Determination of Path-Independent J-Integral for Cracks in Residual Stress Fields Using Finite Element Method

2015 ◽  
Author(s):  
Xian-Kui Zhu
Keyword(s):  
Residual Stress ◽  
Finite Element ◽  
Residual Stresses ◽  
Stress Effect ◽  
J Integral ◽  
Residual Stress Field ◽  
Crack Tip Field ◽  
Path Independence ◽  
Residual Stress Effect ◽  
Senb Specimen

“Hot” residual stresses exist in metal welds due to welding thermal stresses, and “cold” residual stresses occur in mechanical damaged metallic pipes due to large plastic deformation. For a crack in ether a hot or cold residual stress field, residual stresses might have a strong effect on the crack-tip field and the fracture parameter, J-integral. To consider the effect of residual stresses and to ensure the path-independence of J, different correction methods have been developed over the years. Recently, the finite element analysis (FEA) commercial software ABAQUS adopted one of correction methods for determining the residual stress corrected J-integral. This paper intends to evaluate this new function of ABAQUS and to see if the residual stress corrected J-integral is path-independent. A brief review is first given to the J-integral definition, the conditions of J-integral path-independence or dependence, and the modifications of J-integral to consider the residual stress effect. A modified single edge-notched bend (SENB) specimen is then adopted, and a FEA numerical procedure is developed and used in the numerical tests to evaluate the path-independence of the residual stress corrected J-integral using ABAQUS. Detailed elastic-plastic FEA calculations are carried out for the modified SENB specimen in three-point bending. The residual stress field, crack-tip field, and J-integral with and without consideration of the residual stress effect are determined and discussed.

Numerical Calculation of Residual Stress Corrected J-Integral Using ABAQUS

2014 ◽  
Author(s):  
Xian-Kui Zhu
Keyword(s):  
Residual Stress ◽  
Finite Element ◽  
Stress Field ◽  
Residual Stresses ◽  
Stress Effect ◽  
J Integral ◽  
Residual Stress Field ◽  
Path Independence ◽  
Residual Stress Effect ◽  
Senb Specimen

Residual stresses exist in welded structures due to thermal stresses. Without temperature change, large plastic deformation can result in “cold” residual stresses in a wrinkle or dent in a metallic pipe. For a crack in residual stress field, residual stresses might have strong effect on fracture parameter, the J-integral. In order to ensure its path-independence, different correction methods have been developed in consideration of residual stress effect. Recently, the finite element commercial software ABAQUS adopted one of the correction methods, and is able to calculate the residual stress corrected J-integral. A brief review is first given to the J-integral definition, the conditions of path-independence or path-dependence, and the modifications to consider the residual stress effect. A modified single edge-notched bend (SENB) specimen is then used, and a numerical procedure is developed for ABAQUS to evaluate the path-independence of the residual stress corrected J-integral. Detailed elastic-plastic finite element analyses are performed for the SENB specimen in three-point bending. The residual stress field, crack-tip stress field, and J-integral with and without consideration of residual stresses are discussed.

Effects of Finite Strains and Residual Stresses on Path Independence of the J-Integral for Ductile Cracks

2017 ◽  
Author(s):  
Xian-Kui Zhu ◽  
Tom McGaughy
Keyword(s):  
Residual Stress ◽  
Residual Stresses ◽  
Driving Force ◽  
Path Dependence ◽  
New Technology ◽  
Finite Strains ◽  
J Integral ◽  
Residual Stress Field ◽  
Path Independence ◽  
Major Factors

Large plastic deformation and residual stresses exist in mechanical damages to pipelines. If a crack occurs in the damages, residual stresses will affect mechanics behavior of the crack and path independence of the J-integral, and so the J-integral may lose capacity to describe fracture driving force. This paper theoretically investigates basic conditions required for the path independence of the J-integral and major factors affecting the path independence, including the incremental plasticity, finite strains and residual stresses. Residual stress modified J-integrals are then introduced for ensuring the path independence. With use of a notched beam, detailed elastic-plastic finite element analyses are performed in terms of the incremental plasticity for a crack subject to three-point bending. The path dependence of the J-integral due to the three major factors is then evaluated. Numerical results show that the residual stress modified J-integral is path-independent, and able to describe the fracture driving force for ductile cracks in a residual stress field. This provides a new technology to assess pipeline integrity for cracks coupling residual stresses.

J-INTEGRAL FOR A 3-D INTERFACE CRACK CONFIGURATION IN WELDS OF DISSIMILAR STEELS

2006 ◽  
Vol 20 (25n27) ◽  
pp. 4201-4206
Author(s):  
KYONG-HO CHANG ◽  
CHIN-HYUNG LEE
Keyword(s):  
Residual Stress ◽  
Finite Element ◽  
Interface Crack ◽  
Three Dimensional ◽  
Crack Tip ◽  
J Integral ◽  
Residual Stress Field ◽  
Crack Configuration ◽  
Dissimilar Steels ◽  
Path Independence

In this study, path-independent values of the J-integral in the finite element context for an arbitrary three-dimensional interface crack configuration in welds of dissimilar steels are presented. For the fracture mechanics analysis of an interface crack in welds of dissimilar steels, residual stress analysis and fracture analysis must be performed sequentially. In the analysis of cracked bodies containing residual stress, the usual domain integral formation results in path-dependent values of the J-integral. And unlike cracks in homogeneous materials, an interface crack in welds of dissimilar steels always induces both opening and shearing modes of stress in the vicinity of the crack tip. Therefore, this paper discusses modifications of the conventional J-integral that yield path independence in the presence of residual stress and the total J values which can characterize the severity of an interface crack tip in welds of dissimilar steels. A finite element method which can evaluate the J-integral for an interface crack in three-dimensional residual stress bearing bodies is developed using the modified J-integral definition and total J values. The situation when residual stresses only are present is studied as is the case when mechanical stresses are applied in conjunction with a residual stress field.

The Effects of Loadings on Welding Residual Stresses and Assessment of Fracture Parameters in a Welding Residual Stress Field

2011 ◽  
Author(s):  
Liwu Wei ◽  
Weijing He ◽  
Simon Smith
Keyword(s):  
Residual Stress ◽  
Stress Field ◽  
Residual Stresses ◽  
Path Dependence ◽  
Welding Residual Stress ◽  
Assessment Procedure ◽  
Fe Model ◽  
J Integral ◽  
Residual Stress Field ◽  
Growing Crack

The level of welding residual stress is an important consideration in the ECA of a structure or component such as a pipeline girth weld. Such a consideration is further complicated by their variation under load and the complexity involved in the proper assessment of fracture mechanics parameters in a welding residual stress field. In this work, 2D axi-symmetric FEA models for simulation of welding residual stresses in pipe girth welds were first developed. The modelling method was validated using experimental measurements from a 19-pass girth weld. The modeling method was used on a 3-pass pipe girth weld to predict the residual stresses and variation under various static and fatigue loadings. The predicted relaxation in welding residual stress is compared to the solutions recommended in the defect assessment procedure BS 7910. Fully circumferential internal cracks of different sizes were introduced into the FE model of the three-pass girth weld. Two methods were used to introduce a crack. In one method the crack was introduced instantaneously and the other method introduced the crack progressively. Physically, the instantaneously introduced crack represents a crack originated from manufacturing or fabrication processes, while the progressively growing crack simulates a fatigue crack induced during service. The J-integral values for the various cracks in the welding residual stress field were assessed and compared. This analysis was conducted for a welding residual stress field as a result of a welding simulation rather than for a residual stress field due to a prescribed temperature distribution as considered by the majority of previous investigations. The validation with the 19-pass welded pipe demonstrated that the welding residual stress in a pipe girth weld can be predicted reasonably well. The relaxation and redistribution of welding residual stresses in the three-pass weld were found to be significantly affected by the magnitude of applied loads and the strain hardening models. The number of cycles in fatigue loading was shown to have little effect on relaxation of residual stresses, but the range and maximum load together governed the relaxation effect. A significant reduction in residual stresses was induced after first cycle but subsequent cycles had no marked effect. The method of introducing a crack in a FE model, progressively or instantaneously, has a significant effect on J-integral, with a lower value of J obtained for a progressively growing crack. The path-dependence of the J-integral in a welding residual stress field is discussed.

Residual Stress Measurements in Single and Multi-Pass Groove Weld Specimens Using Neutron Diffraction and the Contour Method

2006 ◽  
Vol 524-525 ◽  
pp. 671-676 ◽  
Author(s):  
M. Kartal ◽  
Mark Turski ◽  
Greg Johnson ◽  
Michael E. Fitzpatrick ◽  
S. Gungor ◽  
...  
Keyword(s):  
Residual Stress ◽  
Finite Element ◽  
Neutron Diffraction ◽  
Residual Stresses ◽  
Cross Section ◽  
Welding Process ◽  
Contour Method ◽  
Residual Stress Field ◽  
Process Measurements ◽  
Good Agreement

This paper describes the measurement of longitudinal residual stresses within specially designed 200x180x25mm groove weld specimens. The purpose of these measurements was to compare the residual stress field arising from single and multi-pass weld beads laid down within the constraint of a groove in order to validate finite element simulations of the welding process. Measurements were made over the cross section at the mid-bead length, utilising the relatively new Contour method and neutron diffraction. Results from these measurements indicate a larger peak tensile longitudinal residual stresses within the weld region of the multi-pass weld sample. Good agreement is found between both techniques.

Effects of Repair Weld Residual Stresses on Wide-Panel Specimens Loaded in Tension

1998 ◽  
Vol 120 (2) ◽  
pp. 122-128 ◽  
Author(s):  
P. Dong ◽  
J. K. Hong ◽  
J. Zhang ◽  
P. Rogers ◽  
J. Bynum ◽  
...  
Keyword(s):  
Residual Stress ◽  
Finite Element ◽  
Residual Stresses ◽  
Structural Integrity ◽  
Space Shuttle ◽  
Tensile Tests ◽  
External Loading ◽  
Residual Stress Field ◽  
Fabrication Procedure ◽  
Loading Effects

As a part of the welding fabrication procedure development for the next generation space shuttle external tank, aluminum-lithium wide-panel specimens were used to assess the interactions between repair weld residual stresses and external loading conditions. The detailed residual stress development in the wide panel specimens with a repair weld was analyzed using an advanced finite element procedure. External tension loading effects were then incorporated in the residual stress model to study the interactions between the residual stress field and external tensile loading. Wide-panel tensile tests were also performed to extract photo strain and strain-gage results. A good agreement between the finite element and experimental results was obtained. The results demonstrate that the presence of high tensile residual stresses within a repair weld has a drastic impact on the stress/strain distribution in the wide panel specimens subjected to external loading. Its implications on structural integrity are discussed in light of the wide-panel results. The effects of post-welding mechanical treatment such as planishing were also examined.

Numerical Simulation of Residual Stresses Due to Cladding Process

2007 ◽  
Author(s):  
Dieter Siegele ◽  
Marcus Brand
Keyword(s):  
Numerical Simulation ◽  
Residual Stress ◽  
Finite Element ◽  
Stress Field ◽  
Residual Stresses ◽  
Base Metal ◽  
Base Material ◽  
Pressure Vessels ◽  
Measured Temperature ◽  
Residual Stress Field

The inner surface of reactor pressure vessels is protected against corrosion by an austenitic cladding. Generally, the cladding is welded on the ferritic base metal with two layers to avoid sub-clad cracks and to improve the microstructure of the cladding material. On the other hand, due to the cladding process and the difference of the thermal expansion coefficient of the austenitic cladding and the ferritic base material residual stresses act in the component. This residual stress field is important for assessing crack postulates in the cladding or subclad flaws in the base metal. For the determination of the residual stress field, plates of RPV steel were cladded and heat treated representative to the RPV relevant conditions. During the cladding process the temperature and distortion were measured as basis for the validation of the finite element simulations. The numerical simulation was performed with the finite element code SYSWELD. The heat source of the model was calibrated on the measured temperature profile. In the analysis, the temperature dependent material properties as well as the transformation behavior of the ferritic base metal were taken into account. The calculated residual stresses show tensile stresses in the cladding followed by compressive stresses in the base metal that are in agreement with measurements with X-ray diffraction technique.

Prediction of Residual Stress Distributions in Welded Sections of P92 Pipes with Small Diameter and Thick Wall based on 3D Finite Element Simulation

2015 ◽  
Vol 34 (3) ◽  
Author(s):  
Xiaowei Wang ◽  
Jianming Gong ◽  
Yanping Zhao ◽  
Yanfei Wang
Keyword(s):  
Residual Stress ◽  
Finite Element ◽  
Residual Stresses ◽  
Small Diameter ◽  
Fe Analysis ◽  
Thick Wall ◽  
Fe Model ◽  
Stress Distributions ◽  
Residual Stress Field ◽  
Heat Treated

AbstractThis study used ABAQUS finite element (FE) software to investigate the residual stress distributions of P92 welded pipes in both the as-weld and post weld heat treated (PWHT) condition. Sequential coupling quasi-static thermo-mechanical in conjunction with moving double ellipsoidal heat source and an element add/remove technique to simulate deposition of new weld material, are combined in the 3D FE analysis. To validate the simulation results, the residual stresses in axial direction at the surface of pipe were measured by X-ray diffraction technique and compared with the results of FE analysis. Detailed characteristic distributions of the residual stresses are discussed. Results show that the FE model can predict the residual stress distributions satisfactorily. Highest residual stresses on the outer surface are found in the last weld bead to be deposited. And the highest tensile residual stress for the full welded section take place in heat affected zone (HAZ) near the middle thickness. Larger residual sstress can be found around the welding start point along the pipe circumference. Comparison of heat treated specimen and untreated specimen illustrates that PWHT has a strong effect on the residual stress field.

Crack Tip Behaviour in Residual Stress Field: Finite Element Modelling and Neutron Diffraction Measurements

2011 ◽  
Author(s):  
H. Dai ◽  
J. F. Kelleher ◽  
P. J. Withers
Keyword(s):  
Residual Stress ◽  
Finite Element ◽  
Stress Intensity ◽  
Crack Closure ◽  
Finite Element Modelling ◽  
Applied Load ◽  
Crack Tip ◽  
J Integral ◽  
Residual Stress Field ◽  
Element Modelling

Simple analyses of fracture and fatigue often make use of the stress intensity at a crack tip or the J-integral surrounding it. However, there is no universally accepted method of including the effect of residual stress in these values, even though the qualitative effect of residual stress on crack growth is well known. In this work, we create a cracked compact tension C(T) specimen with a residual stress field that affects the crack tip behaviour, in particular by altering the level of expected crack closure. Neutron diffraction measurements under in situ applied loading reveal strain distributions consistent with an increased level of closure when the crack tip is in a state of compressive residual stress. Through finite element modelling of the samples studied, we show that the residual stress in these samples redistributes as the crack grows, which changes the level of crack closure for any given crack length and applied load. As crack closure is often considered in fatigue analysis by deriving an ‘effective’ stress intensity based on the applied load needed to overcome the closure and open the crack, the model is used to compare this approach with numerical calculations of the J-integral for different crack lengths.

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