Sharif Digital Repository

A mathematical model for cold rolling of two-layer strip is proposed using the upper bound theorem to investigate the plastic deformation behavior of the strip at the roll gap. The effects of total thickness reduction on the rolling power, rolling force, thickness reductions of each layer, and bonding strength of bimetal strip are discussed. Furthermore, experiments on two-layer strip rolling are conducted by employing aluminum-tin alloy and mild steel as the layers of the two-layer strips. It is found that all of theoretical predictions are in good agreement with the experimental measurements. Through the study, it becomes clear that the proposed analytical model is applicable for... 

Thermal behavior and require power in hot continuous strip rolling are predicted by means of a coupled finite element-upper bound approach. A thermal-finite element analysis is utilized to simultaneously determine temperature distributions within the work-piece and the work-rolls while an upper bound solution is employed at the same time to estimate the rate of heat of deformation and the required power in each rolling stand. The proposed model can be applied for determining thermal behaviors of the strip and the work-rolls in single and multi- pass rolling schedules while the effects of different parameters including initial temperature and rolling speed can be considered in the analysis.... 

Effect of deformation path change on the static strain aging of low carbon steel was studied in this work. In the first stage, strip samples were subjected to cold rolling processes under different paths with the same total reduction in thickness while the deformation behaviors of the rolled samples were also evaluated using a mathematical analysis. Then, cold-rolled strips were aged in room temperature up to 45 days while hardness and tensile evaluations were performed to assess the mechanical properties of the as-rolled and the aged samples. Finally, the influence of rolling pass schedule on the subsequent strain aging phenomenon was investigated by means of the experimental results and... 

An integrated mathematical model was developed to study the thermo-mechanical behavior of strips and work-rolls during warm rolling process of steels. A two-dimensional finite element analysis was first employed to solve for the thermo-mechanical response of the rolled strip under steady-state conditions. The calculated roll pressure and temperature fields were then used to apply proper boundary conditions for solving the governing thermo-mechanical problem for the work-roll. The obtained results indicate that in warm strip rolling of steels, the thermal and mechanical stresses developed within the work-roll are comparable; however, the more significant influence is due to heating and... 

This paper presents the results of an experimental study on the application of pre-stressed high strength metal strips in retrofit of RC columns. Six 2/3 scale were deliberately designated with insufficient transverse reinforcement details and tested under constant axial and cyclic lateral load reversals. The level of axial load and the pattern of strengthening were parameters of this study. It was observed that the technique has been capable to enhance the lateral behavior of columns significantly, in terms of ductility. Very ductile behavior was obtained. The height-wise variations of lateral strain on confining strips are studied. The analysis of the fiber-based model of tested columns... 

This paper presents the results of experimental and analytical study on a new technique of seismic retrofitting of concrete columns. In this technique, standard strapping devices, which are used in the packaging industry, are used to post-tension metal strips around concrete columns. The two ends of the strip are tightened in sealed clamps to maintain the pre-stress force in the strip. Experimental program included axial compressive tests on 30 cylindrical as well as 30 prismatic small-scale columns which were actively confined by pre-stressed metal strips. Longitudinal and lateral strain of concrete and strain in the strips were monitored. Test Results showed significant increase in... 

In this work, velocity field and temperature distribution during hot strip rolling are predicted, employing a combined upper bound and finite element analysis. At first, a velocity field is proposed utilizing the principle of volume constancy, and then the velocity field is modified by means of upper bound theorem. At the same time, a thermal-finite element analysis is utilized to determine temperature distribution within the metal as well as to calculate the flow stress of deforming material. The model is capable of considering the effects of different factors on temperature and velocity distributions such as rolling speed and interface heat transfer coefficient. In order to verify the... 

A Non-rigid Air Flow Active Sensor (NAFAS) to detect the respiratory patterns is introduced in this paper. The main part of NAFAS is an ionic electroactive polymer-based ( ${i}$ -EAP) soft sensor. It can accurately detect breathing patterns and has promising features to develop low cost, wearable, and ubiquitous spirometers. Patients with respiratory diseases need to take pulmonary function tests consistently. Hence, it is time-consuming and expensive. To address these problems, NAFAS presents point-of-care testing (POCT) of the respiratory system's function. The proposed ${i}$ -EAP based sensor is a small strip of Ionic Polymer Metal Composite (IPMC) that has been fabricated using a Nafion... 

A mathematical model is proposed for the determination of the thermo-mechanical stresses in work-rolls during hot-strip rolling. The model describes the evolution of the temperature fields in the work-roll and in the work-piece, and in the latter the plastic heat generation is taken into account. The frictional heat generated on the contact surface is also included. The problem is treated in two steps. First, a numerical method is developed for the analysis of the coupled thermal problem of the temperature distributions within the work-roll and metal being rolled, while an admissible velocity field is employed to estimate the heat of deformation. In the second step, the finite-element method... 

This paper presents the results of an experimental study on the application of strapping technique for retrofit of concrete compressive specimens. In this technique, standard strapping devices, which are used in the packaging industry, are applied to post-tension high strength metal strips around the concrete columns. Experimental program included axial compressive tests on 72 cylindrical and prismatic compressive specimens, which were actively confined by pre-stressed metal strips. The effects of various parameters on strength and ductility of confined concrete were studied including compressive strength of concrete, mechanical volumetric ratio of confining strips, post-tensioning force in... 

This paper presents analytical part of an investigation on the application of prestressed strips for concrete confinement. In this paper, an analytical model is proposed to predict the compressive stress-strain curve of strapped concrete as a function of the confinement level. The model was calibrated based on the experimental data of compressive tests which were described in part A of this paper. Various parameters are considered in the proposed model including volumetric ratio, yield strength and ultimate strain of confining material, shape of cross section, strength of plain concrete. Three key points were defined on the stress-stress curve of strapped concrete columns and applied in... 

In this work, a combined finite element analysis and upper bound technique is employed to assess temperature field and thermal stress distribution within the work rolls during continuous hot strip rolling process. Two-dimensional finite element analysis is utilised to simultaneously predict temperature fields within the rolling metal and the work roll as well as thermal stresses in the work rolls. In order to calculate the velocity field and the rate of heat of deformation, an upper bound solution is coupled with the employed finite element analysis. The utilised model makes it possible to estimate the effects of different parameters such as idling revolutions and initial temperature on... 

A thermo-elastic analysis coupled with a phase change model is employed to evaluate thermal stresses as well as progress of austenite decomposition after hot strip rolling operations. The thermo-mechanical finite element analysis is utilized to assess the distributions of temperature and thermal stresses during cooling while at the same time, a model based on the additivity rule is used to determine the rate of austenite to ferrite decomposition. The proposed model is applicable to multi-pass rolling schedules while the effects of different process parameters including the rolling speed and cooling configuration of the run-out table can be taken into account. In order to verify the... 

Strengthening is often a necessary measure to overcome an unsatisfactory deficient situation or where a new code requires the structure or a member of it to be modified to achieve new requirements. In the engineering practice such restraint to lateral dilation, indicated by the name of confinement, has been traditionally provided to compression members through steel transverse reinforcement in the form of spirals, circular hoops or rectangular ties. Steel and concrete jackets are other techniques for providing additional confinement for compression members, too. This paper presents the results of experimental and analytical study on the application of strapping technique for retrofitting of... 

A thermo-mechanical model has been developed to establish a coupled heat conduction and plastic flow analysis in hot-rolling process. This model is capable of predicting temperature, strain, and strain rate distributions during hot rolling as well as the subsequent static recrystallization fraction and grain size changes after hot deformation. Finite element and neural network models are coupled to assess recrystallization kinetics after hot rolling. A new algorithm has been suggested to create differential data sets to train the neural network. The model is then used to predict histories of various deformation variables and recrystallization kinetics in hot rolling of AA5083. Comparison... 

An integrated model based on finite-element method has been proposed to examine the mechanical and thermal responses of strips and work-rolls in tandem and reverse cold rolling operations. The model has been developed such that the influence of various process parameters, such as lubrication, rolling speed, frictional state and back-up rolls, can be examined. Thermal behaviors of the rolled material and the work-rolls have been analyzed using stream-line upwind Petrov-Galerkin approach, in order to make the model applicable to high-speed rolling processes, as well. The results have been compared to the actual on-line measurements and shown to be of acceptable accuracy. Such modeling approach... 

In this paper an integrated model has been developed that is capable of considering the effects of process parameters on the thermo-mechanical behaviour of the work-roll and the strip during hot rolling operations. The commercially finite element package ABAQUS is utilized to solve the governing equations, while an elasto-viscoplastic material behaviour is utilized in the model. The model may be employed in single-pass as well as multi-pass rolling layouts. Various aspects of the hot rolling process are predicted including temperature field and thermo-mechanical stresses within the work-roll as well as temperature, strain, and residual stresses distributions within the strip. To assess the... 

In this work, a numerical-based model has been proposed to calculate distributions of temperature, strain and strain rate during hot rolling as well as the subsequent microstructural changes after hot rolling of an aluminum alloy. For doing so, a transient finite difference analysis together with a stream function method have been coupled to calculate temperature distribution and velocity field within the rolling metal. A new approach considering internal state variables method has been employed to predict the kinetics of static recrystallization after hot rolling. The predicted results were then compared with the experimental ones and a good consistency was observed between the two sets of... 

The respiratory system is a vital organ system which makes breathing and gas exchange possible for human's body. The loss of functionality in this system is due to either genetical problems or environmental issues like pollution or toxic gases which in many cases is inevitable. These circumstances may cause different respiratory diseases which may not be curable presently but their side effects can be partly controlled by careful and timely analysis improving the quality of patient's life. So, an appropriate device for conducting different analysis can be effective for people who suffer from respiratory diseases such as chronic obstructive pulmonary disease (COPD), asthma, occupational lung... 

Temperature and velocity distributions during hot strip rolling of a low-alloy steel are determined using a finite element method together with a neural network model. The finite element method is utilized to solve the governing equations of heat conduction and plastic deformation; at the same time a neural network model is employed for assessing flow stress of the metal being deformed. In this way, the effects of temperature, strain, and strain rate on flow stress could be included in the finite element analysis. In order to examine validity of the mathematical model, laboratory hot rolling experiments are carried out where the surface temperature and roll force are recorded. Comparison...