separate electromagnetic stirrers around each chamber. Initial casts on the rheocaster were plagued by breakouts and very rough as-cast surface morphology. The mechanism for solidification and formation of cast surface morphologies on as-rheocast bars has been determined and verified by comparing predicted surface morphologies to actual surface morphologies. The mechanism was then used to develop new withdrawal patterns to eliminate sticker breakouts and obtain good surface quality.

Ultrasonic technique for residual stress measurement in ductile iron continuous cast round bars : Srinivasan, M N; Chunda, S N; Bray, S N; Alagarsamy, D E & A Journal of testing and evaluation, Vol. 20, No. 5, pp 331–335 (Sep 1992)

Ultrasonic technique for residual stress measurement in ductile iron continuous cast round bars : Srinivasan, M N; Chunda, S N; Bray, S N; Alagarsamy, D E & A Journal of testing and evaluation, Vol. 20, No. 5, pp 331–335 (Sep 1992)

Theoretical calculation method of high-reliability life of rolling bearings: Li, C.G. Jixie Gongcheng Xuebao (Chinese Journal of Mechanical Engineering) (1993) 29 (3), 91–97 (in Chinese)

Some of the more important aspects of the fatigue of land-based structures are reviewed: the types of loading due to vehicles, wind and people are considered and examples are given of fatigue in service, taken from the literature on highway bridges.Several of the most common types of design detail that have to be assessed for fatigue are covered. These include welded connections between plates, with an emphasis on long endurance, and behaviour under pulsating-compression loading. The fatigue performance of reinforcement bars is considered in relation to type of test, type of manufacture and corrosion. The performance of lapped, welded and mechanical connections are summarized and related to continuous bars and to class D for BS5400.Three other types of structural connection are reviewed: high strength bolted connections between plates, shear connectors between steel and concrete, and epoxy resin bonding between steel and concrete.

Micromechanisms of fatigue crack growth and fracture toughness in metal matrix composites. Final Report 27 April 1984-15 April 1993: Davidson, D.L. Southwest Research Institute Report AD-A265 153/7/XAB (1993) 14 pp

Some of the more important aspects of the fatigue of land-based structures are reviewed: the types of loading due to vehicles, wind and people are considered and examples are given of fatigue in service, taken from the literature on highway bridges.Several of the most common types of design detail that have to be assessed for fatigue are covered. These include welded connections between plates, with an emphasis on long endurance, and behaviour under pulsating-compression loading. The fatigue performance of reinforcement bars is considered in relation to type of test, type of manufacture and corrosion. The performance of lapped, welded and mechanical connections are summarized and related to continuous bars and to class D for BS5400.Three other types of structural connection are reviewed: high strength bolted connections between plates, shear connectors between steel and concrete, and epoxy resin bonding between steel and concrete.

High cycle (fatigue) resistance of reinforced concrete beams with lap splices

Full-scale specimens were tested so that lap spliced bottom bars were subjected to cyclic tension loading. The major variable was the degree of transverse confining reinforcement (stirrups) provided along the lap. Lap splices were confined either with the maximum transverse reinforcement deemed to be effective for static loading, permitting the use of shorter lap splice lengths, or with stirrups spaced at approximately one half the effective depth of the beam, requiring the use of a longer lap length. Failure in all specimens with heavier stirrups (shorter laps) occurred with fatiguing of the reinforcing steel, showing fatigue resistances that were comparable with the results for continuous bars tested in flexure. With the lighter (nominal) stirrups, fatigue loading usually produced a splice failure, where the confining concrete split away from the lap in a typical bond failure after fewer load cycles. For comparable bond resistance under static loading, the beams with the heavier stirrup confinement along a shorter lap length were superior under fatigue loading. As previously shown with low cycle, high intensity reversal (seismic) loading, the current study shows that it is prudent to provide a high degree of transverse reinforcing confinement to lap splices that are subjected to fatigue loading. Key words: concrete, reinforcement, lap splices, fatigue, bond, beams, confinement, stirrups, tension.