An Improved Method of Evaluating the Stress Intensity Factor for a Penetrating Circumferential Defect in a Self-Balancing Residual Stress Field in a Weld

2016 ◽  
Author(s):  
Liwu Wei ◽  
Jinhua Shi ◽  
John Buckland
Keyword(s):  
Residual Stress ◽  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Stress Distribution ◽  
Intensity Factor ◽  
Stress Component ◽  
Residual Stress Distribution ◽  
The Self ◽  
Welding Residual Stress ◽  
Stress Profiles

It is required to determine the stress intensity factor (SIF) contributed from a through-wall residual stress distribution when assessing the structural integrity of a welded joint containing flaws. By decomposing the through-wall residual stress distribution into a membrane stress component (σm), bending stress component (σb) and self-balancing stress component (σsb), the total SIF from the through-wall residual stress distribution (Ktotal) comprises Km (due to σm), Kb (due to σb) and Ksb (due to σsb). Km and Kb can be relatively easy to determine as there are standard solutions available for common geometries and flaw types. However, it is not straightforward to calculate Ksb owing to the arbitrary distribution of the self-balancing stress component. In particular, no SIF solutions are available for a through-wall penetrating defect in a plate or a cylinder subjected to an arbitrary through-wall self-balancing stress distribution other than for three special distributions (cosine, triangular and square distributions). Neglecting the contribution of σsb to the Ktotal could significantly underestimate the crack driving force, thus leading to a non-conservative assessment of limiting defect size. Therefore, the calculation of Ksb for a though-wall penetrating defect in a plate or a cylinder under an arbitrary stress distribution is of the primary concern in this work. Understandably, finite element analysis (FEA) can be used to calculate the Ksb in these situations, but it is costly to perform such analysis. In this work, a simple method is proposed for estimating Ksb due to the self-balancing component which has a different distribution from the cosine, triangular and square distributions. This method is an extension of the approach adopted by Annex Q, BS 7910:2013 in dealing with the calculations of Ksb resulted from the σsb profiles which are decomposed from the proposed upper bound through-wall welding residual stress profiles. Some typical through-wall welding residual stress distributions are investigated with the proposed method in estimation of the Ksb for a through-wall penetrating defect in a plate or a cylinder. Discussion and highlights are given in the aspects of the effects of welding residual stress profiles on SIFs, the implications for limiting defect sizes, and the likelihood of underestimating the Ksb when using the equation established in R6 Revision 4 with a cosine distribution for any other distributions.

The Correction of Stress Intensity Factor for Crack Growth Evaluation Under Steep Residual Stress Distribution and Steep Yield Strength Distribution

2013 ◽  
Author(s):  
Tetsuo Yasuoka ◽  
Yoshihiro Mizutani ◽  
Akira Todoroki
Keyword(s):  
Residual Stress ◽  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Stress Distribution ◽  
Intensity Factor ◽  
Yield Strength ◽  
Crack Tip ◽  
Strength Distribution ◽  
Residual Stress Distribution ◽  
Growth Evaluation

Welds and heat affected zones have the distribution of the residual stress or the yield strength. The crack growth evaluation is conventionally conducted using stress intensity factor in those regions. However, the stress intensity factor may be invalid when the residual stress distribution or yield strength distribution changes in the vicinity of a crack tip. The reason is that the distributions around the crack tip affect the plastic zone size and the stress intensity factor inappropriately represents the stress state in the vicinity of a crack tip. In this study, the residual stress distribution and yield strength distribution was assumed along the crack propagation path and the validity of the stress intensity factor was discussed on that condition. As a result, the stress intensity factor tended to be invalid when the steep residual stress distribution or the steep yield strength distribution. When the steep distribution exists, the crack growth evaluation should be conducted using a parameter considering the elastoplastic behavior near the crack tip. For that purpose, the authors proposed new method of the plastic zone correction using a differential term of the stress intensity factor. The new method was demonstrated through the case study for stress corrosion cracking of nuclear power plants.

Stress Intensity Factors due to Residual Stresses in Thin-Walled Girth-Welded Pipes

1981 ◽  
Vol 103 (1) ◽  
pp. 66-75 ◽  
Author(s):  
E. F. Rybicki ◽  
R. B. Stonesifer ◽  
R. J. Olson
Keyword(s):  
Residual Stress ◽  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Stress Distribution ◽  
Intensity Factor ◽  
Crack Growth ◽  
Residual Stress Distribution ◽  
Intensity Factors ◽  
Thin Walled Pipe ◽  
Thin Walled

The effect of a girth-weld-induced residual stress field on the linear elastic fracture mechanics of a thin-walled pipe is examined. The procedure for using the residual stress distribution to compute KI and KII for a circumferential crack which is growing radially is described. In addition to the two-pass girth weld, stress intensity factors are computed for a residual stress distribution in a flat plate and for a hypothetical residual stress state in a second thin-walled pipe. The computed stress intensity factor for the flat plate geometry and its residual stress distribution are compared with a solution from the literature as a check on the computational procedure. The through-the-thickness residual stress distribution due to the two-pass girth weld is similar to a half-cosine wave. For purposes of comparison, the hypothetical through-the-thickness distribution selected for the second pipe is similar to a full cosine wave. The stress intensity factor is presented as a function of crack depth for a crack initiating on the inner surface of the pipe. The redistribution of residual stresses due to crack growth is also shown for selected crack lengths. The study shows that residual stress-induced crack growth in pipes can be significantly different from that in flat plates due to the possibility of locked-in residual bending moments in the pipe. These locked-in moments can have effects similar to externally applied loads and can either promote or restrain crack growth. A residual stress distribution is illustrated in which crack growth, if initiated, would continue through the entire wall. Also, a residual stress distribution is illustrated for which the crack could arrest after a certain amount of growth.

The Effects of Residual Stress Distribution and Component Geometry on the Stress Intensity Factor of Surface Cracks

2011 ◽  
Vol 133 (1) ◽  
Author(s):  
Katsumasa Miyazaki ◽  
Masahito Mochizuki
Keyword(s):  
Residual Stress ◽  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Stress Distribution ◽  
Intensity Factor ◽  
Stress Field ◽  
Crack Growth ◽  
Residual Stress Distribution ◽  
Surface Cracks ◽  
Intensity Factors

The stress intensity factor estimated by the appropriate modeling of components is essential for the evaluation of crack growth behavior in stress corrosion cracking. For the appropriate modeling of a welded component with a crack, it is important to understand the effects of residual stress distribution and the geometry of the component on the stress intensity factor of the surface crack. In this study, the stress intensity factors of surface cracks under two assumed residual stress fields were calculated. As residual stress field, a bending type stress field (tension-compression) and a self-equilibrating stress field (tension-compression-tension) through the thickness were assumed, respectively. The geometries of the components were plate and piping. The assumed surface cracks for those evaluations were a long crack in the surface direction and a semi-elliptical surface crack. In addition, crack growth evaluations were conducted to clarify the effects of residual stress distribution and the geometry of the component. Here, the crack growth evaluation means simulating increments of crack depth and length using crack growth properties and stress intensity factors. The effects of residual stress distribution and component geometry on the stress intensity factor of surface cracks and the appropriate modeling of cracked components are discussed by comparing the stress intensity factors and the crack growth evaluations for surface cracks under residual stress fields.

The Effects of Residual Stress Distribution and Geometry of Component on the Stress Intensity Factor of Surface Crack

2005 ◽  
Author(s):  
Katsumasa Miyazaki ◽  
Masahito Mochizuki
Keyword(s):  
Residual Stress ◽  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Stress Distribution ◽  
Intensity Factor ◽  
Stress Field ◽  
Crack Growth ◽  
Surface Crack ◽  
Residual Stress Distribution ◽  
Intensity Factors

The stress intensity factor estimated by using the appropriate modeling of components is essential for evaluation of crack growth behavior in stress corrosion cracking. For the appropriate modeling of welded components with a crack, it is important to understand the effects of residual stress distribution and geometry of component on the stress intensity factor of surface crack. In this study, the stress intensity factors of surface crack under two assumed residual stress fields were calculated. As residual stress field, the bending type stress field (tension-compression) and the self-equilibrating stress field (tension-compression-tension) through the thickness were assumed. The geometries of components were plate and piping. The assumed surface cracks for evaluations were long crack in surface direction and semi-elliptical surface crack. Furthermore, the crack growth evaluations were conducted to understand the effects of residual stress distribution and geometry of component. Here, the crack growth evaluation means the simulation of increments of crack depth and length by using the crack growth property and stress intensity factors. From the comparison of stress intensity factors and crack growth evaluation for surface crack under residual stress field, the effects of residual stress distribution and geometry of component on the stress intensity factor of surface crack and appropriate modeling of cracked components were discussed.

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.

Study on Evaluation Procedure for Calculating the Stress Intensity Factor of Flaws Beneath RPV Cladding During Pressurised Thermal Shock Events by FE Analysis

2016 ◽  
Author(s):  
Hiroyuki Sakamoto ◽  
Takatoshi Hirota ◽  
Naoki Ogawa
Keyword(s):  
Residual Stress ◽  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Thermal Shock ◽  
Alloy Steel ◽  
Fe Analysis ◽  
Welding Residual Stress ◽  
Low Alloy Steel ◽  
Elastic Plastic

Elastic-plastic finite element (FE) analysis is performed to determine the plastic behavior of the reactor pressure vessel (RPV) inner surface caused by rapid cooling during pressurized thermal shock (PTS) events. However, as the J-integral is not path-independent for elastic-plastic material in the unloading process, it is necessary to apply a suitable correction method using elastic material. In addition, it is also necessary to consider the effect of the welding residual stress appropriately. Therefore, we investigated the stress intensity factor derived from FE analysis based on a model consisting of elastic-plastic cladding and linear elastic low-alloy steel with subsequent plastic zone correction, since the stress level of low-alloy steel remains within the elastic region except the crack front during a PTS event. Furthermore, we examined whether the stress mapping method is applicable for reflecting the effect of welding residual stress in FE analysis, even though the plastic strain generated during welding is ignored.

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