Fracture Assessment Method Using the Weibull Stress - Part II

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.

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Fracture Assessment Method Using the Weibull Stress - Part I

JOURNAL OF THE JAPAN WELDING SOCIETY ◽

10.2207/jjws.75.416 ◽

2006 ◽

Vol 75 (5) ◽

pp. 416-446 ◽

Cited By ~ 7

Author(s):

Fumiyoshi MINAMI

Keyword(s):

Assessment Method ◽

Fracture Assessment ◽

Weibull Stress

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

Volume 1: Codes and Standards ◽

10.1115/pvp2008-61536 ◽

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.

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Reliability Assessment of Piping With Cracks Using Advanced First-Order Second-Moment Method

Volume 1: Codes and Standards ◽

10.1115/pvp2009-77349 ◽

2009 ◽

Author(s):

Shinji Yoshida ◽

Hideo Machida

Keyword(s):

Safety Factor ◽

Reliability Assessment ◽

Limit Load ◽

Service Level ◽

Assessment Method ◽

J Integral ◽

Reference Stress ◽

First Order Second Moment ◽

Fracture Assessment ◽

Second Moment Method

This paper describes applicability of the 2 parameter assessment method using a reference stress method from the viewpoint of reliability. The applicability of the reference stress method was examined comparing both the GE-EPRI method. As a result, J-integral and limit load at the time of fracture evaluated by the reference stress method is almost equivalent to that by the GE-EPRI method. Furthermore, the partial safety factor (PSF) evaluated by reliability assessment has little difference between two methods, and the required safety factor is enveloped by the safety factor for Service Level-A and B defined in fitness for service (FFS) codes. These results show that of the reference stress method is applicable for J-integral calculation in fracture assessment.

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Standardization of CTOD Toughness Correction for Constraint Loss in Steel Components

Volume 1: Codes and Standards ◽

10.1115/pvp2008-61076 ◽

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.

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

Volume 7: Operations, Applications, and Components ◽

10.1115/pvp2006-icpvt-11-94047 ◽

2006 ◽

Cited By ~ 1

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.

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Fracture Assessment of Pipes Having Multiple Flaws Based on Ramberg–Osgood-Type Stress–Strain Relationships

ASME 2011 Pressure Vessels and Piping Conference: Volume 1 ◽

10.1115/pvp2011-57859 ◽

2011 ◽

Cited By ~ 1

Author(s):

Hideo Machida ◽

Tetsuya Hamanaka ◽

Yoshiaki Takahashi ◽

Katsumasa Miyazaki ◽

Fuminori Iwamatsu ◽

...

Keyword(s):

Flow Stress ◽

Stress Concentration ◽

Fracture Strength ◽

Strain Curve ◽

Assessment Method ◽

Experimental Results ◽

Stress Strain Curve ◽

Stress Strain ◽

Strain Relationship ◽

Fracture Assessment

This paper describes a fracture assessment method for a pipe having multiple circumferential flaws. According to Fitness-for-Service (FFS) codes for nuclear facilities published by the Japanese Society of Mechanical Engineers (JSME), the fracture strength of a high-ductility pipe having a circumferential flaw is evaluated using the limit load assessment method assuming the elastic–perfectly-plastic stress–strain relationship. In this assessment, flow stress is used as a proportional stress. However, previous experimental results [1, 2, 3] show that a crack penetrates before the entire flawed pipe section reaches the flow stress. Therefore, stress concentration at a flaw was evaluated on the basis of the Dugdale model [4], and the fracture strength of the crack-ligament was evaluated. This model can predict test results with high accuracy when the ligament fracture strength is assumed to be tensile strength. Based on this examination, a fracture assessment method for pipes having multiple flaws was developed considering the stress concentration in the crack-ligament by using the realistic stress–strain relationship (Ramberg–Osgood-type stress–strain curve). The fracture strength of a multiple-flawed pipe estimated by the developed method was compared with previous experimental results. When the stress concentration in the crack-ligament was taken into consideration, the fracture strength estimated using the Ramberg–Osgood-type stress–strain curve was in good agreement with experimental results, confirming the validity of the proposed method.

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Development of LBB Assessment Method for Japanese Sodium Cooled Fast Reactor (JSFR) Pipes: 3—Fracture Assessment Methods Considering Compliance at a Crack Part

ASME 2010 Pressure Vessels and Piping Conference: Volume 6, Parts A and B ◽

10.1115/pvp2010-25244 ◽

2010 ◽

Cited By ~ 1

Author(s):

Takashi Wakai ◽

Hideo Machida ◽

Shinji Yoshida ◽

Yasuhiro Enuma ◽

Tai Asayama

Keyword(s):

Thermal Expansion ◽

Internal Pressure ◽

Fast Reactor ◽

Load Balance ◽

Assessment Method ◽

Assessment Methods ◽

Piping System ◽

Thin Wall ◽

Fracture Assessment ◽

Leak Before Break

This paper presents a fracture assessment methods used in leak before break (LBB) assessment of sodium piping system in the Japanese sodium cooled fast reactor (JSFR). Use of thin wall pipes and compact layout of piping system are features of the design in JSFR. Since the internal pressure of piping of JSFR is low, the critical load is thermal expansion. Supposing a through wall crack (TWC) in such piping, the stiffness of the crack part will decrease, the load balance of the piping system will change from the condition without crack. The fracture assessment methods paying attention to this stiffness change at the crack part were proposed and these methods enabled rational LBB assessment. The proposed methods are much effective to loosen LBB conditions for the piping system of which the compliance is low. These methods applied to the LBB assessment of the piping system of JSFR which has the compact layout, and it was checked that the validity of these methods to loosen the LBB conditions.

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Revision of ISO 27306 for CTOD Toughness Correction for Constraint Loss

Materials Science Forum ◽

10.4028/www.scientific.net/msf.879.54 ◽

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.

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