Fracture Assessment of Structural Component With Residual Stress on the Basis of the Weibull Stress Criterion

2008 ◽  
Author(s):  
Yoichi Yamashita ◽  
Fumiyoshi Minami
Keyword(s):  
Fracture Toughness ◽  
Residual Stress ◽  
Structural Component ◽  
Welding Residual Stress ◽  
Fracture Toughness Test ◽  
Stress Criterion ◽  
Conventional Procedure ◽  
Calculation Results ◽  
Fracture Assessment ◽  
Weibull Stress

This paper studies the method for estimating the residual stress effects on brittle fracture of structural component based on the Weibull stress criterion. Experiments show that the critical CTOD and the critical load of wide plate with welding residual stress are apparently smaller than those of wide plate without residual stress. It has been found that the critical CTODs of wide plate with and without residual stress can be predicted from the 3PB fracture toughness test results based on the Weibull stress criterion. Constraint loss effects on CTOD of wide plate with residual stress can be assessed by the equivalent CTOD ratio. The equivalent CTOD ratio β is defined as the ratio, β = δ/δWP, where δ and δWP, are CTODs of the standard fracture toughness specimen and wide plate, respectively, at the same level of the Weibull stress. Calculation results of beta are also shown for various residual stress levels and crack lengh based on the Weibull stress criterion. Fracture assessment results using β are shown within the context of CTOD design curve. An excessive conservatism observed in the conventional procedure is reasonably reduced by applying the equivalent CTOD ratio, β.

Fracture Assessment of Welded Joint With Geometrical Discontinuity Using the Weibull Stress

2006 ◽  
Author(s):  
Satoshi Igi ◽  
Takahiro Kubo ◽  
Masayoshi Kurihara ◽  
Fumiyoshi Minami
Keyword(s):  
Fracture Toughness ◽  
Brittle Fracture ◽  
Welded Joint ◽  
Fracture Toughness Test ◽  
Geometrical Condition ◽  
Stress Criterion ◽  
Toughness Test ◽  
Fracture Assessment ◽  
Geometrical Discontinuity ◽  
Weibull Stress

Recently the Weibull stress is used as a fracture driving force parameter in fracture assessment. The Weibull stress is derived from a statistical analysis of local instability of micro cracks leading to brittle fracture initiation. The critical Weibull stress is expected to be a critical parameter independent of the geometrical condition of specimens. Fracture toughness test using 3-point bending and tensile tests of welded joint specimens with geometrical discontinuity were conducted in order to study the applicability of fracture assessment procedure based on Weibull stress criterion. Steel plates prepared for this study had tensile strength of 490 MPa for structural use. Two kinds of welded joint specimens, “one-bead welded joint” and “multi-pass welded joint” were prepared for fracture toughness test by using gas metal are welding. In tensile test specimen, corner flaws were introduced at the geometrical discontinuity part at where stress concentration is existed. Three dimensional elastoplastic finite element analyses were also carried out using the welded joint specimen models in order to calculate the Weibull stress. The critical loads for brittle fracture predicted by the Weibull stress criterion from CTOD test results of one-bead and multi-pass welded joint specimens show fairly good agreement with experimental results of welded joint specimens with geometrical discontinuity.

Method of Constraint Loss Correction for CTOD Fracture Toughness under Welding Residual Stress Field

2010 ◽  
Vol 638-642 ◽  
pp. 3931-3936 ◽  
Author(s):  
Yoichi Yamashita ◽  
Fumiyoshi Minami
Keyword(s):  
Fracture Toughness ◽  
Residual Stress ◽  
Plastic Zone Size ◽  
Assessment Method ◽  
Welding Residual Stress ◽  
Residual Stress Field ◽  
Stress Criterion ◽  
Stress Effects ◽  
Ductile Brittle Transition Temperature ◽  
Size Criterion

This paper studied the assessment method for welding residual stress effects and constraint loss effects on brittle fracture of structural component subjected to membrane stress. The methodology of CTOD fracture toughness correction for welded joints is proposed from lower to upper ductile-brittle transition temperature region. The methodology is based on the tensile plastic zone size criterion and the equivalent CTOD ratio derived from the Weibull stress criterion. It has been found that the proposed methodology has given the reasonable fracture assessment results.

Revision of ISO 27306 for CTOD Toughness Correction for Constraint Loss

2016 ◽  
Vol 879 ◽  
pp. 54-59
Author(s):  
Fumiyoshi Minami ◽  
Mitsuru Ohata ◽  
Yasuhito Takashima
Keyword(s):  
Fracture Toughness ◽  
Fracture Mechanics ◽  
Stress Criterion ◽  
Failure Assessment Diagram ◽  
Failure Assessment ◽  
Fracture Assessment ◽  
International Standardization ◽  
Diagram Approach ◽  
Weibull Stress

As the result of the international standardization work in Japanese IST project, ISO 27306 were published in 2009 for correction of CTOD fracture toughness for constraint loss in steel components. ISO 27306 employs an equivalent CTOD ratio based on the Weibull stress criterion, which leads to more accurate fracture assessment than the conventional fracture mechanics assessment. On the occasion of the 1st periodical review, the revision of ISO 27306 has been proposed from Japan. This paper describes the key contents of the new ISO 27306. A case study is included on the fracture assessment of a wide plate component according to FAD (failure assessment diagram) approach specified in BS 7910:2013.

Equivalent CTOD Concept for Correction of CTOD Toughness for Constraint Loss in Steel Weld Components

2012 ◽  
Vol 706-709 ◽  
pp. 97-104
Author(s):  
Fumiyoshi Minami
Keyword(s):  
Fracture Toughness ◽  
Assessment Method ◽  
Weld Strength ◽  
Steel Weld ◽  
Structural Components ◽  
Conventional Procedure ◽  
Failure Assessment ◽  
Fracture Assessment ◽  
Weibull Stress ◽  
Fracture Toughness Specimen

This paper presents a new fracture assessment method, IST method developed as ISO 27306. The IST method implements an equivalent CTOD ratio,β, for the CTOD toughness correction for constraint loss in structural components. Usingβ, the standard fracture toughness specimen and structural components are linked at the same level of the Weibull stress. This paper extends the equivalent CTOD concept to weld components. Effects of the weld strength mismatch and residual stress onβare discussed. It is shown on the failure assessment diagram (FAD) that the CTOD toughness correction withβleads to accurate fracture assessments of weld panels, whereas the conventional procedure gives much conservative results.

Application of Weibull Stress Criterion to Brittle Fracture Assessment of Heat-Affected Zone-Notched Welds With Residual Stress

2015 ◽  
Vol 138 (2) ◽  
Author(s):  
Yusuke Seko ◽  
Yasuhito Imai ◽  
Masaki Mitsuya ◽  
Noritake Oguchi ◽  
Fumiyoshi Minami
Keyword(s):  
Residual Stress ◽  
Brittle Fracture ◽  
Heat Affected Zone ◽  
Welding Residual Stress ◽  
Specimen Geometry ◽  
Coarse Grained ◽  
Crack Tip Opening Displacement ◽  
Element Analysis ◽  
Stress Criterion ◽  
Weibull Stress

A constraint loss correction procedure using the Weibull stress criterion is specified in ISO 27306. However, this standard is applicable only to structural steel components with defects, not to welded joints. Therefore, we propose a method for estimating the brittle fracture limit of a weld with a notch in the heat-affected zone (HAZ) and residual stress based on the Weibull stress criterion. Three-point bending (3PB) tests and wide-plate (WP) tension tests of HAZ-notched welds made of 780-MPa class high-strength steel were conducted at −40 °C. The minimum critical crack tip opening displacement (CTOD) of the WP specimen fracturing at the coarse-grained region of the HAZ (CGHAZ) was approximately four times that of the 3PB specimen. Then, the effects of specimen geometry, residual stress, crack-front shape, and HAZ microstructure classification on the Weibull stress were investigated by using a finite element analysis (FEA). The results of these analyses showed that the specimen geometry, the welding residual stress, and HAZ microstructure affect the Weibull stress of HAZ-notched welds as crack driving force. Based on above results, the CTOD–Weibull stress curves for 3PB and WP specimens fracturing at CGHAZ were calculated by using an FEA. It was confirmed that the brittle fracture limit of an HAZ-notched weld with residual stress could be predicted from the Weibull stress criterion because predicted critical CTOD of WP specimens obtained by Weibull stress included experimental critical CTOD of WP specimens.

Application of Weibull Stress Criterion to Brittle Fracture Assessment of HAZ-Notched Welds With Residual Stress

2014 ◽  
Author(s):  
Yusuke Seko ◽  
Yasuhito Imai ◽  
Masaki Mitsuya ◽  
Noritake Oguchi ◽  
Fumiyoshi Minami
Keyword(s):  
Residual Stress ◽  
Finite Element ◽  
Brittle Fracture ◽  
Crack Front ◽  
Welding Residual Stress ◽  
Specimen Geometry ◽  
Stress Criterion ◽  
Front Shape ◽  
The Difference ◽  
Weibull Stress

This paper presents a method for estimating the brittle fracture limit of a weld with a notch in the heat-affected zone (HAZ) and residual stress based on the Weibull stress criterion. A constraint loss correction procedure using the Weibull stress criterion is specified in ISO 27306. However, this standard is applicable only to structural steel components with defects, not to welded joints. Therefore, we conducted fracture tests and finite element analyses to propose a new evaluation method for welded structural components. In this study, three-point bending (3PB) tests and wide-plate (WP) tension tests of HAZ-notched welds made of 780-MPa-class high-strength steel were conducted at −40°C. Brittle fractures occurred in the HAZ regions of all the specimens, and the critical crack tip opening displacement (CTOD) values obtained in the 3PB and WP tests were approximately 0.02–0.07 mm and 0.08–0.11 mm, respectively. The minimum critical CTOD of the WP specimen fracturing at the coarse-grained region of the HAZ (CGHAZ) was approximately four times that of the 3PB specimen. These results confirmed that the difference of specimen geometry affects the brittle fracture resistance of a HAZ-notched weld with residual stress. Hence, the assessment of the brittle fracture limit of a welded structural component with a defect obtained by the fracture toughness of a 3PB specimen would be excessively conservative. The effects of specimen geometry, residual stress, crack-front shape and HAZ microstructure classification on the Weibull stress were investigated to clarify the difference of experimental critical CTOD for 3PB and WP by using a finite element analysis. The results of this analysis showed that the Weibull stress of WP specimen was larger than one of 3PB specimen in all CTOD region due to difference of geometry. The welding residual stress increased the Weibull stress only for WP. Compressive residual stress and crack front shape for 3PB specimen did not affect the Weibull stress. The difference of HAZ microstructure distribution for same welded joint affects the Weibull stress for 3PB and WP specimens. Finally, it was confirmed that the brittle fracture limit of a HAZ-notched weld with residual stress could be predicted from the Weibull stress criterion because critical CTOD of WP specimens predicted by critical CTOD of 3PB specimens fracturing at the CGHAZ included critical CTOD of WP specimens obtained by experiments.

Evaluation of Fracture Toughness Test Data for Multilayer Dissimilar Joint Welds Using a Weibull Stress Model

2012 ◽  
pp. 357-376
Author(s):  
Yasuhito Takashima ◽  
Mitsuru Ohata ◽  
Masaru Seto ◽  
Yoshitomi Okazaki ◽  
Fumiyoshi Minami
Keyword(s):  
Fracture Toughness ◽  
Test Data ◽  
Dissimilar Joint ◽  
Fracture Toughness Test ◽  
Stress Model ◽  
Toughness Test ◽  
Weibull Stress

Standardization of CTOD Toughness Correction for Constraint Loss in Steel Components

2008 ◽  
Author(s):  
Fumiyoshi Minami ◽  
Mitsuru Ohata
Keyword(s):  
Fracture Toughness ◽  
Fracture Criterion ◽  
Shape Parameter ◽  
Pipeline Steel ◽  
Fracture Initiation ◽  
Failure Assessment ◽  
Fracture Assessment ◽  
Steel Welds ◽  
Weibull Stress ◽  
Fracture Toughness Specimen

A standardized procedure for correction of CTOD fracture toughness for constraint loss in steel components is presented. The equivalent CTOD ratio β = δ/δWP is developed on the basis of the Weibull stress fracture criterion, where δ and δWP are CTODs of the standard fracture toughness specimen and the wide plate component, respectively, at the same level of the Weibull stress. With the CTOD ratio β, the critical CTOD δWP, cr of the wide plate that is equivalent to δcr at brittle fracture initiation is given as δWP, cr = δcr/β. Nomographs of β are provided as a function of the crack type and size in the component, the yield-to-tensile ratio of the material and the Weibull shape parameter m. The fracture assessment with β is shown within the context of a failure assessment diagram (FAD), which includes the pipeline steel welds with a notch in the weld metal.

Estimates of Mechanical Properties and Residual Stress of Narrow Gap Weld for Leak-Before-Break Application to Nuclear Piping

2011 ◽  
Vol 133 (2) ◽  
Author(s):  
Jun-Seok Yang ◽  
Chi-Yong Park ◽  
Nam-Su Huh
Keyword(s):  
Residual Stress ◽  
Power Plant ◽  
Nuclear Power Plant ◽  
Steam Generator ◽  
Nuclear Power ◽  
Welding Residual Stress ◽  
Fracture Toughness Test ◽  
Narrow Gap ◽  
Main Loop ◽  
Leak Before Break

The present paper addresses the mechanical characteristics of the stainless steel narrow gap weld (NGW) for the leak-before-break (LBB) application to the main loop piping of a nuclear power plant. Recently, in Korea, the connection with the reactor coolant main loop piping and the steam generator has been welded with ER308L NGW after the replacement of a steam generator of a Korean nuclear power plant. The NGW technique has many merits, for instance, the reduction of construction time and the reduction of shrinkage and deformation after welding due to its small groove angle and welding bead width compared with the conventional welds. In this paper, the tensile and fracture toughness test results of the three ER308L test coupons from NGW were presented and compared with those from conventional welds at the operating condition of the nuclear power plant. In addition, the distribution of the welding residual stress as well as the deformation behavior of the ER308L weld due to NGW was predicted through the nonlinear two-dimensional finite element analysis in which the detailed actual welding process of NGW was simulated. The results presented in this paper can be used to evaluate LBB application to nuclear piping with NGW and to provide the important information to perform the flaw evaluation as well as improve the weld procedure of NGW.

Relationship Between Weibull Parameter and Fracture Toughness of Structural Steels

2008 ◽  
Author(s):  
Tsunehisa Handa ◽  
Hiroshi Mimura ◽  
Mitsuru Ohata ◽  
Fumiyoshi Minami
Keyword(s):  
Fracture Toughness ◽  
Test Specimen ◽  
Fracture Process ◽  
Shape Parameter ◽  
Process Zone ◽  
Structural Components ◽  
Stress Criterion ◽  
Plastic Constraint ◽  
Fracture Performance ◽  
Weibull Stress

The brittle fracture assessment for structural components excluding an excessive conservatism should be conducted under the concept of fitness-for-service assessment. One of the factors that lead to such a conservative estimation of brittle fracture performance is no consideration of plastic constraint loss in structural components compared to the fracture toughness test specimen. The Weibull stress criterion is expected to correct the CTOD (Crack Tip Opening Displacement) fracture toughness of materials to the critical CTOD for structural components of concern through the same level of Weibull stress, which take into account not only the difference in plastic constraint but also volume of fracture process zone between toughness test specimen and structural components. On the basis of the Weibull stress criterion, the fracture driving force, that is the Weibull stress, is dependent on the Weibull shape parameter m. Furthermore, such dependency is influenced by both the plastic constraint level and the volume of fracture process zone for specimens of interest. The different m-value would result in the different correction ratio of the fracture toughness to the critical CTOD for structural components. Accordingly, the parameter m should be estimated for the appropriate fracture performance evaluation in consideration of constraint loss correction. In this paper, a simple method for estimating the Weibull shape parameter m were introduced. That is the effort to address the factors to affect the m-value in terms of strength class and toughness level of materials based on the data from literatures, which is for efficient and rational estimation of m-value without any experimental and numerical works.

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