Analytical Evaluation of Residual Stresses in the Transition Zone of Expanded Tube-to-Tubesheet Joints

2018 ◽  
Author(s):  
Abdel-Hakim Bouzid ◽  
Mohammad Pourreza
Keyword(s):  
Residual Stresses ◽  
Transition Zone ◽  
Analytical Model ◽  
Plastic Material ◽  
Plastic Region ◽  
Material Behavior ◽  
Expansion Process ◽  
Maximum Expansion ◽  
Perfectly Plastic ◽  
Comparison Of The Results

The rigorous analysis of tube-to-tubesheet joints requires a particular attention to the transition zone of the expanded tube because of its impact on joint integrity. This transition zone is the weakest part of the joint due to the presence of high tensile residual stresses produced during the expansion process which coupled to other in-service loadings and harsh corrosive fluids results in joint failure. In fact, this zone is often subjected to stress corrosion cracking caused by intergranular attack leading to plant shutdown. Therefore, the evaluation of the residual stresses in the transition zone is of major concern during the design phase and its accurate assessment is necessary in order to achieve a reliable joint in service. In this study, a new analytical model to evaluate the residual axial and hoop stresses in the transition zone of hydraulically expanded tubes based on an elastic perfectly plastic material behavior has been developed. The model is capable of predicting the stress state under the maximum expansion pressure and after the expansion process has been completed. Three main regions are identified in the transition zone: the fully plastic region, the partially plastic region and the elastic region. Therefore, various theories have been applied to analyze the stresses and deformations neglecting the partial plastic region because of simplicity. The validation of analytical model is conducted by comparison of the results with the ones of 3D finite element models representing typical geometry and mechanical properties. The effect of reverse yielding of the expansion zone is also investigated.

Analysis of Residual Stresses in the Transition Zone of Tube-to-Tubesheet Joints

2019 ◽  
Vol 141 (4) ◽  
Author(s):  
Abdel-Hakim Bouzid ◽  
Mohammad Pourreza
Keyword(s):  
Residual Stresses ◽  
Transition Zone ◽  
Analytical Model ◽  
Plastic Material ◽  
Plastic Region ◽  
Material Behavior ◽  
Maximum Expansion ◽  
Perfectly Plastic ◽  
Major Interest ◽  
Comparison Of The Results

The rigorous stress analysis of tube-to-tubesheet joints requires a particular attention to the transition zone of the expanded tube because of its impact on joint integrity. This zone is the weakest part of the joint due to the presence of high tensile residual stresses produced during the expansion process, which coupled to in-service loadings and harsh corrosive fluids results in joint failure. In fact, it is often subjected to stress corrosion cracking caused by intergranular attack leading to plant shutdown. Therefore, the evaluation of the residual stresses in this zone is of major interest during the design phase and its accurate assessment is necessary to achieve a reliable joint in service. In this study, an analytical model to evaluate the residual axial and hoop stresses in the transition zone of hydraulically expanded tubes based on an elastic perfectly plastic material behavior has been developed. The model is capable of predicting the stress state when maximum expansion pressure is applied and after its release. Three main regions are identified in the transition zone: the fully plastic region, the partially plastic region, and the elastic region. Therefore, various theories have been applied to analyze the stresses and deformations neglecting the elastoplastic region because of simplicity. The validation of analytical model is conducted by comparison of the results with those of 3D finite element models of two typical joints of different geometries and mechanical properties. The effect strain hardening and reverse yielding of the expansion zone are also investigated.

Analytical Modeling of Hydraulically Expanded Tube-To-Tubesheet Joints

2008 ◽  
Vol 131 (1) ◽  
Author(s):  
Nor Eddine Laghzale ◽  
Abdel-Hakim Bouzid
Keyword(s):  
Contact Pressure ◽  
Analytical Model ◽  
Plastic Material ◽  
Material Behavior ◽  
Initial Contact ◽  
Expansion Process ◽  
Element Analysis ◽  
Elastoplastic Behavior ◽  
Perfectly Plastic ◽  
Elastic Perfectly Plastic

The loss of the initial tightness during service is one of the major causes of failure of tube-to-tubesheet joints. The initial residual contact pressure and its variation during the lifetime of the joint are among the parameters to blame. A reliable assessment of the initial contact pressure value requires accurate and rigorous modeling of the elastoplastic behavior of the tube and the tubesheet during the expansion process. This paper deals with the development of a new analytical model used to accurately predict the residual contact pressure resulting from a hydraulic expansion process. The analytical model is based on the elastic perfectly plastic material behavior of the tube and the tubesheet and the interaction between these two elements of the expanded joint. The model results have been compared and validated with those of the more accurate finite element analysis models. Additional comparisons have been made with existing methods.

Analytical Modeling of Hydraulically Expanded Tube-to-Tubesheet Joints

2007 ◽  
Author(s):  
Nor Eddine Laghzale ◽  
Abdel-Hakim Bouzid
Keyword(s):  
Contact Pressure ◽  
Analytical Modeling ◽  
Plastic Material ◽  
Material Behavior ◽  
Plastic Behavior ◽  
Initial Contact ◽  
Expansion Process ◽  
Perfectly Plastic ◽  
Reliable Assessment ◽  
Elastic Perfectly Plastic

The loss of the initial tightness during service is one of the major causes of failure of tube-to-tubesheet joints. The initial residual contact pressure and its variation during the lifetime of the joint is among the parameters to blame. A reliable assessment of the initial contact pressure value requires accurate and rigorous modeling of the elasto-plastic behavior of the tube and the tubesheet during the expansion process. This paper deals with the development of a new analytical model used to accurately predict the residual contact pressure resulting from a hydraulic expansion process. It is based on the elastic perfectly plastic material behavior of the tube and the tubesheet and the interaction between them. The model results have been compared and validated with those of the more accurate numerical FEA models. Additional comparisons have been made with existing methods.

Shakedown Limit Load Determination for a Kinematically Hardening 90-Degree Pipe Bend Subjected to Constant Internal Pressure and Cyclic Bending

2007 ◽  
Author(s):  
Hany F. Abdalla ◽  
Mohammad M. Megahed ◽  
Maher Y. A. Younan
Keyword(s):  
Finite Element ◽  
Internal Pressure ◽  
Plastic Material ◽  
Kinematic Hardening ◽  
Limit Load ◽  
Material Behavior ◽  
Pipe Bend ◽  
Cyclic Bending ◽  
Perfectly Plastic ◽  
Shakedown Limit

A simplified technique for determining the shakedown limit load of a structure employing an elastic-perfectly-plastic material behavior was previously developed and successfully applied to a long radius 90-degree pipe bend. The pipe bend is subjected to constant internal pressure and cyclic bending. The cyclic bending includes three different loading patterns namely; in-plane closing, in-plane opening, and out-of-plane bending moment loadings. The simplified technique utilizes the finite element method and employs small displacement formulation to determine the shakedown limit load without performing lengthy time consuming full cyclic loading finite element simulations or conventional iterative elastic techniques. In the present paper, the simplified technique is further modified to handle structures employing elastic-plastic material behavior following the kinematic hardening rule. The shakedown limit load is determined through the calculation of residual stresses developed within the pipe bend structure accounting for the back stresses, determined from the kinematic hardening shift tensor, responsible for the translation of the yield surface. The outcomes of the simplified technique showed very good correlation with the results of full elastic-plastic cyclic loading finite element simulations. The shakedown limit moments output by the simplified technique are used to generate shakedown diagrams of the pipe bend for a spectrum of constant internal pressure magnitudes. The generated shakedown diagrams are compared with the ones previously generated employing an elastic-perfectly-plastic material behavior. These indicated conservative shakedown limit moments compared to the ones employing the kinematic hardening rule.

A Finite Element Based Study on the Elastic-Plastic Transition Behavior in a Hemisphere in Contact With a Rigid Flat

2008 ◽  
Vol 130 (4) ◽  
Author(s):  
S. Shankar ◽  
M. M. Mayuram
Keyword(s):  
Finite Element ◽  
Contact Area ◽  
Plastic Material ◽  
Plastic Region ◽  
Real Contact Area ◽  
Real Contact ◽  
Perfectly Plastic ◽  
The Difference ◽  
Elastic Perfectly Plastic ◽  
Green Model

An axisymmetrical hemispherical asperity in contact with a rigid flat is modeled for an elastic perfectly plastic material. The present analysis extends the work (sphere in contact with a flat plate) of Kogut–Etsion Model and Jackson–Green Model and addresses some aspects uncovered in the above models. This paper shows the critical values in the dimensionless interference ratios (ω∕ωc) for the evolution of the elastic core and the plastic region within the asperity for different Y∕E ratios. The present analysis also covers higher interference ratios, and the results are applied to show the difference in the calculation of real contact area for the entire surface with other existing models. The statistical model developed to calculate the real contact area and the contact load for the entire surfaces based on the finite element method (FEM) single asperity model with the elastic perfectly plastic assumption depends on the Y∕E ratio of the material.

Stress Analysis of SS316L Tube Die Expansion for High Pressure Gas Coolers

2020 ◽  
Author(s):  
Zijian Zhao ◽  
Abdel-Hakim Bouzid
Keyword(s):  
Residual Stress ◽  
High Pressure ◽  
Plastic Material ◽  
Research Work ◽  
Material Behavior ◽  
Isotropic Hardening ◽  
Plastic Behavior ◽  
Expansion Process ◽  
Elastic Plastic ◽  
Stress States

Abstract SS316L finned tubes are becoming very popular in high-pressure gas exchangers and particularly in CO2 cooler applications. Due to the high-pressure requirement during operation, these tubes require an accurate residual stress evaluation during the expansion process. Indeed, die expansion of SS tubes creates not only high stresses when combined with operation stresses but also micro-cracks during expansion when the expansion process is not very well controlled. This research work aims at studying the elastic-plastic behavior and estimating the residual stress states by modeling the die expansion process. The stresses and deformations of the joint are analyzed numerically using the finite element method. The expansion and contraction process is modeled considering elastic-plastic material behavior for different die sizes. The maximum longitudinal, tangential and contact stresses are evaluated to verify the critical stress state of the joint during the expansion process. The importance of the material behavior in evaluating the residual stresses using kinematic and isotropic hardening is addressed.

Analysis of thick-walled spherical shells subjected to external pressure: Elastoplastic and residual stress analysis

2019 ◽  
Vol 234 (1) ◽  
pp. 186-197
Author(s):  
Mohsen Kholdi ◽  
Abbas Loghman ◽  
Hossein Ashrafi ◽  
Mohammad Arefi
Keyword(s):  
Hydrostatic Pressure ◽  
Residual Stresses ◽  
Yield Criterion ◽  
External Pressure ◽  
Material Behavior ◽  
External Hydrostatic Pressure ◽  
Spherical Vessel ◽  
Tangential Stresses ◽  
Perfectly Plastic ◽  
Analytical Relations

When cylindrical and spherical vessels are subjected to the internal pressure, tensile tangential stresses are created throughout the thickness, the maximum of which are located at the inner surface of the vessels. To improve the performance of these vessels, autofrettage process has been devised to produce beneficial compressive residual stresses at the inner part of such vessels. The question arises whether the process such as autofrettage can be useful for vessels such as submarines or other thick walled tanks, which are used in deep sea waters and, therefore, subjected to high external hydrostatic pressure causing both radial and tangential stresses to be compressive across the thickness. On the other hand, is the residual stresses created by unloading from an external pressure beyond elastic limit beneficial and enhance their performances? In this study, elastoplastic and residual stresses in a thick-walled spherical vessel under external hydrostatic pressure has been investigated. The material behavior is considered to be elastic-perfectly plastic. Von Misses yield criterion is used to obtain initial yield point and for the ideal elastoplastic regime analytical relations are presented. It has been found that by applying external hydrostatic pressure yielding process will start from inside of the sphere. Finally after unloading, residual tensile stresses are created at the inner part of the vessel which is useful for the vessel. The residual stresses and the condition of reverse yielding is studied in this paper.

Analytical Solution of Aluminum Alloy Plates with Holes Subjected to Cold Expansion with Reverse Yielding

2021 ◽  
Author(s):  
Abdel-Hakim Bouzid ◽  
Hacène Touahri ◽  
Khaled Benfriha
Keyword(s):  
Aluminum Alloy ◽  
Residual Stresses ◽  
Strain Hardening ◽  
Analytical Model ◽  
Material Behavior ◽  
Thick Wall ◽  
Plastic Behavior ◽  
Good Prediction ◽  
Fatigue Damage Accumulation ◽  
Reverse Yielding

Abstract The expansion induced by cold working is a common process that generates residual stresses. It is used when fatigue damage accumulation and life reduction of aluminum alloy perforated plates is an issue in the aeronautics industry. This process is an attractive solution to extend the fatigue lifetime of these structures. It aims at generating residual stresses and increases thereby the strength of hollow parts including aluminum alloy plates with holes commonly used in the manufacture of airplane fuselage. Unfortunately, the life predictions require a good prediction of the residual stresses and in particular when reverse yielding takes place. An analytical model to predict the residual stresses induced during the expansion process due to the cold strain hardening is developed. The proposed analytical model is based on an elasto-plastic behavior, with a power law material behavior and relies on the theory of autofrettaged thick wall cylinders in plane strain state to which reverse yielding is incorporated. The application of Hencky theory of plastic deformation is used in the analytical calculations of the stresses and strains. Finite-element numerical simulation is used to validate the developed analytical model by comparison of the radial, Hoop, longitudinal and equivalent stresses for both the loading and unloading phases. The obtained results show clearly that the level of residual stresses depends mainly on the interference and strain hardening while reverse yielding reduce the stresses near the hole.

Numerical Fatigue Strength Evaluation of Inhomogeneous, Linear Flow Split Profiles

2008 ◽  
Author(s):  
Volker Landersheim ◽  
Chalid el Dsoki ◽  
Holger Hanselka ◽  
Thomas Bruder ◽  
Desislava Veleva ◽  
...  
Keyword(s):  
Residual Stresses ◽  
Plastic Material ◽  
Material Behavior ◽  
Fatigue Properties ◽  
Forming Process ◽  
Linear Flow ◽  
Local Material ◽  
Durability Analysis ◽  
Flow Splitting ◽  
Local Material Properties

The innovative sheet metal forming technology “Linear Flow Splitting” offers various new options for designing profile-like components. The forming process leads to severe changes in local material properties, inhomogeneities and residual stresses within the manufactured component. These effects influence the mechanical properties of the manufactured components. If the components are designed to endure cyclic mechanical loads, it is especially important to know the components fatigue properties. This paper focuses on a method to derive the fatigue properties of Linear Flow Split Profiles by nonlinear numerical FE analysis, including durability analysis and forming simulations. This numerical approach offers the possibility to estimate the fatigue properties of components before manufacturing physical prototypes, only based on material parameters derived from tests on smooth samples. The Finite-Element analysis of the Linear Flow Splitting Process provides distributions of local material deformation and residual stresses. These results are mapped by an appropriate interface on FE models, which allow simulating the component behavior under external loads. Thus, the inhomogeneous elastic-plastic material behavior and residual stresses are considered in the computed stresses and strains. Further on, a post-processing tool was implemented to interpret the FE results considering the inhomogeneous distribution of materials fatigue properties, the mean stress distribution and the statistical size effect.

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