Magnitude and Distribution of Retained Residual Stresses in Laboratory Fracture Mechanics Specimens Extracted From Welded Components

2012 ◽  
Author(s):  
R. G. Hurlston ◽  
J. K. Sharples ◽  
A. H. Sherry
Keyword(s):  
Fracture Toughness ◽  
Residual Stress ◽  
Fracture Mechanics ◽  
Residual Stresses ◽  
Structural Integrity ◽  
Specimen Size ◽  
Finite Element Analyses ◽  
Structural Components ◽  
Stress Partitioning ◽  
Material Fracture

Quantifying material fracture toughness properties is an important step in ensuring structural integrity of industrial components. Welding of structural components can cause large magnitudes of residual stress to be generated, which can be defined as a stress that exists in a material when it is under no primary loading. These stresses can be retained in laboratory fracture mechanics testing specimens removed from non-stress relieved welds, making the quantification of valid material fracture toughness difficult. The aim of this paper is to investigate, analytically, the levels and distributions of residual stresses retained in fracture mechanics specimens taken from welded components. This was achieved using parametric finite element analyses. Furthermore, in order to ensure the validity of fracture toughness measurements derived from components that contain residual stress, a robust method for the design of stress-free fracture mechanics specimens is proposed. Significant weld residual stresses have been shown to be retained in certain laboratory specimens post extraction from non stress-relieved welds. The magnitude and distribution of retained residual stress has been shown to be dependant on material properties, specimen size, specimen type and removal location. In addition, the stress partitioning method has been shown to provide a useful approach for estimating the levels and distributions of residual stresses retained in fracture mechanics specimens extracted in certain orientations.

Measurement and Modelling of Residual Stresses in Fracture Toughness Specimens Extracted From Large Components

2008 ◽  
Author(s):  
S. J. Lewis ◽  
S. Hossain ◽  
C. E. Truman ◽  
D. J. Smith ◽  
M. Hofmann
Keyword(s):  
Fracture Toughness ◽  
Residual Stress ◽  
Residual Stresses ◽  
Driving Force ◽  
Large Scale ◽  
Structural Integrity ◽  
Mechanical Load ◽  
Crack Driving Force ◽  
Neutron Diffraction Technique ◽  
Fracture Specimens

A number of previously published works have shown that the presence of residual stresses can significantly affect measurements of fracture toughness, unless they are properly accounted for when calculating parameters such as the crack driving force. This in turn requires accurate, quantitative residual stress data for the fracture specimens prior to loading to failure. It is known that material mechanical properties may change while components are in service, for example due to thermo-mechanical load cycles or neutron embrittlement. Fracture specimens are often extracted from large scale components in order to more accurately determine the current fracture resistance of components. In testing these fracture specimens it is generally assumed that any residual stresses present are reduced to a negligible level by the creation of free surfaces during extraction. If this is not the case, the value of toughness obtained from testing the extracted specimen is likely to be affected by the residual stress present and will not represent the true material property. In terms of structural integrity assessments, this can lead to ‘double accounting’ — including the residual stresses in both the material toughness and the crack driving force, which in turn can lead to unnecessary conservatism. This work describes the numerical modelling and measurement of stresses in fracture specimens extracted from two different welded parent components: one component considerably larger than the extracted specimens, where considerable relaxation would be expected as well as a smaller component where appreciable stresses were expected to remain. The results of finite element modelling, along with residual stress measurements obtained using the neutron diffraction technique, are presented and the likely implications of the results in terms of measured fracture toughness are examined.

A method for the measurement of residual stresses using a fracture mechanics approach

1989 ◽  
Vol 24 (1) ◽  
pp. 23-30 ◽  
Author(s):  
K J Kang ◽  
J H Song ◽  
Y Y Earmme
Keyword(s):  
Residual Stress ◽  
Finite Element ◽  
Stress Distribution ◽  
Fracture Mechanics ◽  
Residual Stresses ◽  
Residual Stress Distribution ◽  
The State ◽  
Two Dimensional ◽  
Finite Element Analyses ◽  
Simple Method

A simple method for measuring residual stresses in a plate is described. In this method residual stresses are evaluated using a fracture mechanics approach, that is, the strains or displacements measured at a point on the edge of a plate as a crack is introduced and extended from the edge are used to deduce the state of stresses that existed in the uncracked plate. Through finite element analyses and experiments this method is shown to be valid and effective for measuring the two-dimensional residual stress distribution of a welded plate.

Development of an Alternative Approach to the Acquisition of Fracture Toughness in Laboratory Specimens Containing Residual Stress

2010 ◽  
Author(s):  
R. G. Hurlston ◽  
J. Sharples ◽  
A. H. Sherry
Keyword(s):  
Fracture Toughness ◽  
Residual Stress ◽  
Residual Stresses ◽  
Pressure Vessels ◽  
Relaxation Methods ◽  
Edge Notch ◽  
Material Fracture ◽  
Crack Tip Constraint ◽  
Conservative Values ◽  
Welding Processes

Welding is an essential process in many industries and is used for both the production and repair of nuclear plant, notably pressure vessels and piping. However, traditional welding processes can cause large amounts of residual stress to be generated within the structure. Current methodology for evaluating fracture toughness from specimens containing residual stresses, e.g. BS7448, relies heavily on engineering judgement. This can result in inaccurate, albeit generally conservative, values of fracture toughness being used in defect assessments. The aim of the work presented in this paper is to investigate the use of constraint based fracture mechanics to quantify ‘unique material fracture toughness’ from laboratory specimens containing residual stresses using the ‘apparent fracture toughness’ values derived from standard fracture toughness testing. This is achieved using an analytical knowledge of the effect of residual stress on crack-tip constraint and, if incorporated into fracture toughness methodology, remove the need for unreliable residual stress relaxation methods when using weld coupons for fracture toughness assessments. A novel mechanical method for generating residual stresses in single edge notch bend specimens has been assessed analytically. In this paper, computational analysis of low and high constraint bend specimens, each with and without residual stress, is used to demonstrate the principle and validity of the proposed method.

Investigation Into the Effect of Residual Stress on Crack-Tip Constraint and Brittle Fracture

2011 ◽  
Author(s):  
R. G. Hurlston ◽  
J. K. Sharples ◽  
A. H. Sherry
Keyword(s):  
Fracture Toughness ◽  
Residual Stress ◽  
Fracture Mechanics ◽  
Brittle Fracture ◽  
Plastic Strain ◽  
Residual Stresses ◽  
Crack Tip ◽  
Pressure Vessel Steel ◽  
Vessel Steel ◽  
Unique Material

It is well known that the level of constraint of material at a crack-tip during loading can affect the apparent fracture toughness of components and structures. The effects of geometry and loading on the development of constraint are well defined. Recent research has shown that residual stresses, defined as stresses existing in a material when it is under no primary load, present in the crack-tip region can also affect constraint. However, the effects of this on fracture toughness are not, currently, well understood. The aim of this paper is to investigate the use of constraint based fracture mechanics to quantify unique material fracture toughness curves in two-parameter fracture mechanics type analyses. A novel method for generating residual stresses in single edge notch bend specimens, with minimal associated crack-tip plastic strain, has been devised analytically. Experimental validation has been undertaken to investigate the applicability of constraint based fracture mechanics to characterise the effect of residual stress on brittle fracture of a pressure vessel steel. The results suggest that the use of a unique material toughness curve is possible, certainly when there is a negligible effect of prior plastic strain in the crack-tip region.

Characterisation of Residual Stress Levels Retained in Fracture Mechanics Specimens Machined From Non-Stress Relieved Welds

2013 ◽  
Author(s):  
Robert J. A. McCluskey ◽  
Gang Zheng ◽  
Andrew H. Sherry ◽  
David J. Smith
Keyword(s):  
Fracture Toughness ◽  
Residual Stress ◽  
Fracture Mechanics ◽  
Residual Stresses ◽  
Hole Drilling ◽  
Deep Hole ◽  
Deep Hole Drilling ◽  
Integrity Assessment ◽  
Weld Residual Stress ◽  
Stress Levels

The structural integrity assessment of weldments in engineering components, including piping, is dependent upon the acquisition of valid fracture toughness data. Test standards provide guidance for the preparation of fracture mechanics specimens machined from welds, recognising that under some circumstances retained weld residual stress in the specimens may influence the test, for example, by impairing the ability to establish a valid fatigue pre-crack. To date, however, there are little experimental data quantifying the level and distribution of retained residual stress in fracture mechanics specimens. This paper describes an experimental study characterising the residual stresses retained in single-edge notched bend specimens machined from a non stress-relieved, narrow-gap Tungsten Inert Gas welded pipe, manufactured from 304L stainless steel. The original weld residual stress field was characterised using neutron diffraction and deep hole drilling. The residual stress levels retained in the test specimens were subsequently quantified using deep hole drilling. The results indicated that reasonable levels of residual stress are retained within specimens, although for high toughness, ductile steel, this is insufficient to influence the fracture toughness measurement. The results, however, have implications for testing non stress-relieved welds manufactured from low toughness materials, where retained residual stresses could unduly influence fracture toughness measurements.

Japanese Research Activities on Offshore Fracture Mechanics Applications

1988 ◽  
Vol 41 (2) ◽  
pp. 96-106 ◽  
Author(s):  
S. Machida ◽  
H. Yajima ◽  
M. Toyosada ◽  
Y. Hagiwara ◽  
K. Kajimoto
Keyword(s):  
Fracture Toughness ◽  
Fracture Mechanics ◽  
Structural Integrity ◽  
Local Strain ◽  
Practical Method ◽  
Offshore Structures ◽  
Structural Components ◽  
Research Activities ◽  
Fracture Assessment ◽  
Size Evaluation

The brittle fracture, for its catastrophic nature, is one of the most important factors for designing offshore structures especially operating in the cold sea. Fracture mechanics method can provide a useful tool to maintain the reliability of structural integrity. This paper gives descriptions on a proposed method for fracture assessment with experimental verifications, and also informations from some recent Japanese research activities associated with the application of fracture mechanics to the offshore structures, i.e. initial defect size evaluation, a practical method for evaluation of the local strain in strain concentrated structural components, effect of strain rate on fracture toughness and fracture toughness of weldments.

Analysis on Critical CTOD of Long-Term Used Penstock

2017 ◽  
Vol 741 ◽  
pp. 57-62
Author(s):  
Fumito Kawamura ◽  
Masazumi Miura ◽  
Ryuichiro Ebara ◽  
Keiji Yanase
Keyword(s):  
Fracture Toughness ◽  
Structural Integrity ◽  
Steel Structures ◽  
Chemical Compositions ◽  
Structural Components ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Critical Crack ◽  
Crack Tip Opening

Many studies have been conducted to characterize the fracture toughness of structural steels and their welded joints. However, most studies focus on newly developed steels, and the number of studies on the fracture toughness of long-term used steels in structural components is rather limited. Furthermore, a lack of data on the fracture toughness causes difficulties in evaluating the structural integrity of existing steel structures. In this study, CTOD tests were performed to characterize the fracture toughness of penstock that has been in service for 50 years. By measuring the critical crack tip opening displacement in conjunction with analysis for chemical compositions, the characteristics of fracture toughness were investigated.

An Investigation of the Stress Intensity Factor Along a Corner Crack in Pressurizer Vent Nozzle Penetration Weld

2009 ◽  
Author(s):  
Sang-Min Lee ◽  
Jeong-Soon Park ◽  
Jin-Su Kim ◽  
Young-Hwan Choi ◽  
Hae-Dong Chung
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Fracture Mechanics ◽  
Intensity Factor ◽  
Plastic Zone ◽  
Structural Integrity ◽  
Operating Conditions ◽  
Corner Crack ◽  
Elastic Plastic ◽  
Material Fracture

Elastic-plastic fracture mechanics as well as linear-elastic fracture mechanics may be applied to evaluate a flaw in ferritic low alloy steel components for operating conditions when the material fracture resistance is controlled by upper shelf toughness behavior. In this paper, the distribution of the stress intensity factor along a corner crack using elastic-plastic fracture mechanics technique is investigated to assess the effect of a structural factor on mechanical loads in pressurizer vent nozzle penetration weld. For this purpose, the stress intensity factor and plastic zone correction of a corner crack are calculated under internal pressure, thermal stress and residual stress in accordance with Electric Power Research Institute (EPRI) equation and Irwin’s approach, respectively. The resulting stress intensity factor and plastic zone correction were compared with those obtained from Structural Integrity Associates (SIA) and Kinectrics, and were observed to be good agreement with Kinectrics results.

Estimation of Through-Wall Cracking Frequency of RPV Under PTS Events Using PFM Analysis Method for Identifying Conservatism Included in Current Japanese Code

2014 ◽  
Author(s):  
Kazuya Osakabe ◽  
Koichi Masaki ◽  
Jinya Katsuyama ◽  
Genshichiro Katsumata ◽  
Kunio Onizawa
Keyword(s):  
Fracture Toughness ◽  
Fracture Mechanics ◽  
Crack Initiation ◽  
Structural Integrity ◽  
Probabilistic Approach ◽  
Pressure Vessels ◽  
Assessment Procedure ◽  
Analysis Method ◽  
Integrity Assessment ◽  
The U.S

To assess the structural integrity of reactor pressure vessels (RPVs) during pressurized thermal shock (PTS) events, the deterministic fracture mechanics approach prescribed in Japanese code JEAC 4206-2007 [1] has been used in Japan. The structural integrity is judged to be maintained if the stress intensity factor (SIF) at the crack tip during PTS events is smaller than fracture toughness KIc. On the other hand, the application of a probabilistic fracture mechanics (PFM) analysis method for the structural reliability assessment of pressure components has become attractive recently because uncertainties related to influence parameters can be incorporated rationally. A probabilistic approach has already been adopted as the regulation on fracture toughness requirements against PTS events in the U.S. According to the PFM analysis method in the U.S., through-wall cracking frequencies (TWCFs) are estimated taking frequencies of event occurrence and crack arrest after crack initiation into consideration. In this study, in order to identify the conservatism in the current RPV integrity assessment procedure in the code, probabilistic analyses on TWCF have been performed for certain model of RPVs. The result shows that the current assumption in JEAC 4206-2007, that a semi-elliptic axial crack is postulated on the inside surface of RPV wall, is conservative as compared with realistic conditions. Effects of variation of PTS transients on crack initiation frequency and TWCF have been also discussed.

scholarly journals Residual Stress and Microstructure of a Ti-6Al-4V Wire Arc Additive Manufacturing Hybrid Demonstrator

Metals ◽  
2020 ◽  
Vol 10 (6) ◽  
pp. 701
Author(s):  
Tatiana Mishurova ◽  
Benjamin Sydow ◽  
Tobias Thiede ◽  
Irina Sizova ◽  
Alexander Ulbricht ◽  
...  
Keyword(s):  
Residual Stress ◽  
Additive Manufacturing ◽  
Residual Stresses ◽  
Structural Integrity ◽  
Hybrid Approach ◽  
Aerospace Applications ◽  
Machined Parts ◽  
Functional Features ◽  
Tool Set ◽  
Wire Arc Additive Manufacturing

Wire Arc Additive Manufacturing (WAAM) features high deposition rates and, thus, allows production of large components that are relevant for aerospace applications. However, a lot of aerospace parts are currently produced by forging or machining alone to ensure fast production and to obtain good mechanical properties; the use of these conventional process routes causes high tooling and material costs. A hybrid approach (a combination of forging and WAAM) allows making production more efficient. In this fashion, further structural or functional features can be built in any direction without using additional tools for every part. By using a combination of forging basic geometries with one tool set and adding the functional features by means of WAAM, the tool costs and material waste can be reduced compared to either completely forged or machined parts. One of the factors influencing the structural integrity of additively manufactured parts are (high) residual stresses, generated during the build process. In this study, the triaxial residual stress profiles in a hybrid WAAM part are reported, as determined by neutron diffraction. The analysis is complemented by microstructural investigations, showing a gradient of microstructure (shape and size of grains) along the part height. The highest residual stresses were found in the transition zone (between WAAM and forged part). The total stress range showed to be lower than expected for WAAM components. This could be explained by the thermal history of the component.

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