Evaluation of Fracture Toughness Results and Transferability to Fracture Assessment of Welded Joints

2009 ◽  
pp. 315-315-26 ◽  
Author(s):  
F Minami ◽  
M Toyoda
Keyword(s):  
Fracture Toughness ◽  
Welded Joints ◽  
Fracture Assessment

scholarly journals Fracture Assessment of Weld Joints of High-Strength Steel in Pre-Strained Condition

2019 ◽  
Vol 9 (7) ◽  
pp. 1306
Author(s):  
Gyubaek An ◽  
Jeongung Park ◽  
Mituru Ohata ◽  
Fumiyoshi Minami
Keyword(s):  
Fracture Toughness ◽  
Welded Joints ◽  
Steel Structures ◽  
Great Earthquake ◽  
Small Scale ◽  
Ship Structures ◽  
Strained Condition ◽  
Critical Fracture ◽  
Fracture Assessment ◽  
Unstable Fractures

Unstable fractures tend to occur after ductile crack initiation or propagation. In most collapsed steel structures, a maximum 15% pre-strain was recorded, at the steel structural connections, during the great earthquake of 1995, in Japan. Almost-unstable fractures were observed in the beam-to-column connections, where geometrical discontinuities existed. Structural collapse and unstable failure occurred after large-scale plastic deformations. Ship structures can also suffer from unstable fractures in the welded joints. The fracture resistance of butt-welded joints subjected to tension in the pre-strained condition was estimated by considering the toughness deterioration, due to pre-strain and toughness correction for constraint loss in a tension specimen. The target specimen for this fracture assessment was a double-edged, through-thickness crack panel, with a crack in the weld joint (heat-affected zone (HAZ)). The critical fracture toughness value (crack tip opening displacement (CTOD)) of a large structure with pre-strain, which was applied to the HAZ region, was estimated from a small-scale, pre-stained, three-point bend specimen. Fracture toughness values, evaluated by a CTOD test, were recently mandated for shipbuilding steel plates. The critical fracture toughness value is a very useful parameter to evaluate the safety of huge ship structures.

Fracture assessment of cold-press-formed square hollow sections at welded joints

2012 ◽  
pp. 773-777
Author(s):  
M Arita ◽  
Y Kayamori ◽  
Y Suzuki ◽  
K Hanya ◽  
T Suzuki ◽  
...  
Keyword(s):  
Welded Joints ◽  
Cold Press ◽  
Fracture Assessment

scholarly journals Evaluation of crack resistance of welded joints with soft interlayers

2022 ◽  
Vol 21 (4) ◽  
pp. 308-311
Author(s):  
K. A. Molokov ◽  
V. V. Novikov
Keyword(s):  
Experimental Data ◽  
Fracture Toughness ◽  
Crack Resistance ◽  
Welded Joints ◽  
Low Cycle Fatigue ◽  
Transverse Load ◽  
Structural Elements ◽  
Metal Structures ◽  
Characteristic Appearance ◽  
Reliability Indicator

Introduction. Welded joints in large-sized metal structures (e.g., in the structures of ship hulls) subject to low-cycle fatigue are considered. The characteristic appearance of soft interlayers, which are significantly plastically deformed under working loads, was noted. Deformation of the metal structure with damage, especially in the form of cracks, reduces the strength and reliability of structural elements and joints. Pre-deformation negatively affects plasticity; therefore, much depends on the residual plasticity of the cracking material. At the same time, with a decrease in residual plasticity, such an important reliability indicator as the resistance of the material to crack propagation — the fracture toughness – decreases. The paper is devoted to the development of a model that includes analytical dependences for assessing the crack resistance of metal structures and their welded joints with soft interlayers according to the crack resistance limit for all crack sizes.Materials and Methods. The theory and methods of linear mechanics of materials destruction, structural-mechanical approach are used. The calculation results were analyzed and compared to the experimental data and other analytical solutions. The numerical experiment was performed for the ferrite-perlite steel grades of 10, 50, 22K, St3sp, etc., widely used in industry, as well as for alloy steels hardened to medium and high strength of 30KhGSA, 37KhN3A, etc. Results. Analytical dependences are obtained for calculating the relative crack resistance limit according to three main known mechanical characteristics of the state of the material of the soft interlayer of the welded joint.Discussion and Conclusions. The results obtained can be used to assess the crack resistance of pre-deformed structural elements and welded joints (including those with soft interlayers) operating under a transverse load. The results of experimental data and analytical calculations are shown in dimensionless form, which enables to obtain invariant results with respect to the fracture toughness limit.

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.

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 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.

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