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.

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.

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.

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.

Fracture Assessment Procedure for Steel Structures Subjected to Large Cyclic and Dynamic Strain – Based on WES TR 2808

2002 ◽  
Author(s):  
Fumiyoshi Minami ◽  
Masao Toyoda ◽  
Takahiro Kubo ◽  
Hiroshi Shimanuki ◽  
Noboru Konda ◽  
...  
Keyword(s):  
Fracture Toughness ◽  
Structural Component ◽  
Reference Temperature ◽  
Dynamic Strain ◽  
Great Earthquake ◽  
Assessment Procedure ◽  
Structural Components ◽  
Significant Difference ◽  
Weibull Stress ◽  
Fracture Toughness Specimen

With a lesson leaned from the Kobe Great Earthquake, an engineering method, WES TR 2808, has been developed in Japan for evaluating the structural integrity under the seismic condition. This paper presents a main story of WES TR 2808, which is characterized by two key ideas. One is a reference temperature concept for fracture toughness evaluation. The material fracture toughness under the seismic condition is replaced by the static fracture toughness without prestrain at a reference temperature of T − ΔTPD, where T and ΔTPD are the service temperature and the temperature shift of fracture toughness by prestraining and dynamic loading, respectively. WES TR 2808 gives ΔTPD as a function of the elevation of flow stress in the seismic condition. Another idea is a correction of constraint loss in structural components. A large amount of plastic deformation causes a loss of constraint in structural components, which leads to a significant difference in the fracture driving force of the components and fracture toughness specimen. In WES TR 2808, the CTOD ratio β = δ3P.Equiv/δStruc was defined on the basis of the Weibull stress criterion, where δStruc is the CTOD of the structural component and δ3P.Equiv is an equivalent CTOD of the fracture toughness specimen at which the toughness specimen presents a compatible Weibull stress with the structural component. The CTOD ratio β is apparently less than 1 in a large-scale yielding condition, and roughly 0.4 for the wide plate component with a surface crack. It was shown that WES TR 2808 is applicable to the fracture performance assessment of column-to-beam connections subjected to large cyclic and dynamic strain. The discussion was given on the engineering judgement in WES TR 2808, which was adopted to make the procedures as simple as possible.

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.

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.

Equivalent CTOD Ratio β for Engineering Assessment of CTOD Correction for Constraint Loss

2012 ◽  
Vol 134 (5) ◽  
Author(s):  
Mitsuru Ohata ◽  
Fumiyoshi Minami
Keyword(s):  
Fracture Toughness ◽  
Shape Parameter ◽  
Tensile Load ◽  
Crack Size ◽  
Small Scale ◽  
Structural Components ◽  
Small Scale Yielding ◽  
Stress Criterion ◽  
Scale Yielding ◽  
Weibull Stress

The critical CTOD δWP for structural components associated with plastic constraint loss in case of the brittle fracture over small-scale yielding condition can be corrected from CTOD fracture toughness δ by means of the “equivalent CTOD ratio β” defined as δ/δWP, which is based on the Weibull stress criterion. In this study, taking the case of specific wide plate components subjected to uni-axial tensile load, the effect on β is analyzed taking account of Weibull shape parameter m, loading level, constraint effect that can be influenced by material work-hardening and crack type/size in structural components, etc., and volumetric effect. It is found that the β-value is almost constant beyond the applied CTOD level that is lower than CTOD of small-scale yielding limit (SSY-limit) for 25 mm thick toughness specimen. From an engineering point of view, the β-value at the CTOD level of 0.01 mm is used in the whole loading range beyond SSY-limit CTOD, which provides to some extent conservative measure of fracture toughness of structural components. The defined β is found to decrease with increasing Weibull shape parameter m and yield-to-tensile ratio YR of steel for all type of wide plates concerned. The crack length effect on β is quasi-theoretically formulated, which can convert the β for the wide plate with reference crack size to β for target crack size. These β and quasi-theoretical equations for the correction of crack size effect can be utilized for estimating the CTOD for wide plate in consideration of constraint loss effect without numerical calculation of the Weibull stress.

Equivalent CTOD Ratio β for Engineering Assessment of CTOD Correction for Constraint Loss

2008 ◽  
Author(s):  
Mitsuru Ohata ◽  
Fumiyoshi Minami
Keyword(s):  
Fracture Toughness ◽  
Shape Parameter ◽  
Tensile Load ◽  
Crack Size ◽  
Small Scale ◽  
Structural Components ◽  
Small Scale Yielding ◽  
Stress Criterion ◽  
Scale Yielding ◽  
Weibull Stress

The critical CTOD δWP for structural components associated with plastic constraint loss in case of the brittle fracture over small-scale yielding condition can be corrected from CTOD fracture toughness δ by means of the “equivalent CTOD ratio β” defined as δ/δWP, which is based on the Weibull stress criterion. In this study, taking the case of specific wide plate components subjected to uni-axial tensile load, the effect on β is analyzed taking account of Weibull shape parameter m, loading level, constraint effect that can be influenced by material work-hardening and crack type/size in structural components, etc., and volumetric effect. It is found that the β-value is almost constant beyond the applied CTOD level that is lower than CTOD of small-scale yielding limit (SSY-limit) for 25mm thick toughness specimen. From an engineering point of view, the β-value at the CTOD level of 0.01mm is used in the whole loading range beyond SSY-limit CTOD, which provides to some extent conservative measure of fracture toughness of structural components. The defined β is found to decrease with increasing Weibull shape parameter m and yield-to-tensile ratio YR of steel for all type of wide plates concerned. The crack length effect on β is quasi-theoretically formulated, which can convert the β for the wide plate with reference crack size to β for target crack size. These β and quasi-theoretical equations for correction of crack size effect can be utilized for estimating the CTOD for wide plate in consideration of constraint loss effect without numerical calculation of the Weibull stress.

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