Fracture Performance Evaluation of Laser Beam Welded Joints Based on the Weibull Stress Criterion

2009 ◽  
Author(s):  
Yasuhito Takashima ◽  
Mitsuru Ohata ◽  
Fumiyoshi Minami
Keyword(s):  
Fracture Toughness ◽  
Brittle Fracture ◽  
Laser Beam ◽  
Weld Metal ◽  
Welded Joints ◽  
Shielding Effect ◽  
Stress Criterion ◽  
Fracture Performance ◽  
Weibull Stress ◽  
Fracture Toughness Specimen

This paper examines the fracture performance of laser beam welded joints of a high strength steel with a notch in the weld metal (WM). The standard fracture toughness specimen (3-point bend specimen, 3PB) and tension panel (edge through-thickness crack panel, ETCP) are tested at a low temperature in the brittle fracture range. The focus lies on the difference between near crack-tip plastic constraints for the standard fracture toughness specimen and the tension, and on the very narrow and highly hardened WM shielding high strain in the weld metal from external loading. The ETCP has presented a higher critical CTOD at brittle fracture initiation than the 3PB specimen. The fracture performance of ECTP is predicted from CTOD fracture toughness test results by means of the Weibull stress criterion with the consideration of the shielding effect of the weld metal. The results show an advantage of the Weibull stress criterion for the fracture transferability analysis of toughness results. Furthermore, the influence of very narrow and highly hardened weld metal of laser beam welded joints on the toughness requirement has been analyzed by means of the Weibull stress criterion. The effect of the distinctive strength mismatch of laser beam welded joints on required CTOD fracture toughness of laser beam welded joints in 3PB necessary to meet design requirement of joint performance is discussed taking into account the shielding effect on crack opening behavior and toughness collection due to constraint loss between ETCP and 3PB specimen. The required CTOD in 3PB is a little bit lower than arc welded joints. Therefore, it should be noticed that the very narrow and highly hardened WM does not necessarily lead to poor fracture performance of the welded joints.

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.

Significance of Fracture Toughness of Laser Welds for Structural Steels and Fracture Performance Assessment by Weibull Stress Criterion

2007 ◽  
Vol 25 (1) ◽  
pp. 149-158 ◽  
Author(s):  
Fumiyoshi MINAMI ◽  
Mitsuru OHATA ◽  
Akihiko TANIZAWA ◽  
Yukito HAGIHARA ◽  
Susumu TUKAMOTO ◽  
...  
Keyword(s):  
Fracture Toughness ◽  
Performance Assessment ◽  
Structural Steels ◽  
Stress Criterion ◽  
Laser Welds ◽  
Fracture Performance ◽  
Weibull Stress

Significance of Strength Mismatch in Fracture Performance Evaluation of Welded Joints — Characterization of Mismatch Effect by the Weibull Stress Criterion

2009 ◽  
Vol 53 (5-6) ◽  
pp. R140-R150 ◽  
Author(s):  
Fumiyoshi Minami ◽  
Mitsuru Ohata ◽  
Takamasa Manabe ◽  
Yasutake Chiba ◽  
Keiji Murayama
Keyword(s):  
Performance Evaluation ◽  
Welded Joints ◽  
Stress Criterion ◽  
Fracture Performance ◽  
Weibull Stress ◽  
Mismatch Effect

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.

Evaluation of flexural fracture toughness for quasi-brittle structural materials using a simple test method

2002 ◽  
Vol 29 (4) ◽  
pp. 567-575 ◽  
Author(s):  
M.M Reda Taha ◽  
X Xiao ◽  
J Yi ◽  
N G Shrive
Keyword(s):  
Fracture Toughness ◽  
Fracture Mechanics ◽  
Brittle Fracture ◽  
High Performance ◽  
High Performance Concrete ◽  
Fibre Reinforced Concrete ◽  
Simple Test ◽  
Elastic Crack ◽  
Fracture Performance ◽  
Brittle Fracture Mechanics

As new structural concepts such as partial prestressing and steel-free bridge decks are more widely accepted and used, there is an increasing need for a reliable and reproducible fracture performance criterion that can describe resistance to crack growth. The required criterion should also be easy to determine experimentally so that it can be incorporated in structural specifications. The nonlinear behaviour of concrete and masonry materials suggested that quasi-brittle fracture mechanics approaches may be the most suitable for determining their fracture performance. The effective elastic crack model originally developed by Karihaloo and Nallathambi (1989) was modified to evaluate the critical crack depth under pure flexural stresses. A computer program was developed to calculate this depth iteratively from the experimental results. An experimental programme examining the fracture performance of four different structural materials (high performance concrete, mortar, fibre reinforced concrete, and masonry units) was carried out to examine the applicability of the model. As no post-peak data are required for the analysis, the model allows the use of a simple test setup to evaluate the fracture performance of quasi-brittle materials experimentally.Key words: fracture toughness, linear elastic fracture mechanics (LEFM), elastoplastic fracture mechanics (EPFM), quasi-brittle fracture mechanics, effective elastic crack, high performance concrete, masonry, fibre reinforced concrete.

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.

Evaluation of Residual Stress Effects on Brittle Fracture Strength Based on Weibull Stress Criterion

2008 ◽  
Vol 5 (6) ◽  
pp. 101524 ◽  
Author(s):  
Yoichi Yamashita ◽  
Fumiyoshi Minami ◽  
Richard Neu ◽  
Kim Wellin ◽  
Steven R. Thompson ◽  
...  
Keyword(s):  
Residual Stress ◽  
Brittle Fracture ◽  
Fracture Strength ◽  
Stress Criterion ◽  
Stress Effects ◽  
Strength Based ◽  
Weibull Stress

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.

scholarly journals Method for estimation of fracture toughness from machined-notch specimen based on the Weibull stress criterion

2006 ◽  
Vol 3 (0) ◽  
pp. 261-270 ◽  
Author(s):  
Youichi Yamashita ◽  
Masaki Torigoe ◽  
Kenji Sakano ◽  
Daisuke Watanabe ◽  
Fumiyoshi Minami
Keyword(s):  
Fracture Toughness ◽  
Stress Criterion ◽  
Weibull Stress
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