Measuring and Predicting the Effects of Residual Stresses on Crack Propagation

2006 ◽  
Vol 524-525 ◽  
pp. 77-82 ◽  
Author(s):  
A. Shterenlikht ◽  
Danut Stefanescu ◽  
Matthew E. Fox ◽  
Kerry Taylor ◽  
Joao Quinta da Fonseca ◽  
...  
Keyword(s):  
Residual Stresses ◽  
Driving Force ◽  
Fatigue Cracking ◽  
Image Correlation ◽  
Fe Model ◽  
Fe Modelling ◽  
Crack Driving Force ◽  
Before And After ◽  
Residual Strains ◽  
Good Agreement

This article presents the first part of a study on the interaction between residual stresses and crack driving force. Blunt notched CT specimens were pre-strained to introduce residual stresses at the notch, where a crack is subsequently introduced. FE modelling is used to model the specimen preload and pre-cracking. Modelling predictions are validated by two different methods. The total predicted surface residual strains are compared to image correlation measurements. The predicted residual strains were measured using neutron diffraction, both before and after fatigue cracking. The residual strain profiles show good agreement with the 3D FE model in the far field but the peak strains measured near the notch are smaller those predicted. This is a result of the low spatial resolution of the technique.

scholarly journals Short fatigue crack growth in welded joints described by the effective cyclic J-integral

2018 ◽  
Vol 165 ◽  
pp. 09002
Author(s):  
Désiré Tchoffo Ngoula ◽  
Michael Vormwald
Keyword(s):  
Fatigue Crack ◽  
Fatigue Life ◽  
Fatigue Crack Growth ◽  
Residual Stresses ◽  
Crack Growth ◽  
Welded Joints ◽  
Driving Force ◽  
J Integral ◽  
Crack Driving Force ◽  
Short Fatigue Crack

The purpose of the present contribution is to predict the fatigue life of welded joints by using the effective cyclic J-integral as crack driving force. The plasticity induced crack closure effects and the effects of welding residual stresses are taken into consideration. Here, the fatigue life is regarded as period of short fatigue crack growth. The node release technique is used to perform finite element based crack growth analyses. For fatigue lives calculations, the effective cyclic J-integral is employed in a relation similar to the Paris (crack growth) equation. For this purpose, a specific code was written for the determination of the effective cyclic J-integral for various lifetime relevant crack lengths. The effects of welding residual stresses on the crack driving force and the calculated fatigue lives are investigated. Results reveal that the influence of residual stresses can be neglected only for large load amplitudes. Finally, the predicted fatigue lives are compared with experimental data: a good accordance between both results is achieved.

An Analysis of Residual Stress Improvement for a Dissimilar Metal Nozzle-to-Pipe Weld by Using the Heat Sink Method

2008 ◽  
Author(s):  
J.-S. Park ◽  
J.-M. Kim ◽  
G.-H. Sohn ◽  
Y.-H. Kim
Keyword(s):  
Residual Stress ◽  
Residual Stresses ◽  
Heat Sink ◽  
Nuclear Power ◽  
Power Plants ◽  
Base Alloy ◽  
Fatigue Cracking ◽  
Hole Drilling ◽  
Fe Model ◽  
Dissimilar Metal

This study is concerned with the mechanics analysis of residual stress improvement by the heat sink method applied to a dissimilar metal weld (DMW) for the use in nuclear power plants. The DMW joint considered here is composed of ferritic low-alloy steel nozzle, austenitic stainless steel safe-end, and nickel-base alloy A52 weld metal. To prepare the DMW joint with a narrow-gap, the gas tungsten arc welding (GTAW) process is utilized, and the heat sink method is employed to control thermal gradients developed in the critical region of work pieces during welding. Weld residual stresses are computed by the non-linear thermal elasto-plastic analysis using the axisymmetric finite element (FE) model, for which temperature-dependent thermal and mechanical properties of the materials are considered. A full-scale mock-up test is conducted to validate analytical solution for the DMW joint, and residual stresses are measured by using the hole-drilling method. Results of the FE modeling and mock-up test for the DMW joint are compared and effects of the heat sink method are discussed. It is found that a significant amount of residual compressive stresses can be developed on the inner surface of the DMW joint by using the heat sink method, which can effectively reduce the susceptibility of the welded materials to stress corrosion or fatigue cracking.

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.

An assessment of the Sachs method for measuring residual stresses in cold worked fastener holes

1998 ◽  
Vol 33 (4) ◽  
pp. 263-274 ◽  
Author(s):  
D J Smith ◽  
C G C Poussard ◽  
M J Pavier
Keyword(s):  
Finite Element ◽  
Residual Stresses ◽  
Cold Working ◽  
Element Model ◽  
Fe Model ◽  
Working Process ◽  
Element Analysis ◽  
Near Surface ◽  
Cold Worked ◽  
Good Agreement

Measurements of residual stresses in 6 mm thick aluminium alloy 2024 plates containing 4 per cent cold worked fastener are made using the Sachs method. The measurements are made on discs extracted from the plates. The measured tangential residual stress distribution adjacent to the hole edge are found to be affected by the disc diameter. The measured residual stresses are also in good agreement with averaged through-thickness predictions of residual stresses from an axisymmetric finite element (FE) model of the cold working process. A finite element analysis is also conducted to simulate disc extraction and then the Sachs method. The measured FE residual stresses from the Sachs simulation are found to be in good agreement with the averaged through-thickness predicted residual stresses. The Sachs simulation was not able to reproduce the detailed near-surface residual stresses found from the finite element model of the cold working process.

Simulating Residual Stresses Using a Modified Wedge-Loaded Compact Tension Specimen

2013 ◽  
Author(s):  
P. Kapadia ◽  
H. Zhou ◽  
C. M. Davies ◽  
R. C. Wimpory ◽  
K. M. Nikbin
Keyword(s):  
Stainless Steel ◽  
Residual Stresses ◽  
Crack Growth ◽  
Crack Tip ◽  
Compact Tension ◽  
Image Correlation ◽  
Internal Stresses ◽  
Fe Model ◽  
Creep Ductility ◽  
Crack Tip Plasticity

Residual stresses are induced in components when fabrication processes produce internal stresses or local deformation and cause accelerated creep damage and cracking during service at elevated temperatures. A method of inducing residual stresses in laboratory fracture specimens is proposed where an oversized wedge is inserted into the crack mouth of a compact tension, C(T), type specimen. In this way the extent of internal stresses can be controlled in order to minimise the level of crack tip plasticity which inherently reduces the remaining strain to failure. Numerical simulations of wedge insertion into specimens made of 316H austenitic stainless steel have been developed to calibrate the wedge insertion process. These models have been experimentally validated using surface strains measured during the wedge insertion, using Digital Image Correlation (DIC), and Neutron Diffraction (ND) measurements. The validated Finite Element (FE) model is used to determine the wedge insertion depth required to maximise the residual stresses without causing significant crack tip plasticity. The validated numerical simulation is used to determine the wedge insertion depths of further wedge-loaded C(T) specimens made from uniformly pre-compressed 316H stainless steel. The reduced creep ductility of this material increases the rate of crack growth under creep conditions. This method of inducing residual stresses with limited crack tip plasticity allows creep crack growth under simulated secondary loading conditions to be investigated without the influence of non-uniform creep ductility caused by work hardening.

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.

Displacement Controlled Stress Intensity Factor Solutions for Structural Integrity Assessments of Welding Residual Stress Distributions

2008 ◽  
Author(s):  
Adam Toft ◽  
David Beardsmore ◽  
Colin Madew ◽  
Huego Teng ◽  
Mark Jackson
Keyword(s):  
Residual Stress ◽  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Residual Stresses ◽  
Weight Function ◽  
Driving Force ◽  
Welding Residual Stress ◽  
Crack Plane ◽  
Crack Driving Force

Within the UK nuclear industry the assessment of fracture in pressurised components is often carried out using procedures to calculate the margin of safety between a lower-bound fracture toughness and the crack driving force. Determination of the crack driving force usually requires the calculation of elastic stress intensity factor solutions for primary loads and secondary loads arising from weld residual stresses and/or thermal stresses. Within established UK assessment procedures weight function solutions are available which allow the stress intensity factors to be calculated from the through-wall opening-mode stress distribution in an uncracked component. These weight-function solutions are generally based on models where either no boundary condition is applied, or where one is applied at a distance either side of the crack plane that is very long compared with the crack size and wall thickness. Such solutions do not take into account any reduction in the stress field that might occur as the distance from the crack faces increases. Weld residual stress fields may often be expected to reduce in this manner. A separate, earlier study has shown that the stress intensity factor for a cracked plate loaded in displacement control decreases substantially as the loading plane is moved closer to the crack plane. It would therefore be expected that a similar reduction in stress intensity factor would be obtained for a residual stress analysis when displacement boundary conditions are imposed at a distance relatively close to the crack plane. This paper describes an investigation of the differences, particularly in terms of a reduction in calculated stress intensity factor, which may arise from application of displacement controlled stress intensity factor solutions, as compared with load controlled solutions, when considering weld residual stresses. Consideration is also given as to how new displacement controlled stress intensity factor solutions could be developed by modification of existing load controlled solutions.

Investigation of Transformation Induced Plasticity and Residual Stress Analysis in Stainless Steel Welds

2010 ◽  
Author(s):  
H. Dai ◽  
R. Moat ◽  
A. F. Mark ◽  
P. J. Withers
Keyword(s):  
Residual Stress ◽  
Stainless Steel ◽  
Residual Stresses ◽  
Base Plate ◽  
Element Model ◽  
Image Correlation ◽  
Fe Model ◽  
Transformation Induced Plasticity ◽  
Stress Relieving ◽  
Steel Welds

The aim of this paper is to investigate the implications for weld residual stresses of martensitic transformation induced plasticity (TRIP) in stainless steel filler metal. The TRIP strains occurring during cooling under different uniaxial load levels have been obtained using digital image correlation (DIC) for a residual stress relieving low transformation temperature weld filler known to show little variant selection on cooling as a function of stress. In order to investigate the efficacy of current FE transformation plasticity models of different levels of sophistication in simulating TRIP strains, a finite element model, incorporating the so-called Greenwood-Johnson effect was used to simulate these constrained dilatometry measurements. To assess the implications of the different approaches to modelling TRIP for weld residual stresses, the TRIP coefficients determined from the above experiments were incorporated into an FE model simulating the residual stresses that are generated when a single weld bead is deposited on to a stainless steel base plate. It was found that including TRIP had a significant influence on the weld stresses, while the differences between the models were much smaller.

Residual Stresses in Al2O3/SiC (Whisker) Composites Containing Interfacial Carbon Films

1988 ◽  
Vol 32 ◽  
pp. 471-479 ◽  
Author(s):  
Alias Abuhasan ◽  
Paul K. Predecki
Keyword(s):  
Residual Stresses ◽  
Carbon Coating ◽  
Carbon Film ◽  
Carbon Films ◽  
X Ray Diffraction ◽  
The Matrix ◽  
Sic Whiskers ◽  
Residual Strains ◽  
Residual Microstresses ◽  
Good Agreement

AbstractResidual strains and stresses were measured in hot-pressed α-Al2O3 composites containing 25 wt% β (cubic) SiC whiskers with and without a 50-100Å thick carbon coating. X-ray diffraction methods were used including the separation of macrostresses from the microstresses in the -Al2O3 and SiC phases by the method of Noyan and Cohen. The presence of the carbon coating on the whiskers reduced the magnitude of the residual microstresses in the whiskers by ˜13% and in the matrix by ˜10%. The measured residual stresses in the whiskers and the reduction due to the carbon film were in good agreement with calculations from recent models proposed by Hsueh, Becher and Angelini, and by Li and Bradt.

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