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J C Galvez - One of the best experts on this subject based on the ideXlab platform.
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modelling of concrete cover cracking due to non uniform corrosion of reinforcing steel
Construction and Building Materials, 2017Co-Authors: Santiago Guzman, J C GalvezAbstract:Abstract This paper addresses the modelling of non-uniform corrosion in reinforced concrete. An uneven distribution of rust around the perimeter of the rebar is considered which represents the most common situation in real concrete structures and, especially, when they are exposed to a chloride environment. A comparison with the conventional approach based on a uniform corrosion and Expansion Pressure around the rebar is performed in both cracking Pressure and cracking radial displacement terms. As a result, surface cracking appears much earlier in the case of non-uniform corrosion with corresponding vertical surface displacements being rather higher, with such an effect becoming more evident as cover increases. Finally, distinct cracking patterns are derived through the proposed embedded cohesive crack model by means of a practical example.
Abdel-hakim Bouzid - One of the best experts on this subject based on the ideXlab platform.
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Impact of Grooves in Hydraulically Expanded Tube-to-Tubesheet Joints
Volume 6: Materials and Fabrication, 2020Co-Authors: Dinu Thomas Thekkuden, Abdel-hamid I. Mourad, Abdel-hakim BouzidAbstract:Abstract The stress corrosion cracking of tube-to-tubesheet joints is one of the major faults causing heat exchanger failure. After the Expansion process, the stresses are developed in a plastically deformed tube around the tube-to-tubesheet joint. These residual stressed joints, exposed to tube and shell side fluids, are the main crack initiation sites. Adequate contact Pressure at the tube-to-tubesheet interface is required to produce a quality joint. Insufficient tube-to-tubesheet contact Pressure leads to insufficient joint strength. Therefore, a study on the residual stress and contact Pressure that have a great significance on the quality of the tube-to-tubesheet joint is highly demanded. In this research, a 2D axisymmetric numerical analysis is performed to study the effect of the presence of grooves in the tubesheet and the Expansion Pressure length on the distribution of contact Pressure and stress during loading and unloading of 400 MPa Expansion Pressure. The results show that the maximum contact Pressure is independent of the Expansion Pressure length. However, the presence of grooves significantly increased the maximum contact Pressure. It is proven that the presence of grooves in the tubesheet is distinguishable from the maximum contact Pressure and residual von mises equivalent stress. The tube pull-out strength increases with the Expansion Pressure and the number of grooves. In conclusion, the presence of the grooves affects the tube-to-tubesheet joints.
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Impact of Expansion Pressure on wall thinning and contact Pressure for hydraulically expanded tube-to-tubesheet joints: Numerical analysis
2020 Advances in Science and Engineering Technology International Conferences (ASET), 2020Co-Authors: Dinu Thomasthekkuden, Abdel-hakim Bouzid, Abdel-harnid I. Mourad, Tariq DarabsehAbstract:The design of the tube-to-tubesheet joints is very critical to the functioning of the heat exchangers. In an Expansion process, the Pressure that is applied on the inner tube surface causes the tube to deform radially outward. Further plastic deformation of the tube, while tube in contact with the tubesheet, creates a contact Pressure at the interface. Therefore, an optimum Expansion Pressure adequately develops sufficient contact Pressure at the tube-to-tubesheet interface. Wall thinning percentage is generally used in practice to estimate the right amount of Expansion. This paper focusses on the wall thickness reduction expressed in percentage, radial displacement of the inner tube surface, contact Pressure and theoretical pull-out force for a various Expansion Pressure range. Results show that an Expansion Pressure lower than the yield stress of the tube does not fully close the gap between the tube and tubesheet. There is an evident spring back of radial displacement and contact Pressure due to bauschinger effect upon retrieving the Expansion Pressure. However, the maximum radial displacement and contact Pressure increase as Expansion Pressure increases. All the Expansion Pressures above the tube yield stress were sufficient to close the initial gap of the tube-to-tubesheet joint. A sudden increase in the radial displacement was observed for Expansion Pressures above tubesheet yield stress. Expansion Pressure from 240 MPa to 340 MPa resulted in wall thinning percentage of 1.15% to 2.97%. Since the pullout strength and contact Pressure are interrelated, high Expansion Pressure resulted in greater pull-out strength.
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Impact of Bauschinger Effect on the Residual Contact Pressure of Hydraulically Expanded Tube-to-Tubesheet Joints
Procedia Engineering, 2015Co-Authors: Abdel-hakim Bouzid, Abdel-hamid I. Mourad, A. El DomiatyAbstract:AbstractThe level of the contact Pressure and the stresses induced during the hydraulically expanded tube–to-tubesheet process are the key factors for the integrity of a leak free expanded joint. The modelling of this type of joint requires an adequate representation of the material behavior in order to accurately evaluate important joint parameters such as the residual contact Pressure and induced residual stresses. Maintaining a lower bound safe limit of the initial residual contact Pressure over the lifetime of the expanded joint insures its durability. A design tool that addresses a proper material-geometry combination in conjunction with the required Expansion Pressure is developed.The proposed model is based on strain hardening material behavior of the tube and the tubesheet. The interaction of these two components is simulated during the whole process of the application of the Expansion Pressure. Particular emphasis is put on influence of reverse yielding and Bauschinger effect on the residual contact Pressure. The results from the analytical model are confronted to those of the numerical FEA model. Two joints of different geometries and materials are considered to demonstrate the importance of considering the real material behavior in both models
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Theoretical Analysis of Hydraulically Expanded Tube-to-Tubesheet Joints With Linear Strain Hardening Material Behavior
Journal of Pressure Vessel Technology-transactions of The Asme, 2009Co-Authors: Nor Eddine Laghzale, Abdel-hakim BouzidAbstract:The mechanism of failure of tube-to-tubesheet joints is related to the level of stresses produced in the tube Expansion and transition zones during the Expansion process. Maintaining a lower bound limit of the initial residual contact Pressure over the lifetime of the expanded joint is a key solution to a leak free joint. An accurate model that estimates these stresses can be a useful tool to the design engineer to select the proper material geometry combination in conjunction with the required Expansion Pressure. Most existing design calculations are based on an elastic perfectly plastic behavior of the Expansion joint materials. The proposed model is based on a strain hardening with a bilinear material behavior of the tube and the tubesheet. The interaction of these two components is simulated during the whole process of the application of the Expansion Pressure. The effects of the gap and the material strain hardening are to be emphasized. The model results are validated and confronted against the more accurate numerical finite element analysis models. Additional comparisons have been made to existing methods.
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An analytical solution of hydraulically expanded tube-to-tubesheet joints with linear strain hardening material behaviour
Volume 3: Design and Analysis, 2008Co-Authors: Nor Eddine Laghzale, Abdel-hakim BouzidAbstract:The mechanism of failure of tube-to-tubesheet joints is related to the level of stresses produced in the tube Expansion and transition zones during the Expansion process. Maintaining a lower bound limit of the initial residual contact Pressure over the lifetime of the expanded joint is a key solution to a leak free joint. An accurate model that estimates these stresses can be a useful tool to the design engineer to select the proper material geometry combination in conjunction with the required Expansion Pressure. Most existing design calculations are based on an elastic perfectly plastic behavior of the Expansion joint materials. The proposed model is based on a strain hardening with a bilinear material behavior of the tube and the tubesheet. The interaction of these two components is simulated during the whole process of the application of the Expansion Pressure. The effects of the gap and the material strain hardening will be emphasized. The model results are validated and confronted against the more accurate numerical FEA models. Additional comparisons have been made to existing methods.Copyright © 2008 by ASME
Yong Jin - One of the best experts on this subject based on the ideXlab platform.
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The characteristics of coherent structures in the rapid Expansion flow of the supercritical carbon dioxide
The Journal of Supercritical Fluids, 2002Co-Authors: Xiaoyu Sun, Ting-jie Wang, Zhi-wen Wang, Yong JinAbstract:Abstract By the use of a tiny Pressure-transferring probe and capacitor-type sensor, the dynamic Pressure signals in the jet flow of the rapid Expansion of supercritical carbon dioxide are measured, which distinctively shows the characteristics of quasi-periodical coherent structures. After Fast Fourier Transform (FFT) conversion of the time series signals of the dynamic Pressure, there exist three dominant frequency bands in the power spectrum, which correlate with the scale of the dominant eddies in the turbulent field. The dominant frequencies change little with the distance from the nozzle exit or the pre-Expansion Pressure, while the power density of the dominant frequencies, which correlates with the energy of the dominant eddies in the turbulence, attenuates along the axial direction and with the decrease of the pre-Expansion Pressure. Through analysis, it is inferred that the nozzle structure and initial conditions remarkably affect the coherent structures in the Expansion flow which should be the important factors in the particle nucleation and its growth process in ultra-fine particle preparation by rapid Expansion of supercritical fluid solution (RESS).
Santiago Guzman - One of the best experts on this subject based on the ideXlab platform.
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modelling of concrete cover cracking due to non uniform corrosion of reinforcing steel
Construction and Building Materials, 2017Co-Authors: Santiago Guzman, J C GalvezAbstract:Abstract This paper addresses the modelling of non-uniform corrosion in reinforced concrete. An uneven distribution of rust around the perimeter of the rebar is considered which represents the most common situation in real concrete structures and, especially, when they are exposed to a chloride environment. A comparison with the conventional approach based on a uniform corrosion and Expansion Pressure around the rebar is performed in both cracking Pressure and cracking radial displacement terms. As a result, surface cracking appears much earlier in the case of non-uniform corrosion with corresponding vertical surface displacements being rather higher, with such an effect becoming more evident as cover increases. Finally, distinct cracking patterns are derived through the proposed embedded cohesive crack model by means of a practical example.
G. E. O. Widera - One of the best experts on this subject based on the ideXlab platform.
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Connection strength and tightness of hydraulically expanded tube-to-tubesheet joints
Journal of Materials Processing Technology, 2007Co-Authors: Haifeng Wang, Zhifu Sang, G. E. O. WideraAbstract:Abstract Many investigations and practical experience show that most heat exchanger failures occur at the tube-to-tubesheet joints and that they are affected by the geometry of the tube and tubesheet, the manufacturing process and the operating conditions. This paper focuses on the effect of the Expansion Pressure and operating temperature on the connection capacity of hydraulically expanded joints. Incorporating widely used materials (low carbon steel for the tube and low alloy steel for the tubesheet), the finite element method (FEM) was used to simulate the Expansion process and study the connection capacity of the expanded joints. The occurrence and loss of contact between the tube and tubesheet were modeled using contact elements. Furthermore, the effect of a cyclic change in temperature on the connection capacity of hydraulically expanded tube-to-tubesheet joints was investigated. In order to confirm the credibility of the finite element models employed in this study, some specimens were fabricated and joint strength experiments were performed using a MTS 880 testing machine by straining the joints at a set rate while recording the loads. The latter were found to be in acceptable agreement with the FEM calculated values. The results of this study show that the connection capacity of joints can be greatly enhanced by Expansion Pressure increments, improved at the beginning and lowered gradually with an increase in the temperature. The connection capacity is reduced very little after the first temperature cycle and remains almost unchanged after the second and third cycles. The study also shows that the FEM is a viable method to predict leakage behavior.
