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.

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.

Stress intensity factor and fatigue analysis of cracked cruciform welded joints strengthened by CFRP sheets considering the welding residual stress

2020 ◽  
Vol 154 ◽  
pp. 106818
Author(s):  
Zhiyu Jie ◽  
Wujun Wang ◽  
Rufeng Fang ◽  
Ping Zhuge ◽  
Yong Ding
Keyword(s):  
Residual Stress ◽  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Welded Joints ◽  
Fatigue Analysis ◽  
Welding Residual Stress ◽  
Cfrp Sheets

Influence of Welding Residual Stress on Stress Intensity Factor of Two-Dimensional Cracks

2011 ◽  
Vol 299-300 ◽  
pp. 966-969
Author(s):  
Jin Song Yang ◽  
Wei Jiang
Keyword(s):  
Residual Stress ◽  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Stress Field ◽  
Crack Propagation ◽  
Crack Front ◽  
Welding Residual Stress ◽  
Two Dimensional ◽  
Residual Stress Field

In this paper, a butt-welded plate with cracks of different sizes and locations was used to analyze the crack propagation in the residual stress field. A two-dimensional finite element model was established to study the distributions of stress intensity factor along crack front in the residual stress field. Several cases with different crack lengths and angles were investigated. It was found that the distributions of stress intensity factor along crack front were very sensitive to residual stress. The methods and results presented in this paper are capable of providing a reference for the efficient assessment of the effect of residual stress field on the crack propagation behavior. It also implies that proper welding procedures are required for acceptable residual stress distributions to ensure prolonged service life of weldments.

Evaluation of stress intensity factor for a surface cracked butt welded joint based on real welding residual stress

2017 ◽  
Vol 138 ◽  
pp. 123-139 ◽  
Author(s):  
Ramy Gadallah ◽  
Naoki Osawa ◽  
Satoyuki Tanaka
Keyword(s):  
Residual Stress ◽  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Welded Joint ◽  
Welding Residual Stress

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.

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