Optimisation of Mixed Hardening Material Constitutive Models for Weld Residual Stress Simulation Using the NeT Task Group 1 Single Bead on Plate Benchmark Problem

2009 ◽  
Author(s):  
Michael C. Smith ◽  
Brahim Nadri ◽  
Ann C. Smith ◽  
David G. Carr ◽  
Philip J. Bendeich ◽  
...  
Keyword(s):  
Residual Stress ◽  
Residual Stresses ◽  
Constitutive Models ◽  
Task Group ◽  
Simple Problem ◽  
Benchmark Problem ◽  
Mixed Hardening ◽  
Weld Residual Stress ◽  
Stress Simulation ◽  
Group 1

A single weld bead deposited on a flat plate is a deceptively simple problem that is in practice a challenge for both measurement and prediction of weld residual stresses. Task Group 1 of the NeT collaborative network has examined this problem in an extensive programme of measurement and simulation extending from 2002 to 2008. As a result, the NeT bead on plate forms an ideal benchmark problem for the development of weld residual stress simulation techniques. One of the conclusions of NeT Task Group 1 is that the most accurate predictions of weld residual stresses in austenitic steels are achieved using mixed isotropic-kinematic material constitutive models. However, the use of these models can require both extensive materials data, and compromises in fitting either the monotonic or cyclic responses. This paper reports a detailed matrix of sensitivity studies aimed at optimising the behaviour of mixed hardening models in welding simulation, using the Lemaitre-Chaboche formulation in the ABAQUS finite element code. Predicted stresses and strains in the NeT bead on plate specimen are compared with the extensive database of residual stress measurements. Further studies examine sensitivity to the handling of high temperature inelastic strains, using a novel two-stage annealing functionality implemented within ABAQUS. The results show that, overall, the most accurate predictions are made if the Lemaitre-Chaboche parameters are optimised to fit the monotonic response over the first 2% of plastic strain. However, further improvements in prediction could be achieved if the constitutive model were capable of independently fitting both the monotonic and saturated cyclic response of the material.

Sensitivity of Predicted Weld Residual Stresses in the NeT Task Group 1 Single Bead on Plate Benchmark Problem to Finite Element Mesh Design and Heat Source Characteristics

2009 ◽  
Author(s):  
Philip J. Bendeich ◽  
Mike C. Smith ◽  
David G. Carr ◽  
Lyndon Edwards
Keyword(s):  
Finite Element ◽  
Heat Source ◽  
Residual Stresses ◽  
Task Group ◽  
Simple Problem ◽  
Controlled Study ◽  
Design Element ◽  
Benchmark Problem ◽  
Source Characteristics ◽  
Group 1

A single weld bead deposited on a flat plate is a deceptively simple problem that is, in practice, a significant challenge for both measurement and prediction of weld residual stresses. Task Group 1 of the NeT collaborative network has examined this problem in an extensive programme of measurement and simulation extending from 2002 to 2008. Thus, the NeT bead on plate forms an ideal benchmark problem for the development of weld residual stress simulation techniques. It is often difficult to separate the influence of different analysis variables in a large collaborative study such as NeT Task Group 1. This paper examines sensitivity to mesh design, element type, and heat source characteristics in a closely controlled study using several different mesh designs, element types (both tetrahedral and hexahedral), and heat sources, but the same material constitutive model and finite element analysis code. It complements a companion paper that varies material constitutive models. A dedicated heat source modelling tool with a semi-automatic interface to the ABAQUS finite element code has been used to vary the heat source characteristics, thus facilitating rapid and controlled sensitivity studies without the need for bespoke heat source coding within ABAQUS.

Optimising Residual Stress Measurements and Predictions in a Welded Benchmark Specimen: A Review of Phase 2 of the NeT Task Group 1 Single Bead on Plate Round Robin

2009 ◽  
Author(s):  
Michael C. Smith ◽  
Ann C. Smith ◽  
Robert C. Wimpory ◽  
Carsten Ohms ◽  
Brahim Nadri ◽  
...  
Keyword(s):  
Residual Stress ◽  
Finite Element ◽  
High Temperature ◽  
Residual Stresses ◽  
Constitutive Models ◽  
Finite Element Simulations ◽  
Task Group ◽  
Phase 2 ◽  
Inelastic Strains ◽  
Group 1

A single weld bead deposited on a flat plate is a deceptively simple problem that is in practice a challenge for both measurement and prediction of weld residual stresses. Task Group 1 of the NeT collaborative network has examined this problem in a two-phase programme extending from 2002 to 2008. Ten independent sets of residual stress measurements have been reported using diverse techniques, and over forty finite element simulations have been performed. This paper reviews Phase 2 of the Task Group 1 round robin. Here, the finite element simulations all made use of optimised thermal solutions, in which the global welding parameters, including efficiency, were fixed, and only the detailed heat source geometry was varied. These resulted in accurate far field welding temperature distributions, with significant variability only close to the weld bead itself. The subsequent mechanical analyses made use of kinematic, isotropic, and mixed isotropic-kinematic material constitutive models, and made a variety of assumptions about the introduction of weld filler material to the structure and the handling of high temperature inelastic strains. The large database of measurements allowed the derivation of statistical best estimates using a Bayesian “duff data” approach, and these best estimates were compared with the predictions to establish the most accurate material constitutive models. The most accurate predictions of residual stress were made using non-linear kinematic or mixed isotropic-kinematic constitutive models. The methods used to handle high-temperature inelastic strains influenced the predicted stresses only in regions where very high temperatures were predicted during welding. The results emphasise the importance and value of both well-characterised benchmark problems and international collaboration in the development of technologies to both measure and predict weld residual stresses.

Weld Residual Stress in Large Diameter Nuclear Nozzles

2011 ◽  
Author(s):  
Tao Zhang ◽  
F. W. Brust ◽  
Gery Wilkowski
Keyword(s):  
Residual Stress ◽  
Residual Stresses ◽  
Nuclear Power ◽  
Kinematic Hardening ◽  
Large Diameter ◽  
Thick Wall ◽  
Isotropic Hardening ◽  
Residual Stress Field ◽  
Mixed Hardening ◽  
Weld Residual Stress

Weld residual stresses in nuclear power plant can lead to cracking concerns caused by stress corrosion. These are large diameter thick wall pipe and nozzles. Many factors can lead to the development of the weld residual stresses and the distributions of the stress through the wall thickness can vary markedly. Hence, understanding the residual stress distribution is important to evaluate the reliability of pipe and nozzle joints with welds. This paper represents an examination of the weld residual stress distributions which occur in various different size nozzles. The detailed weld residual stress predictions for these nozzles are summarized. Many such weld residual stress solutions have been developed by the authors in the last five years. These distributions will be categorized and organized in this paper and general trends for the causes of the distributions will be established. The residual stress field can therefore feed into a crack growth analysis. The solutions are made using several different constitutive models such as kinematic hardening, isotropic hardening, and mixed hardening model. Necessary fabrication procedures such as repair, overlay and post weld heat treatment are also considered. Some general discussions and comments will conclude the paper.

Weld Residual Stress in Various Large Diameter Nuclear Nozzles

2012 ◽  
Vol 134 (6) ◽  
Author(s):  
Tao Zhang ◽  
Frederick W. Brust ◽  
Gery Wilkowski
Keyword(s):  
Residual Stress ◽  
Residual Stresses ◽  
Power Plants ◽  
Kinematic Hardening ◽  
Large Diameter ◽  
Postweld Heat Treatment ◽  
Thick Wall ◽  
Isotropic Hardening ◽  
Mixed Hardening ◽  
Weld Residual Stress

Weld residual stresses in nuclear power plants can lead to cracking concerns caused by stress corrosion. Many factors can lead to the development of the weld residual stresses, and the distributions of the stress through the wall thickness can vary markedly depending on the weld processing parameters, nozzle and pipe geometries, among other factors. Hence, understanding the residual stress distribution is important in order to evaluate the reliability of pipe and nozzle welded joints. This paper represents an examination of the weld residual stress distributions which occur in different nozzles. The geometries considered here are large diameter thick wall pipe and nozzles. The detailed weld residual stress predictions for these nozzles are summarized. These results are categorized and organized in this paper and general trends for the causes of the distributions are established. The solutions are obtained using several different constitutive models including kinematic hardening, isotropic hardening, and mixed hardening model. Necessary fabrication procedures such as weld repair, overlay, and postweld heat treatment are also considered. The residual stress field can therefore be used to perform a crack growth and instability analysis. Some general discussions and comments are given in the paper.

scholarly journals Residual stress redistribution during elastic shake down in welded plates

2018 ◽  
Vol 165 ◽  
pp. 21004
Author(s):  
Jazeel R. Chukkan ◽  
Guiyi Wu ◽  
Michael E. Fitzpatrick ◽  
Elvin Eren ◽  
Xiang Zhang ◽  
...  
Keyword(s):  
Residual Stress ◽  
Residual Stresses ◽  
Base Material ◽  
Offshore Structures ◽  
Residual Stress Field ◽  
Mixed Hardening ◽  
Weld Residual Stress ◽  
Shakedown Limit ◽  
Elastic Shakedown ◽  
Different Levels

Residual stresses are a consequence of welding in various structures such as ships and offshore structures. Residual stresses can be relaxed or redistributed according to the load levels during operation. The elastic shakedown phenomenon can be considered as one of the reasons for this change. This paper studies the relaxation/redistribution of weld residual stress during different levels of shakedown in a butt-welded plate chosen according to ship design and welding procedures. Welding was performed on DH36, a ship structural steel. Neutron diffraction was used to measure residual stresses in these plates in the as-welded state and after different levels of shakedown. A mixed hardening model in line with the Chaboche model is determined for both weld and base material. A numerical model is developed to estimate the shakedown limit on butt-welded plate. Further, the redistribution of residual stress in a numerical weld model according to the different levels of shakedown limit is studied. Based on the shakedown limit of the butt-welded plate, a shakedown region is determined, where the structure will undergo elastic shakedown in the presence of an existing residual stress field if the maximum stress on the load section after a few initial cycles is in the shakedown region.

Development of a Residual Stress Simulation Benchmark for a Single Bead-on-Plate Weldment

2006 ◽  
Author(s):  
Peter J. Bouchard ◽  
Lyndon Edwards ◽  
Anastasius G. Youtsos ◽  
Roger Dennis
Keyword(s):  
Residual Stress ◽  
Assessment Procedure ◽  
Defect Assessment ◽  
Best Estimate ◽  
Weld Residual Stress ◽  
Single Bead ◽  
Stress Prediction ◽  
Stainless Steel Bead ◽  
Stress Simulation ◽  
Network Project

Finite element weld residual stress modelling procedures involve complex non-linear analyses where many assumptions and approximations have to be made by the analyst. Weld modelling guidelines for inclusion in the R6 defect assessment procedure are in preparation and will be accompanied by a series of validation benchmarks that can be used to evaluate the accuracy of weld modelling procedures and assess their suitability for use in fracture assessments. It is intended to base one of the benchmarks on a stainless steel bead-on-plate weldment that has been extensively studied by members of Task Group 1 of the NeT European Network project. This paper uses round robin residual stress measurements from the NeT project to derive a statistically based ‘best estimate’ distribution of transverse stress passing through the wall-section at mid-length of the bead-on-plate weldment. The accuracy of a state-of-the-art residual stress prediction is benchmarked against the best estimate measurements using a root mean square error analysis and comparisons of decomposed components of stress. The appropriateness of using the predicted residual stresses in fracture assessments is assessed by comparing stress intensity factors based on the measured and predicted distributions of stress. The results from these studies will be used to help establish accuracy targets and acceptance criteria for the welding benchmark.

On the Mechanics of Residual Stresses in Girth Welds

2006 ◽  
Vol 129 (3) ◽  
pp. 345-354 ◽  
Author(s):  
P. Dong
Keyword(s):  
Residual Stress ◽  
Residual Stresses ◽  
Relative Importance ◽  
Stress Distributions ◽  
Unified Framework ◽  
Joint Geometry ◽  
Weld Residual Stress ◽  
Girth Welds ◽  
Welding Procedure

In this paper, some of the important controlling parameters governing weld residual stress distributions are presented for girth welds in pipe and vessel components, based on a large number of residual stress solutions available to date. The focus is placed upon the understanding of some of the overall characteristics in through-wall residual stress distributions and their generalization for vessel and pipe girth welds. In doing so, a unified framework for prescribing residual stress distributions is outlined for fitness-for-service assessment of vessel and pipe girth welds. The effects of various joint geometry and welding procedure parameters on through thickness residual stress distributions are also demonstrated in the order of their relative importance.

Weld Residual Stress and Fracture Behavior of NASA Layered Pressure Vessels

2019 ◽  
Author(s):  
F. W. Brust ◽  
R. H. Dodds ◽  
J. Hobbs ◽  
B. Stoltz ◽  
D. Wells
Keyword(s):  
Residual Stress ◽  
Residual Stresses ◽  
Fracture Behavior ◽  
Service Evaluation ◽  
Pressure Vessels ◽  
Weld Residual Stress ◽  
Proof Testing ◽  
Fracture Assessment ◽  
High Level ◽  
Initial Results

Abstract NASA has hundreds of non-code layered pressure vessel (LPV) tanks that hold various gases at pressure. Many of the NASA tanks were fabricated in the 1950s and 1960s and are still in use. An agency wide effort is in progress to assess the fitness for continued service of these vessels. Layered tanks typically consist of an inner liner/shell (often about 12.5 mm thick) with different layers of thinner shells surrounding the inner liner each with thickness of about 6.25-mm. The layers serve as crack arrestors for crack growth through the thickness. The number of thinner layers required depends on the thickness required for the complete vessel with most tanks having between 4 and 20 layers. Cylindrical layers are welded longitudinally with staggering so that the weld heat affected zones do not overlap. The built-up shells are then circumferentially welded together or welded to a header to complete the tank construction. This paper presents some initial results which consider weld residual stress and fracture assessment of some layered pressure vessels and is a small part of the much larger fitness for service evaluation of these tanks. This effort considers the effect of weld residual stresses on fracture for an inner layer longitudinal weld. All fabrication steps are modeled, and the high-level proof testing of the vessels has an important effect on the final WRS state. Finally, cracks are introduced, and service loading applied to determine the effects of WRS on fracture.

Simple Benchmark Problems for Finite Element Weld Residual Stress Simulation

2013 ◽  
Author(s):  
Mike C. Smith ◽  
Steve Bate ◽  
P. John Bouchard
Keyword(s):  
Residual Stress ◽  
Finite Element ◽  
Phase Transformation ◽  
Solid State ◽  
Residual Stresses ◽  
Benchmark Problems ◽  
Transient Temperature ◽  
Beam Specimen ◽  
Weld Residual Stress ◽  
Solid State Phase Transformation

Finite element methods are used increasingly to predict weld residual stresses. This is a relatively complex use of the finite element method, and it is important that its practitioners are able to demonstrate their ability to produce accurate predictions. Extensively characterised benchmark problems are a vital tool in achieving this. However, existing benchmarks are relatively complex and not suitable for analysis by novice weld modellers. This paper describes two benchmarks based upon a simple beam specimen with a single autogenous weld bead laid along its top edge. This geometry may be analysed using either 3D or 2D FE models and employing either block-dumped or moving heat source techniques. The first, simpler, benchmark is manufactured from AISI 316 steel, which does not undergo solid state phase transformation, while the second, more complex, benchmark is manufactured from SA508 Cl 3 steel, which undergoes solid state phase transformation during welding. A number of such beams were manufactured using an automated TIG process, and instrumented with thermocouples and strain gauges to record the transient temperature and strain response during welding. The resulting residual stresses were measured using diverse techniques, and showed markedly different distributions in the austenitic and ferritic beams. The paper presents the information necessary to perform and validate finite element weld residual stress simulations in both the simple austenitic beam and the more complex ferritic beam, and provides performance measures for the austenitic beam problem.

Effects of Weld Geometry on Residual Stress and Crack Driving Force for Centerhole Control Rod Drive Mechanism Nozzles: Part I — Weld Residual Stress

2005 ◽  
Author(s):  
Wentao Cheng ◽  
David L. Rudland ◽  
Gery Wilkowski ◽  
Wallace Norris
Keyword(s):  
Residual Stress ◽  
Residual Stresses ◽  
Driving Force ◽  
Nuclear Regulatory Commission ◽  
Crack Driving Force ◽  
Control Rod ◽  
Drive Mechanism ◽  
Weld Geometry ◽  
Weld Residual Stress ◽  
Regulatory Commission

The U.S. Nuclear Regulatory Commission (NRC) has undertaken a program to assess the integrity of control rod drive mechanism (CRDM) nozzles in existing plants that are not immediately replacing their RPV heads. This two-part paper summarizes some of the efforts undertaken on the behalf of the U.S.NRC for the development of detailed residual stress and circumferential crack-driving force solutions to be used in probabilistic determinations of the time from detectable leakage to failure. In this first paper, the finite element (FE) simulations were conducted to investigate the effects of weld geometry on the residual stresses in the J-weld for a centerhole CRDM nozzle. The variables of weld geometry included three weld heights (weld sizes) and three groove angles for each weld height while keeping the same weld size. The analysis results indicate that the overall weld residual stress decreases as the groove angle increases and higher residual stress magnitude is associated with certain weld height. The results also reveal that the axial residual stresses in the Alloy 600 tube are very sensitive to the weld height, and that the tube hoop stresses above the J-weld root increase with the increasing weld height.

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