Creep Crack Initiation in a Weld Steel: Effects of Residual Stress

2005 ◽  
Author(s):  
Noel P. O’Dowd ◽  
Kamran M. Nikbin ◽  
Farid R. Biglari
Keyword(s):  
Residual Stress ◽  
Finite Element ◽  
Crack Initiation ◽  
Equivalent Stress ◽  
Stress Triaxiality ◽  
Compact Tension ◽  
Residual Stress Field ◽  
Element Analysis ◽  
Creep Ductility ◽  
Uniaxial Test

In this paper, the effect of residual stress on the initiation of a crack at high temperature in a Type 347 austenitic steel weld is examined using the finite element method. Both two and three dimensional analyses have been carried out. Residual stresses have been introduced by prior mechanical deformation, using a previously developed notched compact tension specimen. It has been found that for the 347 weld material, peak stresses in the vicinity of the notch are approximately three times the yield strength at room temperature and the level of stress triaxiality (ratio between hydrostatic and equivalent stress) is approximately 1 (considerably higher than that for a uniaxial test). The finite element analysis includes the effects of stress redistribution and damage accumulation under creep conditions. For the case examined the analysis predicts that crack initiation will occur under conditions of stress relaxation if the uniaxial creep ductility of the material is less than 2.5%. Furthermore, the predicted life of the component under constant load (creep conditions) is significantly reduced due to the presence of the residual stress field.

Thermal Simulation of an Arbitrary Residual Stress Field in a Fully or Partially Autofrettaged Thick-Walled Spherical Pressure Vessel

2008 ◽  
Author(s):  
M. Perl
Keyword(s):  
Residual Stress ◽  
Finite Element ◽  
Stress Field ◽  
Pressure Vessel ◽  
Stress Fields ◽  
Equivalent Temperature ◽  
Residual Stress Field ◽  
Element Analysis ◽  
Spherical Pressure ◽  
The Ideal

The equivalent thermal load was previously shown to be the only feasible method by which the residual stresses due to autofrettage and its redistribution, as a result of cracking, can be implemented in a finite element analysis, of a fully or partially autofrettaged thick-walled cylindrical pressure vessel. The present analysis involves developing a similar methodology for treating an autofrettaged thick-walled spherical pressure vessel. A general procedure for evaluating the equivalent temperature loading for simulating an arbitrary, analytical or numerical, spherosymmetric autofrettage residual stress field in a spherical pressure vessel is developed. Once presented, the algorithm is applied to two distinct cases. In the first case, an analytical expression for the equivalent thermal loading is obtained for the ideal autofrettage stress field in a spherical shell. In the second case, the algorithm is applied to the discrete numerical values of a realistic autofrettage residual stress field incorporating the Bauschinger effect. As a result, a discrete equivalent temperature field is obtained. Furthermore, a finite element analysis is performed for each of the above cases, applying the respective temperature field to the spherical vessel. The induced stress fields are evaluated for each case and then compared to the original stress. The finite element results prove that the proposed procedure yields equivalent temperature fields that in turn simulate very accurately the residual stress fields for both the ideal and the realistic autofrettage cases.

Numerical Analysis of the Effect of Machining on the Depth of Yield, Maximum Firing Pressure and Residual Stress Profile in an Autofrettaged Gun Tube

2003 ◽  
Vol 125 (3) ◽  
pp. 342-346 ◽  
Author(s):  
Amer Hameed ◽  
R. D. Brown ◽  
J. G. Hetherington
Keyword(s):  
Residual Stress ◽  
Finite Element ◽  
Optimization Technique ◽  
Circumferential Stress ◽  
Element Model ◽  
Stress Profile ◽  
Residual Stress Field ◽  
Element Analysis ◽  
Residual Stress Profile ◽  
Experimental Findings

A multi-linear kinematic, two dimensional finite element model incorporating Bauschinger effect, developed using ANSYS commercial software is used to determine the effect of machining both at the bore and at the outside diameter, on the depth of yield, maximum firing pressure and final residual stress field present in an autofrettaged gun tube. The model, which is in good agreement with experimental findings, clearly shows that the reduction in maximum compressive circumferential stress is more sensitive to internal machining than to external machining; the depth of yield remains stable and there is no movement of the elastic-plastic interface, relative to its location before material removal. If the internal machining removes material in which reverse yield has occurred, the maximum firing pressure is not affected. The finite element analysis supported by experimental evidence thus leads to an optimization technique for gun tube design.

Three Dimensional Finite Element Analysis of a Split-Sleeve Cold Expansion Process

2009 ◽  
Vol 131 (3) ◽  
Author(s):  
S. Ismonov ◽  
S. R. Daniewicz ◽  
J. C. Newman ◽  
M. R. Hill ◽  
M. R. Urban
Keyword(s):  
Residual Stress ◽  
Finite Element ◽  
Three Dimensional ◽  
Element Model ◽  
Residual Stress Field ◽  
Expansion Process ◽  
Element Analysis ◽  
Cold Expansion ◽  
Dimensional Finite Element ◽  
Three Dimensional Finite Element

A cold expansion process is used to prolong the fatigue life of a structure under cyclic loadings. The process produces a beneficial compressive residual stress zone in the hole vicinity, which retards the initiation and propagation of the crack at the hole edge. In this study, a three-dimensional finite element model of the split-sleeve cold expansion process was developed to predict the resulting residual stress field. A thin rectangular aluminum sheet with a centrally located hole was considered. A rigid mandrel and an elastic steel split sleeve were explicitly modeled with the appropriate contact elements at the interfaces between the mandrel, the sleeve, and the hole. Geometrical and material nonlinearities were included. The simulation results were compared with experimental measurements of the residual stress. The influence of friction and the prescribed boundary conditions for the sheet were studied. Differences between the split-sleeve- and the non-split-sleeve model solutions are discussed.

Finite Element Analysis of the Effect of Mechanical Stress Improvement Process on Weld Residual Stress and Flaw Growth in a Thick-Walled Pressurizer Safety Nozzle

2017 ◽  
Author(s):  
Giovanni G. Facco ◽  
Patrick A. C. Raynaud ◽  
Michael L. Benson
Keyword(s):  
Residual Stress ◽  
Finite Element Analysis ◽  
Finite Element ◽  
Stress Field ◽  
Mechanical Stress ◽  
Residual Stress Field ◽  
Element Analysis ◽  
Wide Range ◽  
Improvement Process ◽  
Stress Prediction

The Mechanical Stress Improvement Process (MSIP) is generally accepted as an effective method to modify the residual stress field in a given component to mitigate subcritical crack growth in susceptible components [1] [2] [3]. In order to properly utilize MSIP, residual stress prediction is needed to determine the parameters of the MSIP application and the expected final residual stress field in the component afterwards. This paper presents the results of a 2D axisymmetric finite element study to predict weld residual stresses (WRS), and associated flaw growth scenarios, in a thick-walled pressurizer safety nozzle that underwent mitigation by application of MSIP. The authors have developed a finite-element analysis methodology to examine the effect of MSIP application on WRS and flaw growth for various hypothetical welding histories and boundary conditions in a thick-walled pressurizer safety nozzle. In doing so, a wide range of repair scenarios was considered, with the understanding that some bounding scenarios may be impractical for this geometry.

Computational and Experimental Studies of High Temperature Crack Initiation in the Presence of Residual Stress

2008 ◽  
Vol 130 (4) ◽  
Author(s):  
Noel P. O’Dowd ◽  
Kamran M. Nikbin ◽  
Robert C. Wimpory ◽  
Farid R. Biglari ◽  
Manus P. O’Donnell
Keyword(s):  
Residual Stress ◽  
Finite Element ◽  
Notch Root ◽  
Experimental Studies ◽  
Compressive Load ◽  
Compact Tension ◽  
Compact Tension Specimen ◽  
Element Analysis ◽  
Weld Material ◽  
Temperature Crack

Residual stresses have been introduced into a notched compact tension specimen of a 347 weld material by mechanical compression. The required level of compressive load has previously been determined from finite-element studies. The residual stress in the vicinity of the notch root has been measured using neutron diffraction and the results compared with those obtained from finite-element analysis. The effect of stress redistribution due to creep has been examined and it is found that a significant reduction in stress is measured after 1000h at 650°C. The implications of these results with regard to the development of damage in the specimen due to creep relaxation are examined.

Finite Element Analysis of Temperature Filed and Stress Field of Reducer

2014 ◽  
Vol 881-883 ◽  
pp. 1447-1450
Author(s):  
Jing Zhang ◽  
Fei Wang
Keyword(s):  
Residual Stress ◽  
Finite Element Analysis ◽  
Finite Element ◽  
Temperature Field ◽  
Stress Field ◽  
Residual Stress Field ◽  
Element Analysis ◽  
Welding Temperature ◽  
Stress And Deformation ◽  
Residual Stress And Deformation

Abstract.The connection mode of reducer with straight tube on both sides are the welding connection. There are two weld at the both side of reducer and there has a great influence on residual stress and deformation in the process of welding . Based on the particularity of reducer welding, the paper is focus on the residual stress and deformation in the process of welding, using large-scale finite element analysis software ANSYS .The DN500X450 reducer model is established.The welding temperature field and residual stress field is analysis and calculation and analysis the influence on temperature and stress distribution of reducer. The results show that the maximum of the temperature and the residual stress is located in the big side and reduce the welding seam, and the obvious deformation also find in the big side and reduce joint . The reducing pipe’s distribution of temperature field and residual stress field are obtained,providing the basis to establish properly and optimize of welding process.

Residual Stress Analysis of Tube Attachment Weld in Pressure Vessel Forging: Baseline FE Analysis and Sensitivity Studies

2005 ◽  
Author(s):  
N. A. Leggatt ◽  
R. J. Dennis ◽  
P. R. Hurrell
Keyword(s):  
Residual Stress ◽  
Finite Element ◽  
Pressure Vessel ◽  
Three Dimensional ◽  
Wall Stress ◽  
Isotropic Hardening ◽  
Residual Stress Field ◽  
Element Analysis ◽  
Hardening Law ◽  
Sensitivity Studies

Full two and three-dimensional single or multi-pass weld simulations are now feasible and practical given the development of improved analysis tools (e.g. ABAQUS), and significantly greater computer power. This paper describes a finite element analysis undertaken to predict the as-welded residual stress field following the welding of a tube attachment weld inside a thick pressure vessel (PV) forging. The coupled thermal-mechanical analysis was performed using the finite element (FE) code ABAQUS, A heat source modelling tool was employed to calculate welding fluxes, which were read into ABAQUS via a user subroutine. The ‘block’ dumped approach was utilised in the 2D thermal analysis such that complete weld rings are deposited instantaneously. Heat inputs were based on the actual weld parameters and bead sizes. The predicted fusion depths matched well with those found in sectioned weld test pieces. 2D FE sensitivity studies were performed examining the effect of variations in a number of parameters (bead sequence, hardening law, inter-pass temperature and annealing temperature). The hardening law was changed from isotropic to kinematic to investigate the effect of material behaviour. Large weld residual tensile stresses were calculated with significant compressive stresses in the adjacent vessel wall. Stress results were generally insensitive in the tube and forging, indicating that the vessel constraint dominates over local welding conditions. Weld hoop stresses were overestimated partly due to the ‘tourniquet’ effect of depositing rings of weld metal and the isotropic hardening law assumed.

Identification of Stress Multiaxiallity Effect on Creep Damage by a Combination of Experiments and Numerical Analyses

2009 ◽  
Author(s):  
Yukio Takahashi
Keyword(s):  
Finite Element ◽  
Synergetic Effect ◽  
Stress Triaxiality ◽  
Creep Damage ◽  
Compact Tension ◽  
Simple Expression ◽  
Creep Rupture ◽  
Creep Tests ◽  
Element Analysis ◽  
Rupture Behavior

Structural materials experience various stress states and their integrity under a wide variety of stress multiaxility needs to be evaluated in design and life management for various components. Especially creep rupture behavior is known to be quite sensitive to the stress multiaxiality. To systematically evaluate the multiaxial effect on creep rupture behavior of modified 9Cr-1Mo steel, a number of creep tests were conducted on round-bar specimens with circumferential notches. Strong effects of temperature and deformation rate on the reduction of area were observed and their synergetic effect was modeled by a simple expression. Then crack growth in compact tension specimens was simulated by finite element analysis to derive ductility under higher stress triaxiality. Finally, true rupture strain was expressed as a function of temperature, inelastic strain rate and triaxiality factor and its validity was demonstrated through finite element analyses on notched bar and compact tension specimens employing it as a local fracture criterion.

Sign in / Sign up

Export Citation Format

Share Document